Because the isolation of sufficient PGCs from genital ridges for its absolute reliable quantification is technically very challenging, we used the human GCT-derived seminoma cell line TCam-2, which is a widely accepted in vitro PGC model (Irie et al., 2015; Sugawa et al., 2015; Nettersheim et al., 2016a, b, c; Mitsunaga et al., 2017; Müller et al., 2020) and expresses high TRIM71 levels, similar to other GCT-derived cell lines (Supplementary Figure 8A). This evidence concerns the gene TRIM71 and seminoma.