| Summary: | Somitogenesis is the process by which the presomitic mesoderm is segmented along the vertebrate axis. A clock and wavefront system has been suggested to control multiple aspects of this process including somite size specification, timing of formation and rostralcaudal patterning of somites. This thesis investigates an ex vivo experimental model that generates multiple somites from non-somitic posterior primitive streak tissue through exposure to the BMP inhibitor Noggin. These somites from almost simultaneously in a nonlinear arrangement and acquire an axial identity of cervical somites, showing a normal size, morphology, expression of somitic markers and giving rise to late somite derivatives when transplanted into a secondary host, but form in the absence of the cyclic expression of key molecular clock genes. However, the experimental somites fail to become patterned into rostral and caudal halves, a feature necessary for the segmentation of the peripheral nervous system. The findings in this thesis raise the possibility that the main function of the clock operating in the presomitic mesoderm cells that generate somites might be distinctive for the different aspects of somitogenesis and suggest that it could be mainly required for rostral-caudal patterning of the somites, coupling it with somite formation.
|
|---|
