Identification of differentiation antigens in mouse testicular germ cells recognized by monoclonal antibody TRA 55

We have isolated a monoclonal antibody (mAb) TRA 55, which recognizes mouse testicular germ cells from mid-pachytene spermatocytes to the early stages of haploid spermatids during differentiation. Immunohistochemical analysis produced strong positive staining of the nuclei and faint staining in the cytoplasm of germ cells. At meiotic division, when the nuclear membrane dis appeared, a specific positive signal could be observed on metaphase chromos omes. When germ cells produced haploid spermatids, antigenicity became sudd enly weak and soon disappeared. TRA 55 did not react with testicular somati c cells, such as Sertoli cells or Leydig cells. Western blot analysis of th e whole testis showed four positive bands with molecular weights of 43, 46, 49 and 55 kDa. Three bands of 43, 49 and 55 kDa, and a single band of 46 k Da were recovered in cytoplasmic and nuclear fractions of testicular germ c ells, respectively. Chronological changes in the Western blot pattern indic ated that these antigens became detectable in the testis at the age of 10 d ays. Furthermore, all antigens were resistant to periodate treatment, sugge sting that the epitope was in an amino acid rather than a sugar moiety. The se antigen molecules may play important roles in the differentiation of ger m cells at the later stages of meiotic prophase and meiotic division in the mouse testis.