PARENT SESSION

(T518) REGULATION OF C-IAP1 AND C-IAP2 EXPRESSION DURING THE SEMINIFEROUS EPITHELIAL CYCLE AND THE ROLE THESE PROTEINS PLAY IN THE PROTECTION OF GERM CELLS FROM FAS-MEDIATED APOPTOSIS IN RAT TESTIS.

Wang, Yangyang¹, Suominen, Janne S¹, Parvinen, Martti ¹, Rivero-Muller, Adolfo¹, Kiiveri, Sanne², Heikinheimo, Markku ², Robbins, Ian ³, Toppari, Jorma¹, ¹ University of Turku, Turku, Finland² University of Helsinki, Helsinki, Finland³ Université Montpellier, Montpellier, France

ABSTRACT- The inhibitor of apoptosis proteins, c-IAP1 and c-IAP2, have been demonstrated to regulate apoptosis in cell culture. They are highly expressed in rat testis. To better understand their functions during spermatogenesis, we have analyzed the spatio-temporal distribution of c-IAP1 and c-IAP2 in rat testis, the regulation of their expression by the paracrine stem-cell factor (SCF) and their effects on Fas-mediated apoptosis. Expression levels of c-IAP1 and c-IAP2 were evaluated, throughout the seminiferous epithelial cycle, using western and northern blotting. Cellular distribution was evaluated by immunohistochemistry and in situ hybridization. In addition, an in vitro seminiferous tubule culture system was used to investigate the regulation of c-IAP expression by SCF and also to study the role IAPs play in protecting germ cells from Fas-mediated induction of apoptosis. Both c-IAP1 and c-IAP2 are transcriptionally regulated throughout the seminiferous epithelial cycle. c-IAP1 protein levels peaked at stage VII-VIII, while c-IAP2 protein varied only slightly. An abundant, small c-IAP2-immunoreactive form was observed specifically at stages VII-VIII. c-IAP1 expression localized to the cytoplasm of preleptotene spermatocytes and became increasingly abundant in the XY body of later stage spermatocytes. Both Leydig and Sertoli cells expressed c-IAP 1. c-IAP2 localized to spermatocytes (from stage V pachytene onwards), round spermatids, elongated spermatids and Leydig cells. Its expression was upregulated by SCF. Inhibition of IAP activity resulted in a greater sensitivity of germ cells to Fas-mediated apoptosis. Taken together, these results illustrate the important role IAPs play in the regulation of spermatogenic apoptosis.

KEY WORDS: c-IAP1, c-IAP2, spermatogenesis, apoptosis