Expression of Bcl-2 family proteins and spontaneous apoptosis in normal human testis

We investigated the frequency of spontaneous apoptosis and expression of th e Bcl-2 family of proteins during normal spermatogenesis in man. Testicular tissue with both normal morphology and DNA content was obtained from necro -donors and fixed in Bouin's solution. A TdT-mediated dUTP end-labelling me thod (TUNEL) was used for the detection of apoptotic cells. Expression of a poptosis regulatory Bcl-2 family proteins and of p53 and p21(Waf1) was asse ssed by immunohistochemistry. Germ cell apoptosis was detected in all teste s and was mainly seen in primary spermatocytes and spermatids and in a few spermatogonia. Bcl-2 and Bak were preferentially expressed in the compartme nts of spermatocytes and differentiating spermatids, while Bcl-x was prefer entially expressed in spermatogonia, Bar showed a preferential expression i n nuclei of round spermatids, whereas Bad was only seen in the acrosome reg ion of various stages of spermatids, Mcl-1 staining was weak without a part icular pattern, whereas expression of Bcl-w, p53 and p21(Waf1) proteins was not detected by immunohistochemistry. The results show that spontaneous ap optosis occurs in all male germ cell compartments in humans. Bcl-2 family p roteins are distributed preferentially within distinct germ cell compartmen ts suggesting a specific role for these proteins in the processes of differ entiation and maturation during human spermatogenesis.