HIGH ACCUMULATION OF COMPONENTS OF THE RNA-POLYMERASE-II TRANSCRIPTION MACHINERY IN RODENT SPERMATIDS

Levels of mRNA and protein encoded by the TATA-binding protein (tbp) g ene are shown to increase dramatically during late spermatogenesis in rodents, culminating in a highly testis-enriched expression pattern, W hereas adult spleen and liver contained roughly 0.7 and 2.3 molecules of TBP mRNA per haploid genome-equivalent, respectively, adult testis contained 80-200 molecules of TBP mRNA per haploid genome-equivalent. Comparison of nuclear and cytoplasmic levels of TBP mRNA in liver and testis suggested that nuclear events (transcription or processing) con tribute roughly 12-fold, and cytoplasmic events (mRNA stability) rough ly 6-fold, to testis-specific overaccumulation, Levels of nuclear TBP protein in testis cells were, on average, 8- and 11-fold higher than t hose in liver and spleen cells, respectively, Overexpression of TBP mR NA in testis began about 20 days after birth and reached a plateau aro und day 40, corresponding to the developmental emergence of haploid ce lls, Besides TBP, two other components of the general RNA polymerase I I machinery, TFIIB and RNA polymerase II, were also overexpressed in t estis. By immunostaining, it was found that TBP and RNA polymerase II rr ere particularly rich in round spermatid nuclei, Our results sugges t a molecular explanation for ho cv early spermatids are able to accum ulate all of the mRNA necessary for the final week of spermiogenesis.