Publications

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xenbase: a genomic, epigenomic and transcriptomic model organism database.xenbase (www.xenbase.org) is an online resource for researchers utilizing xenopus laevis and xenopus tropicalis, and for biomedical scientists seeking access to data generated with these model systems. content is aggregated from a variety of external resources and also generated by in-house curation of scientific literature and bioinformatic analyses. over the past two years many new types of content have been added along with new tools and functionalities to reflect the impact of high-throughpu ...029059324
paternal chromosome loss and metabolic crisis contribute to hybrid inviability in xenopus.hybridization of eggs and sperm from closely related species can give rise to genetic diversity, or can lead to embryo inviability owing to incompatibility. although central to evolution, the cellular and molecular mechanisms underlying post-zygotic barriers that drive reproductive isolation and speciation remain largely unknown. species of the african clawed frog xenopus provide an ideal system to study hybridization and genome evolution. xenopus laevis is an allotetraploid with 36 chromosomes ...029320479
a novel stress hormone response gene in tadpoles of xenopus tropicalis.previous work identified a transcribed locus, str. 34945, induced by the frog stress hormone corticosterone (cort) in xenopus tropicalis tails. because thyroid hormone had no influence on its expression, str. 34945 was dubbed the first "cort-only" gene known from tadpoles. here, we examine the genomic annotation for this transcript, hormone specificity, time course of induction, tissue distribution, and developmental expression profile. the location of str. 34945 on the x. tropicalis genome lies ...029339184
functional characterization of the mucus barrier on the xenopus tropicalis skin surface.mucosal surfaces represent critical routes for entry and exit of pathogens. as such, animals have evolved strategies to combat infection at these sites, in particular the production of mucus to prevent attachment and to promote subsequent movement of the mucus/microbe away from the underlying epithelial surface. using biochemical, biophysical, and infection studies, we have investigated the host protective properties of the skin mucus barrier of the xenopus tropicalis tadpole. specifically, we h ...029311327
orchestrated positioning of post-transcriptional modifications at the branch point recognition region of u2 snrna.the branch point recognition region of spliceosomal snrna u2 is heavily modified post-transcriptionally in most eukaryotic species. we focused on this region to learn how nearby positions may interfere with each other when targeted for modification. using an in vivo yeast saccharomyces cerevisiae cell system, we tested the modification activity of several guide rnas from human, mouse, the frog xenopus tropicalis, the fruit fly drosophila melanogaster, and the worm caenorhabditis elegans we exper ...028974555
evi and mds/evi are required for adult intestinal stem cell formation during postembryonic vertebrate development.the gene ectopic viral integration site 1 (evi) and its variant myelodysplastic syndrome 1 (mds)/evi encode zinc-finger proteins that have been recognized as important oncogenes in various types of cancer. in contrast to the established role of evi and mds/evi in cancer development, their potential function during vertebrate postembryonic development, especially in organ-specific adult stem cells, is unclear. amphibian metamorphosis is strikingly similar to postembryonic development around birth ...028928245
chronic toxicity of 1,3,5-triazine herbicides in the postembryonic development of the western clawed frog silurana tropicalis.seven 1,3,5- triazine (s-triazine) herbicides (ametryn, prometryn, dimethametryn, simazine, atrazine, propazine, and cyanazine) were tested using an amphibian (silurana tropicalis) metamorphosis assay focusing on morphometric, gravimetric, and thyroid-histological endpoints. premetamorphic tadpoles were exposed to each s-triazine at 2 concentrations between 1/1000 and 1/10 of the 96-h acute toxicity values, until all tadpoles in the control group reached either the late prometamorphosic stages o ...028869887
thyroid hormone receptor α- and β-knockout xenopus tropicalis tadpoles reveal subtype-specific roles during development.thyroid hormone (th) binds th receptor α (trα) and β (trβ) to induce amphibian metamorphosis. whereas th signaling has been well studied, functional differences between trα and trβ during this process have not been characterized. to understand how each tr contributes to metamorphosis, we generated trα- and trβ-knockout tadpoles of xenopus tropicalis and examined developmental abnormalities, histology of the tail and intestine, and messenger rna expression of genes encoding extracellular matrix-d ...029126198
karyotype analysis of xenopus tropicalis gray, pipidae. 19734780767
the expression of antibody diversity in natural and laboratory-made polyploid individuals of the clawed toad xenopus.antibody diversity, as measured by isoelectric focusing of dinitrophenol-specific antibodies, was compared in different polyploid species of the clawed toad xenopus. antibody heterogeneity increased with chromosome number and dna content from xenopus tropicalis (2n = 20 chromosome) to xenopus ruwenzoriensis (2n = 108 chromosomes). laboratory allopolyploids made by hybridization between two species showing different antibody diversities and different chromosome numbers gave antibody patterns inte ...19826802750
a comparison of the karyotype, constitutive heterochromatin, and nucleolar organizer regions of the new tetraploid species xenopus epitropicalis fischberg and picard with those of xenopus tropicalis gray (anura, pipidae).a cytological analsis of the recently discovered tetraploid species xenopus epitropicalis was carried out, using, in addition to the classical orcein method, silver staining and alkaline giemsa banding techniques. the chromosome number of x. epitropicalis was found to be 40. the chromosomes can be grouped in to sets of four similar chromosomes (quartets), resembling the karyotype of x. tropicalis (2n = 20). however, c-band patterns revealed heterogeneity within the quartets, dividing each of the ...19827151486
