ht-Pam基因在山羊β-酪蛋白基因座定位整合的研究

利用体细胞基因打靶与核移植技术制备动物乳腺生物反应器是当今转基因定位整合表达的一种新技术。分别克隆山羊的β-酪蛋白基因5′调控区的6.3kb片段，外显子7、外显子8和9三个基因片段，并与克隆的人tPA突变体cDNA一起构建了含有neo和tk正负筛选标记基因的β-酪蛋白基因打靶载体P^GBC4tPA，并验证了neo基因、tk基因以及Cre-LoxP系统的有效性。将线性化的P^GBC4tPA通过电转染整合到山羊胎儿成纤维细胞基因组中，利用G418和GANC进行抗性细胞克隆的药物筛选，初步获得抗性细胞克隆244个，PCR检测后获得阳性细胞克隆31个，其中初步验证2个细胞克隆转植基因整合位点重组后的基因序列正确，并且该细胞克隆能够有效扩增。这为下一步基因打靶体细胞核移植制备山羊乳腺生物反应器奠定了基础。

The ht-PAm cDNA Knock-in the Goat Beta-casein Gene Locus

The production of recombinant protein is one of the major successes of biotechnology, animal cells are required to synthesize proteins with the appropriate post-translational modifications. Transgenic animal mammary gland bioreactor are being used for this purpose. Gene targeting is a more powerful method to produce mammary gland bioreactor, and nuclear transfer from cultured somatic cells provides an wonderful means of cell-mediated transgensis. Here we describe efficient and reproducible gene targeting in goat fetal fibroblasts to place the human tissue plasminogen activator mutant (ht-PAm) cDNA at the beta-casein locus, and would produce the transgenic goat by nuclear transfer. To construct the gene targeting vector pGBC4tPA, the milk goat beta-casein genomic DNA sequence for homologous arms had been cloned firstly. The left arm was 6.3 kb fragment including goat beta-casein gene 5' flanking sequence, and the right arm was 2.4 kb fragement including beta-casein gene from exon 8 to exon 9. The ht-PAm cDNA was subcloned in the goat beta-casein gene exon 2, and the endogenous start condon was replaced by that of ht-PAm. The bacterial neomycin (neo) gene as positive selection marker gene, was placed in the beta-casein gene intron 7, the thymidine kinase (tk) as the negative selection marker gene, was just outside the right arm. The validity of the positive-negative selection vector (PNS), was tested, and targeting homologous recombination (HR) were elevated to 5-fold with the negative selection marker using the drug GANC. The DNA fragment in which two LoxP sequence was delected effectively using Cre recombinase in vitro. Goat fetal fibroblasts were thawed and cultured to subconfluence before transfection, about 10(7) fibroblasts were electoporated at 240V, 600 microF in 0.8 mL PBS buffer containing linear pGBC4tPA. transfected cells were cultured in collagen-coated 96-wellplate for 24h without selection, then added the drug G418 (600 microg/mL) and GANC (2 micromol/L). After 12 days of selection, well separated G418r/GANCr clones were isolated and expanded in 24-wellplate. 244 clones were selected, and only 90 clones could grow and be tested by PCR screening for targeting. The primary result demonstrated that 31 targeting cell clones with homologous recombination events were obtained, and 2 cell clones was verified by DNA sequence analysis on the homologous recombination region.