Growth arrest specific 1 (Gas1) and glial cell line-derived neurotrophic factor receptor α1 (Gfrα1), two mouse oocyte glycosylphosphatidylinositol-anchored proteins, are involved in fertilisation.

Recently, Juno, the oocyte receptor for Izumo1, a male immunoglobulin, was discovered. Juno is an essential glycosylphosphatidylinositol (GIP)-anchored protein. This result did not exclude the participation of other GIP-anchored proteins in this process. After bibliographic and database searches we selected five GIP-anchored proteins (Cpm, Ephrin-A4, Gas1, Gfra1 and Rgmb) as potential oocyte candidates participating in fertilisation. Western blot and immunofluorescence analyses showed that only three were present on the mouse ovulated oocyte membrane and, of these, only two were clearly involved in the fertilisation process, namely growth arrest specific 1 (Gas1) and glial cell line-derived neurotrophic factor receptor α1 (Gfrα1). This was demonstrated by evaluating oocyte fertilisability after treatment of oocytes with antibodies against the selected proteins, with their respective short interference RNA or both. Gfrα1 and Gas1 seem to be neither redundant nor synergistic. In conclusion, oocyte Gas1 and Gfrα1 are both clearly involved in fertilisation.