| proximal sequence element factor binding and species specificity in vertebrate u6 snrna promoters. | the xenopus tropicalis u6 gene is very poorly transcribed both when introduced into human cells by transfection, and in human cell-free extracts. by analysis of hybrid promoters constructed from human and xenopus sequences in various combinations, we show that species specificity is mediated by the proximal sequence elements (pses) of the promoters. we demonstrate the pse-dependence of u6 transcription in a fractionated extract of hela cells. one of the fractions required for transcription conta ... | 1992 | 1538402 |
| isolation and characterization of sarcomeric actin genes expressed in xenopus laevis embryos. | a xenopus laevis complementary dna (cdna) library prepared from messenger rnas extracted from embryos has been screened for actin-coding sequences. two cdna clones corresponding to an alpha cardiac and an alpha skeletal muscle actin mrna have been identified and characterized. from a genomic library, we have furthermore isolated the genes that correspond to the characterized cdnas. in addition we have identified an actin processed gene which seems to be derived from a second type of skeletal mus ... | 1986 | 3009830 |
| xenopus tropicalis u6 snrna genes transcribed by pol iii contain the upstream promoter elements used by pol ii dependent u snrna genes. | we have cloned and sequenced a 977bp dna fragment, pxtu6-2, that represents the transcription unit for a xenopus tropicalis u6 rna gene. this basic repeating unit is reiterated ca.500-fold per haploid genome. oocyte injections of pxtu6-2 led to the transcription of a mature-sized u6 rna that, however, lacked internal 2'-o-methylations. these posttranscriptional modifications of u6 rna might be cytoplasmic and could require its association with u4 rna to be accomplished. the low alpha- amanitin s ... | 1987 | 3031599 |
| globin evolution in the genus xenopus: comparative analysis of cdnas coding for adult globin polypeptides of xenopus borealis and xenopus tropicalis. | globin mrnas of xenopus borealis and xenopus tropicalis have been cloned and sequenced. the nucleotide and derived amino acid sequences were compared with each other and with already available data from xenopus laevis. this analysis rendered clear evidence that the common ancestor of x. laevis and x. borealis, but not of x. tropicalis, had lost one amino acid of the beta-globins prior to a genome duplication event that preceded the segregation of the former two species. replacement-site substitu ... | 1986 | 3100812 |
| primary structure and evolutionary relationship between the adult alpha-globin genes and their 5'-flanking regions of xenopus laevis and xenopus tropicalis. | to investigate the evolution of globin genes in the genus xenopus, we have determined the primary structure of the related adult alpha i- and alpha ii-globin genes of x. laevis and of the adult alpha-globin gene of x. tropicalis, including their 5'-flanking regions. all three genes are comprised of three exons and two introns at homologous positions. the exons are highly conserved and code for 141 amino acids. by contrast, the corresponding introns vary in length and show considerable divergence ... | 1988 | 3148743 |
| a third striated muscle actin gene is expressed during early development in the amphibian xenopus laevis. | during early embryonic development in the frog xenopus laevis, several muscle-specific actin genes encoding distinct actin protein isoforms are activated in cells of the embryonic muscle. in addition to the cardiac (or alpha 1) and skeletal (or alpha 2) actin genes, a third muscle-specific actin gene is expressed in the same embryonic tissue. we have determined the complete nucleotide sequence of this third gene and examined its expression in embryonic and adult tissues. during embryogenesis, th ... | 1988 | 3172214 |
| oocyte and somatic 5s ribosomal rna and 5s rna encoding genes in xenopus tropicalis. | we have investigated the structure of oocyte and somatic 5s ribosomal rna and of 5s rna encoding genes in xenopus tropicalis. the sequences of the two 5s rna families differ in four positions, but only one of these substitutions, a c to u transition in position 79 within the internal control region of the corresponding 5s rna encoding genes, is a distinguishing characteristic of all xenopus somatic and oocyte 5s rnas characterized to date, including those from xenopus laevis and xenopus borealis ... | 1988 | 3174434 |
| a processed gene coding for a sarcomeric actin in xenopus laevis and xenopus tropicalis. | a processed gene potentially coding for a sarcomeric actin has been identified in xenopus laevis and in the more primitive species x. tropicalis. the peptides encoded in these two species differ by two out of 377 amino acid residues. on the basis of the amino acid substitutions, the encoded peptide was identified as an alpha-skeletal actin in x. laevis and as an alpha-cardiac actin in x. tropicalis. northern blot analysis and s1 mapping experiments suggest that in x. tropicalis the gene is expre ... | 1987 | 3653078 |
| sequences coding for the ribosomal protein l14 in xenopus laevis and xenopus tropicalis; homologies in the 5' untranslated region are shared with other r-protein mrnas. | in the haploid genome of xenopus laevis there are two genes coding for the r-protein l14. it is not known if they are located on the same chromosome. cdna clones deriving from the transcripts of the two genes have been isolated from an oocyte messenger cdna bank showing that they are both expressed. we have studied the structure of one of the l14 genes by electron microscopy, restriction mapping and sequencing. an allelic form of the l14 gene was also isolated. it contains a large deletion cover ... | 1986 | 3774540 |
| the expression of creatine kinase isozymes in xenopus tropicalis, xenopus laevis laevis, and their viable hybrid. | starch gel electrophoresis of creatine kinase (ck) isozymes of xenopus tropicalis shows that at least two different genes code for ck in this diploid (2n = 20) species. these genes seen to be orthologous to the ck-a and ck-c genes of extant crossopterygian fish. additional isozymes may be interpreted either as products of duplicate genes or, more probably, as epigenetically modified forms of the homodimers atat and ctct, respectively. the originally tetraploid species x. laevis laevis (2n = 36), ... | 1985 | 3994660 |
| comparative analysis of xenopus tropicalis and xenopus laevis vitellogenin gene sequences. | analysis of cdna clones synthesized from vitellogenin mrna of x. tropicalis revealed three different types of cdna clones, i.e. a, a* and b. a and a* clones have a sequence divergence of about 6% and are both related to x. laevis vitellogenin cdnas of subgroup a1 as well as a2 with a sequence divergence of 6-9%. b clones however, are related to x. laevis cdna clones of subgroup b1 and b2 with a sequence divergence of about 7%. while the a and b clones correspond to vitellogenin mrnas of similar ... | 1982 | 6280148 |
| characterization of histone genes isolated from xenopus laevis and xenopus tropicalis genomic libraries. | using a cdna clone for the histone h3 we have isolated, from two genomic libraries of xenopus laevis and xenopus tropicalis, clones containing four different histone gene clusters. the structural organization of x. laevis histone genes has been determined by restriction mapping, southern blot hybridization and translation of the mrnas which hybridize to the various restriction fragments. the arrangement of the histone genes in x. tropicalis has been determined by southern analysis using x. laevi ... | 1982 | 6296782 |
