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C J Tabin

Publications and source records attributed to C J Tabin.

At least 19 recordsLinked to original sources
PubMed1999

Chamber-specific cardiac expression of Tbx5 and heart defects in Holt-Oram syndrome.

To further define the role of a T-box transcription factor, Tbx5, in cardiac development, we have examined its expression in the developing mouse and chick heart and correlated this pattern with cardiac defects caused by human TBX5 mutations in Holt-Oram syndrome. Early in the developing heart, Tbx5 is uniformly expressed throughout the entire cardiac crescent. Upon formation of the linear heart tube, Tbx5 is expressed in a graded fashion, stronger near the posterior end and weaker at the anterior end. As the heart tube loops, asymmetric Tbx5 expression continues; Tbx5 is expressed in the presumptive left ventricle, but not the right ventricle or outflow tract. This pattern of expression is maintained in more mature hearts. Expression in the ventricular septum is restricted to the left side and is contiguous with left ventricular free wall expression. Trabeculae, vena cavae (inferior and superior), and the atrial aspect of the atrioventricular valves also express high levels of Tbx5. These patterns of Tbx5 expression provide an embryologic basis for the prevalence of atrial septal defects (ostium primum and secundum), ventricular muscular septal defects, and left-sided malformations (endocardial cushion defects, hypoplastic left heart, and aberrant trabeculation) observed in patients with Holt-Oram syndrome.

Amino Acid Sequence↗
PubMed1999

Role of Pitx1 upstream of Tbx4 in specification of hindlimb identity.

In spite of recent breakthroughs in understanding limb patterning, the genetic factors determining the differences between the forelimb and the hindlimb have not been understood. The genes Pitx1 and Tbx4 encode transcription factors that are expressed throughout the developing hindlimb but not forelimb buds. Misexpression of Pitx1 in the chick wing bud induced distal expression of Tbx4, as well as HoxC10 and HoxC11, which are normally restricted to hindlimb expression domains. Wing buds in which Pitx1 was misexpressed developed into limbs with some morphological characteristics of hindlimbs: the flexure was altered to that normally observed in legs, the digits were more toe-like in their relative size and shape, and the muscle pattern was transformed to that of a leg.

Animals↗
PubMed1999

Chick Barx2b, a marker for myogenic cells also expressed in branchial arches and neural structures.

We have isolated a new chicken gene, cBarx2b, which is related to mBarx2 in sequence, although the expression patterns of the two genes are quite different from one another. The cBarx2b gene is expressed in craniofacial structures, regions of the neural tube, and muscle groups in the limb, neck and cloaca. Perturbation of anterior muscle pattern by application of Sonic Hedgehog protein results in a posteriorization of cBarx2b expression.

Amino Acid Sequence↗
PubMed1998

The molecular ZPA.

Signals that instruct the developing limb bud mesenchyme to form the appropriate elements along the anterior posterior axis emanate from the zone of polarizing activity (ZPA). Studies of the last five years have illustrated that the Sonic hedgehog (Shh) protein mediates the activities of the ZPA. This review will focus on three aspects of the ZPA biology. We will address induction of the ZPA in terms of the factors required for activation and maintenance of Shh expression in the posterior limb bud mesenchyme and the evidence for negative regulatory mechanisms that prevent inappropriate Shh expression. Second, we will discuss the current understanding of Shh processing and transduction of the Shh signal, inferring much from the elegant studies on Drosophila Hedgehog (Hh) protein. Finally, we will address the interpretation of the secreted Shh signal by the limb bud mesenchyme that leads to a predictable morphological response.

Animals↗
PubMed1998

The transcription factor Pitx2 mediates situs-specific morphogenesis in response to left-right asymmetric signals.

The mechanism by which asymmetric signals induce left-right-specific morphogenesis has been elusive. Pitx2 encodes a transcription factor expressed throughout the left lateral plate mesoderm and subsequently on the left side of asymmetric organs such as the heart and gut during organogenesis in the chick embryo. Pitx2 is induced by the asymmetric signals encoded by Nodal and Sonic hedgehog, and its expression is blocked by prior treatment with an antibody against Sonic hedgehog. Misexpression of Pitx2 on the right side of the embryo is sufficient to produce reversed heart looping and heart isomerisms, reversed body rotation, and reversed gut situs.

