猪胰岛素启动子调控EGFP表达载体的优化及体外验证

Optimization and in vitro validation of EGFP expression controlled by porcine insulin promoter

目的获得猪胰岛素启动子调控外源基因的高效表达载体,为制备转基因猪胰岛特异性表达目的基因奠定基础。方法利用猪胰岛素启动子(PIP,包含5'调控区、第一外显子、第一内含子及第二外显子ATG前的序列共1.5 kb)构建表达载体,连接PIP和EGFP的酶切位点HindⅢ设计在起始密码子前,命名为PIP-Hind IIIEGFP。鉴于酶切位点的插入位置可能会影响外源基因的表达效率,对载体进行了优化:将Hind III酶切位点删除,实现PIP和EGFP无缝连接,载体命名PIP-EGFP;将第一内含子3'端的内含子剪接受体位点(splicing acceptor site,SA)突变为Hind III内切酶识别位点,命名为PIP-SA(M)-EGFP。三种载体分别电转染小鼠胰岛素瘤β细胞株MIN-6细胞、猪耳成纤维细胞以及猪肾细胞,48 h后通过荧光强度、流式分析、RT-PCR及Western blot检测,验证载体的表达效率。结果转染细胞后,三种载体都仅在MIN-6胰岛β细胞表达绿色荧光。RT-PCR及其产物测序结果显示三种载体的胰岛素启动子第一内含子的剪切存在差异:载体PIP-Hind III-EGFP和PIP-EGFP的内含子存在剪切和不剪切两种情况,剪切不稳定;载体PIP-SA(M)-EGFP的SA位点突变后内含子不剪切,流式细胞及Western blot检测显示,与另外两种载体相比,该载体目的蛋白的表达量最高。结论通过突变胰岛素启动子第一内含子的3'端的剪接受体位点,成功获得了胰岛β细胞的高效表达载体,可用于制备胰岛特异表达外源基因的转基因猪。

Objective Getting the robust exogenous gene expression vector under the control of porcine insulin promoter, and to lay the foundation for pancreaticβ-cells specific transgene expressing pigs.Method Using porcine insu-lin promoter （ PIP, 1500 bp of the 5′UTR from the porcine INS gene including the first exon and the first intron） to construct expression vector, the HindIII restriction site which connected the sequences of PIP and EGFP was designed before ATG, named PIP-HindIII-EGFP.Considering that the different location of restriction site may affect the expression efficiency of the transgene, we optimized the expression vector.Firstly the HindIII restriction site was deleted to realize the seamless connection of PIP and EGFP,the vector was named PIP-EGFP.Also we mutated the 3′intron splicing acceptor site（ SA） of the first intron into HindIII restriction site, named as PIP-SA（ M）-EGFP.Three different EGFP expression vectors were respectively transfected MIN-6 mouse pancreatic β-cells, pig ear fibroblasts and kidney cells.The transfected cells were cultured for 48 h and harvested for RT-PCR, flow cytometry and Western blot analysis, to analyze and compare the expres-sion efficiency of vectors.Results After transfection,green fluorescence was observed only in MIN-6 mouse pancreaticβ-cells.RT-PCR analysis and product sequencing showed that the three expression vectors did have different stability with in-tron splicing.The PIP-HindIII-EGFP construct and PIP-EGFP vector produced two kinds of mRNA with the first intron spliced and no spliced, indicating the instability of intron splicing.Mutation of the PIP splice site would cause the first in-tron not spliced, while flow cytometry and Western blot displayed that the mutation induced a most efficient expression of the downstream gene.Conclusions A robust and specific β-cells expression vector has been successfully generated by mutating the intron splicing acceptor site of the porcine insulin promoter.It provides the foundation for preparation of pigs with pancreaticβ-cells specifically expressing the transgene.