Hormonal Regulation of Transfer Ribonucleic Acid and Transfer Ribonucleic Acid-methylating Enzymes during Development of the Mouse Mammary Gland

Changes in transfer RNA and in specific enzymes for transfer RNA methylation were measured during development of the mouse mammary gland. The cell differentiation which occurs in mammary gland during pregnancy is characterized by a disproportionate increase in transfer RNA in relation to total RNA. This disproportionate increase in transfer RNA also occurs during mammary epithelial cell differentiation in vitro, and depends upon the addition of insulin, hydrocortisone, and prolactin to the synthetic medium. Enzymes which methylate specific bases in exogenous transfer RNA are induced in mammary epithelial cells by insulin and by prolactin. Synchronous increases in transfer RNA and transfer RNA-methylating enzymes were observed throughout development of the mammary gland. Increased transfer RNA-methylating enzyme activity in response to hormones in vitro, or during development in vivo, generally appears to reflect an increased rate of transfer RNA assembly