The doppel gene biology: a scientific journey from brain to testis, and return.

Doppel is a newly recognized prion-like molecule encoded by a novel gene locus, PRND, located on the same chromosomal region of the prion (PRNP) coding gene. Doppel was considered a paralogue and the first member of the prion-gene family, possibly originated through an ancestral gene duplication event. Prion and doppel have different expression patterns, suggesting that the gene products exhibit different biological functions. Actually, doppel is not involved in the aetiology of the Transmissible Spongiform Encephalopathies (TSEs) or “prion diseases” and is highly expressed only within the testicular tissue, suggesting an important physiological role in the process of spermatogenesis. The restricted spatial and temporal expression profile of doppel has suggested its investigation within particular pathological contexts, such as cancers, showing that it might represent a novel and attractive diagnostic molecular marker and that might provide insights into the regulatory pathways of tumor-cell transformation.