NUCLEAR‐CYTOSOL INTERACTIONS THAT MODULATE RNA SYNTHESIS AND TRANSCRIPT SIZE OF MOUSE BRAIN NUCLEI

Abstract– The addition of a dialyzed cytosol preparation from various types of mouse tissue, guinea‐pig brain, and neuroblastoma cells resulted in an increased incorporation of [ 3 H]GTP into RNA by mouse brain nuclei. In addition to a stimulation of the incorporation of [ 3 H]GTP into RNA. the presence of these cytosol preparations also caused a significant increase in nuclear RNA transcript size. Although all cell cytosols appeared to influence nuclear RNA metabolism to some degree, dialyzed mouse serum had little stimulatory effect on brain nuclear RNA synthesis and failed to cause an increase in RNA product size. The polyanion, heparin, was found to be highly stimulatory to brain nuclear RNA synthesis although the size of the resulting RNA products was not significantly altered. RNA synthesis by neuronal and glial nuclei, isolated from adult brain tissue, showed a differential response to the presence of brain cytosol preparations. In the absence of cytosol, RNA synthesis by neuronal nuclei was more active than that measured in glial nuclei, and when the RNA products were analyzed by sucrose gradient centrifugation, those of glial nuclei were considerably larger than those isolated from neuronal nuclei. The addition of cytosol caused a significant increase in RNA transcript size with neuronal nuclei of adult brain tissue while little, if any, change in the size of the RNA products was measured with nuclei isolated from glial cells. Although an overall increase in product size could be measured in response to the addition of dialyzed cytosol with neuronal nuclei of 2,10, 20‐day old and adult (over 60 days of age) brain tissue, a greater response was measured with nuclei prepared from the brains of more mature animals where the proportion of larger RNA products (>10S) was greatly increased.