Publications

excretion and metabolism of phenol, 4-nitrophenol and 2-methylphenol by the frogs rana temporaria and xenopus laevis.	1. rana and xenopus excrete 90-95% dose, and metabolize 50-65% dose of phenol, 4-nitrophenol and 2-methylphenol within 24 h, to about the same extent. 2. kinetic data for the excretion of phenols from both species fit a two-compartment model. the elimination constants of rana and xenopus are not significantly different. 3. metabolism is mostly conjugation by glucuronidation and sulphation of the original phenols. additionally, oxidations leading to dihydroxyphenols and benzoic acid from 2-methyl ...	1987	3501639
properties of a distal regulatory element controlling transcription of the u2 small nuclear rna.	the upstream region of human u2 genes contains a distal transcriptional control element, previously mapped between nucleotide (nt) positions -198 and -258 (westin et al., 1984b). in the present study we show that it resembles transcriptional enhancers in being active even from a distance of 1.4 kb. however, in contrast to most other enhancers it functions unidirectionally in xenopus laevis oocytes. the distal control element was further mapped by construction of truncated templates for u2 rna tr ...	1987	3436529
purification of a novel, nucleoplasmin-like protein from somatic nuclei.	we have purified a nucleoplasmin-like protein from the nuclei of somatic xenopus laevis cells. this protein possesses a number of the distinctive features of nucleoplasmin isolated from oocytes or unfertilized eggs. the protein is recognized by both monoclonal and polyclonal antisera raised against egg nucleoplasmin. the protein has an oligomeric structure, which must be heated in sds to completely dissociate, is acidic, phosphorylated and efficiently promotes the in vitro formation of chromatin ...	1987	3443097
mapping at the nucleotide level of xenopus laevis mitochondrial d-loop h strand: structural features of the 3' region.	the d-loop resulting from limited synthesis of the newly replicated heavy (h) strand of mitochondrial dna provides a good opportunity to examine both the origin and termination of dna synthesis. we report here the precise determination of the 3' and 5' termini of nascent xenopus laevis d-loop h strand. we observe two major classes of newly synthesized d-loop h strands, 1641 and 1675 nucleotides long. a stable putative secondary structure located around its 3' end is described. analogous secondar ...	1987	3453088
differential accumulation of u1 and u4 small nuclear rnas during xenopus development.	we showed previously that those u1 small nuclear rna (snrna) genes of xenopus laevis which are transcribed very actively in early embryos are quiescent in mature (stage vi) oocytes (forbes et al. 1984). although that study demonstrated that differential control of snrna genes occurred, it did not describe snrna accumulation during development. using high-resolution polyacrylamide gels in combination with northern blot hybridization and rna sequence analyses, we show here that xenopus has at leas ...	1987	3428589
dna sequences for typical ribosomal gene spacers from xenopus laevis and xenopus borealis.		1987	3453114
posttranscriptional regulation of albumin gene expression in xenopus liver: evidence for an estrogen receptor-dependent mechanism.	we have previously shown that estrogen administration to male xenopus laevis results in the posttranscriptional suppression of serum albumin mrna concurrent with the transcriptional activation of the genes for the yolk protein precursor vitellogenin. to determine whether the posttranscriptional regulation of albumin gene expression is mediated through a mechanism involving the high affinity estrogen receptor protein or through a receptor-independent mechanism involving a middle affinity cytoplas ...	1987	3454873
heat shock stabilizes highly unstable transcripts of the xenopus ribosomal gene spacer.	we have shown recently that, in xenopus laevis oocytes, the 3' end of the longest detectable ribosomal precursor rna is not formed by transcription termination but by rna processing and that rna polymerase i continues to transcribe through the intergenic spacer region. in oocytes, these spacer transcripts are turned over rapidly, and the only apparent transcription termination site is located 215 base pairs upstream of the 5' end of the next transcription unit. in this paper we show that, at hea ...	1987	3467358
expression of size-selected mrna encoding the intestinal na/glucose cotransporter in xenopus laevis oocytes.	the expression of the rabbit intestinal brushborder na/glucose cotransporter has been studied in xenopus oocytes. poly(a)+ rna isolated from the intestinal mucosa was injected into oocytes, and the expression of the transporter in the oocyte plasma membrane was assayed by measuring the na-dependent phlorizin-sensitive uptake of methyl alpha-d-[14c]glucopyranoside (meglc). expression of the glucose carrier was detected 3-7 days after mrna injection, and the rate of glucose transport was proportio ...	1987	3472228
the phosphorylation of nucleoplasmin by casein kinase-2 is resistant to heparin inhibition.	highly purified preparations of casein kinase-2 from the nuclei of xenopus laevis oocytes and from calf thymus can phosphorylate in vitro purified nucleoplasmin from x. laevis oocytes and eggs. the phosphorylation of nucleoplasmin by both kinase preparations is quite insensitive to heparin in contrast with casein phosphorylation which is completely abolished by heparin concentrations above 10 micrograms/ml. however, the phosphorylation of nucleoplasmin and casein are inhibited in a very similar ...	1987	3480242
the estrogen-responsive element as an inducible enhancer: dna sequence requirements and conversion to a glucocorticoid-responsive element.	the estrogen-responsive element (ere) present in the 5'-flanking region of the xenopus laevis vitellogenin (vit) gene b1 has been characterized by transient expression analysis of chimeric vit-tk-cat (chloramphenicol acetyltransferase) gene constructs transfected into the human estrogen-responsive mcf-7 cell line. the vit b1 ere behaves like an inducible enhancer, since it is able to confer estrogen inducibility to the heterologous hsv thymidine kinase (tk) promoter in a relative position- and o ...	1987	3480798
casein kinase ii is a major protein phosphorylating activity in the nuclei of xenopus laevis oocytes.	the nuclei of xenopus laevis oocytes contain kinases capable of phosphorylating endogenous and exogenous proteins using either atp or gtp as phosphoryl donors. these enzymes are much more active with casein and phosvitin as substrates than with histones or protamines. the protein phosphorylating activity of oocyte nuclear extracts is not regulated by cyclic nucleotides, phorbol esters, calmodulin and calcium, or phospholipids. however, the casein phosphorylating activity can be greatly enhanced ...	1987	3483172