| evolution of proteasome subunits delta and lmp2: complementary dna cloning and linkage analysis with mhc in lower vertebrates. | the class ii region of the mammalian mhc harbors two proteasome subunit genes, lmp2 and lmp7. these genes are induced by ifn-gamma, and their products are incorporated into proteasomes substituting for their closest relatives, the delta and x subunits, respectively. this substitution is believed to change the proteolytic specificity of proteasomes, making it more suitable for generation of peptides to be presented by class i molecules. to elucidate the phylogenetic origin of lmp2 and the linkage ... | 1997 | 9218589 |
| ontogeny of the bizarre: an osteological description of pipa pipa (anura: pipidae), with an account of skeletal development in the species. | the adult osteology of the direct-developing pipid frog, pipa pipa, is described based on cleared-and-stained and dry skeletal specimens. observations on skeletal development are based on cleared-and-stained embryos and young removed from the backs of preserved females. osteologically, p.pipa is distinguished from its congeners and other pipid anurans by its large size and peculiar skull, which is extremely depressed and hyperossified. skulls of the smallest individuals are not significantly dif ... | 2000 | 10629097 |
| chlamydia pneumoniae infection in a breeding colony of african clawed frogs (xenopus tropicalis). | more than 90% of a breeding colony of clawed frogs (xenopus tropicalis) imported to the united states from western africa died in an epizootic of chlamydiosis. chlamydial inclusions were observed by light and electron microscopy in the liver of an infected frog. chlamydia pneumoniae was isolated in cell cultures from four frogs. a cutaneous infection by a chytridiomycete fungus observed in two frogs could have been a cofactor in the die-off.ous diseases | 2000 | 10756157 |
| evolution of hoxa-11 in lineages phylogenetically positioned along the fin-limb transition. | hoxa11 is a transcription factor implicated in paired appendage development. to identify signatures of evolutionary change in the structural, and putative functional, domains of hoxa11, we studied its evolution in tetrapod and nontetrapod lineages that represent approximately 1.5 billion years of evolutionary time. here, hoxa-11 gene proper sequences were determined for frog (xenopus tropicalis), coelacanth (latimeria chalumnae), common zebrafish (danio rerio; hoxa-11a and hoxa-11b paralogs), an ... | 2000 | 11083943 |
| xenopus tropicalis oocytes as an advantageous model system for the study of intracellular ca(2+) signalling. | 1. the purpose of this study was to compare oocytes from the pipid frogs xenopus tropicalis and xenopus laevis, with respect to their utility for studying ca(2+) signalling mechanisms and for expression of heterologous proteins. 2. we show that x. tropicalis oocytes possess an intracellular ca(2+) store that is mobilized by inositol (1,4,5) trisphosphate (ip(3)). ca(2+) signalling is activated by endogenous lysophosphatidic acid receptors and cytosolic ca(2+) activates a plasma membrane chloride ... | 2001 | 11264232 |
| cloning and characterization of three xenopus slug promoters reveal direct regulation by lef/beta-catenin signaling. | in amphibians and birds, one of the first steps of neural crest cell (ncc) determination is expression of the transcription factor slug. this marker has been used to demonstrate that bmp and wnt molecules play a major role in ncc induction. however, it is unknown whether slug expression is directly or indirectly regulated by these signals. we report here the cloning and characterization of three xenopus slug promoters: that of the xenopus tropicalis slug gene and those of two xenopus laevis slug ... | 2001 | 11402039 |
| comparison of morpholino based translational inhibition during the development of xenopus laevis and xenopus tropicalis. | morpholino (mo) based inhibition of translational initiation represents an attractive methodology to eliminate gene function during xenopus development (heasman et al., 2000). however, the degree to which a given target protein can be eliminated and the longevity of this effect during embryogenesis has not been documented. to examine the efficacy of mos, we have used transgenic xenopus lines that harbour known numbers of integrations of a gfp reporter under the control of the ubiquitous and high ... | 2001 | 11477685 |
| an amphibian with ambition: a new role for xenopus in the 21st century. | much of our knowledge about the mechanisms of vertebrate early development comes from studies using xenopus laevis. the recent development of a remarkably efficient method for generating transgenic embryos is now allowing study of late development and organogenesis in xenopus embryos. possibilities are also emerging for genomic studies using the closely related diploid frog xenopus tropicalis. | 2001 | 11597339 |
| cornea-lens transdifferentiation in the anuran, xenopus tropicalis. | previously, the only anuran amphibian known to regenerate the lens of the eye was xenopus laevis. this occurs during larval stages through transdifferentiation of the outer cornea epithelium under control of factors presumably secreted by the neural retina. this study demonstrates that a distantly related species, x. tropicalis, is also able to regenerate lenses through this process. a transgenic line of x. tropicalis was used to examine the process of cornea-lens transdifferentiation in which g ... | 2001 | 11685571 |
| antimicrobial peptides isolated from skin secretions of the diploid frog, xenopus tropicalis (pipidae). | seven peptides (xt-1-xt-7) with antimicrobial activity were isolated from norepinephrine-stimulated skin secretions of the diploid clawed frog, xenopus tropicalis. structural characterization of the peptides demonstrated that amino acid sequence similarity to antimicrobial peptides previously isolated from xenopus laevis was low, suggesting that the species are not closely related phylogenetically. peptides xt-5 and xt-3 are probably the orthologs of x. laevis peptide glycine-leucine amide (pgl( ... | 2001 | 11738090 |
| cloning and expression of the cdx family from the frog xenopus tropicalis. | the caudal-related (cdx) homeodomain transcription factors have a conserved role in the development of posterior structures in both vertebrates and invertebrates. a particularly interesting finding is that cdx proteins have an important function in the regulation of expression from a subset of hox genes. in this study, we report the cloning of cdnas from the cdx genes of the amphibian xenopus tropicalis. xenopus tropicalis is a diploid species, related to the commonly used laboratory animal xeno ... | 2002 | 11803576 |
| characterization of mpf and mapk activities during meiotic maturation of xenopus tropicalis oocytes. | resumption of meiosis in oocytes of xenopus tropicalis required translation but not transcription, and was marked by the appearance of a white spot and a dark ring, coincident with entry into metaphase i and the onset of anaphase i, respectively. cyclin b(2)/p34(cdc2) activity increased prior to the first meiotic division, declined at the onset of anaphase i, and subsequently increased again. the capacity of egg cytoplasm to induce germinal vesicle breakdown (gvbd) was inhibited by cycloheximide ... | 2002 | 11977986 |
| identification and characterization of a unique xenopus laevis egg envelope component, zpd. | we report the identification of a previously undetected xenopus laevis egg envelope component discovered through cloning experiments. a cdna sequence was found that represented a mature protein of 32 kda. peptide antibodies were generated to probe for the protein in egg envelope samples and reactivity was found to a glycoprotein of approximately 80 kda. when deglycosylated egg envelope samples were probed, a 32 kda protein was labeled, confirming the size of the translated cdna sequence. a blast ... | 2002 | 12060070 |
