Expression of a testis-specific member of the olfactory receptor gene family in human primordial germ cells.

Olfactory receptors are G protein-coupled transmembrane receptors. Genes encoding olfactory receptors constitute a large gene family of approximately 1000 total member genes. In mammals, a subset of member genes is specifically expressed in the testis (and not in the olfactory mucosa) and olfactory receptor proteins have been identified in elongated spermatids and mature spermatozoa of dogs. It is postulated that olfactory receptors may recognize signal molecules present in the female genital tract and play a role in chemotaxis of spermatozoa towards the oocyte. In a previous study, we identified 10 cDNA sequences, corresponding to genes specifically expressed in human primordial germ cells (PGC), by differential display. Sequence analysis revealed that one of these sequences appeared to be a member of the olfactory receptor gene family. To investigate this further, we have used degenerate oligonucleotide primers corresponding to conserved amino acid sequences of olfactory receptor proteins to amplify all the olfactory receptor genes expressed in the PGC. Sequence analysis of a total of 30 cloned sequences disclosed that one member gene, which was previously isolated from a human testis cDNA library by others, was also preferentially expressed in our PGC. Our results suggest that specific members of the olfactory receptor gene family may have a function in germ cells in the migratory phase of their life cycle.