Regulation of the cellular behaviors during Xenopus laevis somitogenesis

Somitogenesis is a critical step in vertebrate development as it establishes both\ud the segmented body plan & the progenitors of the skeletal muscle, axial skeleton\ud and dermis of the adult. While many key genes involved in regulating somite\ud morphogenesis are known, the molecular signals underlying this process remain\ud elusive. In the frog, X. laevis, somitogenesis consists of the partitioning of the\ud presomitic mesoderm into somites that undergo a 90?? rotation. These somites\ud are comprised of myotome fibers that are aligned parallel to the notochord. Work\ud from our lab & others suggest that signals from the lateral edge may play a role\ud in somite rotation (Wilson et al., 1989;Afonin et al., 2006). To test this hypothesis,\ud the lateral tissue, adjacent to the paraxial mesoderm was microsurgically\ud removed prior to the formation of somites (St 12-17). The dissected embryos\ud were cultured to the tailbud stage & found to have disorganized muscle fibers\ud suggesting that signals from the lateral edge are important for somite rotation &\ud myotome alignment. Work in zebrafish showed that a secreted cytokine, stromal\ud derived factor (SDF1??) is important in the lateral migration of cells within the\ud anterior compartment of the zebrafish somite (Hollway et at.,2007). The lateral\ud movement of cells is reminiscent of the 90?? rotation that occurs during X. laevis\ud somitogenesis. Subsequent knockdown of xSDFI?? and xCXCR4 caused a\ud disruption in normal myotome alignment. We propose that the xSDFI?? signaling\ud pathway plays a role in coordinating the cell movements that lead to the proper\ud alignment of myotome fibers. This suggests a possible conserved pathway in the\ud regulation of somite rotation among vertebrates