Experiments with transgenic mice have shown that the loss of Hif-2α (Hif-2α–/–) severely reduced the number of PGCs from 20,000 to approximately 20 in E12.5 genital ridges (Covello et al., 2006) and caused azoospermia (Scortegagna et al., 2005). Here, EPAS1 is linked to Azoospermia.