Biology 3338A Lecture Notes - Lecture 11: Paraxial Mesoderm, Spinal Nerve, Myotome
24 Jan 2015
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Somites form from unsegmented mesoderm (called segmental plate in birds) (and heart) Somites play a role in determining the migratory path of neural crest cells and spinal nerve axons. Different types of mesoderm are induced along the d-v axis (partial list) Circulatory system splanchnic mesoderm = heart. Notch (red below) is found at and defines somite borders. Notch genes transcribed in a cyclic fashion and act as an autonomous clock . Initiate many downstream genes, likely with delta, or delta-like receptors. Ephrin and its receptor tyrosine kinase epha4 provide cell-cell repulsion (fissure). Tyrosine kinase eph a4 (blue) and its ligand ephrin (red) form a boundary. Posterior of somite and periodicity of fissure formation associated with wavelike expression of hairy1. Myogenic dna binding bhlh transcription factors can induce the expression of muscle specific genes in a variety of cell types. Once activated cells are committed to becoming muscle cells.
