Estrogen receptor-alpha protein localization in the testis of the rainbow trout (Oncorhynchus mykiss) during different stages of the reproductive cycle

Estrogen receptor-alpha (ER-alpha) is important for male reproduction in ma mmals; however, no information is available on ER-alpha protein distributio n in the testes of fishes. The cellular localization of the rainbow trout ( Oncorhynchus mykiss) ER-alpha (rtER-alpha) protein, throughout the annual r eproductive cycle was determined in this study. An antibody was designed ba sed on a 15-amino acid sequence from the D-domain of the rtER-alpha, and it s specificity was confirmed using Western blot analysis, Immunohistochemica l analysis revealed rtER-alpha protein to be present only in the testicular interstitium, at every stage of the annual reproductive cycle, The localiz ation of rtER-alpha protein in the interstitial fibroblasts, the Leydig cel l precursor in the rainbow trout, suggests a role for estrogens in the diff erentiation of these precursor cells into mature Leydig cells, This is the first study to report the cellular localization of an estrogen receptor pro tein in the testis of any fish species.