Transcription and translation of the outer dense fiber gene (Odf1) during spermiogenesis in the rat. A study by in situ analyses and polysome fractionation.

Transcription and translation of the Odf1 gene encoding the major protein of sperm tail outer dense fibers has been investigated in rat spermatogenesis. Odf1 mRNA was detected by in situ hybridization from step 6 round spermatids up to step 17. The protein was detected immunohistochemically in the cytoplasm of step 7 spermatids up to step 18 and in the sperm tails. The distribution of Odf1 mRNA and the respective transcript sizes in polysomes and translationally inactive nonpolysomal ribonucleoprotein particles has been investigated by fractionation on sucrose gradients and Northern blot analysis of the isolated RNA. In adult rat testis about 30% of Odf1 mRNA is associated with the polysomal fraction, but the bulk is stored in translationally inactive ribonucleoprotein particles. In 35-day old rat testis, in which spermatids have reached step 15 of spermiogenesis, only about 10% of Odf1 mRNA can be found in the polysomal fraction. It seems therefore, that translation of Odf1 is greatly enhanced in the maturation phase of spermiogenesis during which a marked increase in diameter of outer dense fibers takes place. In the polysomal fraction, Odf1 transcripts are of heterogeneous size. Northern blot analysis of fractionated RNA digested with RHaseH revealed the presence of both Odf1 transcripts (Burfeind and Hoyer-Fender, 1991: Dev Biol 148: 195-204; Burfeind et al., 1993: Eur J Biochem 216: 497-505) on polysomes. While the larger transcript population is heterogeneous in size due to variable polyA-shortening, the smaller transcript population is not deadenylated compared to those present in nonpolysomal fractions.