Mol. Hum. Reprod. Advance Access originally published online on July 10, 2008
Molecular Human Reproduction 2008 14(8):465-474; doi:10.1093/molehr/gan041
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Characterization of an acrosome protein VAD1.2/AEP2 which is differentially expressed in spermatogenesis
1Department of Obstetrics and Gynaecology, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, PR China 2Center of Reproduction, Development and Growth, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, PR China 3Department of Surgery, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, PR China 4Department of Pathology, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, PR China 5Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, College of Life Science, Xiamen University, Xiamen, PR China
6 Correspondence address. Department of Obstetrics and Gynaecology, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, PR China. Fax: +852-28161947; E-mail: ckflee{at}hkucc.hku.hk (K-F.L.); jmluk{at}hkucc.hku.hk (J.M.C.L.)
The release of enzymes from the acrosome of the sperm head (acrosome reaction) starts the fertilization process and enables the spermatozoa to penetrate the zona pellucida of the oocytes. Defective acrosome reaction is one of the important causes of infertility in men. To investigate the molecular regulation of spermatogenesis in vivo, we used differential display reverse transcription–polymerase chain reaction to identify stage-specific genes in a retinol-supplemented vitamin-A deficiency (VAD) rat model and identified the VAD1.2 (acrosome-expressed protein 2, AEP2) gene, which was expressed strongly in the rat testis from post-natal day 32 to adult stage. The mouse VAD1.2 mRNA shared 85% and 67% sequence homology, and 74% and 38% amino acid homology, respectively, with the rat and human counterparts. VAD1.2 transcript was abundantly expressed in the rat seminiferous tubules at stage VIII–XII, and the protein was detected in the acrosome region of the round and elongated spermatids of mouse, human, monkey and pig. VAD1.2 co-localized with lectin-PNA to the acrosome region of spermatids. Interestingly, the expression of VAD1.2 protein in human testis diminished in patients with hypospermatogenesis, maturation arrest, undescended testis and Sertoli cell-only syndrome. Co-immunoprecipitation experiments followed by western blotting and mass spectrometry (MS–MS) identified syntaxin 1, β-actin and myosin heavy chain (MHC) proteins as putative interacting partners. Taken together, the stage-specific expression of VAD1.2 in the acrosome of spermatids and the binding of VAD1.2 protein with vesicle forming (syntaxin 1) and structural (β-actin and MHC) proteins suggest that VAD1.2 maybe involved in acrosome formation during spermiogenesis.
Key words: spermatogenesis/acrosome/golgi apparatus/syntaxin/β-actin
Submitted on January 22, 2008; resubmitted on June 30, 2008; accepted on July 4, 2008.
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