Amino Acid Sequence↗
PubMed1998

Distinct WNT pathways regulating AER formation and dorsoventral polarity in the chick limb bud.

The apical ectodermal ridge (AER) is an essential structure for vertebrate limb development. Wnt3a is expressed during the induction of the chick AER, and misexpression of Wnt3a induces ectopic expression of AER-specific genes in the limb ectoderm. The genes beta-catenin and Lef1 can mimic the effect of Wnt3a, and blocking the intrinsic Lef1 activity disrupts AER formation. Hence, Wnt3a functions in AER formation through the beta-catenin/LEF1 pathway. In contrast, neither beta-catenin nor Lef1 affects the Wnt7a-regulated dorsoventral polarity of the limb. Thus, two related Wnt genes elicit distinct responses in the same tissues by using different intracellular pathways.

Amino Acid Sequence↗
PubMed1998

The transfer of left-right positional information during chick embryogenesis.

The earliest known left-right asymmetric genes are expressed at Hensen's node during chick gastrulation. Gene expression following reorientation of the node shows asymmetry is instructed by adjacent tissue, hence left-right information originates outside the node. Subsequently, the node signals back to the lateral tissue, initiating a cascade leading to left-sided expression of nodal in the lateral plate mesoderm. Loss of nodal expression in the presence of blocking antibodies confirms that Sonic hedgehog is the key signal conveying left-right information from the node; however, manipulation of explant cultures suggests that the induction of nodal requires secondary signals produced in the paraxial mesoderm. These experiments establish the time of action of these signals to and from Hensen's node in establishing left-right asymmetry.

Animals↗
PubMed1998

Recapitulation of signals regulating embryonic bone formation during postnatal growth and in fracture repair.

A number of proteins have recently been identified which play roles in regulating bone development. One important example is Indian hedgehog (Ihh) which is secreted by the prehyprtrophic chondrocytes. Ihh acts as an activator of a second secreted factor, parathyroid hormone-related protein (PTHrP), which, in turn, negatively regulates the rate of chondrocyte differentiation. Here we examine the expression of these genes and their molecular targets during different stages of bone development. In addition to regulating PTHrP expression in the perichondrium, we find evidence that Ihh may also act on the chondrocytes themselves at particular stages. As bone growth continues postnatally in mammals and the developmental process is reactivated during fracture repair, understanding the molecular basis regulating bone development is of medical relevance. We find that the same molecules that regulate embryonic endochondral ossification are also expressed during postnatal bone growth and fracture healing, suggesting that these processes are controlled by similar mechanisms.

Animals↗
PubMed1998

Epithelial-mesenchymal signaling during the regionalization of the chick gut.

The development of the vertebrate gut requires signaling between the endoderm and mesoderm for establishing its normal anteroposterior (AP) axis and for tissue-specific differentiation. Factors implicated in positional specification of the AP regions of the gut include endodermally expressed Sonic hedgehog (Shh), mesodermally expressed Bmp4 and members of the Hox gene family. We have investigated the roles of these factors during AP regional specification of the chick embryonic gut. Early in gut development, the endoderm sends inductive signals to the mesoderm. Shh has been implicated as one of these signals. We find a differential response to exposure of the inductive influence of Shh along the AP axis of the gut. Virally mediated misexpression of Shh results in ectopic upregulation of its receptor Ptc and a cellular proliferation throughout the gut mesoderm. Although ectopic Shh can induce Bmp4 in the mesoderm of the midgut and hindgut, Bmp4 is not induced in the stomach region of the foregut. The stomach region has a thicker layer of mesoderm than the rest of the gut suggesting that the normal function of Bmp4 could be to limit mesodermal growth in the non-stomach regions of the gut. Ectopic Bmp4 expression in the stomach results in a reduction of the mesodermal component consistent with this hypothesis. In addition to the regional restriction on Bmp4 induction, Shh can only induce Hoxd-13 in the mesoderm of the hindgut. These findings suggest that a prepattern exists in the primitive gut mesoderm prior to expression of Shh in the endoderm. The gut mesoderm is subsequently responsible for inducing region-specific differentiation of its overlying endoderm. We tested the role of Hoxd-13, normally restricted in its mesodermal expression to the most posterior region of the hindgut (cloaca), in controlling adjacent endodermal differentiation. When virally mediated Hoxd-13 is misexpressed in the primitive midgut mesoderm, there is a transformation of the endoderm to the morphology and mucin content of the hindgut. Thus, the positionally restricted expression of a Hox gene in the gut mesoderm influences the inductive signaling that leads to regionally specific differentiation of gut endoderm.

