A hallmark of
prion diseases or transmissible spongiform encephalopaties is the conversion of the cellular
prion protein (PrP(C)), expressed by the
prion gene (prnp), into an abnormally folded
isoform (PrP(Sc)) with
amyloid-like features that causes
scrapie in sheep among other diseases. prnp together with prnd (which encodes a
prion-like
protein designated as Doppel), and prnt (that encodes the
prion protein testis specific--Prt) with sprn (shadow of
prion protein gene, that encodes Shadoo or Sho) genes, constitute the "
prion gene complex". Whereas a role for prnd in the proper functioning of male reproductive system has been confirmed, the function of prnt, a recently discovered
prion family gene, comprises a conundrum leading to the assumption that ruminant prnt is a pseudogene with no
protein expression. The main objective of the present study was to identify Prt localization in the ram reproductive system and simultaneously to elucidate if ovine prnt gene is transcribed into
protein-coding
RNA. Moreover, as Prt is a prnp-related
protein, the
amyloid propensity was also tested for ovine and caprine Prt. Recombinant Prt was used to immunize BALB/c mice, and the anti-Prt polyclonal antibody (
APPA) immune response was evaluated by ELISA and Western Blot. When tested by indirect immunofluorescence,
APPA showed high avidity to the ram sperm head apical ridge subdomain, before and after induced capacitation, but did not show the same behavior against goat spermatozoa, suggesting high antibody specificity against ovine-Prt. Prt was also found in the testis when assayed by immunohistochemistry during ram spermatogenesis, where spermatogonia, spermatocytes, spermatids and spermatozoa, stained positive. These observations strongly suggest ovine prnt to be a translated
protein-coding gene, pointing to a role for Prt
protein in the ram reproductive physiology. Besides, caprine Prt appears to exhibit a higher
amyloid propensity than ovine Prt, mostly associated with its
phenylalanine residue.