Off limits--integrins holding boundaries in somitogenesis

Borders are essential for demarcating repeated structures such as somites during vertebrate development. Two recent articles describe roles for Integrinalpha5 and its ligand Fibronectin1 in zebrafish anterior intersomitic boundary formation and link them to Notch and Eph-Ephrin pathways in epithelialization of somite boundary cells. Together with these pathways, Integrinalpha5 and Fibronectin1 orchestrate the orderly formation of somite and later myotome borders. These studies shed light on components downstream of the periodic segmentation mechanism - the 'segmentation clock' - in somitogenesis.