Identification of genes expressed in human primordial germ cells at the time of entry of the female germ line into meiosis

In mammals, primordial germ cells (PGCs) are first observed in the extraemb ryonic mesoderm from where they migrate through the hindgut and its mesente ry to the genital ridge to colonize the developing gonads. Soon after reach ing the gonads, the female PGCs enter meiosis, while the male PGCs are arre sted in mitosis and enter meiosis postnatally. To gain an insight into the molecular events controlling human germ cell development, we determined spe cific profiles of gene expression using cDNA prepared from PGCs isolated fr om male and female fetal gonads at 10 weeks gestation, when female PGCs sta rt to enter meiosis. The identity of the isolated PGCs, and the cDNA molecu les prepared from them, was confirmed respectively, by alkaline phosphatase staining and by the presence of transcripts of OCT4, a marker gene for PGC s and pluripotent stem cells in mice. Using differential display to compare the profiles of gene expression of male and female germ cells with each ot her and with that of a whole 10 week old fetus, we have identified eight tr anscripts differentially expressed in male and/or female germ cells. Among these transcripts, we have identified a member of the olfactory receptor ge ne family, which contains genes known to be germline-specific in the dog an d possibly associated with chemotactic function. Another transcript is comm on to a previously isolated sequence from the human testis and we have exte nded this sequence towards the 5' end for partial characterization. The ger mline-specific sequences also include two novel sequences not represented i n the databases. These findings are highly encouraging for the elucidation of the genetic programming of male and female germ line development.