Molecular analyses of Xenopus laevis Mesp-related genes

During vertebrate somitogenesis, somites bud off from the anterior end of the presomitic mesoderm (PSM). Mesodermal posterior (Mesp)‐related genes play essential roles in somitogenesis, particularly in the definition of the somite boundary position. Among vertebrates, two types of Mesp‐related genes have been identified: Mesp1 and Mesp2 in the mouse; Meso‐1 and Meso‐2 in the chicken; Xl‐mespa and Xl‐mespb (also known as Thylacine1) in the African clawed frog (Xenopus laevis); and mesp‐a and mesp‐b in the zebrafish. However, the functional differences between two Mesp‐related genes remain unknown. In the present study, we carried out comparative analyses of the Xl‐mespa and Xl‐mespb genes. The amino acid sequences of the Xl‐mespa and Xl‐mespb proteins showed a high level of similarity. The expression of Xl‐mespa started broadly in the ventrolateral mesoderm and gradually shifted to a striped pattern of expression. In contrast, Xl‐mespb showed a striped pattern of expression from the start. These expression profiles completely overlapped at the PSM during somitogenesis. To investigate the functional differences between Xl‐mespa and Xl‐mespb in terms of target gene regulation, we carried out a luciferase assay using the murine Lunatic fringe (L‐fng) promoter. Transcription of the L‐fng promoter was activated more strongly by Xl‐mespb than by Xl‐mespa. This same pattern was observed for the murine Mesp‐related proteins. These results suggest that the functional differences between the two types of Mesp‐related genes are evolutionally conserved in vertebrates.