Annual changes in cell proliferation and apoptosis and expression of connexin 43 in the testes of domestic seasonal breeding ganders

Molecular mechanisms of seasonal changes in testicular morphology, histoarchitecture, and functions in birds have not been fully elucidated. The aim of the study was to examine the alternations in cell proliferation and apoptosis, these processes-related gene expressions, and gap junction protein (GJA1gene, connexin 43 protein; Cx43) expression and localization in gander testes during annual stages. Testes from domestic ganders (n = 28) in the first reproduction season were obtained at five stages, i.e., prebreeding (PrB), peak of reproduction (PR), postbreeding (PoB), nonbreeding (NB), and onset of reproduction (OR). Males were kept under controlled breeding conditions. Testicular weight, morphometry, and histology (H&E staining) were evaluated, and the following parameters were tested: (1) number of proliferating (PCNA-positive) and apoptotic (TUNEL-positive) cells; (2) mRNA and protein abundances of PCNA, caspase-3, and Cx43 by qRT-PCR and Western blot, respectively; (3) activity of caspase-3 by fluorometric method; and (4) localization of Cx43 by immunofluoresence. Testicular weight was found to decrease by 4-fold at the NB stage with massive depletion of germ cells concomitantly with a reduction of seminiferous tubule (ST) diameter and ST lumen compared to the PR and OR stages. The number of proliferating germ cells was higher at PrB and PR than at the PoB stage, whereas the number of apoptotic cells was higher at PoB and NB compared to PrB and OR. Thus, proliferation-to-apoptosis ratios were lower in PoB and NB than other stages. Moreover, mRNA expression of PCNA exhibited down regulation in these stages compared to PrB and PR. Stage-dependent changes in the Cx43 mRNA level and in the localization pattern in the ST germinal epithelium were observed. Lower abundances of GJA1 transcript during NB and OR than at PoB the stage and irregular distribution of Cx43 protein located near the lumen of ST primarily at PrB and NB compared to the remaining stages were noted. These results suggested that during gander testis development, function, regression, and recrudescence, the interaction between processes of cell proliferation, apoptosis, and changes in the localization of Cx43 protein in the germinal epithelium occurred. The balance between these processes may determine the final functional activity or inactive stage of the testes connected with weight and histoarchitecture changes.