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PubMed2002

Zebrafish M2 muscarinic acetylcholine receptor: cloning, pharmacological characterization, expression patterns and roles in embryonic bradycardia.

1. A zebrafish M2 muscarinic acetylcholine receptor (mAChR) gene was cloned. It encodes 495 amino acids in a single exon. The derived amino acid sequence is 73.5% identical to its human homologue. 2. Competitive binding studies of the zebrafish M2 receptor and [(3)H]-NMS gave negative log dissociation constants (pK(i)) for each antagonist as follows: atropine (9.16)>himbacine (8.05)>/=4-DAMP (7.83)>AF-DX 116 (7.26)>/=pirenzepine (7.18)>/=tropicamide (6.97)>/=methoctramine (6.82)>/=p-F-HHSiD (6.67)>carbachol (5.20). The antagonist affinity profile correlated with the profile of the human M2 receptor, except for pirenzepine. 3. Reverse transcription polymerase chain reaction and Southern blotting analysis demonstrated that the M2 mAChR mRNA levels increased during the segmentation period (12 h post-fertilization; h.p.f.) in zebrafish. By whole-mount in situ hybridization, the M2 mAChR was first detectable in the heart, vagus motor ganglion, and vagus sensory ganglion at 30, 48 and 60 h.p.f., respectively. 4. The muscarinic receptor that mediates carbachol (CCh)-induced bradycardia was functionally mature at 72 h.p.f. The effect of CCh-induced bradycardia was antagonized by several muscarinic receptor antagonists with the order of potency (pIC(50) values): atropine (6.76)>methoctramine (6.47)>himbacine (6.10)>4-DAMP (5.72)>AF-DX 116 (4.77), however, not by pirenzepine, p-F-HHSiD, or tropicamide (<10 micro M). 5. The effect of CCh-induced bradycardia was abolished completely before 56 h.p.f. by M2 RNA interference, and the bradycardia effect gradually recovered after 72 h.p.f. The basal heart rate was increased in embryos injected with M2 mAChR morpholino antisense oligonucleotide (M2 MO) and the effect of CCh-induced bradycardia was abolished by M2 MO in a dose-dependent manner. In conclusion, the results suggest that the M2 mAChR inhibit basal heart rate in zebrafish embryo and the M2 mAChR mediates the CCh-induced bradycardia.

Amino Acid Sequence↗

PubMed1998

Zebrafish wnt11: pattern and regulation of the expression by the yolk cell and No tail activity.

This study analyzed the spatial and temporal expression pattern of zebrafish wnt11 and the regulation of the expression during zebrafish early development, focusing on the interaction with the no tail (ntl) gene, a zebrafish orthologue of mouse Brachyury (T). Zygotic expression of wnt11 was first detected at the late blastula stage in the blastoderm margin, a presumptive mesoderm region. wnt11 expression coincided with mesoderm induction, and the expression was induced by mesoderm inducers such as the yolk cell (Mizuno, T., Yamaha, E., Wakahara, M., Kuroiwa, A., Takeda, H., 1996. Mesoderm induction in zebrafish. Nature 383, 131-132) or FGFs, indicating that, like ntl, wnt11 is one of the immediate-early genes in mesoderm induction. Initial expression domains of wnt11 and ntl overlapped, and these genes showed a similar response to mesoderm inducers. However, analysis of the ntl mutant embryos suggested that wnt11 and ntl are placed in distinct genetic pathways; the ntl mutation had no effect on wnt11 expression in the blastoderm margin. This was further supported by the result of RNA injection experiments showing that overexpression of Wnt11 did not affect ntl expression in the margin. Thus, wnt11 and ntl expression are induced and maintained independently in their initial phase of expression. In later stages, wnt11 was expressed in various organs, such as the somites, particularly in the developing notochord. Since no wnt gene has been reported to be expressed in the axial mesoderm, which is known to act as a signaling source that patterns the neural tube and somites, zebrafish wnt11 is the first wnt gene expressed in the notochord. Furthermore, in contrast to early expression, wnt11 expression in the notochord depended on Ntl activity. In the ntl mutant in which somite patterning is severely affected, wnt11 expression was completely lost, while another signaling molecule, sonic hedgehog is expressed in the mutant notochord precursor cells (Krauss, S., Concordet, J.-P., Ingham, P.W., 1993. A functionally conserved homolog of the Drosophila segment polarity gene hh is expressed in tissues with polarizing activity in zebrafish embryos. Cell 75, 1431-1444). wnt11 expression in the somite also shows a characteristic pattern, correlated with the migration and differentiation of slow muscle precursors. These observations suggest a role for wnt11 in patterning the somites.

