Manipulating milk in mammals.

Manipulating milk in mammals

All mammals produce milk, but not all mammal milk is identical. In ruminants such as cows and sheep, for example, the major milk protein is betalactoglobulin (BLG). Rodents, on the other hand, don't produce any BLG at all. At least they never used to.

J. Paul Simons and fellow researchers at the Edinburgh (Scotland) Research Station report in the Aug. 6 NATURE that they have successfully bred mice carrying the sheep BLG gene, and that these mice now produce milk that is chock full of BLG. The researchers suggest that similar experiments with dairy animals may not be far behind, and that "the manipulation of milk composition by gene transfer has considerable potential.'

The experiments were done by microinjecting genetic material coding for BLG into fertilized mouse eggs that were then reimplanted into "surrogate' female mice. Of the 46 offspring successfully weaned, 16 carried the BLG sequence, and the females among them later produced BLG-rich milk. In the case of one such female, BLG was produced at more than five times the concentration usually found in sheep milk. Moreover, some of the mice passed on the BLG gene to their offspring.

The authors note that milk provides 20 to 30 percent of the total protein intake of people in the industrialized world, and claim that "gene transfer into dairy animals should be viewed as a realistic approach for the production of milk with enhanced nutritional value.'

In addition, they say, it may be possible to engineer dairy animals to produce nonnutritional but otherwise valuable proteins in milk. They have already taken the gene that codes for the production of human Factor IX (a blood protein lacking in certain forms of hemophilia) and fused it to the BLG gene in sheep--with an eye, it seems, toward extracting Factor IX along the whey.