Cxcl12a induces expression to initiate collective migration and sequential Fgf-dependent neuromast formation in the zebrafish posterior lateral line primordium.

The zebrafish posterior lateral line primordium migrates along a path defined by the chemokine Cxcl12a, periodically depositing neuromasts, to pioneer formation of the zebrafish posterior lateral line system. , known for its role in promoting cell migration, is expressed in leading cells of the primordium in response to Cxcl12a, whereas its expression in trailing cells is inhibited by Fgf signaling. knockdown delays initiation of primordium migration. This delay is associated with aberrant expansion of () and reduction of expression in the leading part of the primordium. Co-injection of morpholino with mRNA prevents the initial delay in migration and restores normal expression of and The delay in initiating primordium migration in morphants is accompanied by a delay in sequential formation of trailing Fgf signaling centers and associated protoneuromasts. This delay is not specifically associated with knockdown of but also with other manipulations that delay migration of the primordium. These observations reveal an unexpected link between the initiation of collective migration and sequential formation of protoneuromasts in the primordium.