1. Adult Stem Cells The Stem Cell Niche

2. Stem Cell Niche- Defined A stem cell niche is defined as ‘a specific location in a tissue where stem cells can reside for an indefinite period of time and produce progeny cells while self-renewing’ Self Renewal –Asymmetric Division- 1SC  1SC + 1PC –Populational Asymmetry – 1SC  Many Transient Cells. A defined fraction of TC revert to SC; the remainder differentiate

3. Proposed Niche Types SC Asymmetric Division or Populational asymmetry

4. Repopulation of Tissue From Stem Cells Cells probably restricted in potential

5. The Hair Follicle Bulge Niche

6. Signaling in the Drosophila Germarium SC Niche Germarium Stained for Dpp (BMP4) Schematic of germarium showing signaling CPC –Cap Cell IGS-Inner germarium Sheath cells TF- Terminal Filament cells GSC – Germ Stem Cell CB- Cytoblast

7. Model for Drosophila GSC Regulation

8. Cell-Cell Interactions Mediated by Contact Proteins Adherens junctions –Cadherin-βCatenin  signaling Gap junctions –direct signals small molecules & ions Integrins-GAG –Map kinase signaling ECM –binding and sequestering signal molecules

9. Some Additional Stem Cell Niches SNO (spindle-shaped N-cadherin-positive osteoblastic) cells