Expression and localization of testis developmental related gene 1 (TDRG1) in human spermatozoa

Testis-specific proteins, synthesized during spermatogenesis and spermiogenesis, are necessary for spermatid differentiation and/or for mature sperm function during fertilization. However, majority of these genes have neither been identified nor fully characterized. Testis developmental related gene 1 (TDRG1), a newly identified human testis-specific gene, encodes a 100-amino-acid protein without any characterized protein domains, and it may play a role in spermatogenesis. However, whether this human-specific protein is important for mature sperm function remains unclear. As an initial effort, in this study, we aimed to systematically investigate the expression and localization of TDRG1 in normal human spermatozoa. Thus, immunohistochemistry was used to analyze the distribution of TDRG1 in human testis. Reverse transcription-polymerase chain reaction, western blot analysis and indirect immunofluorescence were used to determine the expression and localization of TDRG1 in normal human spermatozoa. The immunohistochemistry results showed that the TDRG1 protein was expressed in spermatogenic cells in the seminiferous tubules of human testis. Interestingly, the TDRG1 was more abundant in spermatogenic cells at the late stages of spermatogenesis. The TDRG1 antibody specifically recognized an 11-kDa protein only in soluble extracts from normal human spermatozoa. Indirect immunofluorescence assays indicated that TDRG1 located in the midpiece, principal piece and flagellum of normal human spermatozoa. In conclusion, TDRG1 was found not only in spermatogonia, but also in spermatozoa. The localization of TDRG1 in human normal spermatozoa implies its potential regulatory role in sperm motility.