Gene Expression in the Human Mammary Epithelium during Initiation of Lactation.

We have utilized the RNA isolated from breast milk fat globule (MFG) from lactating women from 6h to 42 days following delivery using the HumanHT-12 v4 Expression BeadChip (Illumina, Inc) to determine the temporal coordination of changes in gene expression in milk substrate synthesis processes. Of the 47,323 gene transcripts on the array, 16,623 transcripts were expressed. Major milk protein genes were among the most highly expressed and induced along with those involved in the metabolic and biosynthetic processes of carbohydrate and lipid. Milk fat synthesis mirrors expression of genes involved in fat synthesis, lipolysis and transport. In the lactose synthesis pathway, expression of α-lactalbumin mRNA was high already in the early milk and did not change. Lactose synthesis paralleled the induction of gene expression of proteins involved in UDP-galactose synthesis and transport. Serial milk samples were collected 6h following delivery, q12 h for the first 4 days and then weekly for 6 wks from 7 healthy, lean, exclusively breastfeeding women [7 x 15 = 105 samples]. RNA was isolated from the milk fat globules and utilized for microarray analyses.