Researchers Pinpoint Genetic Basis for Lactation

Their finding was published in the December 15, 2002, issue of Genes & Development.

Knowing that the XOR gene is highly expressed in lactating epithelial tissue, researchers from the University of Utah (Salt Lake City, USA) created two strains of XOR deficient mice. One strain lacked both working copies of the gene, while the other (heterozygotes) contained one copy.

Mice with no XOR died by six weeks of age, showing that XOR has more than one metabolic role to play. The mice with one copy of XOR appeared normal, healthy and fertile, but their pups all died about 12 days after birth. Further study showed that XOR is required for the envelopment of milk fat droplets with a phospholipid bilayer that is necessary for their secretion from the mammary epithelium. The inability of heterozygous XOR-mutant females to secrete milk fat droplets caused severe tissue damage, resulting in the collapse of the mammary epithelium and the subsequent premature involution of the mammary gland. Unable to receive milk from their mothers, the pups starved to death.

The finding that two functional copies of the XOR gene are necessary for females to secrete fat into milk not only broadens the known functional range of XOR, it lends important molecular insight into the process of lactation, and suggests that human females with mutations in the XOR gene may be potential candidates for lactation insufficiencies. Approximately 5% of new mothers have lactation difficulties.



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