Annual profile of mitogen-activated protein kinase (extracellular signal-regulated kinase 1 and 2) in the frog (Rana esculenta) testis

Several lines of evidences support a key role of extracellular regulated-signal kinase 1 and 2 (ERK1/2) in male fertility. Using a non-mammalian vertebrate model, the frog Rana esculenta, we have investigated the regulation of ERK1/2 activity in the testis during the annual sexual cycle. ERK1/2 proteins (molecular weight 44 and 42 kDa respectively) are present in the cytoplasm and nucleus of the primary (I) and secondary (II) spermatogonia (SPG), and in the nucleus of I spermatocytes (SPC). The annual plasma 17β-estradiol profile shows a progressive increase during the active spermatogenesis with a peak in the month of June. Concomitantly, ERK 1/2 are highly phosphorylated during the period of active spermatogenesis (from April to July) respect to the regressive period (September/October) and winter stasis (from November to March). In conclusion these data suggest that ERK1/2 activity have a role, possibly via 17β-estradiol activation, in the regulation of germinal epithelium progression