Synthesis of transferrin and transferrin mRNA in bovine Sertoli cells in culture and in vivo: sequence of partial cDNA clone for bovine transferrin.

Techniques were developed for generating enriched cultures of bovine Sertoli cells and indifferent supporting cells (immature Sertoli cells). The [35S]methionine and [35S]sulfate-labeled proteins secreted by cultured cells were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and fluorography. The electrophoretic pattern of the major Sertoli cell-secreted proteins was distinct from that of the major proteins secreted by cultured peritubular cells (the predominant contaminating cell type). Five major polypeptides ranging in molecular mass from 22 kDa to 77 kDa were resolved by 2D-PAGE in reducing conditions and were assigned numbers for reference purposes. Polypeptides 1 and 2 appeared to be analogous to two rat Sertoli cell-secreted proteins, sulfated glycoprotein-1 and sulfated glycoprotein-2, because of similar molecular mass, isoelectric point, subunit composition, sulfation, and sialation characteristics. Transferrin was detected in conditioned medium by immunoprecipitation using an antibody to bovine serum transferrin. Cultured Sertoli cells isolated from prepubertal bulls secreted higher levels of transferrin than did cells isolated from infant bulls. An 850 bp cDNA corresponding to the 3' portion of bovine transferrin mRNA was cloned and sequenced. Transferrin message was shown to be present in testicular tissue isolated from infant and prepubertal bulls and it increased as bulls matured. Levels of testicular transferrin mRNA were subsequently shown to correlate with daily sperm production in yearling beef bulls.