Uncoupling integrin adhesion and signaling: the beta PS cytoplasmic domain is sufficient to regulate gene expression in the Drosophila embryo

Abstract

Integrin cell surface receptors are ideally suited to coordinate cellular differentiation and tissue assembly during embryogenesis, as they can mediate both signaling and adhesion. We show that integrins regulate gene expression in the intact developing embryo by identifying two genes that require integrin function for their normal expression in Drosophila midgut endodermal cells. We determined the relative roles of integrin adhesion versus signaling in the regulation of these integrin target genes. We find that integrin-mediated adhesion is not required between the endodermal cells and the surrounding visceral mesoderm for integrin target gene expression. In addition, a chimeric protein that lacks integrin-adhesive function, but maintains the ability to signal, can substitute for the endogenous integrin and regulate integrin target genes. This chimera consists of an oligomeric extracellular domain fused to the integrin ␤ PS subunit cytoplasmic domain; a control monomeric extracellular domain fusion does not alter integrin target gene expression. Therefore, oligomerization of the 47-amino-acid ␤ PS intracellular domain is sufficient to initiate a signaling pathway that regulates gene expression in the developing embryo.

Integrin-ECM interactions regulate the changes in cell shape driving the morphogenesis of theDrosophilawing epithelium

“…One of the main problems is how to distinguish between direct integrin signalling and the indirect effects caused by a lack of integrin adhesion. In Drosophila, the differentiation of some but not all cell types depends directly on integrin signalling downstream of di␤ (Martin-Bermudo, 2000;Martin-Bermudo and Brown, 1999). The results presented here support the idea that the regulation of cell morphology by integrins depends more on integrin adhesion to the ECM than on signalling.…”

“…There, they can act both as activated integrins and as dominant negatives. Whereas on one hand, they can substitute for the endogenous integrin and regulate integrin target genes in the Drosophila midgut (Martin-Bermudo and Brown, 1999) they can, on the other hand, also inhibit cell adhesion, matrix Journal of Cell Science 120 (6) assembly and cell migration mediated by the endogenous integrins (Narasimha and Brown, 2004;Tanentzapf et al, 2006). Since the key feature of this chimera appears to be the dimerisation of the ␤PS cytoplasmic tail, we refer to it henceforth as di␤.…”

ojoplano-mediated basal constriction is essential for optic cup morphogenesis

“…Intβ1tail:eGFP was generated by cloning eGFP at the C terminus of the 70 C-terminal amino acids of the Drosophila integrin beta PS. The dominant-negative torso D /βcyt construct was reported previously (Martin-Bermudo and Brown, 1999). The medaka vsx3::OLint-β1⌬21 construct is equivalent to a human dominant-negative variant, previously shown to interfere with cell adhesion to laminin (Retta et al, 1998).…”

“…We made use of the dominant-negative chimera torso D /βcyt, which previously has been shown to interfere with integrin-adhesive function (Martin-Bermudo and Brown, 1999). Injection of this construct under the control of the eye-specific promoter vsx3 (vsx3::torso D /βcyt) in the reporter line rx2::mYFP impaired optic cup folding in 27% of the treated embryos (n=102).…”

Genetic and Electrophysiological Investigation of Learning Memory Mechanisms

“…Intracellular signals alter integrin affinity for ECM ligands (inside-out signaling) and ECM ligands trigger intracellular events such as cytoskeletal re-organization and the modulation of gene expression (outside-in signaling) (34)(35)(36)(37). It is also clear that integrins act by modulating other classes of receptors and that adhesive and signaling functions may be distinct (38)(39). Integrins function in axonal outgrowth, target recognition, and sprouting of synaptic arbors (33,40), but are also involved in mature synaptic function (41)(42).…”