MULLER GLIA CELLS AND THEIR POSSIBLE ROLES DURING RETINA DIFFERENTIATION IN-VIVO AND IN-VITRO

Muller cells are astrocyte-like radial glia cells which are formed exc lusively in the retina. Here we present evidence that Muller cells are crucially involved in the development of the retina's architecture an d circuitry. There is increasing evidence that Muller cells are presen t from the very early beginning of retinogenesis. We postulate the ''g radual maturation hypothesis of Muller cells''. According to this hypo thesis, Muller cells are continuously generated by a gradual transitio n of neuroepithelial stem cells into mature Muller cells. This process may be partly reversible. Muller 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 pr ovide spatial information and microenvironmental cues for differentiat ing 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.