Interaction of basal stem cells in the breast with their cellular environment is crucial for their function, and helps towards the regeneration of the mammary glands during pregnancy, reports a paper online this week in Nature Cell Biology.

The basal stem cells of the breast are enriched in proteins called integrins that mediate contact with the extracellular matrix surrounding the cells. Marina Glukhova and colleagues show that expression of beta 1 integrin in the basal cells is essential for the regenerative potential of these stem cells and for proper development of the mammary gland during pregnancy.

Deletion of the beta 1 integrin gene from the basal layer of mouse mammary tissue led to an abnormal ductal branching pattern in the mammary gland during pregnancy, which results in the regenerative potential of the mammary tissue stem cells being abolished, leading to a dysfunctional gland. In basal stem cells lacking beta 1 integrin, cells divide abnormally and this results in the altered branching pattern.

The environment that surrounds most stem cells, the stem cell niche, is known to be important for a number of stem cells. However, our understanding of stem cell niches remains patchy. These findings establish a central role of direct interaction between basal stem cells and their extracellular matrix in the maintenance of the mammary stem-cell population.