| regulated expression of the x. tropicalis connexin43 promoter. | the spatio-temporal expression pattern of the connexin43 gene during xenopus development has been described (van der heyden et al. 2001). to further investigate the regulation and function of connexin43 (cx43) in amphibians, we have isolated the gene from xenopus tropicalis (xt) and determined its structure. the x. tropicalis cx43 gene displays the typical two exon-one intron connexin configuration, where the first exon is non-coding. the predicted amino acid sequence of the xtcx43 protein is hi ... | 2001 | 12064605 |
| clinical diagnosis and treatment of epidermal chytridiomycosis in african clawed frogs (xenopus tropicalis). | an investigation was conducted to determine the cause of morbidity and mortality in a collection of 55 adult male xenopus (silurana) tropicalis at the university of california, berkeley. more than 80% of affected frogs died during the epizootic. all frogs were anorectic and lethargic, had dark pigmentation and excess skin sloughing, and lacked a slime layer. histologic examination revealed severe hyperplastic and spongiotic dermatitis associated with colonization of the stratum corneum by large ... | 2002 | 12102573 |
| autonomous regulation of muscle fibre fate during metamorphosis in xenopus tropicalis. | a key event in metamorphosis of anuran amphibians is tail resorption. this composite structure includes epidermal cells, spinal cord, muscle fibres and connective tissue. it is unclear how resorption proceeds and to what extent the signals for the death process are transmitted between cells. we determined the kinetics of metamorphosis, apoptosis, and tail regression in the diploid anuran, xenopus tropicalis, a species more suited to genetic analysis than the pseudotetraploid, xenopus laevis. met ... | 2002 | 12203730 |
| inducible control of tissue-specific transgene expression in xenopus tropicalis transgenic lines. | analysis of gene function in vertebrates is facilitated by gain-of-function studies, such as injection of synthetic mrna in amphibian embryos. this approach is hampered by lack of spatial and temporal control of expression of the introduced gene product. an additional level of control is obtained by nuclear-transfer-mediated transgenesis, but functional analyses are complicated by variability and background abnormalities in primary transgenic embryos. the gal4/uas system permits establishment of ... | 2002 | 12204263 |
| oocytes and embryos of xenopus laevis express two different isoforms of germ cell nuclear factor (gcnf, nr6a1). | the germ cell nuclear factor (gcnf) is a nuclear orphan receptor and a putative regulator of the pluripotent state of cells. although it was first described in mouse germ cells, gcnf is also expressed in mouse and xenopus embryos. by means of 5'race we have identified a novel isoform of xenopus laevis gcnf that is predominantly expressed in germ cells, whereas both the oocyte and embryonic forms are expressed during xenopus embryogenesis. est database search revealed that the homologues of both ... | 2002 | 12351198 |
| xenopus, the next generation: x. tropicalis genetics and genomics. | a small, fast-breeding, diploid relative of the frog xenopus laevis, xenopus tropicalis, has recently been adopted for research in developmental genetics and functional genomics. x. tropicalis shares advantages of x. laevis as a classic embryologic system, but its simpler genome and shorter generation time make it more convenient for multigenerational genetic, genomic, and transgenic approaches. its embryos closely resemble those of x. laevis, except for their smaller size, and assays and molecu ... | 2002 | 12454920 |
| techniques and probes for the study of xenopus tropicalis development. | the frog xenopus laevis has provided significant insights into developmental and cellular processes. however, x. laevis has an allotetraploid genome precluding its use in forward genetic analysis. genetic analysis may be applicable to xenopus (silurana) tropicalis, which has a diploid genome and a shorter generation time. here, we show that many tools for the study of x. laevis development can be applied to x. tropicalis. by using the developmental staging system of nieuwkoop and faber, we find ... | 2002 | 12454926 |
| xenopus tropicalis transgenic lines and their use in the study of embryonic induction. | for over a century, amphibian embryos have been a source of significant insight into developmental mechanisms, including fundamental discoveries about the process of induction. the recently developed transgenesis for xenopus offers new approaches to these poorly understood processes, particularly when undertaken in the quickly maturing species xenopus tropicalis, which greatly facilitates establishment of permanent transgenic lines. several x. tropicalis transgenic lines have now been generated, ... | 2002 | 12454928 |
| a study of mesoderm patterning through the analysis of the regulation of xmyf-5 expression. | xenopus laevis has been a particularly useful model organism for identifying factors involved in the induction and patterning of the mesoderm, however, much remains to be learned about how these factors interact. the myogenic transcription factor xmyf-5 is the earliest known gene to be expressed specifically in the dorsolateral mesoderm of the gastrula, a domain that is established by the interaction of dorsal and ventral signals. for this reason, we have begun to investigate how the expression ... | 2002 | 12050139 |
| complementarity of conserved sequence elements present in 28s ribosomal rna and in ribosomal protein genes of xenopus laevis and xenopus tropicalis. | the sequence analysis of the l1 ribosomal protein (r-protein) gene of xenopus laevis has revealed a strong homology in four out of the nine introns of the gene; this homology region spans 60 nucleotides (nt) with 80% homology [loreni et al., embo j. 4 (1985) 3483-3488]. we have extended our analysis to x. tropicalis, a species which is closely related to x. laevis. partial sequencing of the isolated l1 gene has revealed that these 60-nt homology regions are also present in at least two introns o ... | 1986 | 3569921 |
| tcf-1 expression during xenopus development. | we report the cloning and expression of xenopus tcf-1. the amino acid sequence of tcf-1 of xenopus laevis and xenopus tropicalis is closely related to that of chicken, mouse and man. thus, the family of tcf/lef proteins in the amphibian xenopus comprises four members as in higher vertebrates. rt-pcr analysis revealed that tcf-1 rna encoding a beta-catenin binding isoform is maternally present as well as throughout early development. different transcripts are expressed by alternative splicing. in ... | 2003 | 12711535 |
| depletion of the cell-cycle inhibitor p27(xic1) impairs neuronal differentiation and increases the number of elrc(+) progenitor cells in xenopus tropicalis. | the xenopus p27(xic1) gene encodes a cyclin dependent kinase (cdk) inhibitor of the cip/kip family. we have previously shown that p27(xic1) is expressed in the cells of the neural plate as they become post-mitotic (development 127 (2000) 1303). to investigate whether p27(xic1) is necessary for cell cycle exit and/or neuronal differentiation, we used antisense morpholino oligos (mo) to knockdown the protein levels in vivo. for such knockdown studies, xenopus tropicalis is a better model system th ... | 2003 | 12782277 |
