Parity-induced mammary epithelial cells are multipotent and express cell surface markers associated with stem cells

Dev Biol. 2007 Mar 1;303(1):29-44. doi: 10.1016/j.ydbio.2006.12.017. Epub 2006 Dec 13.


Parity-induced mammary epithelial cells (PI-MECs) are defined as a pregnancy hormone-responsive cell population that activates the promoter of late milk protein genes during the second half of pregnancy and lactation. However, unlike their terminally differentiated counterparts, these cells do not undergo programmed cell death during post-lactational remodeling of the gland. We previously demonstrated that upon transplantation into an epithelial-free mammary fat pad, PI-MECs exhibited two important features of multipotent mammary epithelial progenitors: a) self-renewal, and b) contribution to ductal and alveolar morphogenesis. In this new report, we introduce a new method to viably label PI-MECs. Using this methodology, we analyzed the requirement of ovarian hormones for the maintenance of this epithelial subtype in the involuted mammary gland. Furthermore, we examined the expression of putative stem cell markers and found that a portion of GFP-labeled PI-MECs were part of the CD24(+)/CD49f(high) mammary epithelial subtype, which has recently been suggested to contain multipotent stem cells. Subsequently, we demonstrated that isolated PI-MECs were able to form mammospheres in culture, and upon transplantation, these purified epithelial cells were capable of establishing a fully functional mammary gland. These observations suggest that PI-MECs contain multipotent progenitors that are able to self renew and generate diverse epithelial lineages present in the murine mammary gland.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CD24 Antigen / metabolism
  • Cell Differentiation / physiology*
  • Epithelial Cells / cytology*
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism
  • Female
  • Flow Cytometry
  • Fluorescent Antibody Technique
  • Gonadal Steroid Hormones / pharmacology
  • Green Fluorescent Proteins
  • Integrin alpha6 / metabolism
  • Mammary Glands, Animal / cytology*
  • Mammary Glands, Animal / growth & development
  • Mice
  • Mice, Transgenic
  • Multipotent Stem Cells / cytology*
  • Multipotent Stem Cells / metabolism*
  • Parity
  • Pregnancy
  • Stem Cell Transplantation
  • Transgenes / genetics


  • CD24 Antigen
  • Gonadal Steroid Hormones
  • Integrin alpha6
  • Green Fluorescent Proteins