a constitutive nucleolar protein identified as a member of the nucleoplasmin family.	using monoclonal antibodies we have localized a polypeptide, appearing on gel electrophoresis with a mr of approximately 38,000 and a pi of approximately 5.6, to the granular component of the nucleoli of xenopus laevis oocytes and a broad range of cells from various species. the protein (no38) also occurs in certain distinct nucleoplasmic particles but is not detected in ribosomes and other cytoplasmic components. during mitosis no38-containing material dissociates from the nucleolar organizer r ...	1987	3308448
distribution of synaptic specializations along isolated motor units formed in xenopus nerve-muscle cultures.	the capacity of individual muscle cells and neurons to establish synaptic specializations along the entire extent of their neurite-muscle contacts was assessed in culture. spinal cord neurons derived from embryos of xenopus laevis were plated at low density in cultures of xenopus myotomal muscle cells in order to obtain isolated motor units whose neuron and muscle cells were not contacted by any other neuron. these isolated motor units were examined for localization of acetylcholine receptors (a ...	1987	3305801
cytoarchitecture of the xenopus thymus following gamma-irradiation.	this paper describes in vitro and in vivo attempts to deplete the 4- to 8-month-old xenopus laevis (j strain) thymus of its lymphocyte compartment. gamma irradiation (2-3000 rad) of the excised thymus, followed by two weeks in organ culture, is effective in removing lymphocytes, but causes drastic reduction in size and loss of normal architecture. in contrast, in vivo whole-body irradiation (3000 rad) and subsequent in situ residence for 8-14 days proves successful in providing a lymphocyte-depl ...	1987	3308399
pyruvate kinase isozymes in oocytes and embryos from the frog xenopus laevis.	1. the kinetic characteristics of pyruvate kinase isozymes from oocytes, embryos, liver and skeletal muscle from the clawed frog xenopus laevis were measured in cell extracts. 2. the muscle and liver isozymes display michaelis-menten kinetics with kms for phosphoenolpyruvate (pep) of 0.02 and 0.05 mm, respectively. 3. pyruvate kinase from oocytes and embryos displays cooperative kinetics for pep with a km of about 0.15 mm; the kinetics become hyperbolic and the km for pep is reduced to 0.05 mm i ...	1987	3427912
the transcription of xenopus laevis embryonic u1 snrna genes changes when oocytes mature into eggs.	x. laevis stage vi oocytes respond differently from unfertilized eggs when injected with the genes for x. laevis embryonic u1 rnas, xu1b1, and xu1b2. upon maturation of oocytes into eggs, the efficiency of transcription decreases greatly and the ratio of xu1b1 to xu1b2 rna transcription changes. moreover, dna replication is now required for transcription. because of differences in the 5'-flanking regions of the two xu1b genes, xu1b2 rna transcription predominates after injection into oocytes; in ...	1987	3428590
visualization of secretory activities in the xenopus neurohypophysis by a high s/n video camera.	the optical turbidity of neurohypophyses of the frog xenopus laevis was observed with the help of a high signal to noise ratio video camera and a high speed image processor. electrical stimulation of the pituitary stalk induced a decrease in turbidity of the neurohypophysis. this response was visualized on a monitor screen as a diffuse pattern consisting of many bright spots. the diameters of these spots were similar to those of individual nerve terminals, indicating that the optical response ar ...	1987	3427467
nuclear lamin li of xenopus laevis: cdna cloning, amino acid sequence and binding specificity of a member of the lamin b subfamily.	lamins are karyoskeletal proteins associated with the nuclear envelope which can be divided into two groups, i.e. the type a lamins of near neutral pi and the more acidic lamins, including mammalian lamin b. we have isolated cdna clones encoding a representative of the type b subfamily from xenopus laevis, and have deduced its amino acid sequence from the coding portion of the approximately 2.9 kb mrna. the polypeptide (mol. wt 66,433) is identified as a typical lamin by its homology to xenopus ...	1987	3428276
the activation of amplified ribosomal rna genes in the oocytes of xenopus laevis: an electron microscope analysis.		1987	3436833
the distribution of motoneurons supplying hind limb muscles in the clawed toad, xenopus laevis.	the distribution of motoneurons in the lumbar spinal cord (spinal segments 8-10) of the clawed toad, xenopus laevis, was studied with the horseradish peroxidase technique. in a total of 13 different hind limb muscles this tracer was applied in a slow-release gel. motoneurons innervating a particular hind limb muscle were clustered in longitudinally arranged motor pools. motor pools of different muscles did show considerable overlap both in the rostrocaudal and transverse plane. but, the various ...	1987	3439496
atlas of adult xenopus laevis laevis hematology.		1987	3440505
endocytosis in the inner segment of rod photoreceptors: analysis of xenopus laevis retinas using horseradish peroxidase.	to evaluate endocytosis in rod photoreceptor inner segments, isolated retinas from xenopus laevis were maintained in vitro in the presence of the tracer, horseradish peroxidase (hrp). hrp-positive vesicles, 110 +/- 82 nm in diam. (mean +/- s.d.), appeared in the inner segment cytoplasm within 2 min of incubation. within 8-15 min, 20-30% of the vesicles in the ellipsoid were hrp-positive, reaching approx. 50% by 30-60 min and maintaining this level through 4 hr of culture. in retinas incubated 30 ...	1987	3428395
the development of the merkel cells in the tentacles of xenopus laevis larvae.	the merkel cells in the larval tentacles of xenopus laevis were examined by tem. different forms of merkel cells were found, depending on the age of the larvae or the location in the tentacles. these forms have the appearance of intermediate states between merkel cells and superficial epidermal cells; thus an epidermal origin for the merkel cells seems more likely than an immigration from the neural crest. the forms differ in (1) their location in the epidermis, (2) their shape, (3) the number a ...	1987	3688453
disappearance of rohon-beard neurons from the spinal cord of larval xenopus laevis.	rohon-beard neurons are primary sensory cells located in the spinal cord of embryonic lower vertebrates. the kinetics of their normal, gradual, but complete disappearance in xenopus tadpoles has been followed. levels of acid phosphatase activity, a common histochemical correlate of cell death, were assayed and found to increase at the time of onset of disappearance of rohon-beard cells. ultrastructural examination revealed the presence of numerous secondary lysosomes, swelling of endoplasmic ret ...	1987	3680623
functional characterization of x. laevis u5 snrna genes.	xenopus laevis u5 snrna genes are found in several genomic arrangements, represented by a predominant tandem repeat of 583 bp and other minor repeats. several copies of the major tandem repeat have been cloned and expressed in xenopus oocytes. the transcripts assemble into u5 snrnps which are recognized by anti-sm antibodies. we have identified functional elements in the u5 gene promoter. although similar in organization to other u snrna gene promoters, u5 contains significant differences and is ...	1987	3691481
