Changes in hybridizable nuclear RNA during differentiation of mammary cells

Abstract

RNA-DNA hybridization-competition reactions were used to compare nuclear RNA populations from undifferentiated, virginal mouse mammary gland with those of differentiated mammary cells of pregnancy and lactation. Mammary nuclear RNA preparations reacted with DNA from various species in proportion to their known genetic relatedness, and homologous binding to DNA occurred with sufficient saturation to produce values in hybridization-competition experiments which approached a predicted saturation-dependent competition curve. The specificity of the competition system with mammary 3H-labeled RNA and homologous DNA was shown by reactions in which heterologous RNA's from various species competed in proportion to the known relatedness of the DNA's from which they were transcribed. Virginal mammary RNA competed incompletely with lactational RNA, as shown by single-label and double-label experiments with different precursors of RNA. This difference was related specifically to the epithelial cells. The results indicate that differentiated mammary cells synthesize species of RNA which are either absent from the undifferentiated cells or present in undetectable concentrations, and support the concept that different regions of the genome are expressed as mammary cell differentiation occurs.