s-SHIP promoter expression marks activated stem cells in developing mouse mammary tissue

Area of Science:

• Mammary gland biology
• Stem cell research
• Cancer biology

Background:

• Mammary stem cells (MaSCs) are vital for mammary gland development and tumorigenesis.
• Previous methods enriched MaSCs in basal cells but failed to precisely identify them.

Purpose of the Study:

• To identify and characterize mammary stem cells (MaSCs) in vivo.
• To develop a new transgenic mouse model for MaSC identification and isolation.

Main Methods:

• Utilized a transgenic mouse model with s-SHIP promoter driving GFP expression to tag presumptive stem cells.
• Employed cell marker analysis (p63, CD24, CD49f, CD29) and transplantation assays.
• Examined GFP(+) cell populations in developing mammary glands and MMTV-Wnt1 and ErbB2-induced breast tumors.

Main Results:

• GFP(+) cells in cap (puberty) and basal alveolar bud (pregnancy) populations demonstrated self-renewal and regenerative capacity.
• Single GFP(+) cells could regenerate entire mammary epithelial networks.
• GFP(+) cells exhibited specific markers (p63+, CD24mod, CD49fhigh, CD29high) and expressed s-SHIP mRNA.
• Expanded GFP(+) basal cells were observed in MMTV-Wnt1 tumors but not ErbB2 tumors.

Conclusions:

• Identified and characterized activated mammary stem cells (MaSCs) in vivo during key developmental stages.
• The new mouse model allows for in situ identification and isolation of MaSCs using a single parameter.
• Findings have implications for studying normal mammary gland development and breast cancer stem cells.