Androgenic Regulation of Messenger RNA Sequence Complexity in Accessory Sexual Tissues of the Male Rat Studied with Fractionated Complementary DNA

Abstract

Effects of androgens on mRNA sequence complexity in the rat seminal vesicle have been investigated using complementary DNA fractionated on the basis of sequence abundance. Total cDNA complementary to poly(A)‐rich RNA from normal rats was hybridised with an excess of the same RNA to controlled r₀t values and then the free cDNA was separated from cDNA · RNA hybrids by hydroxyapatite chromatography. Three cDNA fractions were obtained with very different hybridisation characteristics. Abundant cDNA hybridised to an excess of its parental RNA with an r₀t_1/2 of 2.46 × 10⁻³ mol 1⁻¹ s and is complementary to about six or seven average‐sized sequences. Use of hybrid‐arrested translation in a cell‐free protein‐synthesising system has shown that this class of mRNA includes mRNAs coding for major androgen‐dependent secretory proteins. Moderate and scarce cDNA fractions each showed more complex hybridization kinetics; computer analysis suggested each is complementary to two groups of average‐sized sequences. Each cDNA fraction was hybridised to excess poly(A)‐rich RNA from normal or castrated rats and the kinetics compared. Castration had no effect on the total number of sequences present in any class and did not alter the relative concentration of the scarce sequences. A small (threefold) decrease was seen in the concentration of abundant sequences with a larger (tenfold) decrease in the moderate class. Both decreases were reversed by testosterone in vivo. The results are consistent with earlier studies where the effects of testosterone on seminal vesicle mRNA were followed using a translation assay and confirm that no gross differential effects are exerted on abundant mRNA coding for major secretory proteins. The cDNA fractions were also used to investigate the overlap in genetic expression between seminal vesicle and ventral prostate. Both tissues share all the scarce sequences in the same relative abundance. Less than 0.0015% and 0.004%, of prostatic mRNA is complementary to seminal vesicle abundant and moderate sequences respectively. Similarly prostatic abundant sequences account for less than 0.004% of seminal vesicle mRNA.