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At least 1,531 records · Page 85Linked to original sources
PubMed1989

A second form of gonadotropin-releasing hormone (GnRH), with chicken GnRH II-like properties, occurs together with mammalian GnRH in marsupial brains.

GnRH peptides in the hypothalami of marsupials (tammar wallaby, short-nosed bandicoot, and eastern quoll) and a monotreme (echidna) were investigated by reverse phase HPLC and RIA with region-specific antisera. In the wallaby hypothalamic extract, a single form of GnRH was present, which eluted in the same position as synthetic mammalian GnRH on HPLC and was recognized by antibodies directed against the NH2- and COOH-termini of mammalian GnRH as well as by antibodies to the middle region. Two GnRH molecular forms were demonstrated in the bandicoot and quoll hypothalamic extracts. One form eluted in the same position as synthetic mammalian GnRH on HPLC and was quantified equally by two mammalian GnRH antisera. The second form eluted in the same position as synthetic chicken GnRH II and was recognized by specific antibodies to this molecule. Quantification of this immunoreactive peak with two chicken GnRH II antisera was not equal, suggesting that the peptide has similar properties to, but may not be identical to, chicken GnRH II. Immunoreactive GnRH was also detected in the echidna hypothalamic extract. These findings demonstrate that in some mammals more than one form of GnRH is present in the brain of a single species, as has previously been found in species from all nonmammalian vertebrate classes. The finding in marsupial brain of a peptide with properties of chicken GnRH II, which has previously been reported in species of Aves, Reptilia, Amphibia, Osteichthyes, and Chondrichthyes, supports our hypothesis that this widespread structural variant may represent an early early evolved and conserved form of GnRH.

Aging↗
PubMed1991

Primary structure of frog pituitary adenylate cyclase-activating polypeptide (PACAP) and effects of ovine PACAP on frog pituitary.

Pituitary adenylate cyclase-activating polypeptide (PACAP), a peptide of the glucagon-secretin-vasoactive intestinal polypeptide superfamily, was isolated in pure form from the brain of the European green frog, Rana ridibunda. The primary structure of the peptide indicates that evolutionary pressure to conserve the complete amino acid sequence has been very strong. Frog PACAP comprises 38 amino acid residues and contains only 1 substitution (isoleucine for valine at position 35) compared with human/ovine/rat PACAP. In the presence of the phosphodiesterase inhibitor isobutylmethylxanthine, synthetic ovine PACAP-(1-38) produced a dose-dependent increase in the concentration of cAMP in isolated frog anterior pituitary fragments (ED50 = 2.1 +/- 0.6 x 10(-7) M; mean +/- SE; n = 6). Maximum stimulation (an approximately 8-fold increase in concentration over basal values) was produced by 10(-6) M peptide. The truncated form of PACAP [PACAP-(1-27)] also produced a dose-dependent increase in cAMP in frog anterior pituitary fragments, and the potency of the peptide (ED50 = 5.9 +/- 0.6 x 10(-8) M) was comparable to that of PACAP-(1-38). The data suggest, therefore, that the function as well as the structure of PACAP have been conserved during the evolution of amphibia to mammals.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Effect of glucocorticoids on thyroid hormone action in cultured red blood cells from Rana catesbeiana tadpoles.

Metamorphosis in anuran amphibia requires thyroid hormone (TH) and can be induced prematurely by the administration of TH. There is also evidence that the developmental effects of TH in these forms are modified by other hormones. For example, PRL has been shown to retard and corticosterone (B) to accelerate some, but not all, components of TH-induced metamorphosis. Red blood cells (RBCs) of Rana catesbeiana tadpoles exhibit a 4- to 5-fold increase in thyroid hormone receptor (TR) number (sites per nucleus) in vivo during either spontaneous or TH-induced metamorphosis. In the present study this TH-induced effect on RBC TR number was examined in an in vitro culture system. RBC TR number was increased by T3 in vitro; the maximum effect (2-fold increase) was obtained after exposure to 0.3 nM T3 for 60 h. This T3-induced increase in TR number was completely abolished in the presence of either 34 nM B or 10 nM dexamethasone, whereas basal TR number was unaffected. The effect appears to be a specific effect of glucocorticoid (GC), because it was not mimicked by the sex steroid, testosterone, and it was not obtained when RU-486, a glucocorticoid antagonist, was included with B in the medium. Other experiments demonstrated that the T3-induced increase in RBC TR was associated with an increase in the TR alpha messenger RNA level. This increase in TR alpha messenger RNA was reduced, but not eliminated, in the presence of concentrations of GC that abolished the TH-induced increase in TR, suggesting that the effects of GC occur in part at a pretranslational level. Using a GC binding assay, tadpole RBCs were found to contain approximately 10(4) GC receptors/cell. These findings indicate that B may be a physiological modulator of TH action in tadpole RBCs. This inhibitory effect of GC contrasts with previous reports that GC accelerates some of the morphological effects of TH in developing tadpoles, indicating that the nature of this modulating effect on TH action is tissue specific.