Amino Acid Sequence↗

PubMed2003

The pteridine pathway in zebrafish: regulation and specification during the determination of neural crest cell-fate.

This review describes pteridine biosynthesis and its relation to the differentiation of neural crest derivatives in zebrafish. During the embryonic development of these fish, neural crest precursor cells segregate into neural elements, ectomesenchymal cells and pigment cells; the latter then diversifying into melanophores, iridophores and xanthophores. The differentiation of neural cells, melanophores, and xanthophores is coupled closely with the onset of pteridine synthesis which starts from GTP and is regulated through the control of GTP cyclohydrolase I activity. De novo pteridine synthesis in embryos of this species increases during the first 72-h postfertilization, producing H4biopterin, which serves as a cofactor for neurotransmitter synthesis in neural cells and for tyrosine production in melanophores. Thereafter, sepiapterin (6-lactoyl-7,8-dihydropterin) accumulates as yellow pigment in xanthophores, together with 7-oxobiopterin, isoxanthopterin and 2,4,7-trioxopteridine. Sepiapterin is the key intermediate in the formation of 7-oxopteridines, which depends on the availability of enzymes belonging to the xanthine oxidoreductase family. Expression of the GTP cyclohydrolase I gene (gch) is found in neural cells, in melanoblasts and in early xanthophores (xanthoblasts) of early zebrafish embryos but steeply declines in xanthophores by 42-h postfertilization. The mechanism(s) whereby sepiapterin branches off from the GTP-H4biopterin pathway is currently unknown and will require further study. The surge of interest in zebrafish as a model for vertebrate development and its amenability to genetic manipulation provide powerful tools for analysing the functional commitment of neural crest-derived cells and the regulation of pteridine synthesis in mammals.

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PubMed2002

BMP signalling regulates anteroposterior endoderm patterning in zebrafish.

In vertebrates, the embryonic dorsoventral asymmetry is regulated by the bone morphogenetic proteins (Bmp) activity gradient. In the present study, we have used dorsalized swirl (bmp2b) and ventralized chordino (chordin) zebrafish mutants to investigate the effects of dorsoventral signalling on endoderm patterning and on the differentiation and positioning of its derivatives. Alterations of dorsoventral Bmp signalling do not perturb the induction of endodermal precursors, as shown by normal amounts of cells expressing cas and sox17 in swirl and chordino gastrulae, but affect dramatically the expression pattern of her5, a regulator of endoderm anteroposterior patterning in zebrafish. In particular, increased levels of Bmp signalling in chordino gastrulae are associated with a markedly reduced her5 expression domain, that may be abolished by injecting bmp2b mRNA. Conversely, in swirl mutants, lacking Bmp2b, the her5 expression domain is expanded. Thus, a gradient of Bmp2b signalling defines the extension of the her5 expression domain at gastrulation and the allocation of anterior endodermal precursors. A balanced Bmp2b signalling is also required for the normal development of the pancreas, as shown by the sharp reduction of the pancreatic primordium in swirl embryos and its expansion in chordino mutants. In the latter, at 3 days post-fertilization, the increased Bmp signalling does not compromise the endocrine/exocrine pancreas compartmentalization, but the right/left positioning of the pancreas and liver is randomized. Our results suggest that by regulating the expression of her5, the Bmp2b/Chordin gradient directs the anteroposterior patterning of endoderm in zebrafish embryos.

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PubMed2002

The homeobox gene mbx is involved in eye and tectum development.