Animals↗
PubMed1997

Left/right patterning signals and the independent regulation of different aspects of situs in the chick embryo.

Recently, a pathway of genes which are part of a cascade regulating the side on which the heart forms during chick development was characterized (M. Levin et al., 1995, Cell 82, 1-20). Here we extend these previous studies, showing that manipulation of at least one member of the cascade, Sonic hedgehog (Shh), can affect the situs of embryonic rotation and of the gut, in addition to the heart. Bilateral expression of Shh, which is normally found exclusively on the left, does not result in left isomerism (a bilaterally symmetrical embryo having two left sides) nor in a complete situs inversus phenotype. Instead, misexpression of Shh on the right side of the node, which in turn leads to bilateral nodal expression, produces a heterotaxia-like condition, where different aspects of laterality are determined independently. Heart situs has previously been shown to be altered by ectopic Shh and activin. However, the most downstream gene identified in the LR pathway, nodal, had not been functionally linked to heart laterality. We show that ectopic (right-sided) nodal expression is able to affect heart situs, suggesting that the randomization of heart laterality observed in Shh and activin misexpression experiments is a result of changes in nodal expression and that nodal is likely to regulate heart situs endogenously. The first defined asymmetric signal in the left-right patterning pathway is Shh, which is initially expressed throughout Hensen's node but becomes restricted to the left side at stage 4(+). It has been hypothesized that the restriction of Shh expression may be due to repression by an upstream activin-like factor. The involvement of such an activin-like factor on the right side of Hensen's node was suggested because ectopic activin protein is able to repress Shh on the left side of the node, as well as to induce ectopic expression of a normally right-sided marker, the activin receptor cAct-RIIa. Here we provide further evidence in favor of this model. We find that a member of this family, Activin betaB, is indeed expressed asymmetrically, only on the right side of Hensen's node, at the correct time for it to be the endogenous asymmetric activin signal. Furthermore, we show that application of follistatin-loaded beads eliminates the asymmetry in Shh expression, consistent with an inhibition of an endogenous member of the activin-BMP superfamily. This combined with the previous data on exogenous activin supports the model that Activin betaB functions in the chick embryo to initiate Shh asymmetry. While these data extend our understanding of the early signals which establish left-right asymmetry, they leave unanswered the interesting question of how the bilateral symmetry of the embryo is initially broken to define a consistent left-right axis. Analysis of spontaneous chick twins suggests that, whatever the molecular mechanism, left-right patterning is unlikely to be due to a blastodermal prepattern but rather is initiated in a streak-autonomous manner.

Animals↗
PubMed1997

Goosecoid misexpression alters the morphology and Hox gene expression of the developing chick limb bud.

The homeobox-containing gene goosecoid (gsc) has been implicated in a variety of embryonic processes from gastrulation to rib patterning. We have analyzed the role it plays during chick limb development. Expression is initially observed at stage 20 in a proximal-anterior-ventral domain of the early limb bud which expands during subsequent stages. Later in limb development a second domain of expression appears distally which resolves to regions which surround the condensing cartilage. In order to understand the function of gsc in limb development, we have examined the effect of misexpressing gsc throughout the limb. Two striking phenotypes are observed. The first, evident at stage 24, is an alteration in the angle of femur outgrowth from the main body axis. The second, which can be detected at day 10 of development, is an overall decrease in the size of the limb with bones that are small, misshapen and bent. These phenotypes correlate with a decrease in levels of Hox gene expression in gsc-infected limb buds. From these results we suggest that gsc may normally function to regulate growth and patterning of the limb, perhaps through regulation of Hox gene expression.