Animals↗
PubMed1995

Frog vasoactive intestinal polypeptide and galanin: primary structures and effects on pituitary adenylate cyclase.

Vasoactive intestinal polypeptide (VIP) and galanin were isolated in pure form from the stomach of the European green frog, Rana ridibunda. Frog VIP is identical to the previously characterized VIP from chicken and alligator. The primary structure of frog galanin contains only two amino acid substitutions (asparagine for histidine at position 23 and histidine for tyrosine at position 26) compared with porcine galanin. The data indicate that evolutionary pressure to conserve the amino acid sequence of both peptides during the evolution of amphibia to mammals has been strong. Synthetic frog VIP produced a dose-dependent increase in cAMP concentration in frog anterior pituitary fragments. The potency of the peptide (ED50 = 1.2 x 10(-6) M; mean +/- SE; n = 8) was comparable to that of porcine VIP (EC50 = 1.3 x 10(-6) M), but was approximately 10-fold less than that of frog pituitary adenylate cyclase-activating polypeptide [PACAP-(1-38); ED50 = 1.1 x 10(-7) M] in the same system. The increases in cAMP concentrations produced by maximal doses of PACAP (10(-5) M) and VIP (10(-5) M) were not additive. The data suggest that the effects of both peptides are mediated through a common PACAP-preferring receptor that is pharmacologically different from the mammalian PACAP type I receptor. Synthetic frog galanin also produced a dose-dependent increase in the concentration of cAMP in isolated frog anterior pituitary fragments (ED50 = 9.3 x 10(-8) M) consistent with a possible role for the peptide as a hypophysiotropic factor in amphibians.

Adenylyl Cyclases↗
PubMed1997

The type 2 and type 3 iodothyronine deiodinases play important roles in coordinating development in Rana catesbeiana tadpoles.

In developing Rana catesbeiana tadpoles, the timing of the thyroid hormone (TH)-dependent metamorphic responses varies markedly among tissues. Yet at any one time these tissues are exposed to the same plasma concentration of TH, suggesting that TH action is regulated in part at the level of the peripheral tissues. A major factor in TH action is the intracellular level of the active TH, T3. This level is dependent not only on the plasma concentration of TH (mostly T4) but also on the intracellular activities of the type 2 5'-deiodinase (D2) and the type 3 5-deiodinase (D3), which are responsible, respectively, for generating and degrading T3. (D1 is not present in this species.) To determine whether differential expression of D2 and D3 among tissues could be a significant factor in the coordination of metamorphic events, the ontogenic profiles of the two enzyme activities and corresponding messenger RNA levels in most tissues of R. catesbeiana tadpoles have been documented. The profiles of D2 expression in tail, hindlimb, forelimb, intestine, skin, and eye differed markedly at both activity and messenger RNA levels, but it was notable that expression was invariably highest in a given tissue at the time of its major metamorphic change. D2 expression was very low in brain and heart and did not vary during development. D2 was not expressed in liver, kidney, or red blood cells. With the exception of red blood cells, D3 expression was detected in all tissues studied. Furthermore, it was evident that in tissues that expressed both deiodinase genes, the two expression profiles were comparable, indicating a potential for tight control of intracellular T3 levels. Direct evidence of the importance of the intracellular conversion of T4 to T3 for TH-dependent metamorphic events was obtained in tadpoles in which endogenous TH synthesis was blocked with methimazole, and the activities of D2 and D3 were inhibited by iopanoic acid. This treatment inhibited metamorphosis. The inhibition could be overcome by the concomitant administration of replacement levels of T3, but not T4. These results strongly support the view that coordinated development in amphibia depends in part on the tissue-specific expression patterns of the D2 and D3 genes, which ensure that the requisite level of intracellular T3 is attained in a given tissue, regardless of the current level of circulating TH, at the appropriate stage of metamorphosis.

