THE RELATIONSHIP BETWEEN MAMMARY GROWTH AND LACTATIONAL ACTIVITY AT THE MOLECULAR LEVEL

我们研究了β-和γ-酪蛋白mRNA的聚(A)尾长度对泌乳小鼠乳腺mRNA稳定性的影响。在实验一中，泌乳乳腺根据乳腺乳汁的积累和清除，对酪蛋白mRNA的聚(A)尾长度进行了急性可逆调节。长聚(A)保护mRNA不被rna酶降解。因此，短聚(A)尾的酪蛋白mRNA的半衰期比长聚(A)尾的更短。在妊娠和哺乳的不同阶段检测酪蛋白mRNA的聚(A)尾长度。在怀孕期间，poly(A)尾巴的长度约为30个核苷酸。一旦酪蛋白mRNA被表达，多聚(A)尾部拉长到超过100个核苷酸。哺乳结束时，乳腺对聚A尾伸长的活跃程度低于哺乳早期和中期，聚A尾长度明显缩短。长聚(A)尾酪蛋白mRNA在哺乳期较短尾酪蛋白mRNA稳定。我们明确了乳腺通过改变酪蛋白mRNA的聚(A)尾长度来调节酪蛋白mRNA的稳定性，并且在转录后水平上调节酪蛋白mRNA的水平。在实验二中，我们检测了tim23mrna在乳发生中的表达。Tim23是一种线粒体内膜蛋白转位酶，由基因组DNA编码。tim23mrna的表达受激素调控，在妊娠末期升高。Tim23基因表达所需的激素与牛奶合成所需的激素基本相同。

We examined the effect of the poly(A) tail length of β- and γ- casein mRNAs on the mRNA stability in the lactating mouse mammary gland. In the experiment I, the lactating mammary gland modulated acutely and reversibly the poly(A) tail length of casein mRNA depending on the accumulation and removal of gland's milk. The long poly(A) protected from mRNA degradation by RNases. Thus, casein mRNA with the short poly(A) tail had a shorter half-life than that with the long one. The poly(A) tail length of casein mRNA was examined a different stages of pregnancy and lactation. The poly(A) tail was about 30 nucleotides in length during pregnancy. Once casein mRNA was expressed, the poly(A) tail elongated to over 100 nucleotides. At the end of lactation, the mammary gland became less active in the elongation of the poly(A) tail than that at early and midlactation, and the poly(A) tail in length was shortened significantly. Casein mRNA with the long poly(A) tail was more stable than that with the shot one during lactation. We cleared that the mammary gland modulated the casein mRNA stability by changing the poly(A) tail length of casein mRNA, and that the level of casein mRNA was regulated at the posttranscriptional level. In the experiment II, we examined the expression of Tim23 mRNA at lactogenesis. Tim23, a mitochondrial of translocase of inner membrane protein, is encoded by genomic DNA. The expression of Tim23 mRNA was regulated by hormones and increased at the end of pregnancy. Hormones required for the Tim23 gene expression were essentially the same as for milk synthesis.