Developmental expression of thyroid hormone receptors in the rat testis

Sertoli cell proliferation in the rat is completed by Days 15-20 postnatall y. Thyroid hormones appear to regulate the duration of Sertoli cell prolife ration, affecting adult Sertoli cell number and hence the capacity of the t estis to produce sperm. In the present study, a combination of immunohistoc hemistry, immunoblot analysis, and reverse transcription-polymerase chain r eaction was used to demonstrate the expression pattern of thyroid hormone r eceptors (TR) in the juvenile and adult rat testis. The results indicated t hat TR alpha 1 was expressed in proliferating Sertoli cell nuclei, its expr ession decreasing coincident with the cessation of proliferation. TR alpha 2, TR alpha 3, and TR beta 1 mRNAs were expressed at low levels during deve lopment; however, the corresponding protein was not detected by immunoblot analysis. In addition, TR alpha 1 was found to be expressed in germ cells f rom intermediate spermatogonia to mid-cycle pachytene spermatocytes. Immuno histochemistry also demonstrated TR expression in a subset of interstitial cells. The demonstration of TR expression in germ cells undergoing spermato genic differentiation suggests a possible role for thyroid hormones in the adult testis.