| estrogen receptors in xenopus: duplicate genes, splice variants, and tissue-specific expression. | the estrogenic steroid hormones, acting primarily through the nuclear estrogen receptors eralpha and erbeta, regulate sexual differentiation in a wide variety of vertebrates. in the frog xenopus laevis, estrogen regulates the strength of vocal neuromuscular synapses and contributes to the physiological basis of sexually differentiated songs. to understand the mechanisms by which estrogen produces these effects, we have characterized the ers of x. laevis and their expression in laryngeal muscle a ... | 2003 | 12899845 |
| regulation of the g2/m transition in oocytes of xenopus tropicalis. | the molecular events regulating hormone-induced oocyte activation and meiotic maturation are probably best understood in xenopus laevis. in x. laevis, progesterone activates the g2-arrested oocyte, induces entry into m phase of meiosis i (mi) and resumption of the meiotic cell cycles, and leads to the formation of a mature, fertilizable egg. oocytes of xenopus tropicalis offer several practical advantages over those of x. laevis, including faster and more synchronous meiotic cell cycle progressi ... | 2003 | 12921744 |
| cross-fertilization and structural comparison of egg extracellular matrix glycoproteins from xenopus laevis and xenopus tropicalis. | while the anuran amphibian xenopus laevis is a widely used vertebrate model system, it is not optimal for genetic manipulations due to its tetraploid genome and long generation time. a current alternative amphibian model system, xenopus tropicalis, has the advantages of a diploid genome and a much shorter generation time. we undertook a comparative investigation of x. tropicalis egg extracellular matrix glycoproteins in relation to those already characterized in x. laevis. fertilization methods ... | 2003 | 14511753 |
| a model of tripeptidyl-peptidase i (cln2), a ubiquitous and highly conserved member of the sedolisin family of serine-carboxyl peptidases. | tripeptidyl-peptidase i, also known as cln2, is a member of the family of sedolisins (serine-carboxyl peptidases). in humans, defects in expression of this enzyme lead to a fatal neurodegenerative disease, classical late-infantile neuronal ceroid lipofuscinosis. similar enzymes have been found in the genomic sequences of several species, but neither systematic analyses of their distribution nor modeling of their structures have been previously attempted. | 2003 | 14609438 |
| identification of the blood group lewis(a) determinant in the oviducal mucins of xenopus tropicalis. | the amphibian xenopus tropicalis appears an increasingly appealing model for both genetic and developmental biology studies, compared to the related species xenopus laevis. study of the glycosylation pattern of its secreted glycoproteins revealed that this species synthesizes large amounts of lewis(a) epitope, whereas this motif has previously only been identified in animals within the primate lineage. the use of (1)h-nuclear magnetic resonance spectroscopy enabled us to resolve the sequence of ... | 2003 | 14623089 |
| cloning and characterisation of myf5 and myod orthologues in xenopus tropicalis. | the myogenic regulatory genes myod and myf5 are members of the bhlh transcription factor superfamily. these genes are expressed as an early response to mesoderm induction in the frog xenopus laevis. this paper describes our work to determine the conservation of sequence, expression and function of the early myogenic genes in the closely related diploid species xenopus tropicalis. to this end we have cloned and sequenced xenopus tropicalis homologues of myf5 and myod and found a high degree of co ... | 2003 | 14630393 |
| molecular components of the endoderm specification pathway in xenopus tropicalis. | xenopus laevis has been instrumental in elucidating a conserved molecular pathway that regulates vertebrate endoderm specification. however, loss-of-function analysis is required to resolve the precise function of the genes involved. for such analysis, antisense oligos and possibly forward genetics are likely to be more effective in the diploid species xenopus tropicalis than in the pseudotetraploid xenopus laevis. here we have isolated most of the tropicalis genes in the endoderm specification ... | 2003 | 12508233 |
| tracing of xenopus tropicalis germ plasm and presumptive primordial germ cells with the xenopus tropicalis daz-like gene. | a gamete is derived initially from a presumptive primordial germ cell (ppgc) and transmits genetic potential to the next generation. xenopus tropicalis, which is a close relative of xenopus laevis, has a diploid genome and advantages for genetic and genomic research; however, little is known about the developmental mechanism of its germinal lineage. here, we identified the xenopus tropicalis daz-like gene (xtdazl), which encodes rna-binding proteins homologous to xdazl in xenopus laevis and exam ... | 2004 | 14745962 |
| genetic linkage maps of the west african clawed frog xenopus tropicalis. | amphibians, and particularly the african clawed frog xenopus laevis, have been used for more than a century as models of vertebrate embryonic development. however, in many cases, elucidation of developmental functions of specific gene sequences could be severely impeded, because x. laevis is a tetraploid species, with multiple functional copies of many genes of interest. recent studies have shifted focus to the west african or tropical clawed frog, x. tropicalis, the only known diploid species o ... | 2003 | 12508229 |
| telomerase activity is widespread in adult somatic tissues of xenopus. | chromosome ends, or telomeres, are maintained by telomerase. work in selected vertebrates has implied that telomerase is often repressed in differentiated cells, and telomere erosion results in senescence of cultured cells. tissues from mature xenopus laevis frogs were examined for telomerase enzymatic activity with the trap (telomere repeat amplification protocol) assay. all tissues contained active telomerase, most abundantly in testis, spleen, liver, and embryos; activity was less abundant bu ... | 2003 | 12548544 |
| pattern and morphogenesis of presumptive superficial mesoderm in two closely related species, xenopus laevis and xenopus tropicalis. | the mesoderm, comprising the tissues that come to lie entirely in the deep layer, originates in both the superficial epithelial and the deep mesenchymal layers of the early amphibian embryo. here, we characterize the mechanisms by which the superficial component of the presumptive mesoderm ingresses into the underlying deep mesenchymal layer in xenopus tropicalis and extend our previous findings for xenopus laevis. fate mapping the superficial epithelium of pregastrula stage embryos demonstrates ... | 2004 | 15136148 |
| the p53-induced wig-1 zinc finger protein is highly conserved from fish to man. | the p53-induced wig-1 gene encodes an unusual nuclear zinc finger protein with high sequence similarity between human, rat and mouse. wig-1 belongs to a group of proteins with widely spaced zinc fingers that bind double stranded (ds) rna. we show here that wig-1 is present in gallus gallus (chicken), silurana tropicalis (frog) and fugu rubripes (fish) by assembly of est sequence data from a range of data bases into putative cdnas. the zinc finger regions of wig-1 are almost completely conserved ... | 2004 | 15138600 |
| characterization of a mycobacterium ulcerans-like infection in a colony of african tropical clawed frogs (xenopus tropicalis). | a nontuberculous mycobacterium ulcerans-like organism was identified as the causative agent of an epizootic of mycobacteriosis in a colony of african tropical clawed frogs, xenopus (silurana) tropicalis, at the university of california, berkeley. diverse clinical signs of disease were observed, including lethargy, excess buoyancy, coelomic effusion, cutaneous ulcers, and granulomas. visceral granulomas, ulcerative and granulomatous dermatitis, coelomitis, and septicemia were common findings at n ... | 2004 | 15253278 |
