Age-dependent expression and localization of the progesterone receptor in the boar testis.

Expression of the progesterone receptor (PR) was monitored in testes of groups of five boars aged 50, 100, 150, 200 and 250 days. The primary monoclonal antibody used for immunohistochemistry (IHC) was raised against a peptide mapping the amino acids 922-933 of the carboxy-terminus of the human PR, negative controls were set up using an irrelevant monoclonal isotype-specific antibody, porcine endometrium served as positive control tissue. In parallel, qualitative reverse transcription-polymerase chain reaction was applied. Based on the developmental status of spermatogenesis the 50- and 100-day-old boars were considered as immature, the boars aged 200 and 250 days as mature. Positive and negative controls confirmed specificity of IHC. In the 50-day-old boars 85.1% of the prespermatogonia that had reached the basal lamina and 18.2% of the centrally located prespermatogonia stained positive, while it was 92.1% respectively 2.1% in the 100-day-old boars. The effect of time and location was highly significant (p < 0.005 resp. 0.0001). In mature boars between 77 and 80% of the A and B spermatogonia stained positive, there was no effect of boar age and stage of spermatogenesis. In both groups also few peritubular myoid cells stained positive. It is hypothesized that Leydig cell-derived progesterone plays a functional role in spermatogoniogenesis in a synergistic manner with Leydig cell-derived oestrogens.