17β‐estradiol induces spermatogonial proliferation through mitogen‐activated protein kinase (extracellular signal‐regulated kinase 1/2) activity in the lizard (Podarcis s. sicula)

There are always more evidences indicating that 17β-estradiol (E2) is necessary for normal male fertility. We have used a nonmammalian vertebrate model (the lizard Podarcis s. sicula) to investigate the regulation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) activity in the testis during the annual sexual cycle and to study whether E2 exerts a role in the spermatogenesis through ERK1/2 activity. Immunocytochemistry analysis shows that ERK1/2 proteins are present in the nucleus of the spermatogonia (SPG), and in primary (I) spermatocytes (SPC). The annual E2 profile shows a progressive increase during the active spermatogenesis (from April to June) and a peak in the month of August (spermatogonial mitosis). In parallel, ERK1/2 (molecular weight 44 and 42 kDa, respectively) are highly phosphorylated during the period of active spermatogenesis and in post-refractory period (August) compared with the winter stasis (from November to March). Present results demonstrate that E2 treatment induces spermatogonial proliferation, possibly via the activation of ERK1/2, and this effect is counteracted by the antiestrogen ICI 182-780. Mol. Reprod. Dev. 61: 218–225, 2002. © 2002 Wiley-Liss, Inc.