Devyn M. Smith

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.

Evolutionary relationships between the amphibian, avian, and mammalian stomachs.

SUMMARY Although the gut is homologous among different vertebrates, morphological differences exist between different species. The most obvious variation in the guts of extant vertebrates appears in the stomach. To investigate the evolution of this structure, we compared the histology of the stomach and gastrointestinal tract in amphibian (Xenopus laevis), avian (Gallus gallus), and mammalian (Mus musculus) organisms, and defined the expression patterns of several genes within the developing guts of these lineages. In all three groups, we find that the anterior portion of the stomach has a similar glandular histology as well as a common embryonic expression of the secreted factors Wnt5a and BMP‐4. Likewise, within the amniote lineages, the posterior nonglandular stomach and pyloric sphincter regions are also comparable in both histological and molecular phenotypes. The posterior stomach expresses Six2, BMPR1B, and Barx1, whereas the pyloric sphincter expresses Nkx2.5. Although the adult Xenopus stomach exhibits both glandular and aglandular regions and a distinct pyloric sphincter similar to that of the amniotic vertebrates, the histology of the Xenopus tadpole gut shows less distinct variation in differentiation in this region, which is most likely a derived condition. The molecular signature of the embryonic Xenopus gut correlates with the more derived morphology of the larval phase. We conclude that the global patterning of the gut is remarkably similar among the different vertebrate lineages. The distinct compartments of gene expression that we find in the gut be necessary for the unique morphological specializations that distinguish the stomachs from terrestrial vertebrates.

BMP signalling specifies the pyloric sphincter.

Sphincters are muscular valves that form at the boundaries between organs of the gut; for example, the pyloric sphincter forms at the junction of the small intestine and stomach. We show here that signalling by bone morphogenetic protein (BMP) from the avian small intestine induces the cells of the adjacent gizzard (the equivalent of the stomach in the chicken) primordium to form a sphincter. This finding and related studies of the role of Hox genes in the specification of the iliocaecal sphincter provide insights into the processes by which new cell fates are specified at the borders between distinct embryological domains.

Cloning and expression of a novel cysteine-rich secreted protein family member expressed in thyroid and pancreatic mesoderm within the chicken embryo

We have isolated a new chicken gene that is a member of the cysteine-rich secreted protein family (CRISP). The CRISP family is composed of over 70 members that are found in many phyla of organisms, including: vertebrates, plants, fungi, yeast, and insects. Here we describe the cloning of a novel member of this family, SugarCrisp, and its expression pattern throughout chicken embryogenesis. We also describe its utility as a marker of thyroid and pancreatic mesoderm in the developing chicken embryo and its expression within the human and mouse in glandular tissue.

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.

Developmental biology: BMP signalling specifies the pyloric sphincter

Sphincters are muscular valves that form at the boundaries between organs of the gut; for example, the pyloric sphincter forms at the junction of the small intestine and stomach. We show here that signalling by bone morphogenetic protein (BMP) from the avian small intestine induces the cells of the adjacent gizzard (the equivalent of the stomach in the chicken) primordium to form a sphincter. This finding and related studies of the role of Hox genes in the specification of the iliocaecal sphincter provide insights into the processes by which new cell fates are specified at the borders between distinct embryological domains.

BMP signalling specifies the pyloric sphincter: Developmental biology

Sphincters are muscular valves that form at the boundaries between organs of the gut; for example, the pyloric sphincter forms at the junction of the small intestine and stomach. We show here that signalling by bone morphogenetic protein (BMP) from the avian small intestine induces the cells of the adjacent gizzard (the equivalent of the stomach in the chicken) primordium to form a sphincter. This finding and related studies of the role of Hox genes in the specification of the iliocaecal sphincter provide insights into the processes by which new cell fates are specified at the borders between distinct embryological domains.