Adult Stem Cells The Stem Cell Niche

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

Proposed Niche Types SC Asymmetric Division or Populational asymmetry

Repopulation of Tissue From Stem Cells Cells probably restricted in potential

The Hair Follicle Bulge Niche

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

Model for Drosophila GSC Regulation

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

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