neurogenesis in the vocalization pathway of xenopus laevis.	we examined possible contributions of neurogenesis to sex differences in the vocalization pathway of the south african clawed frog, xenopus laevis. birthdates of neurons were obtained from autoradiograms of animals receiving tritiated thymidine from gastrulation through 1 month after metamorphosis. thymidine availability studies showed that 80% of the [3h]-thymidine injected into embryos and tadpoles was incorporated into the dna of dividing cells within 3 hours. we observed 3 patterns of neurog ...	1987	3693599
translocation of a localized maternal mrna to the vegetal pole of xenopus oocytes.	a prominent hypothesis in embryology is that localized maternal factors are important in specifying cell fate. there are, however, only a few examples of maternal molecules that have been shown to be localized and very little is known about how such factors are physically localized within an egg (for review see ref. 1). previously, cdna clones were obtained for a class of localized maternal mrnas from xenopus laevis. these mrnas are unusual in that they are concentrated at either the animal or v ...	1987	3600777
dynamics of the control of body pattern in the development of xenopus laevis. iv. timing and pattern in the development of twinned bodies after reorientation of eggs in gravity.	the mesendodermal anatomy of twinned larval axes is described in relation to the normal single pattern, when twinning has been caused by experimental tilting of eggs before first cleavage. the formation of two origins for gastrulation movements (dorsal lips) and their relatively rapid spread and coalescence to give a circular blastopore, is a predictor of twin formation in individual embryos after treatment. the anatomy of twins where development has been disturbed from the outset in this way is ...	1987	3653010
in vivo phosphorylation of titin and nebulin in frog skeletal muscle.	titin and nebulin are two major protein components of the sarcomere matrix in striated muscles. purified titin and nebulin from frog (xenopus laevis) skeletal muscle are similar in size and in amino acid composition to their mammalian or avian counterparts. both proteins contain substantial amounts of protein-bound phosphate: about 5 to 6 per titin subunit and 8 to 9 per nebulin subunit. injection of radioactive inorganic phosphate into the dorsal lymph sacs of xenopus laevis resulted in the sig ...	1987	3663225
thesaurin a, the major protein of xenopus laevis previtellogenic oocytes, present in the 42 s particles, is homologous to elongation factor ef-1 alpha.	we have purified in sds x.laevis thesaurin a (mr 50,000) which is part of the 42 s storage particles. its n-terminal amino acid is blocked and several peptides obtained by v8 protease treatment were purified and sequenced. as expected from one of the functional roles of the 42 s particles (trna binding, protection against deacylation and exchange with the ribosome), the amino acid sequence of thesaurin a was found to be closely related to that of the elongation factor ef-1 alpha. we suggest that ...	1987	3666148
neural crest development in the xenopus laevis embryo, studied by interspecific transplantation and scanning electron microscopy.	the xenopus borealis quinacrine marker and scanning electron microscopy have been used to study the appearance, migration, and homing of neural crest cells in the embryo of xenopus. the analysis shows that the primordium of the neural crest develops from the nervous layer of the ectoderm and consists of three segments at early neurula stages. this primordium is located in the lateral halves of the neural folds behind the prospective eye vesicles. the histological and experimental evidence shows ...	1987	3666314
vocalizations by a sexually dimorphic isolated larynx: peripheral constraints on behavioral expression.	the clawed frog xenopus laevis uses sexually dimorphic vocalizations, mate calling and ticking, to advertise reproductive state. the basic unit of vocalization is a brief click, produced by the movement of cartilagenous disks located within the larynx. the rate of click production in the male-specific mate call (71 hz) is an order of magnitude faster than the rate of click production in female typical ticking (6 hz). to determine if vocalization rate is constrained by the periphery, male and fem ...	1987	3668623
androgen regulation of muscle fiber type in the sexually dimorphic larynx of xenopus laevis.	we used histochemical techniques [assays for adenine triphosphatase (atpase) and succinate dehydrogenase (sdhase) activity] to identify muscle fiber types in the larynx of xenopus laevis. male muscle is made up of one fiber type, medium-sized fibers (approximately 9 microns2) that stain lightly for acid-stable atpase and intensely for sdhase activity. in contrast, the female has 3 fiber types: small fibers (approximately 6 microns2) that stain intensely for atpase and sdhase, medium-sized fibers ...	1987	3668624
expression of human cathepsin d in xenopus oocytes: phosphorylation and intracellular targeting.	we have obtained expression of a cdna clone for human cathepsin d in xenopus laevis oocytes. biosynthetic studies with [35s]methionine labeling demonstrated that most of the cathepsin d remained intracellular and underwent proteolytic cleavage, converting a precursor of mr 47,000 d to a mature form of mr 39,000 d with processing intermediates of mr 43,000-41,000 d. greater than 90% of the cathepsin d synthesized by oocytes bound to a mannose 6-phosphate (man-6-p) receptor affinity column, indica ...	1987	3680368
conserved exon-intron organization in two different caerulein precursor genes of xenopus laevis. additional detection of an exon potentially coding for a new peptide.	from a genomic library of xenopus laevis, two genes coding for different preprocaeruleins have been isolated and sequenced. these correspond to the type i and type iii precursors analyzed previously at the cdna level [richter, k., egger, r. and kreil, g. (1986) j. biol. chem. 261, 3676-3680]. the type iii gene comprises eight exons; the type i apparently contains eight exons as well, of which six have been sequenced. the genetic information for the dekapeptide caerulein is present on small exons ...	1987	3678233
observations on the development of cerebellar afferents in xenopus laevis.	the development of cerebellar afferents has been studied in the clawed toad, xenopus laevis, from stage 46 to 64, with the horseradish peroxidase retrograde tracer technique. already in stage 48 tadpoles, i.e. before the formation of the limbs, a distinct set of cerebellar afferents was found. vestibulocerebellar (mainly arising bilaterally in the nucleus vestibularis caudalis) and contralateral olivo-cerebellar projections dominate. secondary trigeminocerebellar (from the descending nucleus of ...	1987	3688451
cloning and sequence of cdna encoding a peptide c-terminal alpha-amidating enzyme from xenopus laevis.	the c-terminal alpha-amide formation of the peptides is one of the most important events of prohormone processing. we have recently isolated an alpha-amidating enzyme, ae-i, from xenopus laevis skin, which is the only enzyme ever purified to homogeneity. in this study, we report cloning and sequence of cdna encoding ae-i. our results indicate that enzyme ae-i is initially synthesized as a precursor with 400 amino acid residues, which is further processed to the mature enzyme consisting of 344 re ...	1987	3689360
