Characterization of a novel acrosome-expressing protein 2 (AEP2/VAD1.2) during spermatogenesis

Abstract

Spermatogenesis is a complex process in which undifferentiated male germ cells undergo mitotic and meiotic divisions, followed by a dramatic morphological reorganization to generate spermatozoa that are capable of fertilizing an oocyte. Maturation and differentiation of male germ cells take place within seminiferous tubules and the process occurs in a cyclic manner. Recently, we used vitamin A-deficiency (VAD) rat model to synchronize spermatogenesis in rat testis and mRNA differential display to profile the gene expression patterns in retinol re-initiated (PVA-VAD) spermatogenesis. Twelve cDNA fragments including VAD1.2 and VAD1.3 that are differentially expressed in testis were isolated. Objectives: To characterize the acrosome-expressing protein 2 (AEP2/VAD1.2). Methods and Results: AEP2 was expressed in mouse on postnatal Day 25 coincided with the formation of spermatids. The gene coding for AEP2 is located on chromosome 11E1 containing 5 exons. RT-PCR and Northern blot analysis suggested that AEP2 was highly expressed in the germ cell of mouse testis at stages X-XII. Immunohistochemistry and immunofluorescence colocalization studies revealed an acrosome-specific expression pattern in developing spermatids of rat, mouse, human, pig and monkey. Western blot analysis confirmed a protein band of size 40-kDa in both rat and mouse testis lysates. Conclusions: The specific temporal and spatial expression of AEP2 suggested that it may play important roles in the maturation and differentiation of spermatids during spermiogenesis. (This work is supported in part by a RCG grant HKU7357/05M to KFL.)