Apoptosis is not the cause of seasonal testicular involution in roe deer

Apoptosis is involved in the regulation of spermatogenesis. The involution of testes in seasonal breeders might be expected to involve enhanced apoptotic cell elimination. We have compared seasonally changing testicular apoptosis in roe deer with that in non-seasonally breeding cattle. Apoptotic cells were detected as TUNEL-positive cells by both flow-cytometric analysis and in situ localisation of fragmented DNA in tissue sections. Apoptosis-induced DNA fragments were also assessed by enzyme-linked immunosorbent assay (ELISA) in homogenised testicular parenchyma. As expected, the testis mass and the percentage of haploid cells in roe deer showed a seasonal pattern with a significant maximum during the rut (August), whereas no annual variation of these parameters was found in bulls. All three methods for determining apoptosis showed similar findings. Roe deer exhibited significant seasonal fluctuation of total apoptotic activity (ELISA, apoptotic cells per tubule cross section) with a maximum during the breeding season. However, the seasonal differences in the number of apoptotic cells corresponded to the variable total numbers of spermatogonia and spermatocytes per tubule cross section. Thus, the percentages of TUNEL-positive cells related to the combined number of both germ cell types showed no seasonal variance, as confirmed by percentages of apoptotic cells analysed flow-cytometrically. The maximum level of apoptosis during the rut in roe deer was similar to the values obtained during the invariably high spermatogenic activity in cattle. These results suggest that, in roe deer, apoptosis is not the cause of the seasonal involution of testes.