The negative regulation of Mesp2 by mouse Ripply2 is required to establish the rostro-caudal patterning within a somite. 
The Mesp2 transcription factor plays essential roles in segmental border formation and in the establishment of rostro-caudal patterning within a somite.  A possible Mesp2 target gene, Ripply2, was identified by microarray as being downregulated in the Mesp2-null mouse.  Ripply2 encodes a putative transcriptional co-repressor containing a WRPW motif.  We find that Mesp2 binds to the Ripply2 gene enhancer, indicating that Ripply2 is a direct target of Mesp2.  We then examined whether Ripply2 is responsible for the repression of genes under the control of Mesp2 by generating a Ripply2-knockout mouse.  Unexpectedly, Ripply2-null embryos show a rostralized phenotype, in contrast to Mesp2-null mice.  Gene expression studies together with genetic analyses further revealed that Ripply2 is a negative regulator of Mesp2 and that the loss of the Ripply2 gene results in the prolonged expression of Mesp2, leading to a rostralized phenotype via the suppression of Notch signaling.  Our study demonstrates that a Ripply2-Mesp2 negative-feedback loop is essential for the periodic generation of the rostro-caudal polarity within a somite.