The limbal stem cell niche

Stem cells contain intrinsic mechanisms that control their behaviour but the environment immediately surrounding them, known as the niche, also plays a fundamental role. In a host of tissues and organisms the stem cell niche has been shown to maintain stem cells in an undifferentiated state and to regulate their behaviour. This stem cell – niche principle is typified by the corneal limbus. When limbal epithelial stem cells (LESC) are dissociated from their niche in the limbal palisades of Vogt they rapidly differentiate and cease to function as stem cells. It might be imagined that an understanding of the LESC niche would be of the highest priority for researchers in this field but the existence of a surrogate niche, in the form of growth arrested 3T3 fibroblast feeder layers, has allowed research on LESC biology to progress in the absence of a thorough understanding of their native niche. Thankfully LESC niche research has been gathering momentum and several exciting developments hold promise for limbal stem cell deficient patients. Amongst these are the characterisation of the physical structure of the niche and the identification of mesenchymal niche cells, which themselves displaying stem cell properties.