Animals↗
PubMed2004

Hedgehog regulation of superficial slow muscle fibres in Xenopus and the evolution of tetrapod trunk myogenesis.

In tetrapod phylogeny, the dramatic modifications of the trunk have received less attention than the more obvious evolution of limbs. In somites, several waves of muscle precursors are induced by signals from nearby tissues. In both amniotes and fish, the earliest myogenesis requires secreted signals from the ventral midline carried by Hedgehog (Hh) proteins. To determine if this similarity represents evolutionary homology, we have examined myogenesis in Xenopus laevis, the major species from which insight into vertebrate mesoderm patterning has been derived. Xenopus embryos form two distinct kinds of muscle cells analogous to the superficial slow and medial fast muscle fibres of zebrafish. As in zebrafish, Hh signalling is required for XMyf5 expression and generation of a first wave of early superficial slow muscle fibres in tail somites. Thus, Hh-dependent adaxial myogenesis is the likely ancestral condition of teleosts, amphibia and amniotes. Our evidence suggests that midline-derived cells migrate to the lateral somite surface and generate superficial slow muscle. This cell re-orientation contributes to the apparent rotation of Xenopus somites. Xenopus myogenesis in the trunk differs from that in the tail. In the trunk, the first wave of superficial slow fibres is missing, suggesting that significant adaptation of the ancestral myogenic programme occurred during tetrapod trunk evolution. Although notochord is required for early medial XMyf5 expression, Hh signalling fails to drive these cells to slow myogenesis. Later, both trunk and tail somites develop a second wave of Hh-independent slow fibres. These fibres probably derive from an outer cell layer expressing the myogenic determination genes XMyf5, XMyoD and Pax3 in a pattern reminiscent of amniote dermomyotome. Thus, Xenopus somites have characteristics in common with both fish and amniotes that shed light on the evolution of somite differentiation. We propose a model for the evolutionary adaptation of myogenesis in the transition from fish to tetrapod trunk.

Animals↗
PubMed2004

Combinatorial Fgf and Bmp signalling patterns the gastrula ectoderm into prospective neural and epidermal domains.

Studies in fish and amphibia have shown that graded Bmp signalling activity regulates dorsal-to-ventral (DV) patterning of the gastrula embryo. In the ectoderm, it is thought that high levels of Bmp activity promote epidermal development ventrally, whereas secreted Bmp antagonists emanating from the organiser induce neural tissue dorsally. However, in zebrafish embryos, the domain of cells destined to contribute to the spinal cord extends all the way to the ventral side of the gastrula, a long way from the organiser. We show that in vegetal (trunk and tail) regions of the zebrafish gastrula, neural specification is initiated at all DV positions of the ectoderm in a manner that is unaffected by levels of Bmp activity and independent of organiser-derived signals. Instead, we find that Fgf activity is required to induce vegetal prospective neural markers and can do so without suppressing Bmp activity. We further show that Bmp signalling does occur within the vegetal prospective neural domain and that Bmp activity promotes the adoption of caudal fate by this tissue.

Animals↗
PubMed1989

Expression of intermediate filament proteins during development of Xenopus laevis. II. Identification and molecular characterization of desmin.

