Simone Lackner and Jamie Schwendinger-Schreck contributed equally to this article.
Segmental Assembly of Fibronectin Matrix Requires rap1b and integrin α5
Article first published online: 7 JAN 2013
Copyright © 2012 Wiley Periodicals, Inc.
Volume 242, Issue 2, pages 122–131, February 2013
How to Cite
Lackner, S., Schwendinger-Schreck, J., Jülich, D. and Holley, S. A. (2013), Segmental Assembly of Fibronectin Matrix Requires rap1b and integrin α5. Dev. Dyn., 242: 122–131. doi: 10.1002/dvdy.23909
- Issue published online: 22 JAN 2013
- Article first published online: 7 JAN 2013
- Accepted manuscript online: 29 NOV 2012 04:56AM EST
- Manuscript Accepted: 17 NOV 2012
- Manuscript Revised: 18 OCT 2012
- Manuscript Received: 23 AUG 2012
- American Cancer Society
- NSF. Grant Number: IOS-1051839
Background: During segmentation of the zebrafish embryo, inside-out signaling activates Integrin α5, which is necessary for somite border morphogenesis. The direct activator of Integrin α5 during this process is unknown. One candidate is Rap1b, a small monomeric GTPase implicated in Integrin activation in the immune system. Results: Knockdown of rap1b, or overexpression of a dominant negative rap1b, causes a mild axis elongation defect in zebrafish. However, disruption of rap1b function in integrin α5−/− mutants results in a strong reduction in Fibronectin (FN) matrix assembly in the paraxial mesoderm and a failure in somite border morphogenesis along the entire anterior-posterior axis. Somite patterning appears unaffected, as her1 oscillations are maintained in single and double morphants/mutants, but somite polarity is gradually lost in itgα5−/−; rap1b MO embryos. Conclusions: In itgα5−/− mutants, rap1b is required for proper somite border morphogenesis in zebrafish. The loss of somite borders is not a result of aberrant segmental patterning. Rather, somite boundary formation initiates but is not completed, due to the failure to assemble FN matrix along the nascent boundary. We propose a model in which Rap1b activates Integrin/Fibronectin receptors as part of an “inside-out” signaling pathway that promotes Integrin binding to FN, FN matrix assembly, and subsequent stabilization of morphological somite boundaries. Developmental Dynamics 242:122–131, 2013. © 2012 Wiley Periodicals, Inc.