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C J Tabin

Publications and source records attributed to C J Tabin.

At least 55 records · Page 3Linked to original sources
PubMed1996

Regulation of patched by sonic hedgehog in the developing neural tube.

Ventral cell fates in the central nervous system are induced by Sonic hedgehog, a homolog of hedgehog, a secreted Drosophila protein. In the central nervous system, Sonic hedgehog has been identified as the signal inducing floor plate, motor neurons, and dopaminergic neurons. Sonic hedgehog is also involved in the induction of ventral cell type in the developing somites. ptc is a key gene in the Drosophila hedgehog signaling pathway where it is involved in transducing the hedgehog signal and is also a transcriptional target of the signal. PTC, a vertebrate homolog of this Drosophila gene, is genetically downstream of Sonic hedgehog (Shh) in the limb bud. We analyze PTC expression during chicken neural and somite development and find it expressed in all regions of these tissues known to be responsive to Sonic hedgehog signal. As in the limb bud, ectopic expression of Sonic hedgehog leads to ectopic induction of PTC in the neural tube and paraxial mesoderm. This conservation of regulation allows us to use PTC as a marker for Sonic hedgehog response. The pattern of PTC expression suggests that Sonic hedgehog may play an inductive role in more dorsal regions of the neural tube than have been previously demonstrated. Examination of the pattern of PTC expression also suggests that PTC may act in a negative feedback loop to attenuate hedgehog signaling.

Animals↗
PubMed1996

Virally mediated misexpression of Hoxc-6 in the cervical mesoderm results in spinal nerve truncations.

Members of the Hox gene family appear to regulate anterior-posterior (A-P) regionalization in embryos. Genetic manipulation of numerous Hox genes in the developing trunk region of vertebrates results in changes in the morphology of individual vertebrae. We have used virally mediated, targeted misexpression to ectopically express the Hoxc-6 protein in chick embryos. Hoxc-6 has an anterior border of expression at the cervical-thoracic transition in tetrapods. Misexpression of this gene in the cervical mesoderm of chick embryos results in dramatic truncations of the ventral rami of cervical spinal nerves in the infected region. These data point to a role for Hoxc-6 in axon guidance, and suggest that in addition to regulating proliferative rates, Hox gene expression provides positional information utilized in producing domain-specific extracellular signals.

Animals↗
PubMed1996

Regulation of rate of cartilage differentiation by Indian hedgehog and PTH-related protein.

Proper regulation of chondrocyte differentiation is necessary for the morphogenesis of skeletal elements, yet little is known about the molecular regulation of this process. A chicken homolog of Indian hedgehog (Ihh), a member of the conserved Hedgehog family of secreted proteins that is expressed during bone formation, has now been isolated. Ihh has biological properties similar to those of Sonic hedgehog (Shh), including the ability to regulate the conserved targets Patched (Ptc) and Gli. Ihh is expressed in the prehypertrophic chondrocytes of cartilage elements, where it regulates the rate of hypertrophic differentiation. Misexpression of Ihh prevents proliferating chondrocytes from initiating the hypertrophic differentiation process. The direct target of Ihh signaling is the perichondrium, where Gli and Ptc flank the expression domain of Ihh. Ihh induces the expression of a second signal, parathyroid hormone-related protein (PTHrP), in the periarticular perichondrium. Analysis of PTHrP (-/-) mutant mice indicated that the PTHrP protein signals to its receptor in the prehypertrophic chondrocytes, thereby blocking hypertrophic differentiation. In vitro application of Hedgehog or PTHrP protein to normal or PTHrP (-/-) limb explants demonstrated that PTHrP mediates the effects of Ihh through the formation of a negative feedback loop that modulates the rate of chondrocyte differentiation.

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PubMed1996

Conservation in hedgehog signaling: induction of a chicken patched homolog by Sonic hedgehog in the developing limb.