| evaluation of the developmental and reproductive toxicity of methoxychlor using an anuran (xenopus tropicalis) chronic exposure model. | the chronic toxicity of methoxychlor to the south african clawed frog, xenopus (silurana) tropicalis, was evaluated using a life cycle approach. the chronic exposure period ranged from mid-cell blastula stage [nf (nieuwkoop and faber, 1994) stage 8] to 90 days of exposure, during which time the organisms generally completed metamorphosis and emerged as juvenile frogs. methoxychlor concentrations ranged from 1 to 100 micrograms/l. methoxychlor concentrations >10 micrograms/l caused delayed develo ... | 2004 | 15272137 |
| ecotoxicogenomics: the challenge of integrating genomics into aquatic and terrestrial ecotoxicology. | rapid progress in the field of genomics (the study of how an individual's entire genetic make-up, the genome, translates into biological functions) is beginning to provide tools that may assist our understanding of how chemicals can impact on human and ecosystem health. in many ways, if scientific and regulatory efforts in the 20th century have sought to establish which chemicals cause damage to ecosystems, then the challenge in ecotoxicology for the 21st century is to understand the mechanisms ... | 2004 | 15003699 |
| excision of the tol2 transposable element of the medaka fish oryzias latipes in xenopus laevis and xenopus tropicalis. | the tol2 transposable element from the medaka fish belong to the hat family of transposons. in the previous studies, we have identified an autonomous member of this element, which encodes a fully functional transposase, and have shown that it can catalyze transposition in the zebrafish germ lineage. to date, the tol2 element is the only natural transposon in vertebrates from which an autonomous member has been identified. we report here transposase-dependent excision of the tol2 element in xenop ... | 2004 | 15302410 |
| a globin gene of ancient evolutionary origin in lower vertebrates: evidence for two distinct globin families in animals. | hemoglobin, myoglobin, neuroglobin, and cytoglobin are four types of vertebrate globins with distinct tissue distributions and functions. here, we report the identification of a fifth and novel globin gene from fish and amphibians, which has apparently been lost in the evolution of higher vertebrates (amniota). because its function is presently unknown, we tentatively call it globin x (gbx). globin x sequences were obtained from three fish species, the zebrafish danio rerio, the goldfish carassi ... | 2005 | 15356282 |
| construction of bac library for the amphibian xenopus tropicalis. | xenopus tropicalis has become an alternative model to the amphibian xenopus laevis because it is better suited for genetic and genomic studies. we have constructed a genomic bac library consisting of over 100,000 clones from sperm of xenopus tropicalis. analysis by pulsed field gel electrophoresis of representative bac clones indicated the average size of insert dna to be 100 kb, and we estimated the library covers 6 times the xenopus tropicalis genome of 1.7 x 10(9) base pairs. to evaluate the ... | 2004 | 15056936 |
| a downstream enhancer is essential for xenopus foxd5 transcription. | we have isolated and sequenced the pseudo-allelic versions of foxd5 genes in xenopus laevis, xlfoxd5a and xlfoxd5b, and the xtfoxd5 gene of xenopus tropicalis. these genes show a highly conserved structure, they are composed of only one exon, and they exhibit a high degree of sequence conservation within their flanking sequences. the x. tropicalis gene is expressed like its x. laevis orthologues in progenitor cells of the neural floor plate. serial deletions of the 5'- and 3'-flanking region in ... | 2004 | 15555577 |
| expression of xenopus tropicalis noggin1 and noggin2 in early development: two noggin genes in a tetrapod. | we report the identification of two distinct noggin genes in the tetrapod xenopus tropicalis. noggin functions to antagonize bmp signaling in many developmental contexts, and much work has explored its role in early vertebrate development. we have identified two noggin genes in the tropical clawed frog, x. tropicalis, a diploid anuran which is being explored for its potential as a genetic model system for early vertebrate development. here we report the cloning and characterization of the xenopu ... | 2004 | 15567718 |
| xenopus tropicalis peroxidasin gene is expressed within the developing neural tube and pronephric kidney. | peroxidasin, originally identified in drosophila, is a member of the myeloperoxidase family with a novel domain structure. it is proposed that peroxidasin is secreted and has functions associated with stabilization of the extracellular matrix. we report the identification of the xenopus tropicalis orthologue of the peroxidasin gene. we show that the predicted protein sequence of xenopus peroxidasin shows high sequence identity with the human orthologue and that the exon structure is highly conse ... | 2005 | 15614763 |
| xenopus tropicalis nodal-related gene 3 regulates bmp signaling: an essential role for the pro-region. | in vertebrates, nodal-related genes are crucial for specifying mesendodermal cell fates. six nodal-related genes have been identified in xenopus, but only one, nodal, has been identified in the mouse. the xenopus nodal-related gene 3 (xnr3), however, lacks the mesoderm-inducing activity of the other five nodal-related genes in xenopus, and can directly induce neural tissue in animal caps by antagonizing bmp signals. in this study, we isolated three clones of the xenopus (silurana) tropicalis nod ... | 2004 | 14697360 |
| evolution of new hormone function: loss and gain of a receptor. | the vertebrate proglucagon gene encodes three glucagon-like sequences (glucagon, glucagon-like peptide-1 [glp-1], and glucagon-like peptide 2 [glp-2]) that have distinct functions in regulating metabolism in mammals. in contrast, glucagon and glp-1 have similar physiological actions in fish, that of mammalian glucagon. we have identified sequences similar to receptors for proglucagon-derived peptides from the genomes of two fish (pufferfish and zebrafish), a frog (xenopus tropicalis), and a bird ... | 2005 | 15653559 |
| divergence of conserved non-coding sequences: rate estimates and relative rate tests. | in many eukaryotic genomes only a small fraction of the dna codes for proteins, but the non-protein coding dna harbors important genetic elements directing the development and the physiology of the organisms, like promoters, enhancers, insulators, and micro-rna genes. the molecular evolution of these genetic elements is difficult to study because their functional significance is hard to deduce from sequence information alone. here we propose an approach to the study of the rate of evolution of f ... | 2004 | 15282332 |
| vertebrate 2xrbd hnrnp proteins: a comparative analysis of genome, mrna and protein sequences. | hnrnp proteins are involved in many cell functions, primarily in pre-mrna processing. we report here a comparative analysis of the genes of the 2xrbd members of the hnrnp family and of their expression products. starting from the seven well characterized hnrnp members of human and murine origin (a0, a1, a2/b1, a3, ab, d and dl) and the three musashi-like proteins with related rbd tandems (msi1, msi2 and dazap1), we identified through blast search 12 homologous genes in the genome of danio rerio ... | 2005 | 15680582 |
