Stacey A, Schnieke A, Kerr M, Scott A, McKee C, Cottingham I, Binas B, Wilde C, Colman A
PPL Therapeutics, Edinburgh, Scotland.
Proc Natl Acad Sci U S A. 1995 Mar 28;92(7):2835-9. doi: 10.1073/pnas.92.7.2835.
Mice carrying either a deletion of the murine alpha-lactalbumin (alpha-lac) gene (null allele) or its replacement by the human alpha-lac gene (humanized allele) have been generated by gene targeting. Homozygous null females are alpha-lac-deficient, produce reduced amounts of thickened milk containing little or no lactose, and cannot sustain their offspring. This provides definitive evidence that alpha-lac is required for lactose synthesis and that lactose is important for milk production. Females homozygous for the humanized allele lactate normally, indicating that human alpha-lac can replace murine alpha-lac. Mouse and human alpha-lac expression was compared in mice heterozygous for the humanized allele. The human gene expressed approximately 15-fold greater mRNA and approximately 14-fold greater protein than the mouse, indicating that the major determinants of human alpha-lac expression are close to, or within, the human gene and that the mouse locus does not exert a negative influence on alpha-lac expression. Variations in alpha-lac expression levels in nondeficient mice did not affect milk lactose concentration, but the volume of milk increased slightly in mice homozygous for the humanized allele. These variations demonstrated that alpha-lac expression in mice is gene dosage dependent.
通过基因打靶技术已培育出携带鼠α-乳白蛋白（α-lac）基因缺失（无效等位基因）或被人α-lac基因替代（人源化等位基因）的小鼠。纯合无效雌性小鼠α-lac缺乏，分泌的浓稠乳汁量减少，所含乳糖很少或不含乳糖，无法哺育后代。这提供了确凿证据，表明α-lac是乳糖合成所必需的，且乳糖对乳汁分泌很重要。人源化等位基因纯合的雌性小鼠泌乳正常，表明人α-lac可替代鼠α-lac。在人源化等位基因杂合的小鼠中比较了小鼠和人α-lac的表达情况。人基因表达的mRNA约为小鼠的15倍，蛋白质约为小鼠的14倍，这表明人α-lac表达的主要决定因素接近或位于人基因内，且小鼠基因座对α-lac表达没有负面影响。非缺陷小鼠中α-lac表达水平的变化不影响乳汁乳糖浓度，但人源化等位基因纯合的小鼠乳汁量略有增加。这些变化表明小鼠中α-lac的表达是基因剂量依赖性的。
