However, one cannot exclude the possibility that the data obtained with the C18-4 immortalized spermatogonial and the F9 teratoma cell lines might not reflect the function of RNF149 in primary spermatogonia or embryonic stem cells, since these cell lines have deficient cell cycle regulation that could mask a potential role of RNF149 in their proliferation. Here, RNF149 is linked to teratoma.