Background In vertebrate embryos, a "segmentation clock" times somitogenesis. Clock-linked genes, including Lunatic fringe (Lfng), exhibit cyclic expression in the presomitic mesoderm (PSM), with a period matching the rate of somite formation. The clock period varies widely across species, but the mechanisms that underlie this variability are not clear. The half-lives of clock components are proposed to influence the rate of clock oscillations, and are tightly regulated in the PSM. Interactions between Lfng and mir-125a-5p in the embryonic chicken PSM promote Lfng transcript instability, but the conservation of this mechanism in other vertebrates has not been tested. Here, we examine whether this interaction affects clock activity in a mammalian species. Results Mutation of mir-125 binding sites in the Lfng 3'UTR leads to persistent, non-oscillatory reporter transcript expression in the caudal-most mouse PSM, though dynamic transcript expression recovers in the central PSM. Despite this, expression of endogenous mir-125a-5p is dispensable for mouse somitogenesis. Conclusions These results suggest that mir-125a sites in the Lfng 3'UTR influence transcript turnover in both mouse and chicken embryos, and support the existence of position-dependent regulatory mechanisms in the PSM. They further suggest the existence of compensatory mechanisms that can rescue the loss of mir-125a-5p in mice.

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