Hedgehog genes have been implicated in inductive signaling during development in a variety of organisms. A key element of the hedgehog signaling system is encoded by the gene patched. In Drosophila hedgehog regulates gene expression by antagonizing the action of patched. In addition, patched is itself a transcriptional target of hedgehog signaling. We have isolated a chicken patched homolog and find it to be strongly expressed adjacent to all tissues where members of the hedgehog family are expressed. As in Drosophila, ectopic expression of Sonic hedgehog leads to ectopic induction of chicken Patched. Based on this regulatory conservation, vertebrate Patched is likely to be directly downstream of Sonic hedgehog signaling. An important role of Sonic hedgehog is the regulation of anterior/posterior pattern in the developing limb bud. Since Patched is directly downstream of the hedgehog signal, the extent of high level Patched expression provides a measure of the distance that Sonic hedgehog diffuses and directly acts. On this basis, we find that Sonic hedgehog directly acts as a signal over only the posterior third of the limb bud. During limb patterning, secondary signals are secreted in both the mesoderm (e.g. Bone Morphogenetic Protein-2) and apical ectodermal ridge (e.g. Fibroblast Growth Factor-4) in response to Sonic hedgehog. Thus knowing which is the direct target tissue is essential for unraveling the molecular patterning of the limb. The expression of Patched provides a strong indication that the mesoderm and not the ectoderm is the direct target of Sonic hedgehog signaling in the limb bud. Finally we demonstrate that induction of Patched requires Sonic hedgehog but, unlike Bone Morphogenetic Protein-2 and Hox genes, does not require Fibroblast Growth Factor as a co-inducer. It is therefore a more direct target of Sonic hedgehog than previously reported patterning genes.

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PubMed1994

Mechanisms of limb patterning.

The development of the vertebrate limb requires the coordinated action of multiple signals to achieve the proper arrangement of adult tissues. Recently, several molecules have been identified which play central roles in patterning of the limb bud. Sonic hedgehog, a homolog of the Drosophila segment polarity gene hedgehog, is likely to regulate anterior/posterior pattern formation. FGF-2 and FGF-4, members of the fibroblast growth factor family, have been shown to provide important signals for limb bud outgrowth and to indirectly regulate proximal/distal patterning. Some candidate effectors of the activity of Sonic hedgehog and of FGFs are known, including members of the clustered Hox genes.

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PubMed1993

The role of homeobox genes in limb development.

Intensive study of the development of the vertebrate limb has led to a conceptual framework for understanding the specification of a limb primordium, the outgrowth of those cells and their organization and differentiation into a functional appendage. During the past few years, a number of homeobox-containing genes have been identified that are likely to play controlling roles in each of these events.

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PubMed1993

Analysis of Hox-4.5 and Hox-3.6 expression during newt limb regeneration: differential regulation of paralogous Hox genes suggest different roles for members of different Hox clusters.

Adult urodele amphibians can regenerate their limbs and tail. Based on their roles in other developing systems, Hox genes are strong candidates for genes that play a role in regulating pattern formation during regeneration. There are four homologous clusters of Hox genes in vertebrate genomes. We isolated cDNA clones of two newt homeobox genes from homologous positions within two Hox clusters; Hox-4.5 and Hox-3.6. We used RNase protection on nonamputated (normal) and regenerating newt appendages and tissue to compare their transcriptional patterns. Both genes show increased expression upon amputation with similar kinetics. Hox-4.5 and Hox-3.6 transcription is limited to the mesenchymal cells in the regenerates and is not found in the epithelial tissue. In addition to regenerating appendages, both genes are transcriptionally active in adult kidney of the newt. Striking differences were found in the regulation of Hox-4.5 and Hox-3.6 when they were compared in unamputated limbs and in regenerating forelimbs versus regenerating hindlimbs. Hox-4.5 is expressed in the blastema of regenerating fore- and hindlimbs, but Hox-4.5 transcripts are not detectable in normal limbs. In contrast, Hox-3.6 transcripts are found exclusively in posterior appendages, but are present in normal as well as regenerating hindlimbs and tails. Hox-4.5 is also expressed at a higher level in proximal (mid-humerus) regenerates than in distal ones (mid-radius). When we proximalized the positional memory of a distal blastema with retinoic acid, we find that the early expression level of Hox-4.5 is also proximalized. When the expression of these genes is compared to the expression of two previously reported newt Hox genes, a consistent pattern emerges, which can be interpreted in terms of differential roles for the different Hox clusters in determining regenerative limb morphology.