The homeobox gene mbx is first activated at the end of gastrulation in zebrafish in the presumptive forebrain and midbrain region. During somitogenesis stages, the anterior expression of mbx, which partly overlaps the future eye field, gradually decreases, while midbrain expression intensifies and becomes restricted to the presumptive tectum. Knockdown of mbx expression by morpholino antisense oligonucleotides (mbx-MO) leads to a reduction in the size of the eyes and tectum. Expression domains of rx1 and pax6 in the eye field and of mab21l2 in the eye field and tectum anlage were reduced in size in mbx-MO-injected embryos by somitogenesis stages. Further, induction of islet1 and lim3 expression in the eye at 2 days postfertilization (dpf) was suppressed in mbx-MO-injected embryos. In mbx-MO-injected embryos at 2-5 dpf, the lamination of the eye was disorganized and the number of retinal axons was substantially reduced, but the few remaining axons navigated appropriately to the contralateral tectum. A chimeric protein composed of the Mbx DNA-binding domain and the VP16 activation domain affected eye and tectum development similarly to mbx-MO knockdown, suggesting that Mbx acts as a transcriptional repressor in the zebrafish embryo. Based on these data, we propose that the mbx homeobox gene is required for the development of the eyes and tectum.

Amino Acid Sequence↗

PubMed2001

Isolation and characterization of posteriorly restricted genes in the zebrafish gastrula.

In order to understand anteroposterior axis formation in vertebrates, we have used subtractive hybridization to clone genes expressed posteriorly in the zebrafish gastrula-stage embryo. Here we report the initial characterization of eight clones isolated from this screen. We find that all eight genes are expressed in posteriorly restricted domains, suggesting that they are involved in regulating posterior development during zebrafish embryogenesis.

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PubMed2006

Cracking the genome's second code: enhancer detection by combined phylogenetic footprinting and transgenic fish and frog embryos.

Genes involved in vertebrate development are unusually enriched for highly conserved non-coding sequence elements. These regions are readily detected in silico, by genome-wide sequence comparisons between different vertebrates, from mammals to fish (phylogenetic footprinting). It follows that sequence conservation must be the result of positive selection for an essential physiological role. An obvious possibility is that these conserved sequences possess regulatory or structural functions important for gene expression and, thus, an in vivo assay becomes necessary. We have developed a rapid testing system using zebrafish and Xenopus laevis embryos that allows us to assign transcriptional regulatory functions to conserved non-coding sequence elements. The sequences are cloned into a vector containing a minimal promoter and the GFP reporter, and are assayed for their putative cis-regulatory activity in zebrafish or Xenopus transgenic experiments. Vectors used include plasmid DNA and the Tol2 transposon system in fish and X. laevis. We have followed this logic to detect and analyze conserved elements in an intergenic region present in the Iroquois (Irx) gene clusters of zebrafish, Xenopus tropicalis, Fugu rubripes and mouse. We have assayed approximately 50 of these conserved elements and shown that the majority behave as modular positive regulatory elements (enhancers) that contribute to specific temporal and spatial domains that are part of the endogenous gene expression pattern. Moreover, comparison of the activity of cognate Irx enhancers from different organisms demonstrates that conservation of sequence is accompanied by in vivo functional conservation across species. Finally, for some of the most conserved elements, we have been able to identify a critical core sequence, essential for correct enhancer function.

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PubMed1996

The zebrafish as a model system in developmental, toxicological and transgenic research.

The zebrafish has long been used as a model system in fisheries biology and toxicology. More recently, it has also become the focus of a major research effort into understanding the molecular and cellular events which dictate the development of vertebrate embryos. As well, the zebrafish has proven attractive in studies examining the factors which affect the creation of transgenic fish and the expression of transgenes. The advances which have been made in these areas have firmly established this small aquarium fish as a major model system in biological and biotechnological research.

Journal Article↗

PubMed2001

Hedgehog signalling is required for maintenance of myf5 and myoD expression and timely terminal differentiation in zebrafish adaxial myogenesis.

