[Metabolism of poly(A+)mRNA during ontogenesis: changes in half-life and processing time in rat brain cortical cells]

The values of half-life (t 1/2) and processing (to) time of poly(A+) mRNA were calculated from the kinetics of label accumulation by free and membrane-bound polyribosomes of brain cortical cells of 1-, 7-, 30-, 180-, 360-, 540-, and 720-day-old rats and of 17- and 21-day-old embryos. The membrane-bound polyribosomes contain only one class of poly(A+) mRNA, whereas the free ones--predominantly two classes. The most pronounced changes in poly(A+) mRNA metabolism are observed in the case of free polyribosomes. It was found that poly(A+) mRNA of both polyribosomal classes is generally stabilized during late embryogenesis and neonatal period, after which the values of t 1/2 are decreased, showing a drastic fall upon ageing. The changes in to are inversely related to those of t 1/2. Free polyribosomes, beginning with the 30th postnatal day, reveal a short-living rapidly turned over poly(A+) mRNA, whose parameters remain practically unchanged throughout the ontogenesis period under study.