factors guiding optic fibers in developing xenopus retina.	we have characterized, by electron microscopy, the growth of pioneering axons from the retina into the visual pathway during early development of xenopus laevis. the subsequent development of following fibers from the growing retinal margin as they accumulated in the ganglion cell fiber layer (gcfl) of the retina was also studied. extracellular channels bordered by neuroepithelial cells appear in the developing retina in a dorsal to ventral gradient before any pioneering axons are seen. pioneeri ...	1987	3680626
healing and growth of half-eye "compound eyes" in xenopus: application of an interspecific cell marker.	surgically constructed compound eyes have been widely used to examine the development of retinotectal projections in amphibians. such studies have been limited, however, by the lack of an adequate cellular marker with which to assess the contributions of grafted and host tissues to the later larval and adult retina. we have followed the growth of graft- and host-derived ocular tissues in interspecific compound eyes prepared by orthotopic and heterotopic exchanges of half-eye fragments between pi ...	1987	3681411
magnetic effects on tail-fin melanophores of xenopus laevis tadpoles in vitro.		1987	3683589
decay of the oocyte-type heat shock response of xenopus laevis.	xenopus oocytes have a complex heat shock response. during transition of the oocyte into fertilized egg, the heat shock response undergoes several qualitative and quantitative changes culminating in its complete extinction. heat shock induces oocytes to synthesize four heat shock proteins (hsps): 83, 76, 70, and 57. after ovulation, two additional proteins (hsps 22 and 16) are inducible. the heat shock response of spawned eggs can be modified by changing the ionic configuration of the external m ...	1987	3666305
inductive interactions in the spatial and temporal restriction of lens-forming potential in embryonic ectoderm of xenopus laevis.	the process of lens cell determination in amphibians is currently viewed as one involving a series of inductive interactions. on the basis of previous investigations, these interactions are thought to begin during gastrulation when the presumptive foregut endoderm and then the heart mesoderm come into contact with the presumptive lens ectoderm. this earlier period of induction is followed by the later interaction of the optic vesicle with the lens-forming ectoderm. transplantation experiments we ...	1987	3666306
biochemical research on oogenesis. binding of trna to the nucleoprotein particles of xenopus laevis previtellogenic oocytes.	in previtellogenic oocytes of xenopus laevis, nearly all trna is included in nucleoprotein particles (thesaurisomes) sedimenting at 42 s. we evaluate the possibility of a trna exchange between the particles and the ribosomes during protein synthesis. we find that the particles take up trna after a very short incubation in vitro. in the absence of atp, the particles preferentially bind charged trna. in the presence of atp, more trna binds to the particles, and the sedimentation coefficient of the ...	1987	3643212
acceleration of the rate of processing of 40 s pre-rrna during xenopus laevis embryogenesis.	processing of 40 s pre-rrna into 18 and 28 s mature rrnas was studied in xenopus embryonic cells by pulse-chase experiments using actinomycin d as a transcription-inhibitor. gel electrophoretic analyses revealed that the rate of processing was accelerated due to a shortening of the half-life of 40 s pre-rrna from 19 min at the gastrula stage to 9 min at and after the neurula stage. the step under developmental control appeared to be the cleavage of 40 s pre-rrna into 18 s rrna and the 34 s rrna ...	1987	3647911
regional specification within the mesoderm of early embryos of xenopus laevis.	we have further analysed the roles of mesoderm induction and dorsalization in the formation of a regionally specified mesoderm in early embryos of xenopus laevis. first, we have examined the regional specificity of mesoderm induction by isolating single blastomeres from the vegetalmost tier of the 32-cell embryo and combining each with a lineage-labelled (fda) animal blastomere tier. whereas dorsovegetal (d1) blastomeres induce 'dorsal-type' mesoderm (notochord and muscle), laterovegetal and ven ...	1987	3652971
[rearrangement of the morphological structure and degradation of the extracellular matrix in amphibian embryos after short-term disruption of cell contacts].	the changes in cell structure of explants of presumptive early gastrula mesoderm of xenopus laevis and dynamics of extracellular matrix formation has been studied for 6 h after their isolation. after 6 h, control explants of any dorsoventral level turned into dense spheric homogeneous cell clusters. explants of dorsal and lateral sectors, treated with medium without ca2+ and mg2+ for 30 s, bent and separated into several layers, and in ventral sector explants, cavities, surrounded by polarized c ...	1987	3696679
a quantitative analysis of cellular and matrix changes in meckel's cartilage in xenopus laevis.	the changes in cell population and matrix volume fraction in meckel's cartilage during metamorphic climax have been assessed using standard stereological techniques. the period of climax has been divided into three phases, a preliminary 'lag' phase (nf stages 57-60), a 'division' phase (nf stages 60-62) when the cell population rises rapidly and a 'synthesis' phase (nf stages 62-66) when the matrix content of the tissue also increases dramatically. these changes along with the membranous ossific ...	1987	3654355
a complex array of sequences enhances ribosomal transcription in xenopus laevis.	the ribosomal dna spacer in xenopus laevis was shown in previous studies to be involved in regulating the expression of the ribosomal genes. here transcription enhancement by this spacer has been studied in some detail, to fully identify the sequences involved and to determine their relative importance in this phenomenon. it is shown that the 60/81 base-pair (bp) repeats, which were reported to be enhancer elements, act as part of a mode of enhancement whose effect is amplified by the spacer pro ...	1987	3681979
transcriptionally inactive oocyte-type 5s rna genes of xenopus laevis are complexed with tfiiia in vitro.	an extract from whole oocytes of xenopus laevis was shown to transcribe somatic-type 5s rna genes approximately 100-fold more efficiently than oocyte-type 5s rna genes. this preference was at least 10-fold greater than the preference seen upon microinjection of 5s rna genes into oocyte nuclei or upon in vitro transcription in an oocyte nuclear extract. the approximately 100-fold transcriptional bias in favor of the somatic-type 5s rna genes observed in vitro in the whole oocyte extract was simil ...	1987	3683391
