Integrin alpha5 is required for somite rotation and boundary formation in Xenopus

The morphogenesis of somites in Xenopus laevis is characterized by a complex process of cell turning that requires coordinated regulation of cell shape, adhesion, and motility. The integrin alpha5 subunit has been implicated in the formation of somite boundaries in organisms utilizing epithelialization to create morphologically distinct somites, but its function has not been examined in Xenopus. We used a splice-blocking morpholino to knock down expression of integrin alpha5 during somite formation. Loss of integrin alpha5 delayed somite turning and accumulation of integrin beta1 at somite boundaries, and disrupted the fibronectin matrix surrounding developing somites. Irregular somite boundaries with a sparse and discontinuous fibronectin matrix formed upon eventual completion of somite turning. Recovery of somite morphology was improved, but still incomplete in far posterior somites. These data demonstrate that the role of integrin alpha5 in somite boundary formation is conserved in a species using a unique mechanism of somitogenesis.