During embryogenesis of avian and mammalian species the formation of intermediate filaments (IFs) containing desmin is characteristic for myogenesis. In view of important differences of patterns of IF protein expression in embryogenic pathways of amphibia on the one hand and birds and mammals on the other, we have decided to study the expression of desmin during early embryogenesis of Xenopus laevis by cDNA hybridization and antibody reactions. Here we describe the isolation of a cDNA clone encoding Xenopus desmin and the deduced amino acid sequence (458 residues; Mr 52,800) which displays a very high degree of conservation during vertebrate evolution from Xenopus to chicken and hamster, with a similar degree of sequence divergence between all three species compared. In addition, we have noted, by both cDNA-hybrid-selection-translation and immunoblotting of cytoskeletal proteins a second desmin-related polypeptide of Mr approximately 49,000. RNA (Northern) blot analyses show the occurrence of three different desmin mRNAs (1.9, 2.6 and 3.0 kb) which seem to represent different polyadenylation sites, displaying quantitative differences in different kinds of muscle tissues. During embryogenesis, desmin mRNA has first been detected in stage-14 embryos and then increases drastically to high levels at stage 18 and thereafter. Immunofluorescence microscopy using desmin-specific antibodies shows that this synthesis of desmin is restricted to somite tissue. The embryonic time course of synthesis of desmin and desmin mRNA is discussed in relation to those of other muscle proteins.

Amino Acid Sequence↗
PubMed1989

Inducing factors and the control of mesodermal pattern in Xenopus laevis.

The mesoderm of Xenopus laevis and other amphibia is formed through an inductive interaction during which cells of the vegetal hemisphere act on cells of the animal hemisphere. Two groups of factors mimic the effects of the vegetal hemisphere. One group consists of members of the fibroblast growth factor (FGF) family, while the other is related to transforming growth factor type beta (TGF-beta). In this paper we discuss the evidence that the FGF family represents 'ventral' mesoderm-inducing signals, and the TGF-beta family 'dorsal' signals. The evidence includes a discussion of the cell types formed in response to each type of factor, the fact that only XTC-MIF (a member of the TGF-beta family) and not bFGF can induce animal pole ectoderm to become Spemann's organizer, and an analysis of the timing of the gastrulation movements induced by the factors.

Animals↗
PubMed1991

Hensen's node induces neural tissue in Xenopus ectoderm. Implications for the action of the organizer in neural induction.

The development of the vertebrate nervous system is initiated in amphibia by inductive interactions between ectoderm and a region of the embryo called the organizer. The organizer tissue in the dorsal lip of the blastopore of Xenopus and Hensen's node in chick embryos have similar neural inducing properties when transplanted into ectopic sites in their respective embryos. To begin to determine the nature of the inducing signals of the organizer and whether they are conserved across species we have examined the ability of Hensen's node to induce neural tissue in Xenopus ectoderm. We show that Hensen's node induces large amounts of neural tissue in Xenopus ectoderm. Neural induction proceeds in the absence of mesodermal differentiation and is accompanied by tissue movements which may reflect notoplate induction. The competence of the ectoderm to respond to Hensen's node extends much later in development than that to activin-A or to induction by vegetal cells, and parallels the extended competence to neural induction by axial mesoderm. The actions of activin-A and Hensen's node are further distinguished by their effects on lithium-treated ectoderm. These results suggest that neural induction can occur efficiently in response to inducing signals from organizer tissue arrested at a stage prior to gastrulation, and that such early interactions in the blastula may be an important component of neural induction in vertebrate embryos.

Activins↗
PubMed1992

Thyroid hormone receptors in chick retinal development: differential expression of mRNAs for alpha and N-terminal variant beta receptors.

Thyroid-hormone-dependent development of the neuroretina has principally been described in amphibia. Here, we show by in situ hybridisation that mRNAs coding for three distinct thyroid hormone receptors (TRs), TR alpha and two TR beta variants, are differentially expressed during chick retinal development. We isolated a cDNA for a novel N-terminal variant of chick TR beta (cTR beta 2) that is predominantly expressed in retinal development. Interestingly, in its N-terminal A/B domain cTR beta 2 is 70% homologous to the rat pituitary-specific TR beta 2. Expression of cTR beta 2 mRNA was high at embryonic day 6 (E6) in the retinal outer nuclear layer (ONL) and decreased to low levels at hatching. mRNA for the previously described chick beta receptor, cTR beta 0, was expressed at low levels in both the ONL and the inner nuclear layer (INL) after E10. In contrast, cTR alpha expression occurred in the ONL, INL and ganglion cell layer at intermediate and later stages. Finally, cTR beta 2 confers a stronger trans-activation of reporter gene transcription than cTR beta 0. The distinctive kinetics and localisation of TR alpha and beta gene expression suggest cell- and stage-specific functions for TRs, both individually and in combinations, in chick neuroretinal development.