| comparative sensitivity of xenopus tropicalis and xenopus laevis as test species for the fetax model. | the use of xenopus tropicalis as an alternative test species for the frog embryo teratogenesis assay-xenopus (fetax) model was evaluated. five test substances with varying developmental toxicity potential were evaluated using the traditional fetax (x. laevis) and a modified assay to accommodate the use of x. tropicalis. two separate definitive concentration-response tests were performed with ethanol, semicarbazide, copper, 6-aminonicotinamide (6-an) and atrazine. in order to evaluate the impact ... | 2004 | 15551382 |
| cryopreservation of sperm of xenopus laevis and xenopus tropicalis. | now that transgenic strains of xenopus laevis and x. tropicalis can be generated efficiently and with genomic sequence resources available for x. tropicalis, early amphibian development can be studied using integrated biochemical and genetic approaches. however, housing large numbers of animals generated during genetic screens or produced as novel transgenic lines presents a considerable challenge. we describe a method for cryopreserving xenopus sperm that should facilitate low maintenance, long ... | 2005 | 15645449 |
| phylogenomic analysis and expression patterns of large maf genes in xenopus tropicalis provide new insights into the functional evolution of the gene family in osteichthyans. | we have performed an exhaustive characterization of the large maf family of basic leucine zipper transcription factors in vertebrates using the genome data available, and studied the embryonic expression patterns of the four paralogous genes thus identified in xenopus tropicalis. our phylogenetic analysis shows that, in osteichthyans, the large maf family contains four orthology classes, mafa, mafb, c-maf and nrl, which have emerged in vertebrates prior to the split between actinopterygians and ... | 2005 | 15759153 |
| a gynogenetic screen to isolate naturally occurring recessive mutations in xenopus tropicalis. | in the rapidly developing, diploid amphibian xenopus tropicalis, genetics can be married to the already powerful tools of the amphibian system to overcome a disability that has hampered xenopus laevis as a model organism: the difficulties inherent in conducting genetic analyses in a tetraploid organism with a longer generation time. we describe here a gynogenetic screen to uncover naturally occurring recessive mutations in wild x. tropicalis populations, a procedure that is both faster and easie ... | 2005 | 15763208 |
| a xenopus tropicalis oligonucleotide microarray works across species using rna from xenopus laevis. | microarrays have great potential for the study of developmental biology. as a model system xenopus is well suited for making the most of this potential. however, xenopus laevis has undergone a genome wide duplication meaning that most genes are represented by two paralogues. this causes a number of problems. most importantly the presence of duplicated genes mean that a x. laevis microarray will have less or even half the coverage of a similar sized microarray from the closely related but diploid ... | 2004 | 15763212 |
| hnrnp a3 genes and pseudogenes in the vertebrate genomes. | the hnrnp a/b type proteins are abundant nuclear factors that bind to pol ii transcripts and are involved in numerous rna-related activities. to date most data on the hnrnp a/b family have been obtained with recombinant proteins and cell cultures. further characterization can result from an examination of the impact of various modifications in intact functional loci; however, such characterization is hampered by the presence of numerous and widely dispersed hnrnp a/b-related sequences in the mam ... | 2005 | 15776420 |
| recombineered xenopus tropicalis bac expresses a gfp reporter under the control of arx transcriptional regulatory elements in transgenic xenopus laevis embryos. | the aristaless-related homeobox (arx) gene is expressed in a dynamic pattern in the developing vertebrate forebrain. we identified a bacterial artificial chromosome (bac) containing the xenopus tropicalis arx gene and replaced a portion of the first coding exon with a green fluorescent protein (gfp) expression cassette by homologous recombination in bacteria (recombineering). transgenic x. laevis embryos obtained by microinjecting the modified bac expressed gfp in the developing forebrain in a p ... | 2005 | 15789419 |
| cloning and characterization of xenopus beta2-microglobulin. | cdnas for xenopus beta2-microglobulin (beta2m), the obligatory light chain of most vertebrate major histocompatibility complex (mhc) class i molecules, were isolated and ests were identified. alignment of the deduced amino acid sequence to other species' beta2m showed that the overall structure is evolutionarily conserved, and phylogenetic analysis showed that the xenopus beta2m sequence is intermediate between fish and bird/mammal beta2m. the xenopus beta2m mrna is expressed ubiquitously with h ... | 2005 | 15854684 |
| a newly discovered mycobacterial pathogen isolated from laboratory colonies of xenopus species with lethal infections produces a novel form of mycolactone, the mycobacterium ulcerans macrolide toxin. | mycobacterium ulcerans, the causative agent of buruli ulcer, produces a macrolide toxin, mycolactone a/b, which is thought to play a major role in virulence. a disease similar to buruli ulcer recently appeared in united states frog colonies following importation of the west african frog, xenopus tropicalis. the taxonomic position of the frog pathogen has not been fully elucidated, but this organism, tentatively designated mycobacterium liflandii, is closely related to m. ulcerans and mycobacteri ... | 2005 | 15908356 |
| two members of the fxr gene family, fmr1 and fxr1, are differentially expressed in xenopus tropicalis. | the fxr gene family is composed of three members, fmr1, fxr1 and fxr2. the fmr1 gene is involved in the fragile x syndrome, whereas for the other two members, no human disorder has been identified yet. an appropriate animal model to study in vivo gene function is essential to unravel the cellular function of the gene products fmrp, fxr1p and fxr2p, respectively. in xenopus tropicalis both fmr1 and fxr1 were identified; however, unexpectedly fxr2 was not. here we describe the characterization of ... | 2005 | 15968590 |
| strategies for characterising cis-regulatory elements in xenopus. | understanding the cis-regulatory architecture of metazoan organisms is the greatest challenge facing genome biology today. in vertebrate organisms, distinct sequence elements mediate transcriptional regulation and are scattered throughout the genome, either proximal or distal to promoters. the identification of transcriptional enhancers has proven rather difficult by conventional experimental approaches. in the past decade, the rapid generation of genomic sequences for multiple vertebrate organi ... | 2005 | 15975265 |
| terrestrial vertebrates have two keratin gene clusters; striking differences in teleost fish. | keratins i and ii form the largest subgroups of mammalian intermediate filament (if) proteins and account as obligatory heteropolymers for the keratin filaments of epithelia. all human type i genes except for the k18 gene are clustered on chromosome 17q21, while all type ii genes form a cluster on chromosome 12q13, that ends with the type i gene k18. highly related keratin gene clusters are found in rat and mouse. since fish seem to lack a keratin ii cluster we screened the recently established ... | 2005 | 16032930 |
| comparative genomics on sox2 orthologs. | sox2 and pou5f1 (oct3 or oct4) transcription factors are implicated in fgf4 expression in embryonic stem (es) cells. sox2, pou5f1, and fgf4 are key molecules for the integrome network in oncology and stem cell biology. sox2 gene at human chromosome 3q26.33, sox1 gene at 13q34, and sox3 gene at xq27.1 constitute a subfamily among the sox gene family. here, rat sox2 and xenopus sox2 genes were identified and characterized by using bioinformatics for comparative genomics and comparative proteomics ... | 2005 | 16077994 |
