Somites in Developing Embryos: (118 NATO Science Series A:)

Somite development is a unique and important topic; unique because somitic mesoderm is the first tissue to become segmented, important because the somites - once established - exert a profound influence on other seg­ mental structures which form later. Somite development is of interest at a number of levels. In one aspect, demarcation of a specific number of somites and size regulation, it is a particularly intriguing example of embryonic pattern formation, 'especially in vew of its possible relation to homoeobox-controlled segmentation in insects. At another level, somite development has long been studied by compara­ tive anatomists, but only recently has new light been thrown on such sub­ jects as segmentation of the head, proposed in the 18th century by Goethe and now a live issue for developmental biologists. Somit es are simple when they first appear, but very complex structures arise from them. These include the vertebrae and the axial and other muscles and consequently there is a wealth of morphogenetic problems to be explored. Sometimes their morphogenesis is disturbed, by genetic or environ­ mental factors, and there are many clinical conditions which arise as a result.

Table of Contents:
Somitomeres: The primordial body segments.- The metameric organization of the presomitic mesoderm and somite specification in the mouse embryo.- The epiblast origin of avian somite cells.- Aspects of somite formation in the early chick embryo.- The early development of the intermediate mesoderm in the chick.- The effects on vertebral development of removing a single somite from a 2-day old chick embryo.- On the problem of metamerism in the head mesenchyme of chick embryos.- The pattern of communication through gap junctions during formation of the embryonic axis.- A unique population of non-dividing cells in the somites.- Somitogenesis in the frog.- Heat shock effects in chick embryos.- Cell lineage and the formation and maintenance of half somites.- The tail bud and cessation of segmentation in the chick embryo.- Models of segmentation.- A comparison of the adhesiveness of somitic cells from chick and quail embryos.- The adhesion recognition signal of fibronectin: A possible trigger mechanism for compaction during somitogenesis.- Genetic modifications of developmental acts in chick and mouse somite development.- CSAT antibody interferes with in vivo migration of somitic myoblast precursors into the body wall.- Somite chondrogenesis: Extracellular matrix production and intracellular changes.- Initiation of chondrogenesis in somitic, limb and craniofacial mesenchyme: Search for a common mechanism.- Myogenesis: A problem of Cell Distribution and Cell Interactions.- The distribution of somite-derived, myogenic cells during early development of the wing bud.- Somites and neural development.- The programming of vertebral development.