Abstract:  In order to investigate the involvement of Bcl-2 family protein in germ cell apoptosis during spermatogenesis and explore the differences of gonad development between reproductive caste and nonreproductive caste in termites, the expression of Bcl-2 and Bax proteins in germ cells during spermatogenesis of reproductives and workers of termite Reticulitermes aculabialis was investigated using immunocytochemical localization method. The results showed that both the immunopositive Bcl-2-like and Bax-like protein existed in germ cells from spermatogonia to sperm stage during spermatogenesis in reproductives and workers. In the reproductives, the expression level of Bcl-2-like was higher in secondary spermatocyte, spermatid and sperm, while lower in spermatogonia and primary spermatocyte. In the workers, a strong expression of Bcl-2-like was shown in secondary spermatocytes, and a lower expression level in spermatogonia and primary spermatocytes. Except for the stage of primary spermatocytes, the expression ratio of Bax-like during spermatogenesis in workers was significantly higher than that in the reproductives. In reproductives, the expression level of Bax-like was higher in spermatogonia, primary spermatocytes and secondary spermatocytes, while the lowest in sperms. Workers had higher expression levels of Bax-like in the secondary spermatocytes, spermatids and sperms, and the lowest expression levels in primary spermaocyte. During spermatogenesis, the expression ratio of Bax/Bcl-2 gradually decreased in germ cells of reproductives. However, in workers the expression ratio only decreased in the secondary spermatocytes and increased in other germ cells. According to the expression ratio of Bax/Bcl-2, spermatogonia and primary spermatocytes were the main targets of apoptosis in reproductives, while in workers the main targets of apoptosis included spermatogonia, primary spermatocytes, spermatids and sperms. The results suggest that in the testis of termite, apoptosis of germ cells is regulated by the pro-and anti-apoptotic members of the Bcl-2 family proteins and the expression of Bcl-2-like and Bax-like show a dynamic change which determines the fate of survival or death of germ cells during spermatogenesis. Bcl-2-like and Bax-like not only play critical roles germ cell apoptosis in the testis, but also can be involved in caste differentiation of termites.

Key words: Reticulitermes aculabialis, Bcl-2 family protein, Bax protein, spermatogenesis, apoptosis