Figure 10. Summary of dorsal somite extension in Wt and the Da mutant.

(A) Zic1 induces or maintains the expression of wnt11 during somite differentiation. This leads to a reduced proliferative activity of the dorsal DM and increases protrusion formation of the dorsal DM cells which are non-myogenic. Ultimately, the non-myogenic DM guides the epaxial myotomes dorsally where the myotomes form a gapless muscle layer covering the neural tube at the end of embryonic development. (B) In the Da mutant wnt11 expression is reduced in the dorsal somites. The dorsal DM cells show a high proliferative activity and reduced ability to form numerous large protrusions causing insufficient dorsal somite extension. This results in the incomplete coverage of the neural tube by the epaxial myotomes at the end of embryonic development.