Lactosaminoglycans synthesized by mouse male germ cells are fucosylated by an epididymal fucosyltransferase.

We have studied the synthesis of protein-bound carbohydrates in differentiating male germ cells in the mouse. Spermatocytes and spermatids synthesize asparagine-linked and high-molecular-weight glycopeptides as the major classes of protein bound carbohydrates. Asparagine-linked glycopeptides were found to be mainly composed of the complex bi-antennary type as shown by affinity chromatography on concanavalin-A Sepharose; high-molecular-weight glycopeptides were represented by nonfucosylated lactosaminoglycans since they were metabolically labeled with [14C]glucosamine but not with [3H]fucose, did not bind to DEAE-cellulose, and were susceptible to endo-beta-galactosidase. Labeling with galactose oxidase/Na B3H4 technique demonstrated that lactosaminoglycans were present on the surface of differentiating germ cells and of testicular and epididymal spermatozoa. Since lactosaminoglycans from germ cells and testicular spermatozoa were not retained on a column of fucose-binding lectin, it was concluded that these molecules do not contain fucose. On the other hand, epididymal spermatozoa lactosaminoglycans bound to the lectin and therefore contained fucose. A soluble fucosyltransferase, capable of transferring fucose to germ cell lactosaminoglycans, was found to be present in the epididymis but not in the testis. These data show that developing germ cells synthesize nonfucosylated lactosaminoglycans which are probably preserved throughout spermiogenesis. We suggest that these molecules are fucosylated in vivo by a fucosyltransferase secreted by the epididymal epithelium.