Yabe, T., Hoshijima, K., Yamamoto, T., Takada, S. (2016) Mesp quadruple zebrafish mutant reveals different roles of mesp genes in somite segmentation between mouse and zebrafish. Development (Cambridge, England). 143(15):2842-52.
The segmental pattern of somites is generated by sequential conversion of the temporal periodicity provided by the molecular clock. Whereas the basic structure of this clock is conserved among different species, diversity also exists especially in terms of the molecular network. The temporal periodicity is subsequently converted into the spatial pattern of somites, and Mesp2 plays critical roles in this conversion in the mouse. However, it remains unclear whether Mesp plays similar roles in other vertebrates. In this study, we generated zebrafish mutants lacking all 4 zebrafish mesp genes by using TALEN-mediated genome editing. Contrary to the case for the mouse Mesp2 mutant, in the zebrafish mesp quadruple mutant embryos, the positions of somite boundaries were clearly determined and morphological boundaries were formed, although their formation was not completely normal. On the other hand, each somite was caudalized similarly to the mouse Mesp2 mutant and superficial horizontal myoseptum, and lateral line primordia were not properly formed in the quadruple mutants. These results clarify the conserved and species-specific roles of Mesp in the connection of the molecular clock to somite morphogenesis.