title: Functional and molecular characterisation of mammary side population cells.
abstract: BACKGROUND
  Breast cancer is thought to arise in mammary epithelial stem cells. However, the identity of these stem cells is unknown.
  
  
  METHODS
  Studies in the haematopoetic and muscle systems show that stem cells have the ability to efflux the dye Hoechst 33342. Cells with this phenotype are referred to as the side population (SP). We have adapted the techniques from the haematopoetic and muscle systems to look for a mammary epithelial SP.
  
  
  RESULTS
  Of mammary epithelial cells isolated from both the human and mouse mammary epithelia, 0.2-0.45% formed a distinct SP. The SP was relatively undifferentiated but grew as typical differentiated epithelial clones when cultured. Transplantation of murine SP cells at limiting dilution into cleared mammary fat pads generated epithelial ductal and lobuloalveolar structures.
  
  
  CONCLUSIONS
  These data demonstrate the existence of an undifferentiated SP in human and murine mammary epithelium. Purified SP cells are a live single-cell population that retain the ability to differentiate in vitro and in vivo. Studies of haematopoetic cells have suggested that the SP phenotype constitutes a universal stem cell marker. This work therefore has implications for mammary stem cell biology.
authors.affiliation: Breakthrough Toby Robins Breast Cancer Centre, Institute of Cancer Research, London, UK.
authors.forename: Azra J
authors.initials: AJ
authors.lastname: Alvi
authors.forename: Helen
authors.initials: H
authors.lastname: Clayton
authors.forename: Chirag
authors.initials: C
authors.lastname: Joshi
authors.forename: Tariq
authors.initials: T
authors.lastname: Enver
authors.forename: Alan
authors.initials: A
authors.lastname: Ashworth
authors.forename: Maria d M
authors.initials: Md
authors.lastname: Vivanco
authors.forename: Trevor C
authors.initials: TC
authors.lastname: Dale
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Smalley
mesh_terms: D016475:3T3 Cells; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000273:Adipose Tissue / Q000166:cytology*; D000818:Animals; D001562:Benzimidazoles / Q000378:metabolism; D001940:Breast / Q000166:cytology*; D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects; D017690:Cell Transplantation; D002478:Cells, Cultured; D002999:Clone Cells / Q000166:cytology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D053547:Keratin-14; D007633:Keratins / Q000096:biosynthesis; D008321:Mammary Glands, Animal / Q000166:cytology*; D051379:Mice; D009363:Neoplasm Proteins; D012313:RNA / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014700:Verapamil / Q000494:pharmacology
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D001562:Benzimidazoles; C507540:KRT14 protein, human; D053547:Keratin-14; C507446:Krt14 protein, mouse; D009363:Neoplasm Proteins; D012313:RNA; D007633:Keratins; D014700:Verapamil; C017807:bisbenzimide ethoxide trihydrochloride