Genetic engineering of milk composition: modification of milk components in lactating transgenic animals.

Recent progress in recombinant DNA technology as well as in embryo manipulation and transfer has made the introduction of specific genes into the germline of animals relatively commonplace. With appropriate genetic constructs expression of the inserted genes in transgenic animals can be controlled in a tissue-specific and in a differentiation-specific manner; thus, it is now possible to consider alteration of the composition of milk produced by a lactating animal in any of a variety of ways. There is a growing list of foreign milk proteins that have been expressed, and one can envisage placing almost any protein gene of interest under the control of the cis-acting promoter and enhancer elements of a milk protein gene. Modification of milk composition can be extended not only to the proteins of commodity value but also, by manipulation of key metabolic enzymes, to fat, lactose, and other minerals in milk.

Xerographic paper as a transfer medium for western blots: quantification of bovine alpha S1-casein by western blot.

We have found that xerographic paper (regular photocopy or laser printer paper) can be used as a transfer medium for protein blots for the immunodetection of low concentrations (a few nanograms) of bovine alpha S1-casein. With paper blotting, we could detect the protein with three times more sensitivity than with polyvinylidene difluoride. Blotting was achieved by transfer from sodium dodecyl sulfate-polyacrylamide gel electrophoresis to the methanol-wet paper. The blot was incubated with chicken anti-casein antibodies, sequentially peroxidase-labeled rabbit anti-chicken antibodies, and diaminobenzidine substrate. The blots were directly scanned and the pixel intensity of the band areas was integrated. An analysis of the scanned blots showed that the log of protein concentration was linearly related with the square root of an integrated pixel intensity (r2 greater than 0.96). This linear relationship was observed in a wide range of protein concentration from 5 ng to 15 micrograms. The coefficients of variation were 12.4% for intraassay and 15.7% for interassay. This new analytical procedure can be applied to estimate the concentration of proteins by immunological blotting.

Alteration of milk composition using molecular genetics.

Advances in genetic technology have made it possible to consider making substantial changes either in the composition of milk or in the production of entirely new products in milk. The technological capabilities that have given rise to the introduction and expression of new genes in animals are discussed. Examples are given of transgenic animals that express foreign proteins in their milk. Advantages of the mammary synthesis of proteins are discussed and potential alterations of milk composition and scenarios for introduction of new proteins are considered. Technological capabilities that either currently exist or are being developed are discussed along with the requirements for making it feasible to utilize the technology on a broad scale in dairy cattle.