Immunolocalization of estrogens and progesterone receptors within the ovary of the lizard Uromastyx acanthinura from vitellogenesis to rest season.

The sites of action and the physiological role of estrogens and progesterone in the ovary are poorly understood in Reptiles. We have undertaken a systematic study of the immunoexpression of classical oestrogen receptor (ER or ERalpha) and progesterone receptor (PR) in the female lizard during the reproductive cycle. During vitellogenesis, ER was not expressed in vitellogenic follicles whereas PR was weakly detected in the nucleus of some follicular cells and well expressed in the internal theca cells. The follicular and theca cells were immunopositive for ER in the previtellogenic follicles, the signal in both was cytosolic. PR was strongly expressed in the follicular cells, the signal was localised in the nucleus. In the post-reproductive period, ER was detected in the previtellogenic follicles in the same manner as in the breeding period. The staining for PR was expressed in both the nucleus and cytoplasm of follicular cells and theca cells. In the sexual rest, the previtellogenic follicles were all negative for ER and PR immunoexpression. These findings suggest that the main action of estrogens in the ovary is not mediated by ER. The expression of cytosolic PR only in the post-reproduction period, at the same time at the progesterone synthesis, supports the hypothesis which stipulates an exclusive nuclear localization in the absence of progesterone.