Immunolocalization of androgen receptors in early and immature testis of Anguilla anguilla (L.)

The first androgen receptors (AR) immunolocalization in yellow eels occurs in the early Syrski organ. At this stage, the AR immunoreactivity is detected in pre-Leydig cells and in pre-Sertoli cells, but not in germ cells. In early testis the AR immunoreactivity appears in Leydig and Sertoli cells. In immature testis of silver eels immunoreactivity gradually appears also in the nuclei of primary spermatocytes and increases as the number of meiotic cells increase. A positive immunoreaction is also detected in nuclei of epithelial cells of spermatic duct. When germ cell rows assume a tubular appearance, the immunostaining gradually disappears from Sertoli cells. In more advanced testis stages of silver eels with anastomosing tubular organization, the immunoreactivity extends also to nuclei of secondary spermatocytes and disappears from Leydig cells. In A. anguilla the AR is expressed in many gonad cell types, including spermatocytes. This suggests that androgens play different roles in testis differentiation and development, sequentially acting first on somatic and later on germ cells to regulate spermatogenesis.