No abstract

Sertoli cells cultured in the presence of germ cells responded by increasing the level of transferrin mRNA 3-fold as determined by solution hybridization and Northern blot analysis. In contrast, the steady state levels of other mRNAs, including sulfated glycoprotein 1 (SGP-1), sulfated glycoprotein 2 (SGP-2), transferrin receptor, regulatory subunit of cAMP dependent protein kinase, and ferritin light chain, were not influenced by coculture with germ cells. The transferrin mRNA stimulatory activity was found in conditioned medium from germ cells but was not associated with germ cell membrane components. The activity was abolished by treatment of the medium with trypsin. Partial characterization and isolation of the protein(s) from conditioned medium indicated that it has an apparent mol wt between 10 and 30 K. Studies using inhibitors of protein and nucleic acid synthesis indicated that the stimulation of transferrin mRNA by germ cell conditioned medium required both transcription and translation. Sertoli cell enriched (germ cell depleted) testes were obtained from male offspring of pregnant females irradiated at the 19th day of gestation. Testicular transferrin mRNA levels from irradiated rats decreased in comparison to levels in the normal rat, whereas SGP-2 mRNA levels were unchanged. These studies demonstrate that germ cell secretions may interact with Sertoli cells to specifically increase the level of transferrin mRNA and that this interaction may be a mechanism by which germ cells regulate the flow of iron across the seminiferous epithelium.

In the testis, germ cells which are separated from the serum by the blood-testis barrier rely primarily on the Sertoli cell to obtain nutrients. For example, transferrin synthesized by the Sertoli cell is important in delivering iron from the serum to the developing germ cells. Because of its role in the testis, Sertoli cell transferrin protein and mRNA have been extensively studied. By using RNA blot analysis of rat testicular tissue, we detected a transcript of 2.6 kb which is attributed to transferrin. In addition, we detected a novel mRNA of 0.9 kb which had sequence similarity to the 3' end of transferrin. This 0.9-kb mRNA was present in germ cells, but not Sertoli cells, liver, or brain. The primary source of this mRNA in the testis was round spermatids. Sequence analysis of a cDNA clone showed that this mRNA encoded a protein with sequence similarity to the carboxy terminus of transferrin. Polysome analysis indicated that this transcript was translated and may therefore have importance in the iron metabolism of germ cells. The evolutionary implications between the transferrinlike mRNA germ cells and the gene duplication event which resulted in the diferric binding of transferrin are discussed.

No abstract

In the testis, germ cells which are separated from the serum by the blood-testis barrier rely primarily on the Sertoli cell to obtain nutrients. For example, transferrin synthesized by the Sertoli cell is important in delivering iron from the serum to the developing germ cells. Because of its role in the testis, Sertoli cell transferrin protein and mRNA have been extensively studied. By using RNA blot analysis of rat testicular tissue, we detected a transcript of 2.6 kb which is attributed to transferrin. In addition, we detected a novel mRNA of 0.9 kb which had sequence similarity to the 3' end of transferrin. This 0.9-kb mRNA was present in germ cells, but not Sertoli cells, liver, or brain. The primary source of this mRNA in the testis was round spermatids. Sequence analysis of a cDNA clone showed that this mRNA encoded a protein with sequence similarity to the carboxy terminus of transferrin. Polysome analysis indicated that this transcript was translated and may therefore have importance in the iron metabolism of germ cells. The evolutionary implications between the transferrinlike mRNA germ cells and the gene duplication event which resulted in the diferric binding of transferrin are discussed.