None of the integrins known to be present on the mouse egg or to be ADAM receptors are essential for sperm-egg binding and fusion

Antibody inhibition and α6β1 ligand binding experiments indicate that the egg integrin α6β1 functions as a receptor for sperm during gamete fusion; yet, eggs null for the α6 integrin exhibit normal fertilization. Alternative integrins may be involved in sperm-egg binding and fusion and could compensate for the absence of α6β1. Various β1 integrins and αv integrins are present on mouse eggs. Some of these integrins are also reported to be receptors for ADAMs, which are expressed on sperm. Using α3 integrin null eggs, we found that the α3β1 integrin was not essential for sperm-egg binding and fusion. Oocyte-specific, β1 integrin conditional knockout mice allowed us to obtain mature eggs lacking all β1 integrins. We found that the β1 integrin null eggs were fully functional in fertilization both in vivo and in vitro. Furthermore, neither anti-mouse β3 integrin function-blocking monoclonal antibody (mAb) nor αv integrin function-blocking mAb inhibited sperm binding to or fusion with β1 integrin null eggs. Thus, function of β3 or αv integrins does not seem to be involved in compensating for the absence of β1 integrins. These results indicate that none of the integrins known to be present on mouse eggs or to be ADAM receptors are essential for sperm-egg binding/fusion, and thus, egg integrins may not play the role in gamete fusion previously attributed to them.