Co-expression of multiple gene constructs in transgenic mice

Multiple-transgene co-integration offers a powerful means by which several transgenes can be co-expressed in mammary glands. Independent gene construc ts, including bovine alpha -casein-hG-CSF, mWAP-hEPO, and CMV-EGFP, were co -injected into fertilized mouse eggs whereupon 32% (17/54) of the transgeni c mice showed integration of all the three constructs. The co-expression ra tio of hG-CSF and hEPO proteins in the mouse milk was up to 54% (6/11), att ributable to co-integration. Maximal expression of human EPO and G-CSF was about 1 mg l(-1) and 540 mg l(-1) milk, respectively. There was an inverse relationship between transgene fragment length and integration ratio, and e vidence that co-integration events are favoured above single integration ev ents, suggesting that integration of multiple genes may be more facilitated than a single gene. The results have important practical implications for the generation of mammary gland bioreactors, multiple transgene co-integrat ion appearing to be a useful strategy for generating animals expressing sev eral transgenes simultaneously.