Amino Acid Sequence↗
PubMed1993

The role of Hox genes in limb development.

In order to directly test the function of Hox genes in vertebrate limb development, we have employed a replication-competent retroviral vector to express the genes ectopically in developing chick limb buds. It has been hypothesized that the sum of all Hox genes expressed in a developing region forms a "Hox code" which determines the fate of structures arising from that region. When the Hox code of the of the anlage of the chicken hind limb digit I is altered to match that of digit II, the resulting foot has two similar toes both resembling digit II in morphology. This suggests that the misexpressed gene, Hox-4.6, plays a role in controlling digit morphological identity. Other phenotypes observed in the proximal parts of the hind limb and in similar experiments in the wing also lend support to this interpretation. The retroviral vector system used in these experiments provides a powerful approach for testing the function of genes in limb development.

Amino Acid Sequence↗
PubMed1992

Targeted misexpression of Hox-4.6 in the avian limb bud causes apparent homeotic transformations.

In the limb bud the 5' members of the Hox-4 gene cluster are expressed in a nested set of overlapping domains which are progressively restricted in the posterior and distal directions. These domains arise early in limb bud development and come to approximate the primordia of the major structural elements of the limb along the anterior/posterior axis (Fig. 1). This pattern, and the fact that surgical manipulations which lead to mirror image duplications along the anterior/posterior axis give rise to mirror image duplications of the domains of expression of these genes, have led to the proposal that these transcription factors specify positional identity along the anterior/posterior axis. Here we test this hypothesis directly using replication-competent retroviral vectors to expand the domain of expression of the Hox-4.6 gene anteriorly during limb development in vivo. We report that alteration of the domain of expression of the Hox-4.6 gene in the developing limb leads to reproducible pattern alterations consistent with a posterior homeotic transformation.

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PubMed1992

Identification of polymorphic simple sequence repeats in the genome of the zebrafish.

The zebrafish has drawn a great deal of attention as a developmental system because it offers the ability to combine excellent embryology and genetics. Here, we report that simple sequence repeats are abundant in the zebrafish genome and are highly polymorphic between two outbred lines, making them useful markers for the construction of a genetic map of this organism.

Animals↗
PubMed1992

Why we have (only) five fingers per hand: hox genes and the evolution of paired limbs.

Limb development has long been a model system for studying vertebrate pattern formation. The advent of molecular biology has allowed the identification of some of the key genes that regulate limb morphogenesis. One important class of such genes are the homeobox-containing, or Hox genes. Understanding of the roles these genes play in development additionally provides insights into the evolution of limb pattern. Hox gene expression patterns divide the embryonic limb bud into five sectors along the anterior/posterior axis. The expression of specific Hox genes in each domain specifies the developmental fate of that region. Because there are only five distinct Hox-encoded domains across the limb bud there is a developmental constraint prohibiting the evolution of more than five different types of digits. The expression patterns of Hox genes in modern embryonic limb buds also gives clues to the shape of the ancestral fin field from which the limb evolved, hence elucidating the evolution of the tetrapod limb.

Animals↗
PubMed1989

Spatial and temporal expression of the retinoic acid receptor in the regenerating amphibian limb.

Retinoic acid is known to have dramatic effects on vertebrate limb pattern in development and regeneration, supporting a model in which a gradient of retinoic acid serves as a morphogen to differentially supply positional information to a developing limb. The discovery of a retinoic acid receptor (RAR) and its homology to the steroid and thyroid hormone receptors provided a potential molecular mechanism for limb morphogenesis. One prediction of this model is that the receptor must be expressed in the developing and regenerating limb anlage. We investigated the expression of the RAR in the adult newt, Notophthalmus viridescens, whose amputated limbs are capable of regenerating and upon which retinoic acid can act to alter pattern. We report the cloning of cDNAs encoding a functional newt RAR and the localization of high and uniform levels of RAR mRNA specifically in the regenerating cells that control limb pattern. These results indicate that the morphogenic field is established through differential activation of pre-existing retinoic acid receptors rather than differential expression of the RAR gene.

