טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHalperin Einat
SubjectPatterning the Somite: Interplay between Signaling
Molecules Determine Somitic Domains
DepartmentDepartment of Biology
Supervisor Mr. Reshef Ram


Abstract

In terrestrial vertebrates, the segmented somites, are the entity giving rise to skeletal muscle and axial bones. Somites are divided into different domains along the dorso-ventral axis. The large ventral compartment forms the axial skeleton, whereas the small, narrow dorsal compartment forms the skeletal muscle and dermis. In this study, we aim at understanding the molecular mechanisms that govern somite compartmentalization and their possible implications on the evolution of terrestrial vertebrates. Ectopic Wnt-1 or Noggin administration has been shown to alter somite compartmentalization in vivo. Ectopic expression of Wnt protein adjacent to the ventral aspect of the somite caused ventro-medial or ventro-lateral expansion of the dorsal somitic compartment. This expansion was at the expense of the somite’s ventral domain. The ectopic Wnt expression also prevented the epithelial-mesenchymal transition, which is essential for the formation of the ventral somitic compartment. Ectopic expression of Noggin caused lateral or medial expansion of the dorsal compartment, a result of the inhibition of BMP-4 emanating from lateral tissues. The combination of both factors keeps the somite at the epithelial stage and forces the expression of muscle gene regulators. These results suggest that changes in gene regulation within the somitic morphogenetic field during the course of evolution may be responsible for creating a new proportion between the different domains within the somite, resulting in different muscle-bone ratio.