Transgenic modification of cows milk for value-added processing

Abstract

The application of transgenic technologies in dairy cattle has been restrictedlargely to producing potential pharmaceutical or nutriceutical products in themammary gland. Broader application of transgenesis in dairy cattle productionwill require identifying target traits that are both amenable to transgenicmodification and economically important to the dairy industry. The caseinproteins are the most valuable component of cows milk destined for value-addedprocessing. The four bovine casein genes lie within a single, multi-gene locusof approximately 200 kb in length. The working hypothesis is that thismulti-gene locus contains all of the DNA sequences required to regulate thecoordinated expression of all four individual casein genes (i.e. a locuscontrol region or LCR). The initial research aim is to clone the entire caseinlocus into a bacterial artificial chromosome (BAC) vector, thus preserving theextended 5′and 3′ regions that flank the locus, as well asmaintaining the spatial integrity of the four individual casein genes thatcomprise the locus. The author's laboratory has prepared a bacterialartificial chromosome (BAC) library of genomic DNA from elite dairy cattle.Partial, non-elite BAC clones of the casein gene locus are being tested intransgenic mice to establish proof of concept. Advances in nuclear transfer oftransfected somatic cells should improve the efficiency of producingtransgenic calves that possess a BAC casein construct introduced into an elitegenetic background.