Transgenic expression of the proneural transcription factor Ascl1 in Müller glia stimulates retinal regeneration in young mice

Abstract

Müller glial cells are the source of retinal regeneration in fish and birds; although this process is efficient in fish, it is less so in birds and very limited in mammals. It has been proposed that factors necessary for providing neurogenic competence to Müller glia in fish and birds after retinal injury are not expressed in mammals. One such factor, the proneural transcription factor Ascl1, is necessary for retinal regeneration in fish but is not expressed after retinal damage in mice. We previously reported that forced expression of Ascl1 in vitro reprograms Müller glia to a neurogenic state. We now test whether forced expression of Ascl1 in mouse Müller glia in vivo stimulates their capacity for retinal regeneration. We find that transgenic expression of Ascl1 in adult Müller glia in undamaged retina does not overtly affect their phenotype; however, when the retina is damaged, the Ascl1-expressing glia initiate a response that resembles the early stages of retinal regeneration in zebrafish. The reaction to injury is even more pronounced in Müller glia in young mice, where the Ascl1-expressing Müller glia give rise to amacrine and bipolar cells and photoreceptors. DNaseI-seq analysis of the retina and Müller glia shows progressive reduction in accessibility of progenitor gene cis-regulatory regions consistent with the reduction in their reprogramming. These results show that at least one of the differences between mammal and fish Müller glia that bears on their difference in regenerative potential is the proneural transcription factor Ascl1.reprogramming | glia | regeneration | neurogenesis | eye

Stimulation of functional neuronal regeneration from Müller glia in adult mice

“…The proneural transcription factor Ascl1 is upregulated in MG after retinal damage 1,7 in zebrafish and is necessary for regeneration 8 . Although Ascl1 is not expressed in mammalian MG after injury 9 , forced expression of Ascl1 in mouse MG induces a neurogenic state in vitro 10 and in vivo after NMDA ( N -methyl-D-aspartate) damage in young mice 11 . However, by postnatal day 16, mouse MG lose neurogenic capacity, despite Ascl1 overexpression 11 .…”

“…Although Ascl1 is not expressed in mammalian MG after injury 9 , forced expression of Ascl1 in mouse MG induces a neurogenic state in vitro 10 and in vivo after NMDA ( N -methyl-D-aspartate) damage in young mice 11 . However, by postnatal day 16, mouse MG lose neurogenic capacity, despite Ascl1 overexpression 11 . Loss of neurogenic capacity in mature MG is accompanied by reduced chromatin accessibility, suggesting that epigenetic factors limit regeneration.…”

In Vivo Cellular Reprogramming: The Next Generation

“…2b) (Qian et al, 2012). As was the case for the stoichiometry of GMT in vitro, introduction of a polycistronic cassette of MGT, which produced the highest levels of Mef2c, resulted in more optimal reprogramming in vivo (Ueki et al, 2015), highlighting the importance of the dosage of each factor.…”

“…Ascl1 expression in retinal Müller glia in vivo also appeared to reprogram them to a neuronal fate (Ueki et al, 2015). Adult glial cells were reprogrammed to a neurogenic state based on gene expression and morphological criteria, but only in mice with retinal damage induced by chemicals or excessive light.…”

The chick eye in vision research: An excellent model for the study of ocular disease

“…The network of pathways that control the formation of MGPCs is known to include Notch-, Wnt-, MAPK-, Jak/Stat-, mTor-, Hedgehog-, and glucocorticoid-signaling (Fischer et al, 2009a, 2009b, Gallina et al, 2015, 2014; Ghai et al, 2010; Hayes et al, 2007; Todd et al, 2016; Todd and Fischer, 2015; Zelinka et al, 2016). In the mammalian retina, Müller glia retain a severely limited capacity to become MGPCs and this process requires damage followed by growth factor stimulation, or transgenic overexpression of the proneural transcription factor ascl1 (Karl et al, 2008; Ooto et al, 2004; Ueki et al, 2015). Similar to the fish and avian retina, MAPK and Wnt have been implicated in driving MGPC formation in the rodent retina (reviewed by (Hamon et al, 2016)).…”