利用Cre/LoxP系统删除转基因山羊体内的选择标记基因

Deletion of marker gene in transgenic goat by Cre/LoxP system

摘要:

在制备转基因家畜过程中的一个关键步骤是使用选择标记基因 (Selectable marker genes，SMGs) 将转基因整合细胞从大量的正常细胞中筛选出来，这导致了SMGs整合入家畜的基因组内持续传递给后代。SMGs已被证明能够显著影响基因组内整合位点处的基因调控，也增加了对转基因动物安全评价的复杂性。为了确定转基因山羊制备过程中SMGs的删除时机和删除方法，在体细胞克隆前后两个时段内，利用Cre/LoxP系统删除SMGs的可行性，同时比较了蛋白转导和质粒共转染两种Cre导入方式的删除效率。结果表明：尽管在首次对山羊成纤维细胞进行遗传修饰后即可进行SMGs删除，但两次遗传修饰导致细胞严重老化，无法用于后续的体细胞克隆羊制备。在转基因山羊的成体细胞中删除SMGs不存在上述问题，成功率高，缺点是试验周期长、耗资增大。Cre表达质粒瞬时转染能够删除SMGs，但有超过30%的无SMGs细胞克隆中整合有质粒序列。TAT-CRE蛋白质转导方法可以避免引入的新外源基因，SMGs删除率达到43.9%~72.8%，是一种较佳的SMGs删除手段。

Abstract:

In producing transgenic livestock, selectable marker genes (SMGs) are usually used to screen transgenic cells from numerous normal cells. That results in SMGs integrating into the genome and transmitting to offspring. In fact, SMGs could dramatically affect gene regulation at integration sites and also make the safety evaluation of transgenic animals complicated. In order to determine the deletion time and methods in the process of producing transgenic goats, the feasibility of deleting SMGs was explored by Cre/LoxP before or after somatic cell cloning. In addition, we compared the efficiency of protein transduction with plasmids co-transduction. We could delete 43.9% SMGs after screening out the transgenic cell clones, but these cells could not be applied to somatic cells cloning because of serious aging after two gene modifications. The SMG-free cells suitable for nuclear transfer were accessible by using the cells of transgenic goats, but this approach was more time consuming. Finally, we found that the Cre plasmid could delete SMGs with an efficiency of 7.81%, but about 30% in SMG-free cells had sequences of Cre plasmid. Compared with Cre plasmid, the integration of new exogenous gene could be avoided by TAT-CRE protein transduction, and the deletion rate of TAT-CRE transduction was between 43.9 and 72.8%. Therefore, TAT-Cre transduction could be an effective method for deleting selectable marker genes.