Amino Acid Sequence↗
PubMed1996

Basic fibroblast growth factor induces notochord formation and the expression of As-T, a Brachyury homolog, during ascidian embryogenesis.

The tadpole larva of an ascidian develops 40 notochord cells in the center of its tail. Most of the notochord cells originate from the A-line precursors, among which inductive interactions are required for the subsequent differentiation of notochord. The presumptive-endoderm blastomeres or presumptive-notochord blastomeres themselves are inducers of notochord formation. Notochord induction takes place during the 32-cell stage. In amphibia, mesoderm induction is thought to be mediated by several growth factors, for example, activins and basic fibroblast growth factor (bFGF). In the ascidian, Halocynthia roretzi, treatment with bFGF of presumptive-notochord blastomeres that had been isolated at the early 32-cell stage promoted the formation of notochord at a low concentration of bFGF (0.02 ng/ml), while activin failed to induce notochord differentiation. The effect of bFGF reached a maximum at the end of the 32-cell stage and rapidly faded at the beginning of the subsequent cleavage, the time for full induction of notochord being at least 20 minutes. The expression of As-T, a previously isolated ascidian homolog of the mouse Brachyury (T) gene, starts at the 64-cell stage and is detectable exclusively in the presumptive-notochord blastomeres. The present study showed that presumptive-notochord blastomeres, isolated at the early 32-cell stage, neither differentiated into notochord nor expressed the As-T gene. However, when the presumptive-notochord blastomeres were coisolated or recombined with inducer blastomeres, transcripts of As-T were detected. When presumptive-notochord blastomeres were treated with bFGF, the expression of the As-T gene was also detected. These results suggest that inductive interaction is required for the expression of the As-T gene and that the expression of the As-T gene is closely correlated with the determined state of the notochord-precursor cells.

Activins↗
PubMed1999

Nuclear beta-catenin and the development of bilateral symmetry in normal and LiCl-exposed chick embryos.

Studies in Xenopus laevis and zebrafish suggest a key role for beta-catenin in the specification of the axis of bilateral symmetry. In these organisms, nuclear beta-catenin demarcates the dorsalizing centers. We have asked whether beta-catenin plays a comparable role in the chick embryo and how it is adapted to the particular developmental constraints of chick development. The first nuclear localization of beta-catenin is observed in late intrauterine stages of development in the periphery of the blastoderm, the developing area opaca and marginal zone. Obviously, this early, radially symmetric domain does not predict the future organizing center of the embryo. During further development, cells containing nuclear beta-catenin spread under the epiblast and form the secondary hypoblast. The onset of hypoblast formation thus demarcates the first bilateral symmetry in nuclear beta-catenin distribution. Lithium chloride exposure also causes ectopic nuclear localization of beta-catenin in cells of the epiblast in the area pellucida. Embryos treated before primitive streak formation become completely radialized, as shown by the expression of molecular markers, CMIX and GSC. Lithium treatments performed during early or medium streak stages cause excessive development of the anterior primitive streak, node and notochord, and lead to a degeneration of prospective ventral and posterior structures, as shown by the expression of the molecular markers GSC, CNOT1, BMP2 and Ch-Tbx6L. In summary, we found that in spite of remarkable spatiotemporal differences, beta-catenin acts in the chick in a manner similar to that in fish and amphibia.

Animals↗
PubMed1999

Head induction in the chick by primitive endoderm of mammalian, but not avian origin.

Different types of endoderm, including primitive, definitive and mesendoderm, play a role in the induction and patterning of the vertebrate head. We have studied the formation of the anterior neural plate in chick embryos using the homeobox gene GANF as a marker. GANF is first expressed after mesendoderm ingression from Hensen's node. We found that, after transplantation, neither the avian hypoblast nor the anterior definitive endoderm is capable of GANF induction, whereas the mesendoderm (young head process, prechordal plate) exhibits a strong inductive potential. GANF induction cannot be separated from the formation of a proper neural plate, which requires an intact lower layer and the presence of the prechordal mesendoderm. It is inhibited by BMP4 and promoted by the presence of the BMP antagonist Noggin. In order to investigate the inductive potential of the mammalian visceral endoderm, we used rabbit embryos which, in contrast to mouse embryos, allow the morphological recognition of the prospective anterior pole in the living, pre-primitive-streak embryo. The anterior visceral endoderm from such rabbit embryos induced neuralization and independent, ectopic GANF expression domains in the area pellucida or the area opaca of chick hosts. Thus, the signals for head induction reside in the anterior visceral endoderm of mammals whereas, in birds and amphibia, they reside in the prechordal mesendoderm, indicating a heterochronic shift of the head inductive capacity during the evolution of mammalia.

