Enhancer of split-related-2 mRNA shows cyclic expression during somitogenesis in Xenopus laevis

Somitogenesis is responsible for production of the segmented body plan typical of vertebrate embryos. The somites are blocks of mesoderm, produced by this process, that give rise to the vertebrae and ribs, the dermis of the skin and all the skeletal muscle of the body. Many genes that regulate somitogenesis have been identified in chick and mouse, whereas considerably fewer are known in Xenopus laevis. The expression of Hairy/Enhancer of split-related genes is known to cycle during somitogenesis and provides a mechanism for the regular formation of somites. In this project, in situ hybridizations were carried out on bowline, Thylacine1, Enhancer of split-related-1 (ESR1), ESR2 and ESR-5 in order to study their expression in relation to somitogenesis. All genes were found to be expressed during somitogenesis, even as early on as late gastrula stages in some cases. In addition, the expression of ESR2 is shown to be oscillating in the presegmented mesoderm of neurula and early-tailbud embryos. This study has identified ESR2 as the second known gene (after esr9) to show periodic oscillations of gene expression which can be considered as cycling during somitogenesis in X. laevis.