Müller glia cells and their possible roles during retina differentiation in vivo and in vitro.

Müller cells are astrocyte-like radial glia cells which are formed exclusively in the retina. Here we present evidence that Müller cells are crucially involved in the development of the retina's architecture and circuitry. There is increasing evidence that Müller cells are present from the very early beginning of retinogenesis. We postulate the "gradual maturation hypothesis of Müller cells". According to this hypothesis, Müller cells are continuously generated by a gradual transition of neuroepithelial stem cells into mature Müller cells. This process may be partly reversible. Müller cells, or their immature precursors, are able to subserve different functions. They are primary candidates for stabilizing the complex retinal architecture and for providing an orientation scaffold. Thereby, they introduce a reference system for the migration and correct allocation of neurons. Moreover, they may provide spatial information and microenvironmental cues for differentiating neurons, and may also be important for the segregation of cell and fibre layers. Additionally, they seem to be involved in the guidance of axonal fibres both in radial and in lateral directions, as they are involved in the support and stabilization of synapses.