biosynthesis and degradation of peptides derived from xenopus laevis prohormones.	peptides present in the skin secretion of the south african frog, xenopus laevis, have been analysed by fast atom bombardment mass spectrometry and h.p.l.c. in the mass range 500-3200 da. we have investigated the effects of successive glandular secretions induced by noradrenaline injections on these peptide levels and have found that the replenishment of the whole range of peptides is complete within 2-6 days. intact secretory vesicles free of cellular contaminants contain a relatively large num ...	1987	3606567
the enhancement of ribosomal transcription by the recycling of rna polymerase i.	it has been suggested that the tandemly repeated ribosomal genes of eukaryotes may be subject to a special mechanism of transcriptional enhancement, called readthrough enhancement, in which transcription factors are recycled. recent experiments with the mouse ribosomal genes, although consistent with this possibility, were unable to distinguish between true readthrough enhancement and promoter occlusion. to test directly for readthrough enhancement, the pre-ribosomal rna of xenopus laevis was pr ...	1987	3684604
electron microscopic visualization of protein-dna interactions at the estrogen responsive element and in the first intron of the xenopus laevis vitellogenin gene.	stable protein-dna complexes can be assembled in vitro at the 5' end of xenopus laevis vitellogenin genes using extracts of nuclei from estrogen-induced frog liver and visualized by electron microscopy. complexes at the three following sites can be identified on the gene b2: the transcription initiation site, the estrogen responsive element (ere) and in the first intron. the complex at the transcription initiation site is stabilized by dinucleotides and thus represents a ternary transcription co ...	1987	3608991
kinetic and electrophoretic analysis of transmethylation reactions in intact xenopus laevis oocytes.	transmethylation reactions in fully grown xenopus oocytes were analyzed following the microinjection of s-adenosyl-l-[methyl-3h]methionine (adomet). the size of the endogenous adomet pool, measured by cation exchange high pressure liquid chromatography is 5.91 pmol/oocyte. the adomet pool turns over with a half-time of 2 h, at a rate of 2.07 pmol/h/oocyte. fractionation experiments indicate that approximately one-third of the adomet in oocytes is utilized for protein carboxylmethylation reaction ...	1987	3611067
sequence of a 3.18 kb tandem repeat of xenopus laevis dna containing 8 trna genes.		1987	3658682
linker scanner mutagenesis of the xenopus laevis ribosomal gene promoter.	we have assayed a series of linker scanner mutants which cover the xenopus laevis ribosomal gene promoter at approximately ten base pair intervals. all of these mutations adversely affect promoter activity with the exception of one mutation which stimulates activity. thus, none are neutral. we show that most of the mutations can be partially rescued by ligating a block of enhancer elements upstream of the promoter. in addition, we have made extracts from liver nuclei which produce dnasei protect ...	1987	3658698
observations on the structure of two human 7sk pseudogenes and on homologous transcripts in vertebrate species.	a comparison of the sequence of two human 7sk rna pseudogenes, covering approx. 190 and 240 base-pairs of the structural gene, is presented. both repeated elements are flanked by direct repeats and begin at the 5' end of the gene. each terminates approx. 90 base-pairs short of the 3' end, the latter representing a continuous sequence and the former carrying an internal deletion of about 40 base-pairs, this region being flanked in the progenitor gene by short repeated sequences. southern blotting ...	1987	3663152
suppressive rod-cone interaction in distal vertebrate retina: intracellular records from xenopus and necturus.	the influence of dim diffuse adapting fields upon the sensitivity to focal photic stimulation was studied by means of intracellular recording in retinal neurons of the south african clawed frog, xenopus and the mudpuppy, necturus. in cones and in most horizontal and bipolar cells lacking color opponency, dim diffuse backgrounds have little influence upon the response to diffuse flicker of low (less than 2 hz) temporal frequencies; however, with small diameter test probes of higher temporal frequ ...	1987	3585472
fate map for the 32-cell stage of xenopus laevis.	a complete fate map has been produced for the 32-cell stage of xenopus laevis. embryos with a regular cleavage pattern were selected and individual blastomeres were injected with the lineage label fluorescein-dextran-amine (fda). the spatial location of the clones was deduced from three-dimensional (3d) reconstructions of later stages and the volume of each tissue colonized by labelled cells in each tissue was measured. the results from 107 cases were pooled to give a fate map which shows the fa ...	1987	3665770
in vitro maintenance of spermatogenesis in xenopus laevis testis explants cultured in serum-free media.	spermatogenesis has been maintained for extended periods in xenopus laevis testis explants cultured in serum-free media supplemented with bovine serum albumin, insulin, transferrin, follicle-stimulating hormone, dihydrotestosterone, testosterone, retinol, ascorbate, and tocopherol. the organization of the testis fragments was maintained for 28 days, and all stages of development were present throughout the culture period. 3h-thymidine-labeled secondary (type b) spermatogonia developed in 28 days ...	1987	3593863
ribosomal precursor 3' end formation requires a conserved element upstream of the promoter.	in xenopus laevis the 3' end of the longest intact ribosomal rna precursor is formed by a processing event at site t2, which is located 7860 bp downstream of the site of transcription initiation. processing at t2 is eliminated by mutations within the t2 box, a 7 nucleotide conserved element, gacttgc, located 15 bp downstream of the 3' ends. the same conserved box is also present at t3, a site 60 bp upstream of the gene promoter and that is part of a termination site. surprisingly, mutations with ...	1987	3594564
structural organization of the proopiomelanocortin gene in xenopus laevis. 5'-end homologies within the toad and mammalian genes.	this study reports the isolation and characterization of the entire proopiomelanocortin (pomc) gene of the amphibian xenopus laevis. the xenopus pomc gene consists of three exons of which the main exon 3 codes for all of the bioactive domains of the precursor protein. intron a (2.6 kb) separates the segments encoding the 5'-untranslated mrna region and intron b (2.5 kb) interrupts the protein-coding sequence near the signal peptide coding region. in that this structural organization of the xenop ...	1987	3595598
differentiation of the animal-vegetal axis in xenopus laevis oocytes. i. polarized intracellular translocation of platelets establishes the yolk gradient.	the animal-vegetal axis of the oocyte of xenopus laevis is recognizable not only by the pattern of surface pigmentation, but also by the distribution of yolk platelets, with the largest platelets (congruent to 14 microns in diameter) and 70% of the total yolk protein localized in the vegetal hemisphere. we have used fluorescent and radioactive vitellogenins (yolk protein precursors) to study the spatial and temporal patterns of yolk deposition along this axis. we find that the rate of uptake of ...	1987	3596006
