I'm sure that this paper from Zhou et al., which reports direct conversion of Muller glia to retinal ganglion cells, will be attracting a lot of attention, but first some important words of caution. https://www.cell.com/cell/fulltext/S0092-8674(20)30286-5

Much like another recent study (Yao, et al. Nature 2018), which reported conversion of Muller glia to photoreceptors using a cocktail of transcription factors, this work relies exclusively on the use of AAV-GFAP expression vectors to target expression constructs to Muller glia.

AAV-based minipromoters don't function in a vacuum -- their specificity may be affected by whatever cargo they happen to carry, which in turn may also affect the properties of the tissue culture cells in which these vectors are produced.

The use of conventional empty vector controls for cellular specificity are thus insufficient here. The use of AAV-based GFAP-Cre to demonstrate a lineage relationship between Muller glia and RGCs is particularly suspect in this context.

Two additional tests need to be applied here. First, Muller glia need to be labeled using a conditional cell-specific Cre prior to any infection with AAV. This will ensure reliable fate mapping.