In addition to the five 70-kDa heat shock proteins (HSP70) (13) and an additional thymidine kinase (TK) gene (see Fig. 1 A-C

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Germ cells of the rat have been studied at the fine structural level from the time they are present in the epithelium of the embryonic gut until near the time of production of mature gametes in the adult. Particular attention has been paid to the form and location of dense, fibrous material (nuage) in the germ cells during that period of the life cycle. The nuage either exists as small discrete bodies in the cytoplasm or as “cementing material” situated in the interstices of mitochondrial clusters. It is present in primordial germ cells in the gut epithelium, in germ cells in indifferent gonads and in germ cells in sexually differentiated fetal, neonatal and adult rat gonads. It is sometimes associated with nuclear pores. Because it is present throughout much of the life cycle of the germ cells of male and female rats and it has been observed in various other mammals by previous workers, it is suggested here that it is a characteristic morphological feature of mammalian germ cells. In addition, there is considerable similarity in form and distribution of the nuage to the “polar granules” in insects and the “germinal plasm” in amphibians which are suggested to play a role in the determination of germ cells in these animals. The possibility that nuage may play a comparable role in mammals is considered.

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We have identified cDNAs representing three hexokinase mRNAs (Hk1-sa, Hk1-sb, Hk1-sc) by screening mouse spermatogenic cell cDNA libraries with a mouse hepatoma cell line hexokinase (Hk1) cDNA [Arora KK, Fanciulli M, Pederson PL. J Biol Chem 1990; 265:6481-6488]. Although all three cDNAs show 99% identity to the somatic Hk1 cDNA sequence throughout most of their coding region, they differ from this sequence at the 5' end. They contain a common spermatogenic cell-specific sequence and a sequence unique to each cDNA immediately 5' to the common domain. However, they lack the porin-binding domain (PBD) present in this region of Hk1, used for binding to a pore-forming protein in the outer mitochondrial membrane. These observations appear to support a model proposed by others for hexokinase gene evolution in mammals. In addition, we found that Hk1-sb has an internal sequence that is not present in Hk1, Hk1-sa, or Hk1-sc. Moreover, Hk1-sa and Hk1-sb transcripts are developmentally expressed in mouse spermatogenic cells. Hk1-sa mRNA is first expressed during meiosis and continues to be present in postmeiotic germ cells, while the more abundant Hk1-sb mRNA is detected only in postmeiotic germ cells. These and other findings suggest that enzymes encoded by Hk1-sa, Hk1-sb, and Hk1-sc are present only in spermatogenic cells.

Many stage-specific embryonic antigens (SSEAs) have been identified as glycoconjugates. These molecules may play diverse roles in the development of the embryo, including regulation of cell growth, recognition, and differentiation. The example of SSEA-1 is described in detail. This molecule appears to play an essential role in compaction of the early mouse embryo, and may illustrate the general importance of carbohydrate-carbohydrate interactions in controlling cell surface interactions in development.

We have previously shown that several mycoplasma species associated with infertility bind specifically to sulfated glycolipids isolated from the mammalian reproductive tract. We now show that a germ cell-specific sulfoglycolipid binding protein (SLIP 1), which is a potent inhibitor of sperm/egg binding in vitro, is immunologically related to the heat shock protein(Hsp) 70 family of stress proteins and that Hsps are surface antigens in male germ cells. Our present data demonstrate that several mycoplasma and mammalian Hsps share this glycolipid binding specificity in vitro, and suggest that surface Hsps can function as adhesins which mediate sulfoglycolipid recognition in infectious disease and normal reproductive physiology.