Lowering the lactose content of milk in vivo has
two potential benefits: to develop
milk products for lactose intolerant people (Delmont, 1983) and to produce
concentrated milk, reducing milk storage volume and milking frequency without
affecting the overall fat and protein yields. Lactose synthesis in the
mammary gland results from the interaction of α-lactalbumin
(α-la) with a Golgian
UDP-galactosyltransferase (EC 220.127.116.11), and it has been suggested that
α-la contents are directly related (Fitzgerald et al.
1970). Evidence that α-la is the
only protein responsible for the in vivo induction of
lactose synthesis came recently
from knock-out experiments of the relevant gene (Stinnakre
et al. 1994; Stacey et al.
1995), which disrupt lactation, as lactose-deprived milk of
α-la-deficient mice is
highly viscous. However, although the lactose, fat and protein contents
of the milk
were found to be directly related to the quantity of α-la present
(Stinnakre et al.
1994), only in mice homozygous for the α-la null allele was there
alteration of milk concentration (Stacey et al. 1995).
Stacey et al. (1995) also
demonstrated that human α-la could substitute for its mouse counterpart
In the present study, we report the generation of transgenic mice producing
bovine α-la by back-crossing animals from four independent
bovine α-la transgenic
lines with α-la-deficient mice. Our work confirms that foreign
α-la can substitute for
the mouse protein and suggests a negative correlation between the
α-la content and protein and fat concentrations in milk.