Mammary epithelial cells, extracellular matrix, and gene expression

TLDR: The mammary gland is an appropriate system with which to study mechanisms that control gene expression during both growth and differentiation, since following the onset of pregnancy, epithelial cells in the mammary glands proliferate and differentiate into milk-secreting cells.

Abstract: The mammary gland is an appropriate system with which to study mechanisms that control gene expression during both growth and differentiation. It is one of the few tissues with a developmental potential after birth, since following the onset of pregnancy, epithelial cells in the mammary gland proliferate and differentiate into milk-secreting cells. A schematic cross- section of one of the ten mammary glands of the mouse shows the gross changes in structure that occur during progression of the gland in pregnancy (figure 1, upper panel), from the virgin state (V) to lactation (L). During pregnancy (P), certain epithelial cells lining the ducts (which themselves are embedded in stromal tissue) proliferate and form alveolar buds. By the time of parturition, cells in the alveoli become secretory and occupy the entire gland. This structural development is accompanied by the onset of lactogenic function, in which expression of milk proteins begins during pregnancy and culminates with the secretion of milk after parturition [1]. The steady-state levels of the mRNA for β—casein (figure 1, lower panel) illustrate this type of progression with no expression in the virgin state, some during pregnancy, and the highest levels at lactation. After weaning when the gland involutes, β—casein expression is down regulated (figure 1, lower panel, lane I).