fates of the blastomeres of the 32-cell-stage xenopus embryo.	a detailed fate map of all of the progeny derived from each of the blastomeres of the 32-cell-stage south african clawed frog embryo (xenopus laevis), which were selected for stereotypic cleavages, is presented. individual blastomeres were injected with horseradish peroxidase and all of their descendants in the late tailbud embryo (stages 32 to 34) were identified after histochemical processing of serial tissue sections and whole-mount preparations. the progeny of each blastomere were distribute ...	1987	3596014
precursor-product relationship between vitellogenin and the yolk proteins as derived from the complete sequence of a xenopus vitellogenin gene.	in xenopus laevis four estrogen-responsive genes are expressed simultaneously to produce vitellogenin, the precursor of the yolk proteins. one of these four genes, the gene a2, was sequenced completely, as well as cdnas representing 75% of the coding region of the gene. from this data the exon-intron structure of the gene was established, revealing 35 exons that give a transcript of 5,619 bp without the poly a-tail. this a2 transcript encodes a vitellogenin of 1,807 amino acids, whose structure ...	1987	3601655
cytoplasmic effect on gene function in xenopus laevis.	the pigmentation gene of xenopus laevis is dominant and that of albino ap mutant recessive. heterologous haploid hybrids are produced by uv inactivation of the egg nuclei during second polar body formation in the mutant sperm-fertilized xenopus eggs. during development of these hybrids, melanin appeared in the eye and melanophores in the skin at stages comparable to those of the wild type, but much earlier than in the albino mutant. the number and intensity of pigment cells are intermediate betw ...	1987	3672098
a nerve growth factor-induced gene encodes a possible transcriptional regulatory factor.	nerve growth factor (ngf) is a trophic agent that promotes the outgrowth of nerve fibers from sympathetic and sensory ganglia. the neuronal differentiation stimulated by this hormone was examined in the ngf-responsive cell line pc12. differential hybridization was used to screen a complementary dna library constructed from pc12 cells treated with ngf and cycloheximide. one of the complementary dna clones that was rapidly induced by ngf was found to have a nucleotide sequence that predicts a 54-k ...	1987	3672127
a comparative sem-study on the teeth of 10 anuran species.	teeth of 10 anuran species have been investigated by means of scanning electron microscopy (sem). generally a great variability of the structure of dentine crowns and the zone of division was noted not only between the single species, but also within one species on the same dentigerous bone. 4 species (hyla cinerea, rana ridibunda, r. hosei, ptychadena spec.) mostly have more or less bladed bicuspid and clearly divided teeth corresponding to the "lissamphibia"-pattern. 2 species (xenopus laevis, ...	1987	3674455
development of the connective tissue in the digestive tract of the larval and metamorphosing xenopus laevis.	developmental changes, until the completion of metamorphosis, of the connective tissue of the digestive tract in the south african clawed frog xenopus laevis were examined by light and scanning electron microscopy. during the pre- and prometamorphosis (stages 50 through 59) the layer of connective tissue was prominent in the typhlosole, while that in the rest of the intestine and stomach remained very thin. most of the connective tissue cells were fibroblasts and were concentrated mainly in the ...	1987	3674459
synthesis and expression of functional angiotensin ii receptors in xenopus oocytes injected with rat brain mrna.	xenopus laevis oocytes were injected with poly(a)+ mrna isolated from rat brain and superfused in a medium containing either serotonin, angiotensin ii or bradykinin. applications of serotonin or angiotensin ii to injected oocytes elicited, in a dose-dependent manner, changes in membrane potential. the angiotensin ii receptor was desensitized fairly rapidly in the continued presence of the agonist. no response was obtained with bradykinin. the selectivity of the angiotensin ii-induced response wa ...	1987	3676711
regional differences of proteins in isolated cells of early embryos of xenopus laevis.	regional differences of proteins were studied by two-dimensional gel electrophoresis in early embryos of xenopus laevis. pairs of blastomeres on the dorso-ventral axis were isolated from 16- and 32-cell embryos. some dorso-ventral differences have been detected at 32-cell embryos. the proteins which were clearly detectable in the vegetal cells of the ventral marginal zone were only faintly detectable or undetectable in those of the dorsal marginal zone, and a regionally specific spot was detecte ...	1987	3607883
the compatibility of xenopus antibody and homoiothermic complement.	adult xenopus laevis serum containing an anti-chicken erythrocyte antibody exhibits complement (c) activity by both the classical and the alternative pathways. lytic activity is removed by heating serum to 50 degrees c for at least 20 min; it is also removed by polysaccharides and by 7.5 mm edta. the optimum temperature for xenopus c activation is 25 degrees c. the ability of xenopus antibody against chicken erythrocytes to co-operate with homoiothermic c in in vitro by lysis of chicken erythroc ...	1987	3678560
comparison of the organization and fine structure of a chicken and a xenopus laevis vitellogenin gene.	the structural organization and the coding nucleotide sequence of the xenopus laevis a2 and the chicken major vitellogenin genes have been compared. both genes show the same exon-intron organization. however, the degree of homology between the nucleotide and derived amino acid sequences varies extensively along the genes. several of the 35 exons are quite similar, and a unique cysteine motif in the lipovitellin ii domain is conserved between the two genes. in contrast, one internal region is qui ...	1987	3680202
regulation and subcellular distribution of a protein methyltransferase and its damaged aspartyl substrate sites in developing xenopus oocytes.	a protein methyltransferase which recognizes racemized and isomerized aspartyl residues in proteins has been identified in both the cytoplasm and nucleus of xenopus laevis oocytes by enzymatic and immunochemical assays. the methyltransferase activity is maintained at a constant concentration of approximately 0.2 microm throughout vitellogenesis. two forms of the enzyme can be identified on immunoblots by their cross-reactivity with an antibody prepared against the purified enzyme from bovine bra ...	1987	3611066
expression sequences and distribution of two primary cell adhesion molecules during embryonic development of xenopus laevis.	studies of chicken embryos have demonstrated that cell adhesion molecules are important in embryonic induction and are expressed in defined sequences during embryogenesis and histogenesis. to extend these observations and to provide comparable evidence for heterochronic changes in such sequences during evolution, the local distributions of the neural cell adhesion molecule (n-cam) and of the liver cell adhesion molecule (l-cam) were examined in xenopus laevis embryos by immunohistochemical and b ...	1987	3680386
