Stem Cells and Differentiation
The luminal progenitor marker β3 integrin identifies cancer stem cells in mouse models of mammary tumorigenesis
F Vaillant, M-L Asselin-Labat, G Lindeman, J Visvader
The cells of origin and molecular mechanisms that underpin tumour heterogeneity in breast cancer are poorly understood. To clarify these issues, we are examining different mouse models of mammary tumourigenesis for changes in their epithelial cell hierarchy during the preneoplastic and neoplastic stages of tumour progression.
In preneoplastic tissue, only MMTV-wnt-1 mice had perturbed epithelial subpopulations. Both their mammary stem and progenitor cells exhibited increased repopulating activity and produced profoundly hyperplastic glands. Thus, wnt-1 activation perturbs the mammary epithelial hierarchy in the preneoplastic phase. Significantly, in mammary tumours arising in MMTV-Wnt-1 and p53+/- mice, the luminal progenitor marker β3 integrin (CD61) identified a cancer stem cell (CSC) population that was highly enriched for tumorigenic capability. An ~20-fold enrichment was observed in wnt-1 tumours, while the tumour-maintaining cells were enriched 7-fold in some p53+/- tumours.
In contrast, no cancer stem cells could be identified in the more homogeneous MMTV-erbB2 model. These tumours exhibit luminal characteristics and a “luminal” gene expression profile. Accumulated data suggest that this model may utilise a stochastic rather than CSC model of tumorigenesis.
Our findings thus demonstrate the utility of the luminal epithelial progenitor marker CD61 in the identification of CSCs that sustain specific types of mammary tumours but suggest that other tumour types may be maintained by the dominant cell population.
The stem cells in preneoplastic mammary tissue of MMTV-wnt-1 mice show increased repopulating ability upon transplantation and give rise to hyperplastic outgrowths.
Bim expression defines the pathway to retinal cell death in development and degeneration
P Bouillet in collaboration with F Doonan, M Donovan, V Gomez-Vicente,
T Cotter (University College of Cork, Ireland) Pub ref: 39
Programmed cell death during development of the mouse retina activates the mitochondrial pathway, which requires the Bcl-2 family proteins Bax and Bak. We have now shown that the BH3-only protein Bim plays a role in retinal development and degeneration upstream of Bax and Bak. Bim-/- mice exhibit an increase in retinal thickness and a delay in programmed cell death. In response to certain apoptotic stimuli, Bim+/- retinal explants up-regulate Bim and die, whereas Bim-/- explants are resistant to apoptosis.
Characterisation of epithelial cells in human breast tissue
E Lim, F Vaillant, N Forrest, J Visvader, G Lindeman
We are attempting to extend our identification of stem and progenitor cells within the mouse mammary gland to human breast tissue. Elucidation of its epithelial hierarchy may help to identify the cells of origin for different subtypes of breast cancer. Using reduction mammoplasty specimens, we have identified distinct epithelial cell populations by their cell surface markers and shown, by culture in extracellular matrix, that they generate structures of distinct morphology: the luminal population yields small homogeneous structures, while the basal population generates larger heterogeneous structures. Transplantation of these subpopulations into “humanised” fat pads of immuno-compromised mice has revealed one population that yields mammary outgrowths.
Identification of genes that specify cell fate in the mammary gland
T Bouras, B Pal, F Vaillant, G Harburg, G Lindeman, J Visvader
We have recently identified mouse mammary stem cells on the basis of their multi-lineage differentiation and self-renewal properties in vivo. To explore the role of specific genes in regulating the function of the stem cells and luminal progenitors, we have developed a short-term culture system for retroviral transduction of specific cell subpopulations, followed by analysis of their in vivo repopulating capacity and in vitro colony forming potential. We showed that Notch signalling is preferentially activated in ductal luminal epithelium in vivo and that it specifically instructs commitment along the luminal lineage. These findings reveal a key role for Notch signalling in luminal cell commitment and suggest that inappropriate Notch activation promotes the transformation of luminal progenitors.