β1 integrins activate a MAPK signalling pathway in neural stem cells that contributes to their maintenance

The emerging evidence that stem cells develop in specialised niches highlights the potential role of environmental factors in their regulation. Here we examine the role of β1 integrin/extracellular matrix interactions in neural stem cells. We find high levels of β1 integrin expression in the stem-cell containing regions of the embryonic CNS, with-associated expression of the laminin α2 chain. Expression levels of laminin α2 are reduced in the postnatal CNS, but a population of cells expressing high levels of β1 remains. Using neurospheres - aggregate cultures, derived from single stem cells, that have a three-dimensional architecture that results in the localisation of the stem cell population around the edge of the sphere - we show directly that β1 integrins are expressed at high levels on neural stem cells and can be used for their selection. MAPK, but not PI3K, signalling is required for neural stem cell maintenance, as assessed by neurosphere formation, and inhibition or genetic ablation of β1 integrin using cre/lox technology reduces the level of MAPK activity. We conclude that integrins are therefore an important part of the signalling mechanisms that control neural stem cell behaviour in specific areas of the CNS.