The use of transgenic animals to manipulate milk composition has considerable
potential, both for the production of biomedical proteins and for the direct
manipulation of milk composition for the improvement of dairy animals and their
products (for reviews, see Wall et al. 1992; Yom & Bremel, 1993). Promoters from a
number of milk protein genes from a variety of species have been tested for their
ability to direct the expression of foreign proteins to the mammary gland (for review,
see Maga & Murray, 1995).
β-Lactoglobulin (β-lg) is the major whey protein produced in ruminant milk and
is part of the normal milk composition of most mammals except humans and rodents
(Pervaiz & Brew, 1985). It is expressed at high levels in the mammary gland and is
developmentally regulated. Transgenic mice have been produced using the complete
ovine (Simons et al. 1987; Shani et al. 1992)
and caprine (Ibañez et al. 1997) β-lg genes.
In general, high levels of expression were obtained with the ovine β-lg gene, and
expression was also seen in a position-independent manner (Whitelaw et al. 1992).
Lower levels of expression were reported using the caprine β-lg gene. Here we report
the production of transgenic mice using the bovine β-lg gene. We describe high
expression, position-dependent, and copy number-related expression of bovine β-lg
protein in the milk of six lines of transgenic mice.