Characterization of the annual regulation of reproductive and immune parameters on the testis of European sea bass

Abstract

The European sea bass, Dicentrarchus labrax L., is a seasonal gonochoristic species, which males are generally mature during the second year of life. It has been demonstrated that cytokines and immune cells play a key role in the testicular development. This reproductive-immune interaction might be very important in the sea bass since several pathogens are able to colonize the gonad and persist in this tissue, altering further reproductive functions and spreading the disease. This study aims to investigate the reproductive cycle of one year European sea bass males by analyzing cell proliferation and apoptosis and expression profile of some reproductive and immune-related genes in the testis as well as the serum sex steroid levels. Our data demonstrate that in one year old European sea bass males, the testis undergoes the spermatogenesis process and that the reproductive and immune parameters analyzed varied during the reproductive cycle. In the testis, the highest proliferative rates were recorded at spermatogenesis stage, while the highest apoptotic rates were recorded at spawning stage. We have also analyzed, for the first time in European sea bass males, the serum levels of 17β-estradiol (E2) and dihydrotestosterone and the gene expression profile of the enzymes implied in their production, determining that at least E2 might be involved in the regulation of the reproductive cycle. Some immune relevant genes, including cytokines, lymphocyte receptors, anti-viral and antibacterial molecules were detected in the testis of naïve European sea bass specimens and their expression profile was related with the stages of the reproductive cycle, suggesting an important role for the defence of the reproductive tissues.