Betzl G, Brem G, Weidle U H
Boehringer Mannheim GmbH, Penzberg, Germany.
Biol Chem. 1996 Nov;377(11):711-9. doi: 10.1515/bchm3.1996.377.11.711.
Transgenic mice expressing human urokinase, as well as animals expressing human urokinase receptor under the control of the murine mammary tumor virus (MMTV) long terminal repeat, were established. In the vast majority of the founder animals and their descendants, the transgene was completely methylated, corresponding to down-regulation of transgene expression in the mammary gland. Two lineages with human urokinase receptor as the transgene with mixed methylation of the transgenes were analyzed in more detail. We show here for the first time that the methylation status of the transgene is identical in different organs of an animal, but may differ from animal to animal among the descendents. In the mammary gland, complete methylation of the transgene was incompatible with expression; unmethylated and mixed methylation transgenes gave rise to expression at the RNA as well as at the protein level. The methylation observed was not the consequence of an imprinting process. Surprisingly, in organs other than the mammary gland, such as liver, kidney and spleen, weak expression of the transgene was noted independent of the methylation status of the MMTV promoter. With respect to the molecular mechanism it is unresolved whether the human growth hormone sequence of the transgene harbors a methylation inducing element responsible for the observed methylation pattern.
建立了表达人尿激酶的转基因小鼠，以及在鼠乳腺肿瘤病毒（MMTV）长末端重复序列控制下表达人尿激酶受体的动物。在绝大多数奠基动物及其后代中，转基因完全甲基化，这与乳腺中转基因表达的下调相对应。对两个以人尿激酶受体为转基因且转基因存在混合甲基化的品系进行了更详细的分析。我们首次在此表明，转基因的甲基化状态在动物的不同器官中是相同的，但在后代动物之间可能存在差异。在乳腺中，转基因的完全甲基化与表达不兼容；未甲基化和混合甲基化的转基因在RNA和蛋白质水平均产生表达。观察到的甲基化不是印记过程的结果。令人惊讶的是，在乳腺以外的器官，如肝脏、肾脏和脾脏中，无论MMTV启动子的甲基化状态如何，均注意到转基因的弱表达。关于分子机制，转基因的人生长激素序列是否含有负责观察到的甲基化模式的甲基化诱导元件尚不清楚。