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 ...19826296782
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 ...19826280148
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), ...19853994660
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 ...19863774540
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 ...19863569921
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 ...19863100812
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 ...19863009830
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 ...19873031599
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 ...19873653078
nucleotide sequence of the xenopus tropicalis larval beta globin gene. 19873697074
changing the rna polymerase specificity of u snrna gene promoters.the promoter of a xenopus tropicalis u6 gene can be transcribed by both rna polymerases ii and iii. two distinct elements, a tata-like sequence and the region of transcription initiation, are only required for transcription by rna polymerase iii, while further common elements are required for transcription by both polymerases. based on the unusually stringent requirement for a purine at the normal position of polymerase iii transcription initiation and on the properties of mutants in this region ...19883180217
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 ...19883174434
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 ...19883172214
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 ...19883148743
phylogenetic relationships of the pipid frogs xenopus and silurana: an integration of ribosomal dna and morphology.relationships of the pipid frog genus silurana (= xenopus tropicalis group of some authors) are of particular interest to developmental and molecular biologists because of the purported ancestral (i.e., unduplicated) karyotype of s. tropicalis relative to the genus xenopus. although most previous studies have assumed that silurana is the sister group of xenopus, recent morphological work suggests that silurana is more closely related both to the south american genus pipa and to the african gener ...19902385174
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 ...19921538402
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 ...19979218589
frog genetics: xenopus tropicalis jumps into the future. 19989676522
the development of xenopus tropicalis transgenic lines and their use in studying lens developmental timing in living embryos.the generation of reporter lines for observing lens differentiation in vivo demonstrates a new strategy for embryological manipulation and allows us to address a long-standing question concerning the timing of the onset of differentiation. xenopus tropicalis was used to make gfp reporter lines with (gamma)1-crystallin promoter elements directing gfp expression within the early lens. x. tropicalis is a close relative of x. laevis that shares the same ease of tissue manipulation with the added ben ...200010751168
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 ...200011083943
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 diseases200010756157
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 ...200010629097
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( ...200111738090
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 ...200111477685
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 ...200111402039
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 ...200111264232
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.200111597339
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 ...200112064605
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 ...200111685571
structure and expression of xenopus tropicalis bmp-2 and bmp-4 genes.the xenopus tropicalis bmp-2 and bmp-4 genes have been cloned and sequenced. a comparison with the corresponding genes from x. laevis reveals that the bmp-4 genes are conserved at a higher extent than the bmp-2 genes. this is especially evident for the intron sequences, but is also reflected by the exon sequences. while the amino acids of x. tropicalis and x. laevis bmp-4 proteins diverge at about 4%, those of bmp-2 proteins diverge at about 7%. by reverse transcriptase polymerase chain reaction ...200111677055
chromosome mapping of xenopus tropicalis using the g- and ag-bands: tandem duplication and polyploidization of larvae heads.developmental cytogenetic analyses of xenopus tropicalis larvae from two origins were performed on stage 27-34 heads treated with colchicine. standard g-band karyotyping using trypsin and chromosome mapping of 184 bands were examined. although the main karyotype was 2n = 20, polyploidy (3n = 30 or 4n = 40) and aneuploidy were detected in each individual treated with colchicine, even those treated for only 1 h. the percentage of polyploid karyotypes was 10-20% across the total of measured metapha ...200212392576
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 ...200212454926
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 ...200211803576
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 ...200212454920
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 ...200212203730
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 ...200212102573
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 ...200211977986
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 ...200212351198
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 ...200212204263
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 ...200212060070
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 ...200212050139
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, ...200212454928
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 ...200312508229
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 ...200312548544
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 ...200312711535
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 ...200312782277
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 ...200312899845
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 ...200314511753
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 ...200314623089
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 ...200314630393
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 ...200312508233
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.200314609438
