Expression of the spermatid-specific Hsp70 antigen is conserved in mammalsincluding marsupials

The anatomical location of testes in mammals ranges from a location close t o that observed in the embryo to a lower position usually involving a penda nt scrotum. In scrotal mammals, the abdominal position of the cryptorchid t estis, which elevates its temperature, is detrimental to spermatogenesis an d causes infertility. Spermatocytes are sensitive but late spermatids are r elatively resistant to thermal stress suggesting that the latter might be p rotected in some way. In general, most organisms express Hsp70 proteins, wh ich play a crucial role in the protection of cells against thermal stress. We have found previously that the Hsc70t protein, a member of the Hsp70 fam ily of proteins, is constitutively expressed in the late spermatids of mice . Here, we have utilized immunohistochemistry with anti-mouse Hsc70t antise rum to examine the: expression of the spermatid-specific Hsp70 antigen in t he testes of several mammalian species with different degrees of testes mig ration. Our data indicate that the antigen is conserved in the mammals incl uding marsupials. We also examined whether antigens of Hsp70-related protei ns were expressed in non-mammalian vertebrates including not only homoiothe rmal but also poikilothermal animals. The spermatid-specific Hsp70 antigens were not detectable in the testes of the animals examined. From results of immunohistochemistry with BRM22 monoclonal antibody which reacts broadly w ith Hsp70 family proteins, however, we revealed constitutive expression of antigens of Hsp70-related proteins in spermatogenic cells of the vertebrate s. These results suggest that the expression of spermatid-specific Hsp70 pr otein may be involved in the developmental pathway during spermiogenesis in mammals rather than in thermotolerance.