The project aimed at identifying the cofactors regulating Polycomb complex PRC2 enzymatic activity in gonads. We used a knock-in mouse model where the enzymatic subunit of PRC2 (either EZH2 or EZH1) is tagged (Flag-tag) to purify PRC2 from mouse adult testis. This experiment revealed the existence of a new cofactor for PRC2 that we called GPIF (AU022751).