Messenger RNA coding for glutamine synthetase in cerebral hemispheres and astroglial cultures from mouse brain: A...

Messenger RNAs from mouse brain hemispheres and from an enriched astroglial population of the same area were isolated, characterized and used to study Glutamine Synthetase (GS) processing during postnatal development using a m-RNA stimulated reticulocyte lysate system. The RNA preparations yielded distinct polypeptide products upon translation including high molecular weight species. Polypeptides in the range of 43-55 kDa appeared developmentally regulated in brain hemispheres but not in astroglia. After immunoprecipitation of the translation products with a GS antibody a major monomeric polypeptide was isolated on SDS/PAGE which migrated at the same position as the purified brain GS antigen (43 kDa). The translatable mRNA were optimal in the perinatal period and decreased until 300 days while GS-mRNA increased during the same period of time and closely paralleled the previously described GS activity profile in this brain area reaching an optimum at 15 days. Astroglial mRNAs were optimal at 18 days in vitro and decreased thereafter. The GS-mRNA was much lower in control astroglial cultures than in brain tissue, but in the presence of 10(?6)M hydrocortisone increased all over the growth period. The highest stimulation of GS-mRNA was observed at 18 days whereas the global mRNA decreased in the presence of the hormone. The GS-mRNAs from either 15-day-old brain hemispheres or 18-day in vitro hydrocortisone stimulated cultures were partially purified on a 5-30% linear sucrose gradient. Two GS-mRNAs, which sedimented respectively at 17S and 23S, were characterized. In addition, based on the profile of total proteins translated in vitro, we estimated that GS-mRNA constituted 0.01% of the brain hemisphere fraction and 0.3% in the astroglial hormone stimulated cells.