PR domain zinc finger protein 1 (PRDM1; also known as BLIMP-1) is a transcriptional repressor expressed in all three layers of the blastocyst (ectoderm, endoderm and mesoderm), including the primitive streak (Ohinata et al., 2009) and in migratory PGCs (Chang et al., 2002). Its structure includes zinc fingers for DNA binding (Saiti and Lacham-Kaplan, 2007). Lineage tracing using a Prdm1-Cre-GFP transgenic mouse strain demonstrated that it is only found in cells destined to be PGCs and its expression in PGCs appears to precede both Developmental pluripotency-associated protein 3 (Dppa3) and Interferon-induced transmembrane protein 3 (Ifitm3) expression thereby making it the earliest marker of mouse PGCs (Saiti and Lacham-Kaplan, 2007, Ohinata et al., 2009). Furthermore, Prdm1-mutant mice have a reduced number of PGCs which neither proliferate nor migrate correctly, indicating the critical role of the protein in PGC development (Vincent et al., 2005, Ohinata et al., 2009). Bmp4 (which, as mentioned in section 1.1.1., is necessary for germ cell specification) has been shown to be important in the induction of epiblast cells to express Prdm1 and thus facilitates germ cell specification (Ohinata et al., 2009).

In humans, PRDM1 expression has also been demonstrated in fetal ovaries, whilst hESCs upregulate its expression during differentiation into germ cells (Lin et al., 2014). Chronologically, it appears to be expressed at the same stage of differentiation as POU5F1, but prior to DEAD (Asp-Glu-Ala-Asp) box polypeptide 4 (DDX4) and SYCP3 (Lin et al., 2014), indicating it may be a premeiotic marker of germ cells. Data on the role of PRDM1 in bovine germ cell development are not available. Of note, although PRDM1 is clearly a marker of PGCs, it has many other roles throughout the body, including differentiation of B lymphocytes (Chang et al., 2002), therefore it cannot be considered a germ cell-specific marker.