Mouse Ripply2 is downstream of Wnt3a and is dynamically expressed during somitogenesis

Somites are blocks of mesoderm that form when segment boundaries are periodically generated in the anterior presomitic mesoderm (PSM). Periodicity is thought to be driven by an oscillating Notch-centered segmentation clock, whereas boundaries are spatially positioned by the secreted signaling molecules Wnt3a and Fgf8. We identified the putative transcriptional corepressor Ripply2 as a differentially expressed gene in wild-type and Wnt3a(-/-) embryos. Here, we show that Ripply2 is expressed in the anterior PSM and that it indeed lies downstream of Wnt3a. Dynamic Ripply2 expression in prospective somites S0 and S-I overlaps with the rostral expression of cycling genes in the Notch pathway, suggesting that Ripply2 may be controlled by the segmentation clock. Continued expression of Ripply2 in embryos lacking Hes7, a molecular oscillator in the Notch clock, indicates that Hes7 is not a major regulator of Ripply2. Our data are consistent with Ripply2 functioning as a segment boundary determination gene during mammalian embryogenesis.