Animals↗
PubMed1994

Uric acid degrading enzymes, urate oxidase and allantoinase, are associated with different subcellular organelles in frog liver and kidney.

On the basis of differential and density gradient centrifugation studies, the site of the uric acid degrading enzymes, urate oxidase and allantoinase, in amphibia was previously assigned to the hepatic peroxisomes. Using specific antibodies against frog urate oxidase and allantoinase, we have undertaken an immunocytochemical study of the localization of these two proteins in frog liver and kidney, and demonstrate that whereas urate oxidase is present in peroxisomes, allantoinase is localized in mitochondria. Urate oxidase and allantoinase were detected by immunoblot analysis in both frog liver and kidney. The subcellular localization of these two enzymes was ascertained by Protein A-gold immunocytochemical staining of Lowicryl K4M-embedded tissue. Peroxisomes in frog liver parenchymal cells and kidney proximal tubular epithelium contained a semi-dense subcrystalloid core, which was found to be the exclusive site of urate oxidase localization. Allantoinase was detected within mitochondria, but not in peroxisomes of hepatocytes or proximal tubular epithelium. No allantoinase was detected in the mitochondria of nonhepatic parenchymal cells in liver and of the cells lining the distal convoluted tubules of the kidney. These results demonstrate that, unlike rat kidney peroxisomes which lack urate oxidase, peroxisomes of frog kidney contain this enzyme. Contrary to previous assumptions, these studies also clearly establish that urate oxidase and allantoinase, the first two enzymes involved in uric acid degradation, are localized in different subcellular organelles in frog liver and kidney.

Amidohydrolases↗
PubMed1984

Karyoskeletal proteins and the organization of the amphibian oocyte nucleus.

We have investigated the existence of structural components in the nucleus of the oocyte of Xenopus laevis and other amphibia that are insoluble in non-denaturing detergents and buffers of low and high ionic strength. These cells are particularly suitable for such studies as they have a high frequency of extrachromosomal amplified nucleoli and pore complexes of the nuclear envelope. Using biochemical and immunological techniques, we have shown these structures to contain only two major proteins. These are a polypeptide of Mr 145000, which is located in a meshwork of filaments specific to the nucleolar cortex, and certain nucleoplasmic bodies probably derived therefrom, and a polypeptide of Mr 68000, which is the predominant constituent of the lamina-pore complex structure. We show that the latter protein is related to, but not identical to, lamina proteins ('lamins') of somatic cells, indicating cell type-specificity of the expression of polypeptides of the lamin family. In addition, we describe a protein of Mr 180000, which is the major constituent of the dense fibrillar component of the nucleolus. This can be partially solubilized in buffers of moderately high ionic strength. We interpret proteins of this category as karyoskeletal components involved in the architectural organization of specific functional topology within the nucleus. In contrast to previous reports for other cell types we have found no other prominent high-salt-insoluble structures in the nuclear interior, indicating the absence of an extended internal nuclear matrix in this kind of nucleus.

Animals↗
PubMed1976

Classification of loops of lampbrush chromosomes according to the arrangement of transcriptional complexes.

The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include 'spacer' regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes.

Acetabularia↗
PubMed1983

C value and cell volume: their significance in the evolution and development of amphibians.

Cell volume has been determined in 18 species of amphibian, ranging in C value from 1.4 pg to 62 pg DNA. There is a strong linear relationship between C value and both erythrocyte volume and erythrocyte nuclear volume. We have collected data on the timing of early embryogenesis from fertilization of the egg to the hatching tadpole in some amphibians ranging in C value from 1.4 pg to 83 pg. The species with large genomes take up to 24 times longer to reach a comparable state of development. Polyploid species develop faster than closely related diploid species. These data are discussed in relation to genome expansion and increase in cell cycle time as factors in the evolution of the Amphibia.

Amphibians↗