Hedgehog proteins have been implicated in the control of myogenesis in the medial vertebrate somite. In the mouse, normal epaxial expression of the myogenic transcription factor gene myf5 is dependent on Sonic hedgehog. Here we examine in zebrafish the interaction between Hedgehog signals, the expression of myoD family genes, including the newly cloned zebrafish myf5, and slow myogenesis. We show that Sonic hedgehog is necessary for normal expression of both myf5 and myoD in adaxial slow muscle precursors, but not in lateral paraxial mesoderm. Expression of both genes is initiated normally in rostral presomitic mesoderm in sonic you mutants, which lack all Sonic hedgehog. Similar initiation continues during tailbud outgrowth when the cells forming caudal somites are generated. However, adaxial cells in sonic you embryos are delayed in terminal differentiation and caudal adaxial cells fail to maintain myogenic regulatory factor expression. Despite these defects, other signals are able to maintain, or reinitiate, some slow muscle development in sonic you mutants. In the cyclops mutant, the absence of floorplate-derived Tiggywinkle hedgehog and Sonic hedgehog has no discernible effect on slow adaxial myogenesis. Similarly, the absence of notochord-derived Sonic hedgehog and Echidna hedgehog in mutants lacking notochord delays, but does not prevent, adaxial slow muscle development. In contrast, removal of both Sonic hedgehog and a floorplate signal, probably Tiggywinkle hedgehog, from the embryonic midline in cyclops;sonic you double mutants essentially abolishes slow myogenesis. We conclude that several midline signals, likely to be various Hedgehogs, collaborate to maintain adaxial slow myogenesis in the zebrafish embryo. Moreover, the data demonstrate that, in the absence of this required Hedgehog signalling, expression of myf5 and myoD is insufficient to commit cells to adaxial myogenesis.

Amino Acid Sequence↗

PubMed2002

Progress towards cell-mediated gene transfer in zebrafish.

Although the zebrafish possesses several favourable characteristics that make it an ideal model for genetic studies of vertebrate development, one disadvantage of this model system is the absence of methods for the production of gene knockouts. The authors' laboratory, and others, are working to develop zebrafish pluripotent embryonic stem (ES) and primordial germ cell (PGC) cultures that can be used for cell-mediated gene transfer and the production of knockout mutant lines of fish. Progress has been made in developing short-term cell cultures that possess the ability to contribute to multiple tissues, including the germ line of a host embryo, and transgenic lines of zebrafish have been established using the embryo cell cultures. Work is in progress to extend the length of time that the embryo cells can be maintained in culture without losing their ability to generate germ-line chimeras.

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PubMed1994

The expression pattern of two zebrafish achaete-scute homolog (ash) genes is altered in the embryonic brain of the cyclops mutant.

Two achaete-scute homolog sequences, Zash-1a and Zash-1b, were isolated from a zebrafish embryonic cDNA library. The Zash-1a cDNA encodes a protein very similar to rat Mash-1 and Xenopus Xash-1, with over 94% identity in the C-terminal three-fourths of all three polypeptides. The Zash-1b cDNA encodes a more distantly related protein, with 80% identity of amino acids to Mash-1 in this part of the sequence. At 24 hr, the Zash-1a transcripts are found in the hindbrain in two bilaterally symmetrical lines of cells which mark the boundary between the alar and basal plates and in rhombomere 1 in ventral cells near the floorplate. The gene is also expressed in particular regions of the telencephalon and diencephalon, in the epiphysis, the ventral tegmentum, the neural retina, and in specific cells in the spinal cord. Zash-1b transcripts are found in the hindbrain in segmentally arranged fan-like groups of cells which are located close to the anterior and posterior boundaries of each of rhombomeres 2-6 and in ventral cells close to the floor plate of most rhombomeres. The gene is also expressed at sites distinct from cells expressing Zash-1a in the tegmentum, diencephalon, telencephalon, and spinal cord. In the mutant cyclops, Zash-1a transcripts are absent from the ventral region of the tegmentum and in the ventral cells of rhombomere 1, while more dorsal expression regions are unaffected. The effects of the mutation on Zash-1b expression, however, are more complex. In the hindbrain, the ventral expression zone of this gene is absent, the more dorsal segmented expression is disorganized, and ectopic expression in the alar plate is observed. A dramatic ectopic expression is also observed in the anterior tegmentum. The cyclops gene, therefore, has both positive and negative effects on the CNS of the wild-type embryo: it is required for activation of both Zash-1a and -1b in particular ventral cells, but it also restricts the expression of Zash-1b in other ventral cells and in some dorsal regions. Zash-1a and -1b gene probes will be extremely useful in the analysis of additional mutations affecting development of the central nervous system in zebrafish embryos.

