Abstract: Proto-oncogene product c-fos protein（Fos） plays a central role in the regulation of cellular growth and differentiation．The role of Fos in the regulation of germ cell progression during spermatogenesis and oogenesis has been studied in vertebrates, but little is known about the expression and role of Fos during spermatogenesis and oogenesis in insects. In order to identify c-fos proto-oncogene in different gonad of termites and the difference of germ cell development between non-reproductive and reproductive caste, the expression of Fos was examined in gonads of termite Reticulitermes aculabialis with immunocytochemical localization method. The results showed that c-fos-like protein (Fos-like) existed in the nucleus of oocytes and follicle cells at the growth stage of oogenesis in the last instar nymphs, but its expression was not detected during the oogenesis in workers．During the spermatogenesis of the termite, Fos-like immunopositive substance was localized in spermatogonial nuclei of reproductive adults, no immunoreactivity for Fos-like was detected in spermatogenesis of workers. The results suggest that Fos-like activity exerts a regulatory role in the spermatogenesis and oogenesis of the termite. The spermatogenesis is affected by Fos-like which directly regulates spermatogonial proliferation to form sufficient spermatozoa for fertilization, and Fos-like is also required in follicle cells for oocyte growth. Therefore, the absence of c-fos expression in the germ cells of worker may be one of reasons that the worker caste is curtailed in fertility to functional or complete sterility.

Key words: Termite, Reticulitermes aculabialis, c-Fos protein, oogenesis, spermatogenesis, reproductive termite, worker termite, immunocytochemical localization