Two Roles in Cell Adhesion

Abstract

Bécam et al. used a genetic approach to examine the role of integrins and associated proteins in Drosophila oogenesis and discovered an unexpected role in oocyte positioning for talin, a protein that links integrins to the cytoskeleton. Oocyte positioning in the Drosophila egg chamber during oogenesis, which is critical to the establishment of the embryo's anterior-posterior axis, depends on the increased abundance of DE-cadherin (which mediates cell-cell adhesion) in the oocyte and the posterior follicular epithelial cells (see Tepass and Godt). Investigating a possible role for integrins (which mediate cell-substrate adhesion) and associated proteins, Bécam et al. found that a null mutation of rhea (which encodes the Drosophila homolog of talin) in follicle cells disrupted oocyte positioning, as did a mutant that encoded truncated talin. When some follicle cells contained wild-type rhea and others contained mutant rhea , oocytes localized and adhered to the talin-mutant cells. Mutant rhea in germline cells did not disrupt localization. Unexpectedly, lack of integrin expression in either germline or follicle cells failed to affect oocyte localization, talin distribution, or organization of the actin cytoskeleton. Rather, talin-mutant follicle cells showed increased abundance of CE-cadherin and of shotgun mRNA, which encodes it. Oocytes adhered to cells induced to overexpress DE-cadherin, whereas the simultaneous loss of DE-cadherin from cells lacking talin prevented oocyte mislocalization. Cells mutant for talin showed increased expression of a fusion gene reporter regulated by the shotgun promoter, whereas the expression of green fluorescent protein (GFP)-tagged DE-cadherin under the control of an independent promoter was not affected. Thus, talin appears to play a role in regulating the transcription--and thereby the abundance--of DE-cadherin independent of its role in integrin signaling. I. E. Bécam, G. Tanentzapf, J.-A. Lepesant, N. H. Brown, J.-R. Huynh, Integrin-independent repression of cadherin transcription by talin during axis formation in Drosophila . Nat. Cell Biol. 7 , 510-516 (2005). [PubMed] U. Tepass, D. Godt, Talin's second persona. Nat. Cell Biol. 7 , 443-444 (2005). [PubMed]