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PubMed2006

Developmental patterning of the cardiac atrioventricular canal by Notch and Hairy-related transcription factors.

Mutations in Notch2, Jagged1 or homologs of the Hairy-related transcriptional repressor Hey2 cause congenital malformations involving the non-chamber atrioventricular canal (AVC) and inner curvature (IC) regions of the heart, but the underlying mechanisms have not been investigated. By manipulating signaling directly within the developing chick heart, we demonstrated that Notch2, Hey1 and Hey2 initiate a signaling cascade that delimits the non-chamber AVC and IC regions. Specifically, misactivation of Notch2 signaling, or misexpression of either Hey1 or Hey2, repressed Bmp2. Because Jagged (also known as Serrate in non-mammalian species) ligands were found to be present in prospective chamber myocardium, these data support the model that Notch2 and Hey proteins cause the progressive restriction of Bmp2 expression to within the developing AVC and IC, where it is essential for differentiation. Misactivation or inhibition of Notch2 specifically induced or inhibited Hey1, respectively, but these manipulations did not affect Hey2, implicating Hey1 as the direct mediator of Notch2. Bmp2 within the developing AVC and IC has been shown to induce Tbx2, and we found that Tbx2 misexpression inhibited the expression of both Hey1 and Hey2. Tbx2, therefore, is envisaged to constitute a feedback loop that sharpens the border with the developing AVC and IC by delimiting Hey gene expression to within prospective chamber regions. Analysis of the loss-of-function phenotype in mouse embryos homozygous for targeted disruption of Hey2 revealed an expanded AVC domain of Bmp2. Similarly, zebrafish gridlock (Hey2 homolog) mutant embryos showed ectopic expression of Bmp4, which normally marks AVC myocardium in this species. Thus, Hey pathway regulation of cardiac Bmp appears to be an evolutionarily conserved mechanism to delimit AVC and IC fate, and provides a potential mechanistic explanation for cardiac malformations caused by mutations in Serrate/Jagged1 and Notch signaling components.

Animals↗

PubMed2002

Making the connection: retinal axon guidance in the zebrafish.

Genetic screens in zebrafish have identified a large number of mutations that affect neural connectivity in the developing visual system. These mutants define genes essential for accurate retinal axon guidance in the eye and brain and the characterization of these mutants is helping to define the cellular and molecular mechanisms that guide axons in the vertebrate embryo. The combination of zebrafish genetic and embryological approaches promises to greatly increase our understanding of how multiple guidance mechanisms establish the complex neural interconnectivity of the vertebrate brain.

Animals↗

PubMed2006

Characterization of retinoid-X receptor genes rxra, rxrba, rxrbb and rxrg during zebrafish development.

During development of vertebrate embryos, retinoic acid plays a variety of roles that are mediated by binding to retinoic acid receptors (Rars) and their heterodimerization partners, the retinoid receptors (Rxrs). Here, we characterize the expression patterns of four zebrafish rxr genes during development and provide an analysis of the phylogenetic relationships between zebrafish and tetrapod Rxr genes based on sequence similarities and conserved syntenies. This analysis prompted the renaming of several of the zebrafish rxr genes to match their tetrapod orthologs. Understanding phylogenetic relationships among Rxr genes and their expression patterns during development provides a foundation for future studies of Rxr functions.

Animals↗

PubMed2002

Developmental expression of zebrafish emx1 during early embryogenesis.

