Müller glia, or Müller cells

Muller glia

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3D animation of Müller cell processes (red) interconnected with a retinal microglia cell (green).

Müller glia, or Müller cells, are a type of retinal glial cells. They are found in the vertebrate retina, which serve as support cells for the neurons of the retina as all glial cells do. They are the most common type of glial cell found in the retina. They span across the entire thickness of the neural retina.
The major function of the Müller cells is to maintain the stability of the retinal extracellular environment by regulation of K+ levels, uptake of neurotransmitters, removal of debris, storage of glycogen, electrical insulation of receptors and other neurons, and mechanical support of the neural retina.

Role in development

Müller glia have been shown to be critical to the development of the retina in mice, serving as promoters of retinal growth and histogenesis via a non-specific esterase mediated mechanism.^[1] Müller glia have also been implicated to serve as guidepost cells for the developing axons of neurons in the chick retina.^[2] Studies using a zebrafish model of Usher syndrome have implicated a role for Müller glia in synaptogenesis, the formation of synapses.^[3]

Neuronal support

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Spatial relationship between Müller cells and microglia

As glial cells, Müller glia serve a secondary but important role to neurons. As such, Müller glia have been shown to serve as important mediators of neurotransmitter (acetylcholine and GABA specifically) degradation and maintenance of a favorable retinal microenvironment in turtles.^[4] Müller glia have also been shown to be important in the induction of the enzyme glutamine synthetase in chicken embryos,^[5] which is an important actor in the regulation of glutamine and ammonia concentrations in the central nervous system. Müller glia have been further identified as fundamental to the transmission of light through the vertebrate retina due to their unique funnel shape, orientation within the retina and more favorable physical properties.^[6]

Use in research

Müller glia are currently being studied for their role in neural regeneration, a phenomenon that is not known to occur in humans.^[7] Studies to this end of Müller glia in both the zebrafish^[8][9] and chicken^[10] retina have been performed, with the exact molecular mechanism of regeneration remaining unclear. Further studies performed in mice have shown that Müller glia begin to dedifferentiate and exhibit cell cycle markers, yet do not complete mitosis, which implies there is a block of the regeneration process that is unique to mammals.^[11] Studies in human models have demonstrated that Müller glia have the potential to serve as stem cells in the adult retina^[12] and are efficient rod photoreceptor progenitors.^[13]
Following injury to the retina, it has been shown in zebrafish that Müller glia undergo dedifferentiation into multipotent progenitor cells. The progenitor cell can then divide and differentiate into a number of retinal cell types, including photoreceptor cells, that may have been damaged during injury.^[14] Additionally, further research has shown that Müller glia act as light collectors in the mammalian eye, analogous to the fiber optic plate, funneling light to the rod and cone photoreceptors