Regulation of somitogenesis by Ena/VASP proteins and FAK duringXenopusdevelopment

Abstract

The metameric organization of the vertebrate body plan is established during somitogenesis as somite pairs sequentially form along the anteroposterior axis. Coordinated regulation of cell shape, motility and adhesion are crucial for directing the morphological segmentation of somites. We show that members of the Ena/VASP family of actin regulatory proteins are required for somitogenesis in Xenopus. Xenopus Ena (Xena) localizes to the cell periphery in the presomitic mesoderm (PSM), and is enriched at intersomitic junctions and at myotendinous junctions in somites and the myotome, where it co-localizes with ␤1-integrin, vinculin and FAK. Inhibition of Ena/VASP function with dominant-negative mutants results in abnormal somite formation that correlates with later defects in intermyotomal junctions. Neutralization of Ena/VASP activity disrupts cell rearrangements during somite rotation and leads to defects in the fibronectin (FN) matrix surrounding somites. Furthermore, inhibition of Ena/VASP function impairs FN matrix assembly, spreading of somitic cells on FN and autophosphorylation of FAK, suggesting a role for Ena/VASP proteins in the modulation of integrin-mediated processes. We also show that inhibition of FAK results in defects in somite formation, blocks FN matrix deposition and alters Xena localization. Together, these results provide evidence that Ena/VASP proteins and FAK are required for somite formation in Xenopus and support the idea that Ena/VASP and FAK function in a common pathway to regulate integrin-dependent migration and adhesion during somitogenesis.

Integrin α5 is required for somite rotation and boundary formation in Xenopus

“…Furthermore, fibronectin matrix is laid down at the anterior boundaries of turning somites, and lines the junction between somites and surrounding tissues ( Fig. 6; Kragtorp and Miller, 2006). Finally, our data showing that somite rotation is substantially delayed in intg␣5 MO injected embryos demonstrates that integrin ␣5␤1 plays a critical role in regulating rotation.…”

“…As cells eventually attain their final, anterior/posterior orientation, some irregular boundary formation is observed in the form of disjointed integrin ␤1 and fibronectin accumulation. We previously observed that, in anterior somites, fibronectin accumulation at the presumptive somite boundary occasionally preceded somite turning (Kragtorp and Miller, 2006). This would suggest that, in anterior somites, deposition the fibronectin matrix may serve an initial instructional role in boundary formation by creating a "track" for rotating cells to follow.…”

From segment to somite: Segmentation to epithelialization analyzed within quantitative frameworks

“…Kragtorp and Miller (2006) have found that inhibition of Ena/ VASP or FAK leads to abnormal somite rotation and failure to form intersomitic boundaries. Ena/VASP proteins appear to act as a molecular link between cell-surface integrins and the actin cytoskeleton to orchestrate changes in adhesive strength and cell motility (Schlaepfer and Mitra, 2004).…”

“…Ena/VASP proteins appear to act as a molecular link between cell-surface integrins and the actin cytoskeleton to orchestrate changes in adhesive strength and cell motility (Schlaepfer and Mitra, 2004). Another potential mechanism by which these proteins might regulate cell motility is through activation of integrin adhesion and fibronectin matrix assembly (Kragtorp and Miller, 2006).…”

Cell behaviors associated with somite segmentation and rotation in Xenopus laevis

“…Alternatively, it could be that cadherin/protocadherin function is required for the directional movement of filopodia during rotation. Another possible mediator of this process is Xena, an actin regulatory molecule (Kragtorp and Miller, 2006). Inhibition of Xena function led to enlarged and disorganized somites.…”