Animals↗
PubMed1997

Analysis of Hoxd-13 and Hoxd-11 misexpression in chick limb buds reveals that Hox genes affect both bone condensation and growth.

Hox genes are important regulators of limb pattern in vertebrate development. Misexpression of Hox genes in chicks using retroviral vectors provides an opportunity to analyze gain-of-function phenotypes and to assess their modes of action. Here we report the misexpression phenotype for Hoxd-13 and compare it to the misexpression phenotype of Hoxd-11. Hoxd-13 misexpression in the hindlimb results in a shortening of the long bones, including the femur, the tibia, the fibula and the tarsometatarsals. Mutations in an alanine repeat region in the N-terminus of Hoxd-13 have recently been implicated in human synpolydactyly (Muragaki, Y., Mundlos, S., Upton, J. and Olsen, B. R. (1996) Science 272, 548-551). N-terminal truncations of Hoxd-13 which lack this repeat were constructed and were found to produce a similar, although slightly milder, misexpression phenotype than the full-length Hoxd-13. The stage of bone development regulated by Hox genes has not previously been examined. The changes in bone lengths caused by Hoxd-13 misexpression are late phenotypes that first become apparent during the growth phase of the bones. Analysis of tritiated thymidine uptake by the tibia and fibula demonstrates that Hox genes can pattern the limb skeleton by regulating the rates of cell division in the proliferative zone of growing cartilage. Hoxd-11, in contrast to Hoxd-13, acts both at the initial cartilage condensation phase in the foot and during the later growth phase in the lower leg. Ectopic Hoxd-13 appears to act in a dominant negative manner in regions where it is not normally expressed. We propose a model in which all Hox genes are growth promoters, regulating the expression of the same target genes, with some Hox genes being more effective promoters of growth than other Hox genes. According to this model, the overall rate of growth in a given region is the result of the combined action of all of the Hox genes expressed in that region competing for the same target genes.

Animals↗
PubMed1996

Sonic hedgehog differentially regulates expression of GLI and GLI3 during limb development.

Sonic hedgehog is a secreted factor regulating patterning of the anterior-posterior axis in the developing limb. The signaling pathway mediating the transduction of the signal is still poorly understood. In Drosophila several genes are known to act downstream of hedgehog, the fly homolog of Sonic hedgehog. An important gene epistatic to hedgehog is cubitus interruptus, which encodes the fly homolog of a family of vertebrate putative transcription factors, the GLI genes. We have isolated two members of the GLI family from chick, called GLI and GLI3. Their expression patterns in a variety of tissues during embryogenesis suggest that these genes may be targets of the Sonic hedgehog signal. We demonstrate that the two GLI genes are differentially regulated by Sonic hedgehog during limb development. Sonic hedgehog up-regulates GLI transcription, while down-regulating GLI3 expression in the mesenchymal cells of the developing limb bud. Finally, we demonstrate that an activated form of GLI can induce expression of Patched, a known target of Sonic hedgehog, thus implicating GLI as a key transcription factor in the vertebrate hedgehog signaling pathway. In conjunction with evidence from a mouse Gli3 mutant, our data suggest that GLI and GLI3 may have taken two different functions of their Drosophila homolog cubitus interruptus.

Animals↗
PubMed1996

Biochemical evidence that patched is the Hedgehog receptor.

The protein Sonic hedgehog (Shh) is essential for a variety of patterning events during development. It is the signal from the notochord that induces ventral cell fate in the neural tube and somites, and is the polarizing signal for patterning of the anterior-posterior axis of the developing limb bud. Because of these and other inductive functions of Shh, it is important to understand how the Hedgehog (Hh) signal is received by the target cells. Here we describe binding studies using labelled Shh that strongly suggest that the Hh receptor is encoded by patched (ptc), a gene first identified in genetic screens in Drosophila.

Animals↗
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.

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