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Position‐independent and tissue‐specific expression of porcine whey acidic protein gene from a bacterial artificial chromosome in transgenic mice

Silencing of transgenes is a frequent event after the random integration of foreign DNA in the host genome following microinjection. Long genomic fragments are expected to contain all the regulatory elements necessary to induce an appropriate expression of transgenes. A bacterial artificial chromosome containing the porcine wap gene with approximately 145 and 5 kb of 5′‐ and 3′‐flanking sequences, respectively, was microinjected into fertilized mouse ovocytes. In the six transgenic lines studied, expression was strictly specific to the mammary gland of lactating animals and was position‐independent. Levels of exogenous porcine wap mRNA per copy compared favorably with the porcine wap mRNA yield in the mammary gland of a 9‐day lactating pig. These findings suggest that this insert contained most if not all of the cis‐acting elements involved in the full specific expression of the porcine wap gene. These elements constitute good candidates for directing the optimized expression of protein recombinant‐encoding genes in the mammary gland of lactating animals Mol. Reprod. Dev. 63: 161–167, 2002. © 2002 Wiley‐Liss, Inc.