Distinct models have been proposed to explain the specific cellular mechanism underlying PS formation (reviewed in ).
Gastrulation begins with the formation of the primitive streak (PS), first identified as a posterior thickening of the epiblast. PSM is formed during gastrulation, in which extensive cellular rearrangements take place to form the three embryonic germinative layers: ectoderm, mesoderm, and endoderm. Somites are blocks of cells formed from the anterior end of the mesenchymal presomitic mesoderm (PSM) and have a key role in the subsequent patterning of the body giving rise to all segmented structures in the adult body, such as vertebrae, intervertebral disks and ribs, the dermis of the back, and body skeletal muscles, except those of the head. Early Events in Vertebrate Developmentīody segmentation can be detected early in development through the formation of repeated segments, the somites, along the anterior-posterior (A-P) body axis. Thus, a better comprehension of the molecular mechanisms regulating somite formation is required in order to fully understand the origin of human skeletal malformations. Human congenital vertebral malformations have been associated with perturbations in these oscillatory mechanisms. Herein, we provide an overview of the molecular clock operating during somite formation and its underlying molecular regulatory mechanisms. The sequential formation of the segmented precursors of the vertebral column during embryonic development, the somites, is governed by an oscillating genetic network, the somitogenesis molecular clock. All vertebrate species present a segmented body, easily observed in the vertebrate column and its associated components, which provides a high degree of motility to the adult body and efficient protection of the internal organs.
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