Gland Research Paper

The mammary gland is composed of an outer layer of myoepithelial cells and an inner layer of luminal epithelial cells, which can be further categorized into ductal or alveolar subtypes. Stems cells are present in the basal position between the myoepithelial and luminal cells (Tiede and Kang, 2011; Figure 1c). At birth, the gland begins as a rudimentary tree occupying a small portion of the mammary fat pad and remains quiescent. With the onset of puberty, mammary gland morphogenesis is stimulated by estrogen and progesterone and is characterized by ducal outgrowth led by stem like epithelial cap cells located on the terminal end buds. Body cells inside the terminal end buds can either undergo apoptosis or form luminal cells that line the ducts

During pregnancy, progesterone, prolactin, and lactogens stimulate the gland to undergo extensive proliferation (Hennighausen and Robinson, 2005). Alveolar buds begin to form. They will fully mature for lactation, where the alveolar cells will produce and secrete milk into the lumina. Once the pups stop weening, the mammary gland will decrease in functional activity, as well as decrease in size, in a process called involution (Figure 1b). The vast majority of alveoli will undergo apoptosis until the gland resembles an adult virgin state (University of

Using K8-CreER/Rosa-YFP mice, they administered tamoxifen to 4 week pubescent mice and also mature virgin mice and found that YFP expression was exclusive to the luminal cells. They concluded that K8 positive cells contained luminal stem cells, which were unipotent. Clonal YFP expression was induced in the luminal cells during puberty and the fates of these cells were followed into pregnancy and lactation. Results showed only YFP+ luminal cell clones were found. It seemed that two different types of lineage restricted unipotent MaSC were responsible for the rise, expansion, and maintenance of myoepithelial and luminal lineages inside the mammary gland and these unipotent stem cells controlling a specific lineage governs mammary gland morphogenesis during puberty, adulthood, pregnancy, and