Lineage specific methylation of the Elf5 promoter in mammary epithelial cells.

Recent characterization of mammary stem and progenitor cells has improved our understanding of the transcriptional network that coordinates mammary development; however, little is known about the mechanisms that enforce lineage commitment and prevent transdifferentiation in the mammary gland. The E-twenty six transcription factor Elf5 forces the differentiation of mammary luminal progenitor cells to establish the milk producing alveolar lineage. Methylation of the Elf5 promoter has been proposed to act as a lineage gatekeeper during embryonic development. We used bisulphite sequencing to investigate in detail whether Elf5 promoter methylation plays a role in lineage commitment during mammary development. An increase in Elf5 expression was associated with decreasing Elf5 promoter methylation in differentiating HC11 mammary cells. Similarly, purified mammary epithelial cells from mice had increased Elf5 expression and decreased promoter methylation during pregnancy. Finally, analysis of epithelial subpopulations revealed that the Elf5 promoter is methylated and silenced in the basal, stem cell-containing population relative to luminal cells. These results demonstrate that Elf5 promoter methylation is lineage-specific and developmentally regulated in the mammary gland in vivo, and suggest that loss of Elf5 methylation specifies the mammary luminal lineage, while continued Elf5 methylation maintains the stem cell and myoepithelial lineages.