Evidence that an Arg-Gly-Asp Adhesion Sequence Plays a Role in Mammalian Fertilization

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Abstract
The Arg-Gly-Asp (RGD) sequence is known to play a role in many recognition systems involved in cell-to-cell and cell-to-matrix adhesion. In our experiments we demonstrated that an RGD-dependent recognition is involved in sperm-oolemmal adhesion and egg penetration. Following coincubation of RGD-containing oligopeptides in a heterologous system (human sperm and zona-free hamster eggs), a significant decrease in the number of oolemma-adherent sperm was noted at 15 .mu.M RGDV (Arg-Gly-Asp-Val) and at 5 .mu.M GRGDTP (Gly-Arg-Gly-Asp-Thr-Pro), and fertilization was completely inhibited at 250 .mu.M RGDV and 30 .mu.M GRGDTP. In a homologous system (hamster sperm and zona-free hamster eggs), a concentration-dependent decrease in oolemmal adhesion and egg penetration was also noted, with complete inhibition of fertilization at 200 .mu.M GRGDTP. The specificity of the receptor was confirmed by the fact that small changes in aminoacid composition impaired the peptide''s effectiveness and that peptide-dependent inhibition of fertilization was partially reversible in competition studies. The presence of a molecule on the oolemma capable of binding the RGD sequence was demonstrated by using immunobeads coupled with an RGD-containing hexapeptide (GRGDTP), which rosetted over the egg surface in a manner reversible by the addition of free GRGDTP in the medium.