Development of mammary luminal progenitor cells is controlled by the transcription factor STAT5A

Mammary alveologenesis is abrogated in the absence of the transcription factors STAT5A/5B that mediate cytokine signaling. To reveal the underlying causes for this developmental block we studied mammary stem and progenitor cells. While loss of STAT5A/5B did not affect the stem cell population and their ability to form mammary ducts, luminal progenitors were greatly reduced and unable to form alveoli during pregnancy. Temporally-controlled expression of transgenic STAT5A in mammary epithelium lacking STAT5A/5B restored the luminal progenitor population and rescued alveologenesis in a reversible fashion in vivo. Taken together, STAT5A is necessary and sufficient for the establishment of luminal progenitor cells. The mammary tissues from two mice of each genotype were collected 6 days (sample 9 and 11 were WT)