Glia hold it together

MacDonald et al. show that glial cells within the zebrafish retina hold its layers of neural tissue together.

Glia are nonneuronal cells that reside within neural tissues, performing various functions ranging from myelination to immune surveillance. Glia are also thought to provide physical support to neurons by holding notoriously “squishy” nerve cells together into a coherent tissue, but this idea has never been directly tested.

MacDonald et al. investigated this function of glial cells in zebrafish retina, an easily accessible neural tissue. In the vertebrate retina, the development of several cell types including glia depends upon Notch signaling, so the researchers determined the exact time when Notch is critical for genesis of Müller glial cells (MG), the sole glial cell type in the retina. Blocking Notch signaling at this time prevented development of MG, while sparing neurons.

MG cell bodies reside between the retinal photoreceptor layer and the ganglion cell layer, and extend processes to connect both retinal surfaces. Retinas lacking MG were morphologically normal except they developed rips (a condition called retinoschisis) in their ganglion cell layer. Pushing or pulling on retinas using atomic force microscopy showed that tissue lacking MG was abnormally stretchy and soft. MG cell bodies recoiled after laser ablation of MG processes, showing that these processes are normally under stress. This suggests that MG compress retinal tissue and prevent it from tearing. The next questions to ask, says first author Ryan MacDonald, are how MG do this and to what extent MG loss impacts vision.