Milking mice for mammary gland genes.

The Hox family of genes helps sculpt the bodies of animals from head to toe--assuming the animal has toes, of course. These genes encode DNA-binding proteins that switch on arrays of other genes during an embryo's growth (SN: 8/20/94, p. 116). Some Hox genes might regulate arm-forming genes, for example, while others guide the growth of a head.

The myriad developmental roles of the Hox genes have obscured the fact that some of them also operate within the adult animal. Two scientists now report that at least three Hox genes are crucial to the pregnancy-related changes that occur in the mouse mammary gland. Female mice with mutations in all the genes can't raise their pups because they're unable to supply sufficient milk.

Until pregnancy, the mammary glands of these mutant mice appear normal, Feng Chen and Mario R. Capecchi of the Howard Hughes Medical Institute at the University of Utah School of Medicine in Salt Lake City report in the Jan. 19 Proceedings of the National Academy of Sciences. Their examinations of mammary tissue in pregnant mice with the Hox mutations revealed, however, that the animals had inadequate cell proliferation to form a proper network of milk-carrying ducts.