Absorptive cellsEnterocyte: nutrient absorption

Secretory cellsGoblet cell: mucus secretionPaneth cells: antimicrobial product secretionEnteroendocrine cells: hormone secretion

OtherTuft cellsM-cells

Cells proposed to be derived from ISCs at the crypt base

Colon similar to small intestine:Similar cell types are derived from ISCs at the crypt base

Labeling proliferating cells and following their migration: ~5 days from birth to death

ISCs – Crypt base columnar (CBC) cells or +4 cells?

+4 cells were proliferating, label-retaining cells: proposed to possess an immortal DNA strand maintained by asymmetric cell division

CBC cells were traced to all the lineages and formed crypts when cultured ex vivo

Barker N. et al, Nature 449:1003, 2007

Lgr5 expressionMarks CBCs

Lgr5 expression restricted to CBC cells

Use of an Lgr5-GFP-Cre transgene to mark Lgr5-expressing cells and their descendents

1 5 60 days following Cre activation

Use of an Lgr5-GFP-Cre transgene to mark Lgr5-expressing cells and their descendents

CBC stem cells mapping below +4

T Sato et al. Nature 000, 1-4 (2009) doi:10.1038/nature07935

Single Lgr5+ cells generate crypt–villus structures.

T Sato et al. Nature 000, 1-4 (2009) doi:10.1038/nature07935

Composition of single stem cell-derived organoids.

Barker N. et al, Nature 449:1003, 2007

Fun facts: Lgr5 ISCs do not undergo asymmetric division – they divide symmetrically, producing either 2 TA cells or 2 ISCs.

No evidence of an immortal DNA strand in Lgr5 ISCs obtained

An Lgr5-Diptheria toxin receptor fusion gene can trigger the elimination of Lgr5-expressing cells

Tian et al. Nature 2011

Crypts develop normally even when Lgr5 cells depleted

Tian et al. Nature 2011

Tian et al. Nature 2011

Bmi1-positive “+4 ISCs” expand when Lgr5 cells depleted

Lineage tracing shows Bmi1 cells contribute cells to the crypt and this contribution increases when Lgr5 cells are eliminated

Are there two ISC populations?

How many cells can serve as stem cells in the injured tissue?

Contribution of epithelial cells to IBD