Emx family homeobox genes, Emx1 and Emx2, play an essential role in rostral brain development in mammalian embryos. Here we report a zebrafish emx family gene, emx1, which is more similar to the mouse Emx1 gene than the previously reported zebrafish emx1 gene; we propose to rename that gene emx3. The expression of emx1 is first detected around the 10-somite stage in the pineal gland (epiphysis) primodium in the developing anterior brain and in the pronephric primodium within the intermediate mesoderm. emx1 expression in the epiphysis has not been reported in other species. Expression in the epiphysis is suppressed at 23 h post-fertilization (hpf) in the floating head (flh) mutant, in which development of the epiphysis is impaired. Subsequently, emx1 is expressed in the telencephalon, as reported in mammals, and can be detected in the olfactory placode and in a small group of cells in the forebrain at 25 hpf. In the mesoderm, emx1 expression is gradually concentrated in the posterior pronephric duct during somitogenesis, and becomes expressed predominantly in the urogenital opening at 25 hpf. Thus, emx1 displays a unique expression pattern that is distinct from the patterns of emx2 and emx3.

Amino Acid Sequence↗

PubMed2004

Agonist-induced internalization of leukotriene B(4) receptor 1 requires G-protein-coupled receptor kinase 2 but not arrestins.

The leukotriene B(4) (LTB(4)) receptor (BLT1) becomes desensitized upon repeated agonist stimulation. Little is known, however, about BLT1 internalization, which follows desensitization in most G-protein-coupled receptors (GPCR). In the current study, transiently expressed BLT1 readily internalized, after LTB(4) stimulation, in RBL-2H3 cells that express high levels of endogenous GPCR kinase 2 (GRK2) but did not in COS-7 or human embryonic kidney (HEK) 293 cells, which do not overexpress GRK. The internalization of BLT1 could be blocked in RBL-2H3 cells by coexpressing dominant-negative (DN) GRK2 K220R and could be promoted in HEK293 cells by coexpressing wild-type (WT) GRK2. Coexpression of WT or DN nonvisual arrestins had no effect on BLT1 internalization. Moreover, upon stimulation with LTB(4), BLT1 did not induce arrestin-green fluorescence protein redistribution in either cell type, even in the presence of overexpressed GRK2. Coimmunoprecipitation experiments confirmed that BLT1 could associate with GRK2 but not with arrestins. A C-tail-truncated mutant of BLT1 lost the capacity to internalize and associate with GRK2 upon exposure to LTB(4), suggesting that the C-tail was required for receptor internalization and association with GRK2. Taken together, our results indicate that the C terminus of BLT1 plays a pivotal role in receptor internalization and GRK2 association. Moreover, ligand-induced BLT1 internalization is dependent on GRK2 but independent of arrestins. This may allow differential, cell-type-specific signaling in response to LTB(4), depending on GRK expression levels.

Animals↗

PubMed2002

Developmental plasticity in the cardiovascular system of fish, with special reference to the zebrafish.

During development the circulatory system of vertebrates typically starts operating earlier than any other organ. In these early stages, however, blood flow is not yet linked to metabolic requirements of tissues, as is well established for adults. While the autonomic nervous system becomes functional only quite late during development, in the early stages control of blood flow appears to be possible by blood-borne and/or local hormones. This study presents methods based on video-imaging techniques and fluorescence microscopy to visualize cardiac activity, as well as the vascular bed of developing lower vertebrates, and tests the idea that environmental factors, such as hypoxia, may modify cardiac activity, or even the early formation of blood vessels in embryos and larvae. In zebrafish larvae, adaptations of cardiovascular activity to chronic hypoxia become visible shortly after hatching, and the formation of some blood vessels is enhanced under chronic hypoxia. Exposure of early larval stages of zebrafish to a constant water current induces physiological adaptations, resulting in enhanced swimming efficiency and increased tolerance towards hypoxia. Furthermore, application of hormones such as NO can modify cardiac activity as well as peripheral resistance, and they can stimulate blood vessel formation. In consequence, even during early development of fish or amphibian larvae, the performance of cardiac muscle and of skeletal muscle can be modified by environmental influences and peripheral resistance can be adjusted. Even blood vessel formation can be stimulated by hypoxia, for example, or by the presence of specific hormones. Thus, at approximately the time of hatching the physiological performance of vertebrate larvae is already determined by the combined action of environmental influences and of genetic information.

Animals↗

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.

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