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

Abstract

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 ␣5 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 spliceblocking morpholino to knock down expression of integrin ␣5 during somite formation. Loss of integrin ␣5 delayed somite turning and accumulation of integrin ␤1 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 ␣5 in somite boundary formation is conserved in a species using a unique mechanism of somitogenesis.

In vivo analyzes of dystroglycan function during somitogenesis in Xenopus laevis

“…A dominant negative form of integrin ␤1 subunit alters somite formation (Marsden and DeSimone, 2003). Knockdown of the ␣5 integrin prevents fibronectin deposition in the matrix and cell rotation within somites (Kragtorp and Miller, 2007). Together these findings suggest that Dg and ␤1-integrin functions are nonoverlapping during somitogenesis and support the following model for integrins and Dg functions during Xenopus laevis somitogenesis (Fig.…”

“…Ch, notochord; TN, neural tube; WT, wild-type; Mo, injected side. Scale bar ϭ 100 m. mello et al, 2002;Marsden and DeSimone, 2003;Kragtorp and Miller, 2007). These data contrast with phenotypes obtained with inhibition of type I cadherins where MyoD is downregulated (Giacomello et al, 2002).…”

“…They establish interactions with the extracellular matrix (ECM) at the notochord/somite boundaries. Interactions between ␣5 integrins and fibronectin allow cells to bend anteriorly and to undergo a 90°rotation relative to the anteroposterior axis (Kragtorp and Miller, 2007). The model predicts that after their rotation the somitic cells expressing Dg assemble laminin in the ECM at the intersomitic boundaries.…”

“…8). In this model, integrin/ fibronectin interactions allow fibronectin fibrillogenesis at the intersomitic junctions and rotation of somitic cells (Wedlich et al, 1989;Danker et al, 1992;Kragtorp and Miller, 2007), whereas Dg/ laminin interactions ensure the deposition of laminin in the intersomitic matrix and the elongation of cells within somites. These two steps are required for cell orientation, intersomitic cohesion and organization, and then muscle cell differentiation.…”

Control of extracellular matrix assembly along tissue boundaries via Integrin and Eph/Ephrin signaling

“…However, most of our understanding of EMC assembly comes from studies in 2D cell culture, although subsequent analyses in 3D culture suggest the regulation and cellular responses to Itgα5β1 differ in these more complex environments (Cukierman et al, 2001;Larsen et al, 2006;Mao and Schwarzbauer, 2005a;Mao and Schwarzbauer, 2005b). Separate genetic analyses have broadly defined the roles of Integrins in vivo and specifically have indicated that itga5 and fn are required for somite formation in mouse, zebrafish and Xenopus (Georges-Labouesse et al, 1996;Hynes, 2002;Jülich et al, 2005;Koshida et al, 2005;Kragtorp and Miller, 2007;Yang et al, 1999). Somites are the segmented anlagen of the skeletal muscle and vertebral column.…”