| the genomic environment around the aromatase gene: evolutionary insights. | the cytochrome p450 aromatase (cyp19), catalyses the aromatisation of androgens to estrogens, a key mechanism in vertebrate reproductive physiology. a current evolutionary hypothesis suggests that cyp19 gene arose at the origin of vertebrates, given that it has not been found outside this clade. the human cyp19 gene is located in one of the proposed mhc-paralogon regions (hsa15q). at present it is unclear whether this genomic location is ancestral (which would suggest an invertebrate origin for ... | 2005 | 16098224 |
| development of metamorphosis assay using silurana tropicalis for the detection of thyroid system-disrupting chemicals. | the west african clawed frog (silurana tropicalis), which resembles the south african clawed frog (xenopus laevis), but is somewhat smaller, has a diploid genome and a shorter generation time. therefore, s. tropicalis has the potential for use as a new model in ecotoxicology. we demonstrated a s. tropicalis metamorphosis assay based on xenopus metamorphosis assay (xema) using 1 microg/l thyroxine (t4) and 75 mg/l propylthiouracil (ptu). tadpoles at developmental stages 48-50 were exposed to chem ... | 2006 | 16139362 |
| multiple noggins in vertebrate genome: cloning and expression of noggin2 and noggin4 in xenopus laevis. | noggin is a neural inducer secreted by cells of the spemann organizer. a single noggin gene was identified until very recently in all tested vertebrates. the only exception was zebrafish, in which two close homologs of noggin, named noggin1 and noggin3, and one gene more diverged from them, noggin2, were cloned. nevertheless, finding of three zebrafish noggins was attributed exclusively to specific genomic duplications in the fish evolutionary branch. however, very recently it was shown that xen ... | 2006 | 16168719 |
| specific expression of olfactory binding protein in the aerial olfactory cavity of adult and developing xenopus. | olfactory binding proteins (obp), commonly associated with aerial olfaction, are found in the olfactory mucus of mammals but have never been identified in fish. it is still not clear whether the presence of obp in aerial olfactory systems is due to phylogenetic or to functional differences linked to the adaptation of the olfactory system to an aerial environment. to test this alternative, the olfactory system of xenopus offers a unique opportunity because it includes two olfactory cavities, one ... | 2005 | 16190893 |
| contrasting modes of evolution between vertebrate sweet/umami receptor genes and bitter receptor genes. | taste reception is fundamental to diet selection in many animals. the genetic basis underlying the evolution and diversity of taste reception, however, is not well understood. recent discoveries of t1r sweet/umami receptor genes and t2r bitter receptor genes in humans and mice provided an opportunity to address this question. here, we report the identification of 20 putatively functional t1r genes and 167 t2r genes from the genome sequences of nine vertebrates, including three fishes, one amphib ... | 2006 | 16207936 |
| a truncated acidic domain in xenopus trf1. | telomere function is mediated by a complex of proteins bound to double-stranded and single-stranded telomeric repeats. a key player in this complex is trf1, which binds to duplex ttaggg repeats and acts as a negative regulator of telomere length. this protein's domain structure, as defined by studies with mammalian orthologs, consists of an n-terminal acidic domain, a dimerization domain, and a c-terminal myb dna binding domain. trf1 from xenopus laevis was cloned and sequenced, and the encoded ... | 2006 | 16309855 |
| mice have a transcribed l-threonine aldolase/gly1 gene, but the human gly1 gene is a non-processed pseudogene. | there are three pathways of l-threonine catabolism. the enzyme l-threonine aldolase (ta) has been shown to catalyse the conversion of l-threonine to yield glycine and acetaldehyde in bacteria, fungi and plants. low levels of ta enzymatic activity have been found in vertebrates. it has been suggested that any detectable activity is due to serine hydroxymethyltransferase and that mammals lack a genuine threonine aldolase. | 2005 | 15757516 |
| a new method to remove hybridization bias for interspecies comparison of global gene expression profiles uncovers an association between mrna sequence divergence and differential gene expression in xenopus. | the recent sequencing of a large number of xenopus tropicalis expressed sequences has allowed development of a high-throughput approach to study xenopus global rna gene expression. we examined the global gene expression similarities and differences between the historically significant xenopus laevis model system and the increasingly used x.tropicalis model system and assessed whether an x.tropicalis microarray platform can be used for x.laevis. these closely related species were also used to inv ... | 2006 | 16397297 |
| the mariner transposons belonging to the irritans subfamily were maintained in chordate genomes by vertical transmission. | mariner-like elements (mles) belong to the tc1-mariner superfamily of dna transposons, which is very widespread in animal genomes. we report here the first complete description of a mle, xtmar1, within the genome of a poikilotherm vertebrate, the amphibian xenopus tropicalis. a close relative, xlmle, is also characterized within the genome of a sibling species, xenopus laevis. the phylogenetic analysis of the relationships between mle transposases reveals that xtmar1 is closely related to hsmar2 ... | 2006 | 16408242 |
| highly efficient transgenesis in xenopus tropicalis using i-scei meganuclease. | in this study, we report a highly efficient transgenesis technique for xenopus tropicalis based on a method described first for medaka. this simple procedure entails co-injection of meganuclease i-scei and a transgene construct flanked by two i-scei sites into fertilized eggs. approximately 30% of injected embryos express transgenes in a promoter-dependent manner. about 1/3 of such embryos show incorporation of the transgene at the one-cell stage and the remainder are 'half-transgenics' suggesti ... | 2006 | 16413175 |
| genetic and genomic prospects for xenopus tropicalis research. | research using xenopus laevis has made enormous contributions to our understanding of vertebrate development, control of the eukaryotic cell cycle and the cytoskeleton. one limitation, however, has been the lack of systematic genetic studies in xenopus to complement molecular and cell biological investigations. work with the closely related diploid frog xenopus tropicalis is beginning to address this limitation. here, we review the resources that will make genetic studies using x. tropicalis a r ... | 2006 | 16427790 |
| a developmental switch induced by thyroid hormone: xenopus laevis metamorphosis. | thyroid hormone induces the complete metamorphosis of anuran tadpoles into juvenile frogs. arguably, anuran metamorphosis is the most dramatic effect of a hormone in any vertebrate. recent advances in pharmacology and molecular biology have made the study of this remarkable process in the frog xenopus laevis attractive to developmental biologists and endocrinologists alike. in particular, the availability of a straightforward transgenesis assay and the near completion of the xenopus tropicalis g ... | 2006 | 16464605 |
