Establishment of artifically induced lactogenesis and its application to improvement of milk production in dairy cattle

为了建立人工有效诱导泌乳的方法，在本实验中，我们检查了乳腺功能的妊娠和泌乳依赖性变化：（1）一个是线粒体内膜蛋白（Tim 23）mRNA的表达，（2）另一个是酪蛋白mRNA的转录后调节，和（3）最后一种是初乳和正常乳的乳成分。（一）.克隆了小鼠Tim 23的4个cDNA克隆，其中最长的克隆已被GDB登录号为AB 020987（Mus musculus plasmid pCR（R）II mRNA）。4个克隆的5'端非翻译区和翻译区长度相同，3'端非翻译区长度不同。根据其长度，预计将在3'非翻译区形成一个或两个环。Tim 23 mRNA水平在妊娠期间较低，但在妊娠结束时升高约5倍。在泌乳早期水平较高，在泌乳中期观察到最高水平。（二）、酪蛋白mRNA的poly（A）尾长度在断奶后缩短，但在去除腺乳后可逆地延长。酪蛋白mRNA的另一部分与此相同。poly（A）尾短的酪蛋白mRNA在体外半衰期短，而poly（A）尾长的酪蛋白mRNA半衰期长约2倍。酪蛋白mRNA的稳定性在哺乳期乳腺中在转录后水平上受到调节。（三）、初乳中酪蛋白的胶束结构与正常乳中的不同。这特别是由于g-酪蛋白mRNA在泌乳时的低表达。新生儿初乳中酪蛋白易被胃酶消化。此外，初乳酪蛋白中还出现了初乳特异性的新肽。

In order to establish the methods for inducing lactogenesis artificially and efficiently, in the present experiments, we examined pregnancy-and lactation-dependent changes in the mammary gland functions : (1) one being the expression of mitochondrial inner membrane protein(Tim23)mRNA, (2) the other being the post-transcriptional regulation of casein mRNA, and(3) the last one being the milk compositions of colostrum and normal milk. (1). We cloned and sequenced four clones of the Tim23 cDNA.The sequence of the longest mouse Tim23 cDNA clone has been registered as GDB accession No : AB020987(Mus musculus plasmid pCR(R)II mRNA). Among four clones, 5' untranslated and translated regions were the same but 3' untranslated were different in length. Depending on their lengths, it is expected that one or two loops at the 3' untranslated region will be formed. The level of Tim23 mRNA was low during pregnancy but elevated about 5 folds at the end of pregnancy. The level was high at the early stage of lactation and the highest level was observed at mid lactation. (2). The poly(A)tail length of casein mRNA was shortened after weaning but elongated reversibly after the removal of gland's milk. The other part of casein mRNA was the same. Casein mRNA with the short poly(A)tail showed a short half-life in vitro, while that with the longest one had about 2 times longer half-life. The stability of casein mRNA is regulated at the post-transcriptional level in the lactating mammary gland. (3). The micelle structure of casein in colostrum is different from that in normal milk. This is particularly due to the low expression of g-casein mRNA at lactogenesis. The caseins in colostrum was easily digested by gastric enzyme in new-born neonates. Moreover, colostrum-specific new peptide appeared from colostral caseins.