The relationship between the poly(A) tail of casein mRNA and the ageing of the mammary gland

小鼠的乳腺在分娩前就开始合成乳汁。泌乳量在泌乳12-13天达到最大值，在泌乳18天左右终止。哺乳期不发生有丝分裂。因此，乳腺的乳汁合成活性在哺乳期发生变化。利用妊娠和哺乳期小鼠乳腺，研究酪蛋白mRNA聚(A)尾与乳腺衰老的关系。在存在和不存在寡核苷酸（dT）的情况下，用RNase H酶切确定酪蛋白mRNA的聚(A)尾。mRNA的半衰期通过mRNA合成抑制剂α -amanitin的存在来确定。聚(A)尾长度约为50个核苷酸，但在泌乳开始时延长至约100个核苷酸。酪蛋白mRNA的近似半衰期在乳合成开始后从10 h变化到19 h。在哺乳结束时，酪蛋白mRNA具有较短的聚(A)尾，半衰期较短。细胞质中未见聚A尾缩短现象。因此，我们认为乳腺通过poly(A)尾巴长度的变化来决定酪蛋白mRNA的稳定性。

In mice, the mammary gland begins to synthesize milk prior to parturition. Milk production reaches a maximum at 12-13 days of lactation and is terminated at around 18 day. During lactation, mitosis does not occur. Thus, the milk-synthesizing activity of the mammary gland changes during lactation. Using the pregnant and lactating mouse mammary gland, the relationship between the poly(A) tail of casein mRNA and the ageing of the mammary gland was examined. The poly(A) tail of casein mRNA was determined by the digestion with RNase H in the presence and absence of oligo(dT). The mRNA half-life was determined by the presence of mRNA synthesis inhibitor, alfa-amanitin. The poly(A) tail length was about 50 nucleotides but elongated to about 100 nucleotides upon the onset of lactation. Approximate half-life of casein mRNA changed from 10 h to 19 h after the onset of milk synthesis. At the end of lactation, casein mRNA had the short poly(A) tail and a short half-life. The poly(A) tail shortening did not observe in the cytoplasm. Thus, we concluded that the mammary gland determined the casein mRNA stability through the change in the poly(A) tail length.