In male germ cells, many marked morphological changes occur during spermatogenesis, particularly in haploid spermatids after meiotic division64. In various mammals, male germ cell differentiations proceed actively and continuously in the testis after puberty, and sperms are produced throughout adulthood64. Mice require 1 month for completion of spermatogonial stem cell proliferation and differentiation, meiosis, generation of haploid germ cells, and morphogenesis of the developing testicular spermatozoa in seminiferous tubules64. After meiotic division (during the process of haploid germ cell differentiation, or spermiogenesis), the rounded spermatids undergo marked morphological changes to become testicular spermatozoa: the nucleus assumes a compact shape, the mitochondria are rearranged, the flagellum forms, and the acrosome is generated. During this period of differentiation, which occurs within 5–6 weeks in humans6566 and 2–3 weeks in mice67, haploid germ cells do not divide but morphogenesis occurs, indicating that some regulatory mechanism arrests the cell cycle. Searching for functional changes in genes and gene products involved in male infertility would increase our understanding of the causes of this condition and perhaps lead to new treatments for some cases. The simplest strategy for elucidating the mechanism of spermatogenesis is to identify and characterize differentiation-specific molecules and their associated genes in germ cells. In this study, the mRNA expressions of 10 AIs, excluding Dnpep, were significantly higher in mice at 8 weeks of age compared with those at 2 weeks and in TGC compared with epididymal spermatozoa (ES). Thus, these proteins may be involved in the development of testicular spermatozoa.