Morphogenetic time ; example of main axis segmentation in vertebrates, somitogenesis, somite embryology and functionality, segmentation clock, theoretical prediction and mechanism

This lesson begins with a review of basic embryology , with particular reference to the origin of the three embryonic layers (ectoderm, mesoderm and endoderm) and their derivatives. Next, the formation of somites and their differentiation into different parts is discussed, before moving on to a description of the somitic clock, first from a theoretical point of view ( clock and wavefront model  ), and then describing the mechanisms involved, discovered in the years 1990. The focus is on the mechanisms involved in the production of cellular oscillators and their phasing, as well as some results describing possible reasons for significant differences in the periods of these oscillators within different vertebrate species.