Abstract: Objective：To explore the expression of SET protein in the testes of mice at different developmental stages, and to discuss its potential function in regulating spermatogenesis and androgen production. Methods：Forty-eight ICR male mice at different developmental stages (one week as the infancy group; 4 weeks as the prepubertal group; 12 weeks as the adult group; 12 months as the ageing group) were used in this study. Expression of SET protein in testes was observed by immunohistochemistry. Expression levels of SET mRNA and protein were quantificationally analyzed by real time RT-PCR and western blot. Results：SET protein was expressed in spermatogonial cells and spermatocytes cells, the highest level of SET protein expression mainly showed in haploid and tetraploid sperm cells of 4 weeks mice and 12 weeks mice, and Leydig cells of 12 weeks and 1.2 months. Expression of SET mRNA in the prepubertal group was significantly higher than that in the infancy group （P=0.020）, while expression level of SET protein in the adult group was highest. Conclusions：SET protein expressed in spermatogonial cells and spermatocytes cells, and in haploid and tetraploid spermatogenic cells, which suggested that SET protein was involved in the deformation process of spermatocytes and sperm cells meiosis. SET was also expressed in Leydig cells, suggesting the possible role in testicular steroidogenesis.

Key words: Spermatogenesis, Leydig cells, Testis, Mice, inbred ICR, Androgens, SET