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2024 APR 20 (NewsRx) -- By a News Reporter-Staff News Editor at Obesity, Fitness & Wellness Week -- New research on iron-binding proteins is the subject of a new report. [...]

It is now possible to change the protein composition of milk by direct manipulation of the germline. At present it is feasible only to add new milk-protein genes to dairy animals. If embryonic stem cells become available then it will also be possible to remove or replace endogenous genes. Various modifications made to milk proteins by using these germline-manipulation techniques are described. These are expected to enhance the processing, nutritional, and biomedical properties of milk. Am J Clin Nutr 1996;63:633S-8S.

Specific regulatory regions required for hormonal regulation and tissue-specific expression of rat [beta]-casein and whey acidic protein (WAP) genes in the mammary gland have been defined. Composite response elements with multiple binding sites for several transcription factors have been identified. Mammary gland--specific gene expression appears not to be mediated by a single transcription factor, but instead requires cooperative interactions among several factors. Signal transduction pathways regulated by lactogenic hormones result in transcription factor binding and interaction within these elements, chromatin-structure changes, and milk-protein gene expression. Intragenic sequences in the 5' and 3' untranslated regions of the [beta]-casein and WAP mRNAs, respectively, also appear crucial for the efficient expression of these genes. Vectors to target the expression of heterologous genes, such as insulin-like growth factor I, to the mammary gland can be designed. This technology can be used to manipulate milk composition in transgenic animals, one result being improved infant formulas. Am J Clin Nutr 1996;63:627S-32S.

The milk of livestock can be modified dramatically by introducing foreign DNA into the germline. Exclusive expression of this DNA is ensured by the presence of regulatory sequences from mammary gland-specific genes. In sheep > 50% of the protein in milk can be encoded by a transgene and it appears that the foreign protein is additional to the normal complement of proteins. However, many technical hurdles (DNA configuration, low efficiency of transgenesis, and transgene stability) still prevent the routine use of this technology. In addition, such milk products have not yet received regulatory approval. These difficulties are not insurmountable. Transgenic methods can also be used to study the molecular basis of milk biogenesis. The effect on milk production in mice with all endogenous [alpha]-lactalbumin genes removed and in mice in which the murine genes were then replaced with human homologues is described. [alpha]-Lactalbumin, and consequently lactose, is essential for normal milk formation, and the human gene is expressed more efficiently than the murine gene. Am J Clin Nutr 1996;63:639S-45S.

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.