Xenopus Rnd1 and Rnd3 GTP‐binding proteins are expressed under the control of segmentation clock and required for somite formation

The process of segmentation in vertebrates is described by a clock and wavefront model consisting of a Notch signal and an fibroblast growth factor‐8 (FGF8) gradient, respectively. To further investigate the segmentation process, we screened gene expression profiles for downstream targets of the segmentation clock. The Rnd1 and Rnd3 GTP‐binding proteins comprise a subgroup of the Rho GTPase family that show a specific expression pattern similar to the Notch signal component ESR5, suggesting an association between Rnd1/3 and the segmentation clock. Rnd1/3 expression patterns are disrupted by overexpression of dominant‐negative or active forms of Notch signaling genes, and responds to the FGF inhibitor SU5402 by a posterior shift analogous to other segmentation‐related genes, suggesting that Rnd1/3 expressions are regulated by the segmentation clock machinery. We also show that antisense morpholino oligonucleotides to Rnd1/3 inhibit somite segmentation and differentiation in Xenopus embryos. These results suggest that Rnd1/3 are required for Xenopus somitogenesis. Developmental Dynamics 238:2867–2876, 2009. © 2009 Wiley‐Liss, Inc.