the early development of neurons with gaba immunoreactivity in the cns of xenopus laevis embryos.	we have used an antibody to glutaraldehyde fixation complexes of gamma-amino butyric acid (gaba) to stain the developing central nervous system of xenopus laevis embryos. neuronal somata, growth cones, axons, and dendrites were found with gaba-like immunoreactivity. transmission electron microscope (tem) observations were made of axons and synapses. by observation of the earliest stages of differentiation of neurons, seven classes of putative gabaergic interneurons were discerned. 1) ascending n ...	1987	3611420
visual experience and the maturation of the ipsilateral visuotectal projection in xenopus laevis.	the effect of visual deprivation upon the maturation of the ipsilateral visuotectal projection has been studied in xenopus laevis. this topographically ordered projection is polysynaptic. the first stage involves the retinal projection to the contralateral optic tectum. the tectum projects to the nucleus isthmi on the same side. the final stage is the crossed isthmotectal projection from the nucleus isthmi to the tectum ipsilateral to the eye. the topographic precision of connections at various ...	1987	3614642
kinetic behavior of 30s rrna intermediate labeled in developing embryonic cells of xenopus laevis.	in xenopus neurula cells, "30s" rna was found to be labeled with 3h-uridine after a relatively short labeling period. results obtained from cumulative labeling and pulse-labeling and chase experiments with cells from late gastrulae, yolk plug-stage embryos, and neurulae showed that the 30s rna is an intermediate in rrna processing and is derived from 40s pre-rrna and processed to 28s rrna. the half-life of the 30s rrna intermediate was about 7.5 min or less at the three stages examined.	1987	3621362
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
periodic dna synthesis in cell-free extracts of xenopus eggs.	cell-free extracts prepared from unfertilized eggs of xenopus laevis support dna synthesis on sperm pronuclei. continuous labelling studies using [3h]dctp and pulse labelling studies using [32p]dctp demonstrate that synthesis occurs in short bursts of 40 min, which are punctuated by periods of 20-40 min during which no synthesis occurs. density substitution experiments using bromodeoxyuridine demonstrate that this synthesis involves the initiation of replication and reveals that re-initiation ev ...	1987	3653080
autoantibodies in hypertrophic cardiomyopathy and their clinical significance.	data concerning autoantibodies in hypertrophic cardiomyopathy are rare and controversial and only the results of indirect immunofluorescence methods are available in the literature. the aim of this study was to determine the frequency and clinical significance of autoantibodies in hypertrophic cardiomyopathy by means of the western blot which is a highly sensitive immunological technique. sera from twelve (48.0%) of the whole group of 25 patients with hypertrophic cardiomyopathy reacted with act ...	1987	3653127
xenopus transcription factor iiia binds primarily at junctions between double helical stems and internal loops in oocyte 5s rna.	rnases and chemical probes were used to study the accessibility of each nucleotide of 5s rna in the native and reconstituted 7s particle from xenopus laevis oocytes. rnase or chemically treated 5s rna from intact 7s particles was isolated and analysed using an oligodeoxynucleotide primer and reverse transcriptase. the results were superimposed on a cylindrical projection of an rna double helix and the protection effects were shown to cluster at two regions on the molecular surface. a three-dimen ...	1987	3582366
the effects of various nutritional supplements on the growth, migration and differentiation of xenopus laevis neural crest cells in vitro.	this study investigates the nutritional requirements of xenopus laevis neural crest cells and melanophores developing in vitro. a comparison is made between the growth and differentiation of cells in serum-containing medium and a chemically defined, serum-free medium that we have designed. our chemically defined medium is more efficient than serum-supplemented medium in promoting proliferation of these cells. several supplements are required to enhance culture development. these include insulin, ...	1987	3583983
dnaase i sensitivities in chromatin of the xenopus laevis somatic and oocyte 5 s dnas.	the dnaase i sensitivities of the somatic-type 5 s dna and oocyte-type 5 s dna have been compared in nuclei from adult somatic tissues of xenopus laevis. neither of these type iii genes is expressed in mature erythrocytes and only somatic-type 5 s dna is expressed in liver. we find that somatic-type 5 s dna is dnaase-i-sensitive in liver nuclei and less sensitive in erythrocyte nuclei, while oocyte-type 5 s dna is insensitive in both tissues. the dnaase i sensitivity appears to be uniform across ...	1987	3567198
melatonin and rhythmic photoreceptor metabolism: melatonin-induced cone elongation is blocked at high light intensity.	we have proposed a model for circadian regulation of cone position in xenopus laevis that involves interaction of melatonin and dopamine as signals for darkness and light respectively. one problem, however, is that the effects of melatonin have not been detected in eye cups prepared from animals maintained on a cyclic light schedule. since melatonin's effect would be expected to occur in low light intensity at night, we have investigated the relationship among melatonin, light intensity, and con ...	1987	3567617
do calcium and calmodulin trigger maturation in amphibian oocytes?	in contrast to earlier reports (j. l. maller and e. g. krebs, 1980, curr. top. cell. regul. 16, 271-311; m. moreau, j. p. vilian, and p. guerrier, 1980, dev. biol. 78, 201-214; w. j. wasserman and l. d. smith, 1981, j. cell biol. 89, 389-394; d. huchon, r. ozon, e. h. fischer, and j. g. demaille, 1981, mol. cell. endocrinol. 22, 211-222) calmodulin preparations isolated from xenopus laevis ovaries or obtained commercially rarely induced maturation upon microinjection into individual oocytes. cal ...	1987	3569665
mode of action of ammonia and amine on rrna synthesis in xenopus laevis embryonic cells.	recently, we found that rrna synthesis in dissociated embryonic cells of xenopus laevis is selectively inhibited by ammonium salts added to their surrounding medium. similar effects were also observed in cells treated with amines. in this report, we analysed in more detail the effects of an ammonium salt and trimethylamine on rrna synthesis in xenopus embryonic cells cultured under several different conditions. results obtained showed that ammonia and trimethylamine inhibit formation of 40s pre- ...	1987	3652983