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 ...200312921744
lack of expression of the t-cell marker xtla-1 in xenopus tropicalis: exploitation in thymus restoration studies.flow cytometric studies employing the monoclonal antibody xt-1 reveal that, in contrast to other strains and species of xenopus examined, thymocytes and splenocytes from x. tropicalis do not express the t lineage-specific antigen xtla-1. thymus dependence of xtla-1 expression in splenocytes is confirmed in x. laevis by early thymectomy experiments. when x. tropicalis larval thymus is implanted to thymectomized x. borealis larvae, histological studies reveal extensive colonisation by host-derived ...20031773855
evaluation of xenopus tropicalis as an alternative test organism for frog embryo teratogenesis assay--xenopus (fetax).as a formal recommendation from an interagency coordinating committee for the validation of alternative methods (iccvam) workshop review of the frog embryo teratogenesis assay--xenopus (fetax) developmental toxicity model, the use of xenopus tropicalis as an alternative test species for this model was evaluated. three test substances with varying developmental toxicity potentials were evaluated using fetax modified to accommodate the use of x. tropicalis. two separate definitive concentration-re ...200312953658
defining a large set of full-length clones from a xenopus tropicalis est project.amphibian embryos from the genus xenopus are among the best species for understanding early vertebrate development and for studying basic cell biological processes. xenopus, and in particular the diploid xenopus tropicalis, is also ideal for functional genomics. understanding the behavior of genes in this accessible model system will have a significant and beneficial impact on the understanding of similar genes in other vertebrate systems. here we describe the analysis of 219,270 x. tropicalis e ...200415223350
pilot morpholino screen in xenopus tropicalis identifies a novel gene involved in head development.the diploid frog x. tropicalis has recently been adopted as a model genetic system, but loss-of-function screens in xenopus have not yet been performed. we have undertaken a pilot functional knockdown screen in x. tropicalis for genes involved in nervous system development by injecting antisense morpholino (mo) oligos directed against x. tropicalis mrnas. twenty-six genes with primary expression in the nervous system were selected as targets based on an expression screen previously conducted in ...200414745953
strategy for profiling and structure elucidation of mucin-type oligosaccharides by mass spectrometry.a strategy combining accurate mass determination, tandem mass spectrometry, structure homology, and exoglycosidases is described that allows the structural characterization of mucin-type o-linked oligosaccharides. the method is used to profile with quantitation the o-linked oligosaccharide (both neutral and anionic) components of the only diploid xenopus frog, xenopus tropicalis. collision-induced dissociation was used to determine connectivity, to identify previously characterized oligosacchari ...200415481946
analysis of the tcf-3 promoter during early development of xenopus.xtcf-3 functions as a transcriptional regulator in the canonical wnt signaling cascade and can repress or activate downstream target genes. expression of xtcf-3 is differentially regulated in time and place during development (molenaar et al. [1998] mech dev. 75:151-154), but little is known about the mechanisms that control transcriptional activation and repression. a 15-kb genomic fragment of tcf-3 sequences from xenopus tropicalis was cloned, including the 5' untranslated region; exons 1, 2, ...200415376330
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 ...200415272137
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 ...200415763212
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 ...200414697360
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 ...200415567718
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 ...200415551382
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 ...200415555577
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 ...200414745962
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 ...200415003699
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 ...200415056936
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 ...200415136148
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 ...200415138600
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 ...200415253278
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 ...200415282332
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 ...200415302410
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 ...200515645449
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 ...200515653559
the arid domain protein dril1 is necessary for tgf(beta) signaling in xenopus embryos.arid domain proteins are members of a highly conserved family involved in chromatin remodeling and cell-fate determination. dril1 is the founding member of the arid family and is involved in developmental processes in both drosophila and caenorhabditis elegans. we describe the first embryological characterization of this gene in chordates. dril1 mrna expression is spatiotemporally regulated and is detected in the involuting mesoderm during gastrulation. inhibition of dril1 by either a morpholino ...200515680369
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 ...200515680582
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 ...200515696369
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.200515757516
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 ...200515759153
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 ...200515763208
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 ...200515908356
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 ...200516098224
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 ...200515776420
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 ...200515614763
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 ...200515356282
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 ...200515789419
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 ...200515854684
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 ...200515968590
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