Integrin signaling in early sea urchin development

Abstract

The eggs and cleavage stage embryos of many animals express integrins and signal transduction components, yet comparatively little is known of the signaling complexes formed or the role of integrin signaling in early development. Genomic approaches have revealed the complement of integrin signaling components expressed in early sea urchin development. We review what is known about the distribution and function of integrins, integrin ligands, and integrin signal transduction proteins expressed during this critical phase of development. Immediately after fertilization integrins are expressed on the apical surface of the egg where the receptors interact with several potential ligands in the hyaline layer. The apical integrin complex is essential for reorganization of the egg cortex. During cleavage the blastocoel forms and a second integrin complex forms on the basal surface of blastomeres interacting with basal lamina components of the extracellular matrix. The integrin subunits of the apical and basal complexes differ and localization data indicate the apical and basal complexes may contain different scaffolding proteins and different kinases. We propose that there are two independent integrin-based signaling complexes formed during cleavage and blastula formation that may have distinct and essential functions in early development. The sea urchin is an excellent model for studies of these pathways and a number of approaches are available to determine their roles in early development.