lithium inhibits morphogenesis of the nervous system but not neuronal differentiation in xenopus laevis.	xenopus embryos treated with 100 mm-lithium from the 2- to 4-cell stage to the early blastula stage (4h) failed to neurulate and developed without a discernible anteroposterior axis. the internal structure of defective embryos was grossly disorganized, but immunohistochemical staining with cell-type-specific antibodies revealed differentiated nerve and muscle cells. quantitative assay in tissue cultures from control and acutely abnormal lithium-treated embryos showed that neural differentiation ...	1987	3653007
the lampbrush chromosomes of xenopus laevis: preparation, identification, and distribution of 5s dna sequences.	details are given of a technique for making permanent preparations of the lampbrush chromosomes of xenopus laevis. stained preparations allow all 18 bivalent chromosomes to be identified, and a working map showing the major features has been constructed. fifteen of the xenopus chromosomes have one telomere conspicuously larger than the other; the two smallest chromosomes, and one other, lack large telomeres. similar preparations, extracted with rnase and denatured, have been hybridized in situ w ...	1987	3622079
cerulein mrna and peptide alpha-amidation activity in the skin of xenopus laevis: stimulation by norepinephrine.	the skin of xenopus laevis, because of its high concentrations of amidated peptides, is an excellent model for the study of neuropeptide biosynthesis. in this paper we determined levels of the mrnas which encode cerulin and characterized the enzymatic activity which likely produces the carboxyl terminal alpha-amide moiety of cerulein. this enzyme is stimulated by the addition of cuso4 and ascorbate and requires the presence of molecular oxygen and is thus similar to the peptidyl-glycine alpha-am ...	1987	3623070
the primary structure of rat ribosomal protein l5. a comparison of the sequence of amino acids in the proteins that interact with 5 s rrna.	the covalent structure of rat ribosomal protein l5, which associates with 5 s rrna in the organelle, was deduced from the sequence of nucleotides in a recombinant cdna (pl5-6-4) and confirmed from the sequences of amino acids in portions of the protein. ribosomal protein l5, encoded by pl5-6-4, contains 296 amino acids and has a molecular weight of 34,298. however, a second recombinant cdna, pl5-8-5, encodes a protein with an additional methionyl residue at position 236 and may be the product of ...	1987	3624282
effect of ouabain on the meiotic maturation of stage iv-v xenopus laevis oocytes.	full-grown stage vi xenopus laevis oocytes (1,200 to 1,300 micron) respond to progesterone stimulation by undergoing a series of physiological and morphological changes that are referred to as meiotic maturation. oocytes in earlier stages of oogenesis (i through v) do not undergo these changes and remain in prophase arrest when exposed to this steroid. we have found that oocytes ranging from 850 micron (stage iv) to 1,000 micron (stage v) are capable of responding to progesterone under the appro ...	1987	3559500
contractile properties and myosin isoenzymes of various kinds of xenopus twitch muscle fibres.	single twitch muscle fibres have been isolated from various parts of the iliofibularis muscle of xenopus laevis. after measurements of their isotonic contractile properties, myosin extraction was performed on individual fibres and the extract analysed by various forms of gel electrophoresis. in agreement with previous results three major fibre types, types 1, 2, and 3 could be discerned. both mechanical data and native isomyosin patterns indicated a further subdivision of types 1 and 2 into subt ...	1987	3611330
estrogen induction of a 45 kda secreted protein coordinately with vitellogenin in xenopus liver.	in the frog xenopus laevis, vitellogenin is the major estrogen-induced protein in the liver. we have characterized an additional secreted protein, of 45,000 da and designated ep45, which is also responsive to estrogen treatment. like vitellogenin, ep45 is not normally found in the plasma nor synthesized by the liver of the male frog. its synthesis increases 6-fold between days 2 and 8 following a single 2 mg injection of estradiol-17 beta. for comparison, we have also studied a third estrogen-re ...	1987	3556750
protamine polymorphism in xenopus laevis laevis.	protamines from individual frogs of the subspecies xenopus laevis laevis were compared by electrophoresis on polyacrylamide gels containing acetic acid, urea, and triton x-100 to determine if the expression of protamine genes differs among individuals. two electrophoretic bands, sp2a and sp2b, appeared to be expressed as allelic variants. of 33 frogs, 19 expressed only sp2a, 11 expressed both sp2a and sp2b, and three expressed only sp2b. electrophoretic analysis of partial v8 protease digests co ...	1987	3612054
ultrastructural changes in the intestinal connective tissue of xenopus laevis during metamorphosis.	ultrastructural changes in the intestinal connective tissue of xenopus laevis during metamorphosis have been studied. throughout the larval period to stage 60, the connective tissue consists of a few immature fibroblasts surrounded by a sparse extracellular matrix: few collagen fibrils are visible except close to the thin basal lamina. at the beginning of the transition from larval to adult epithelial form around stage 60, extensive changes are observed in connective tissue. the cells become mor ...	1987	3612815
epidermal capillariasis in south african clawed frogs (xenopus laevis).	significant morbidity and mortality of south african clawed frogs, xenopus laevis, can be caused by parasitism of the epidermis by a capillarid nematode. these worms produce an erosive dermatitis that is complicated by infection with gram-negative microorganisms. the nematode apparently has a direct life cycle that can be completed within the epidermis of the frog. these characteristics are suggested by the lack of an intermediate host and failure to detect visceral migration. another unique fea ...	1987	3613514
sequence and transcription of trnaval gene from xenopus laevis.	a dna fraction enriched in trna genes has been prepared by cscl density gradient centrifugation of xenopus laevis dna in the presence of actinomycin d. this dna fraction was cut with the restriction endonuclease ecori and the fragments 800-900 base pairs in size were cloned into the plasmid pbr325. recombinant dnas were screened by hybridization to labeled trna and for the ability to support transcription in vitro. the entire sequence of one fragment was determined by sequencing the ends of an o ...	1987	3801487
toxicity of mixtures of heavy metals and petrochemicals to xenopus laevis.		1987	3801708
relationship between natural variations in motoneuron number and body size in xenopus laevis: a test for size matching.	during normal development, tadpoles of xenopus laevis demonstrate large variations in body size that are carried through metamorphosis. this variation in size exists at the stages when lumbar lateral motor column (l-lmc) motoneurons are produced and when neuronal cell death in this neuron population occurs. body size, hindlimb size, motoneuron number, and motoneuron size (i.e., neuron nuclear cross-sectional area) were measured in animals from three developmental stages: one prior to significant ...	1987	3680631