Calponin modulates the exclusion of Otx-expressing cells from convergence extension movements

Otx2, a vertebrate homologue of the Drosophila orthodenticle gene, coordina tes two processes in early embryonic development. Not only does it specify cell fate in the anterior regions of the embryo, it also prevents the cells that express it from participating in the convergence extension movements that shape the rest of the body axis. Here we show that, in Xenopus, this l atter function is mediated by XclpH3, transcription of which is directly st imulated by Xotx2. XclpH3 is a Xenopus homologue of the mammalian calponin gene, the product of which binds both actin and myosin and prevents the gen eration of contractile force by actin filaments.