Showing papers by "Ruijin Huang published in 1997"

Segmentation of the vertebrate body.

Abstract: The segmental character of the vertebrate body wall is reflected by metamerically arranged tissues that are patterned during embryonic life as a consequence of somite formation, compartmentalization and differentiation. The somites bud off the paraxial mesoderm in a cranio-caudal sequence and are compartmentalized by local signals from adjacent structures. These signals may be mediated by diffusible substances such as Sonic hedgehog (Shh), Wnts and Bone morphogenetic protein (BMPs) or by cell–cell interactions via membrane-bound receptors and ligands such as Delta and Notch. Compartmentalization of the somites and their derivatives is reflected by the differential expression of developmental regulatory genes such as Pax-1, 3, 7 and 9, MyoD, paraxis, twist and others. Secondary segmentation is imposed upon other tissues, such as blood vessels and nerves, by the rearrangement and regionalization of the somitic derivatives, especially the sclerotome. Early cranio-caudal identity is determined by the expression of different Hox genes. Finally, fusion of segmental anlagen occurs to form segment-overbridging skeletal elements and muscles. The expression of homologous genes indicates that the process of segmentation in vertebrates and invertebrates is homologous, derived by descent from a common ancestor.

The fate of the first avian somite.

Abstract: We have studied the derivatives of the first somite using the quail-chick marking technique. After transplantation of the somite, the chick embryos were reincubated for periods ranging from 4 h to 11 days. Coronal and sagittal sections of the embryos were prepared for parallel staining with Feulgen-reaction, anti-quail antibody, anti-desmin antibody and QH-1 antibody. The first somite consists of an epithelial envelope surrounding somitocoele cells. Like other somites, it forms sclerotome, dermatome and myotome. Cells contribute to the occipital and parasphenoid bone, the meninges, the dermis in the occipital region and the pharyngeal connective tissue. The contribution of the first somite to bones, meninges, dermis and pharyngeal connective tissue is characterised by sharp anterior and posterior boundaries. In contrast, other derivatives such as connective tissue surrounding the vagus nerve, the carotid artery, and jugular vein exceed 10 to 18 segments. This is also true for myogenic cells participating in the formation of the cucullaris capitis muscle that extends from the temporal bone to the shoulder. In one third of the embryos, myocytes of the intrinsic laryngeal muscles are derived from the grafted first somite. Moreover, endothelial cells originate from this somite and migrate into the head (hindbrain, meninges, dermis), neck (pharynx, connective tissue surrounding the vagus nerve, carotid artery and jugular vein) and thorax. With respect to differentiation and derivatives the first somite is similar to other somites.