Mammalian oocytes exhibit specific recognition of the RGD (ARG‐Gly‐Asp) tripeptide and express oolemmal integrins

Abstract

Integrins are a family of cell adhesion receptors involved in many cell-cell and cell-matrix interactions. Some of these heterodimeric receptors, such as alpha 5 beta 1 and alpha v beta 1, specifically recognize the amino acid sequence Arg-Gly-Asp (RGD) within their ligands. The RGD sequence is found in fibronectin, vitronectin, and other extracellular matrix proteins. Our results demonstrate that the oolemmas of eggs from human and several other mammalian species contain receptors capable of binding to RGD ligands, and that integrin subunits are expressed by oocytes. Four distinct techniques were utilized to identify the presence of functional integrins on mammalian eggs. RGD-binding receptors were detected on the surfaces of zona-free eggs from all species tested. Covaspheres coated with PepTite-2000, which contains RGD, bound to the eggs and formed rosettes. Rosetting was competitively inhibited by PepTite-2000 and by GRGDTP, a soluble RGD peptide, but not by RGES. An ELISA using polyclonal antibodies directed against the cytoplasmic tails of the integrin subunits identified the integrin subunits alpha 5, beta 1, and alpha v, but not beta 3, in detergent extracts of Syrian hamster eggs. A dot blot confirmed the presence of alpha v in hamster egg lysates. Finally, the integrin subunits alpha 2, alpha 5, alpha 6, but not alpha 4, were detected on the surfaces of zona-free eggs from human and Syrian hamster. Immunobeads coated with monoclonal antibodies specific for alpha 2, alpha 5, and alpha 6 bound to the eggs and formed rosettes.(ABSTRACT TRUNCATED AT 250 WORDS)