PgmNr M305: Snai1 is required for stem cell maintenance in the mouse intestinal epithelium.

Authors:
Helen Abud 1 ; Katja Horvay 1 ; Thierry Jarde 1 ; Franca Casagranda 2 ; Katharina Haigh 3,6 ; Christian Nefzger 4 ; Reyhan Akhtar 1 ; Thomas Gridley 5 ; Geert Berx 6,7 ; Jody Haigh 3,6 ; Jose Polo 4 ; Gary Hime 2

Institutes
1) Cancer Program, Monash Biomedicine Discovery Institute, Clayton, Victoria, Australia; 2) Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Australia,; 3) Australian Centre for Blood Diseases, Monash University, Clayton, Australia; 4) Australian Regenerative Medicine Institute, Monash University, Clayton, Australia; 5) Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine, USA; 6) Molecular and Cellular Oncology, Inflammation Research Center, VIB, Ghent, Belgium; 7) Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium.

Abstract:

The Snail family of transcription factors are well known for mediating epithelial to mesenchymal transitions and cell motility during both embryonic development and tumour invasion. Although they are generally regarded as markers of mesenchymal cells, Snail proteins have recently been implicated in regulating stem cell populations in several organs. Snai1 is normally expressed in the intestinal epithelium within the crypt base columnar (CBC) stem cells and transit amplifying cell populations.  Our studies have shown that both the expression and cellular localisation of Snai1 is dependent on canonical Wnt signalling, a key regulatory pathway of intestinal stem cells.  Snai1 is up-regulated in polyps from Apcmin/+ mice indicating that Snai1 may also play a part in the early stages of tumorigenesis in addition to  promoting invasion of intestinal tumours. We investigated Snai1 function in the mouse intestinal epithelium using an inducible conditional knockout approach and found that Snai1 is required for maintenance of CBC stem cells and the appropriate balance of differentiated cell types.   Further analysis of the effects of Snai1 loss on the CBC stem cell population using a combination of Fluorescent Activated Cell Sorting (FACS), lineage tracing and in vitro organoid culture showed that loss of Snai1 results in a decrease in cell proliferation and apoptotic loss of stem cells. In contrast, ectopic expression of Snai1 using a conditional transgenic approach results in an increase in cell proliferation at the crypt base which correlates with elevated levels of expression of CBC stem cell markers. In addition, a decrease in secretory Paneth and enteroendocrine cells is observed. Our functional studies show that intestinal epithelium where Snai1 is depleted fails to produce a proliferative response following radiation induced damage. These studies demonstrate a critical role for Snai1 in survival of CBC cells and regeneration of the epithelial cell layer following damage.    In conclusion, this suggests that Snai1 has a key role in stem cell maintenance and control of lineage choice during cellular differentiation in the intestinal epithelium.