| identification of post-transcriptionally regulated xenopus tropicalis maternal mrnas by microarray. | cytoplasmic control of the adenylation state of mrnas is a critical post-transcriptional process involved in the regulation of mrnas stability and translational efficiency. the early development of xenopus laevis has been a major model for the study of such regulations. we describe here a microarray analysis to identify mrnas that are regulated by changes in their adenylation state during oogenesis and early development of the diploid frog xenopus tropicalis. the microarray data were validated u ... | 2006 | 16464828 |
| gene silencing in xenopus laevis by dna vector-based rna interference and transgenesis. | a vector-based rnai expression system was developed using the xenopus tropicalis u6 promoter, which transcribes small rna genes by rna polymerase iii. the system was first validated in a xenopus laevis cell line, designing a short hairpin dna specific for the gfp gene. co-transfection of the vector-based rnai and the gfp gene into xenopus xr1 cells significantly decreased the number of gfp-expressing cells and overall gfp fluorescence. vector-based rnai was subsequently validated in gfp transgen ... | 2006 | 16467881 |
| developmental expression patterns of tbx1, tbx2, tbx5, and tbx20 in xenopus tropicalis. | t-box genes have diverse functions during embryogenesis and are implicated in several human congenital disorders. here, we report the identification, sequence analysis, and developmental expression patterns of four members of the t-box gene family in the diploid frog xenopus tropicalis. these four genes-tbx1, tbx2, tbx5, and tbx20-have been shown to influence cardiac development in a variety of organisms, in addition to their individual roles in regulating other aspects of embryonic development. ... | 2006 | 16477648 |
| proceedings of the smbe tri-national young investigators' workshop 2005. lineage-specific expansions and contractions of the bitter taste receptor gene repertoire in vertebrates. | the sense of bitter taste plays a critical role in how organisms avoid generally bitter toxic and harmful substances. previous studies revealed that there were 25 intact bitter taste receptor (t2r) genes in humans and 34 in mice. however, because the recent chicken genome project reported only three t2r genes, it appears that extensive gene expansions occurred in the lineage leading to mammals or extensive gene contractions occurred in the lineage leading to birds. here, i examined the t2r gene ... | 2006 | 16484289 |
| the amphibian globin gene repertoire as revealed by the xenopus genome. | the draft genome sequence of the western clawed frog xenopus (silurana) tropicalis facilitates the identification, expression analysis and phylogenetic classification of the amphibian globin gene repertoire. frog and mammalian neuroglobin display about 67% protein sequence identity, with the expected predominant expression in frog brain and eye. frog and mammalian cytoglobins share about 69% of their amino acids, but the frog protein lacks the mammalian-type extension at the c-terminus. like in ... | 2006 | 16484786 |
| [importance of development of ecotoxicogenomics in understanding molecular mechanisms of chemicals in developing animals]. | developing organisms are sensitive to estrogenic chemicals. exposure to estrogens or estrogenic chemicals during critical periods of development induces persistent changes in reproductive as well as nonreproductive organs, including persistent molecular alterations. chemicals released into the environment potentially disrupt the endocrine system in wild animals and humans, some of which exhibit estrogenic or anti-androgenic activity by binding to estrogen or androgen receptors. estrogen-responsi ... | 2006 | 16506650 |
| ancestral organization of the mhc revealed in the amphibian xenopus. | with the advent of the xenopus tropicalis genome project, we analyzed scaffolds containing mhc genes. on eight scaffolds encompassing 3.65 mbp, 122 mhc genes were found of which 110 genes were annotated. expressed sequence tag database screening showed that most of these genes are expressed. in the extended class ii and class iii regions the genomic organization, excluding several block inversions, is remarkably similar to that of the human mhc. genes in the human extended class i region are als ... | 2006 | 16517736 |
| comparison of induction during development between xenopus tropicalis and xenopus laevis. | several in vitro systems exist for the induction of animal caps using growth factors such as activin. in this paper, we compared the competence of activin-treated animal cap cells dissected from the late blastulae of xenopus tropicalis and xenopus laevis. the resultant tissue explants from both species differentiated into mesodermal and endodermal tissues in a dose-dependent manner. in addition, rt-pcr analysis revealed that organizer and mesoderm markers were expressed in a similar temporal and ... | 2006 | 16525933 |
| evolution of abca4 proteins in vertebrates. | the abca4 (abcr) gene encodes a retinal-specific atp-binding cassette transporter. mutations in abca4 are responsible for several recessive macular dystrophies and susceptibility to age related macular degeneration (amd). the protein appears to function as a flippase of all-trans-retinaldehyde and/or its derivatives across the membrane of outer segment disks and is a potentially important element in recycling visual cycle metabolites. however, the understanding of abca4's role in the visual cycl ... | 2005 | 15696369 |
| sequencing and analysis of 10,967 full-length cdna clones from xenopus laevis and xenopus tropicalis reveals post-tetraploidization transcriptome remodeling. | sequencing of full-insert clones from full-length cdna libraries from both xenopus laevis and xenopus tropicalis has been ongoing as part of the xenopus gene collection initiative. here we present 10,967 full orf verified cdna clones (8049 from x. laevis and 2918 from x. tropicalis) as a community resource. because the genome of x. laevis, but not x. tropicalis, has undergone allotetraploidization, comparison of coding sequences from these two clawed (pipid) frogs provides a unique angle for exp ... | 2006 | 16672307 |
| one of the duplicated matrix metalloproteinase-9 genes is expressed in regressing tail during anuran metamorphosis. | the drastic morphological changes of the tadpole are induced during the climax of anuran metamorphosis, when the concentration of endogenous thyroid hormone is maximal. the tadpole tail, which is twice as long as the body, shortens rapidly and disappears completely in several days. we isolated a cdna clone, designated as xl mmp-9th, similar to the previously reported xenopus laevis mmp-9 gene, and showed that their xenopus tropicalis counterparts are located tandemly about 9 kb apart from each o ... | 2006 | 16681648 |
| experimental analysis of lens-forming capacity in xenopus borealis larvae. | previously, the only anuran amphibians known to have the capacity to regenerate a lens after lentectomy were xenopus laevis and xenopus tropicalis. this regeneration process occurs during the larval life through transdifferentiation of the outer cornea promoted by inductive factors produced by the retina and accumulated inside the vitreous chamber. however, the capacity of x. tropicalis to regenerate a lens is much lower than that of x. laevis. this study demonstrates that xenopus borealis, a sp ... | 2006 | 16703619 |
| xenopus tropicalis oocytes: more than just a beautiful genome. | for more than 30 yr, xenopus laevis has been the animal of choice for studying the biochemical regulation of the meiotic and early mitotic vertebrate cell cycles. attracted by its diploid genome, several laboratories have begun using the similar, although evolutionarily distinct, frog xenopus tropicalis for studies of vertebrate development. comparisons between the two species indicate that their development is similar in most respects. both frogs share many advantages, including their amenabili ... | 2006 | 16739715 |