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.

Mechanisms of the epithelial-to-mesenchymal transition in sea urchin embryos

“…Because integrins are involved in multiple morphogenetic movements, including cellular attachment, migration, proliferation, differentiation and tissue assembly, it has yet to be elucidated whether the difference in components indicates a functional difference as well. 85 Integrins bind to Pl-nectin and also to a large modular protein called polydom, which contains a von Willebrand factor A domain, a pentraxin domain, EGF-like domains and an array of CCP domains. The genes that encode its homolog have been reported in sea urchins and other widespread vertebrates and invertebrates.…”

Pl-nectin, a discoidin family member, is a ligand for βC integrins in the sea urchin embryo

“…These heterodimeric transmembrane receptors regulate a wide range of cellular functions, including adhesion, motility, shape, polarity, growth, and differentiation, in many different organisms (Burke, 1999;Hynes, 2002). In sea urchins, there appear to be at least 4 β and 7 α subunits similar to those characterised in other animals and many of these are expressed during early development (Burke et al, 2007;Sea Urchin Genome Sequencing Consortium et al, 2006;Whittaker et al, 2006). In Strongylocentrotus purpuratus, βC-containing integrins are expressed on the surface of unfertilized eggs and, after fertilization, on the apical surface of developing embryos (Burke et al, 2004, Murray et al, 2000.…”