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Notch signaling in Stem Cells and Tumors

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Team leader : Silvia Fre
Notch signaling in Stem Cells and Tumors

Keywords

Lineage specification, mouse development, Notch, cancer, stem cells, mammary gland, intestine

How cells coordinate their action to build epithelial tissues during development, tissue morphogenesis and remodeling is a fundamental question that remains only superficially understood. Two tissues that are particularly suited to approach this question are the mouse intestine and the mammary gland, where somatic stem cells ensure continuous cell renewal. We study the signals controlling stem cell homeostasis, with the final goal of gaining mechanistic insights into organ morphogenesis during development, and also adult stem cell maintenance in both normal and pathological conditions.

 

 

 

 

Our goal:

A deep comprehension of the cellular hierarchies originating from tissue-specific stem cells and the factors that regulate their behaviour will have a major impact in exploring therapeutic avenues for cancer. Given the very well documented involvement of Notch signaling in the maintenance and differentiation of stem and progenitor cells in a broad organ spectrum, the in vivo identification of Notch lineages provides an essential tool to discover critical early progenitors both for organ homeostasis and cancer development. Our group seeks to examine the behaviour of normal stem cells in the mouse intestine and the mammary gland, with the goal of gaining insights into the cellular hierarchy of the highly heterogeneous tumor cell populations. We have chosen to focus our research on these two epithelial tissues because they are very dynamic and contain highly active stem cells, to ensure extremely rapid and continuous cell renewal in the case of the intestinal epithelium and to guarantee remarkable tissue remodeling upon hormonal stimulation for the mammary gland. Our studies on one hand, use Notch as a tool to study stem/progenitor cells homeostasis in vivo, and on the other, aim at revealing if Notch signals can change the fate of normal and cancer stem cells in our model systems, a possibility with important therapeutic implications, given that colon and breast cancer are among the most common tumors.

 

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Figure 1: A section of a mouse colon showing crypts derived from Notch-expressing stem cells in green and mucus-producing secretory cells in red. Blue illustrates nuclei.Figure 1: A section of a mouse colon showing crypts derived from Notch-expressing stem cells in green and mucus-producing secretory cells in red. Blue illustrates nuclei.

 

 

Figure 2: Section of a mammary bud from a mouse embryo showing     Notch1-expressing cells in green, myoepithelial cells in cyan and     luminal cells in red.Figure 2: Section of a mammary bud from a mouse embryo showing Notch1-expressing cells in green, myoepithelial cells in cyan and luminal cells in red.

Our questions:

1) Can we use Notch as a marker of specific stem/progenitor cells as well as “stem-cell like” tumor cell populations? We are addressing this question through the systematic identification and functional characterization of Notch-expressing lineages in vivo in normal and tumor cells of the mouse intestinal and mammary epithelia.
2) How are stem cell division and migration dynamically coordinated within a crypt and during mammary tubulogenesis? In order to visualize stem cell behaviour and response to injury by time-lapse imaging, we use 3D organoids ex vivo (“miniguts” for the intestine and “miniglands” for the mammary gland) derived from normal or malignant Notch-expressing cells.
3) Are Notch signals required for stem cell survival in normal tissues and in tumors? We aim at establishing, by in vivo genetic ablation and gain of function studies, the functional role of Notch signaling in maintaining stem/progenitor cells and in the transformation of the intestinal and mammary epithelia.
4) Can niche signals affect the establishment of a stem cell pool during intestinal development? Our group investigates how the mesenchyme influences Notch-expressing intestinal stem cells both temporally, during embryonic gut development, and topologically, as regional differences are established along the antero-posterior axis.
 

Figure 3: Example of a “minigut” derived from a single crypt cultured for 7 days after tamoxifen induction. Double fluorescence illustrates the complete switch from Tomato to GFP membrane-bound signal upon Cre recombination in Notch1-derived lineages.Figure 3: Example of a “minigut” derived from a single crypt cultured for 7 days after tamoxifen induction. Double fluorescence illustrates the complete switch from Tomato to GFP membrane-bound signal upon Cre recombination in Notch1-derived lineages.

Our Tools: novel knock-in transgenic mice

We have recently generated and characterized a novel collection of unique transgenic mice that give us now the opportunity to assess Notch expression and function in vivo in an unprecedented fashion. Specifically, these mice permit the conditional expression of a given transgene in the cells where the promoters of the four Notch receptor paralogues are endogenously active. In addition, we have also developed reporter mice, allowing us to visualize cells with an active Notch pathway and transgenic animals allowing conditional activation of the four Notch paralogues. These three groups of novel reagents define exceptional tools, which allow us to probe the relationship between Notch-related activity and normal and cancer stem cells in vivo.