Amino Acid Sequence↗
PubMed1989

Isolation of potential vertebrate limb-identity genes.

Forelimbs and hindlimbs of tetrapods have different morphological patterns. One plausible explanation for the difference is that the cells that give rise to the limbs differentially express genes which control their pattern of development. Amphibian limb regeneration is an excellent system to test this hypothesis, since the same ultimate morphology is attained in regeneration as through embryogenesis. Using a combination of homeobox probes and differential screening, I have isolated two newt genes which are differentially expressed in regenerating forelimbs and hindlimbs. One of these genes displays properties expected of a gene involved in controlling limb morphology, including expression in mesodermal tissue and constancy of expression upon transplantation. Based on sequence analysis, this gene appears to be homologous to a homeobox-containing gene previously isolated from frog and human libraries.

Amino Acid Sequence↗
PubMed1986

Embryonic expression and nuclear localization of Xenopus homeobox (Xhox) gene products.

We have isolated a Xenopus genomic clone (Xhox-1) that contains two homeoboxes, at least one of which is highly conserved in vertebrates. Two transcripts are derived from Xhox-1 and these are present from early in development through swimming tadpole stages. A detailed analysis of one of the genes shows that it is expressed maternally and that transcription from the zygotic genome begins at mid-gastrulation. Examination of exogastrula shows that the expression of these genes does not depend on neural induction. We have determined the DNA sequence of a Xhox-1 cDNA and this allows us to predict the complete sequence of a vertebrate homeobox protein. Synthetic mRNAs made from this cDNA are translated efficiently in Xenopus oocytes where the homeobox protein localizes to the oocyte nucleus.

Amino Acid Sequence↗
PubMed1986

Antibodies to the ras gene product inhibit adenylate cyclase and accelerate progesterone-induced cell division in Xenopus laevis oocytes.

Microinjection of monoclonal antibodies (lines 238, 172, and 259) directed against the ras gene product, p21, into Xenopus laevis oocytes accelerated progesterone-induced germinal vesicle breakdown. Antibody 238 had the greatest effect on the acceleration of progesterone-induced oocyte maturation, and this effect was correlated with in vitro inhibition of adenylate cyclase (EC 4.6.1.1) activity in a concentration-dependent manner. Inhibition of adenylate cyclase by antibody 238 was also measured in membranes prepared from oocytes pretreated with either cholera toxin or pertussis toxin. These results suggest a role for the ras gene product in the regulation of vertebrate cell adenylate cyclase activity.

Adenylyl Cyclase Inhibitors↗
PubMed1985

Analysis of viral and somatic activations of the cHa-ras gene.

The activation of the cHa-ras oncogene in the EJ/T24 bladder carcinoma cell line was compared with the activation of the same gene in the rat-derived Harvey murine sarcoma virus. The results indicate that, like the human oncogene, the Harvey murine sarcoma virus-borne ras gene owes its oncogenic capacity to point mutations in coding sequences rather than to the alteration in transcriptional control that occurred when the formerly cellular ras sequences were acquired by the virus. The viral gene retained its transforming ability when its transcription was removed from the influence of the retroviral long terminal repeat promoter and was placed under the regulation of the cHa-ras promoter. Conversely, the viral long terminal repeat was insufficient to activate the normal cHa-ras allele when a single copy of such a construct was delivered to a cell by viral infection. In addition to their mode of activation, the biological properties of the EJ/T24 and Harvey murine sarcoma virus oncogenes were compared by infecting newborn mice with chimeric retroviruses bearing each form. The two alleles acted equivalently, causing erythroleukemias and sarcomas with similar kinetics.

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