In our previous study,we identified a novel testis-specific expressed gene 2(TSEG-2)from mouse testis.To further investigate its functions,35 male Balb/c mice(8 weeks old)were divided into cryptorchidism group(n=20),sham group(n=10),and control group(n=5).In cryptorchidism group,the right testes were anchored to the inner lateral abdominal wall.In situ hybridization(ISH)was applied to measure the localization of TSEG-2 in mouse testis.Real-time quantitative PCR was performed to detect the expression of TSEG-2 gene.Meanwhile,under the mediation of polyethylenimine(PEI),the recombinant vector pEGFP-TSEG-2(n=5)or empty vector(mock,n=5)was transfected into the testis of male mice.The transfection efficiencies were measured under a fluorescence microscope.The apoptosis of spermatogenic cells was detected by terminal deoxynuleotidyl-mediated nick end labeling(TUNEL).The results showed that TSEG-2 was expressed in convoluted seminiferous tubules,more precisely,in spermatogonia and spermatocytes.As compared with sham and control groups,the TSEG-2 transcription was significantly enhanced(P<0.05)and was correlated with apoptosis of spermatogenic cells in cryptorchid testes(P<0.05).PEI was efficient in mediating transfection of TSEG-2 into seminiferous tubules of testis.One week post-transfection,intratesticular injection of TSEG-2 resulted in increased apoptosis of spermatogenic cells in vivo (P<0.05).These results indicate that TSEG-2 may participate in the apoptosis of spermatogenic cells and the pathogenesis of cryptorchidism.