Testis-like steroidogenesis in the ovotestis of the European mole, Talpa europaea

The female European mole (Talpa europaea) presents a vivid paradox in relation to our contemporary understanding of mam-malian sexual differentiation. These animals are exceptional among female mammals in that they possess bilateral ovotestes. The ovotestis contains a morphologically normal ovarian com-ponent that develops during the spring breeding season and a histologically defined testicular region, the interstitial gland, which enlarges during autumn when the ovarian component de-creases in size. In correlation with this unusual gonadal situa-tion, the female mole displays a penile clitoris traversed by a urethral canal. Although the histology of the ovotestis is well documented and has recently been extended to an additional three species of the genus Talpa, there have been no clear in-dications of the physiological function, particularly androgen production, of the ovotestis in these female moles. This paper presents the first clear evidence of seasonal variation in plasma testosterone concentrations, which parallel the growth and re-gression of the ‘‘testicular’ ’ interstitial gland, in T. europaea. Plasma androstenedione did not show significant seasonal vari-ation, but plasma testosterone (1.06 6 0.2 ng/ml) and gonadal testosterone concentration (1.57 6 0.65 mg/mg protein) in fe-males in autumn were significantly higher (p, 0.02) than plas-ma (0.4 6 0.2 ng/ml) and gonadal (0.24 6 0.21 mg/mg) con-centrations in pregnant or immediately postpartum females in spring. Our data also reveal selective metabolic production of testosterone from radiolabeled steroid precursors (progesterone and androstenedione) by these ovarian interstitial tissues and male testes; estradiol is produced by ovarian tissue but not in-terstitial gland or testis