AbstractDuring segmentation (somitogenesis) in vertebrate embryos, somites form in a rostral‐to‐caudal sequence according to a species‐specific rhythm called the somitogenesis clock. The expression of genes participating in somitogenesis oscillates in the presomitic mesoderm (PSM) in time with this clock. We previously reported that the Dact1 gene (aka Dpr1/Frd1/ThyEx3), which encodes a Dishevelled‐binding intracellular regulator of Wnt signaling, is prominently expressed in the PSM as well as in a caudal‐rostral gradient across the somites of mouse embryos. This observation led us to examine whether Dact1 expression oscillates in the PSM. We have found that Dact1 PSM expression does indeed oscillate in time with the somitogenesis clock. Consistent with its known signaling functions and with the “clock and wavefront” model of signal regulation during somitogenesis, the oscillation of Dact1 occurs in phase with the Wnt signaling component Axin2, and out of phase with the Notch signaling component Lfng. Developmental Dynamics 235:3177–3183, 2006. © 2006 Wiley‐Liss, Inc.