Nuclear Factor I in neurons, glia and during the formation of Müller glia‐derived progenitor cells in avian, porcine and primate retinas

Abstract

The regenerative potential of Müller glia (MG) is extraordinary in fish, poor in chick and terrible in mammals. In the chick model, MG readily reprogram into proliferating Müller glia-derived progenitor cells (MGPCs), but neuronal differentiation is very limited. The factors that suppress the neurogenic potential of MGPCs in the chick are slowly being revealed. Isoforms of Nuclear Factor I (NFI) are cell-intrinsic factors that limit neurogenic potential; these factors are required for the formation of MG in the developing mouse retina and deletion of these factors reprograms MG into neuronlike cells in mature mouse retina. Accordingly, we sought to characterize the patterns of expression of NFIs in the developing, mature and damaged chick retina. In addition, we characterized patterns of expression of NFIs in the retinas of large mammals, pigs and monkeys. Using a combination of single-cell RNA-sequencing (scRNA-seq) and immunolabeling, we probed for patterns of expression. In embryonic chick, levels of NFIs are very low in early E5 (embryonic day 5) retinal progenitor cells (RPCs), upregulated in E8 RPCs, further upregulated in differentiating MG at E12 and E15. NFIs are maintained in mature resting MG, microglia and neurons. Levels of NFIs are reduced in activated MG in retinas treated with NMDA and/or insulin+FGF2, and further downregulated in proliferating MGPCs. However, levels of NFIs in MGPCs were significantly higher than those seen in RPCs. Immunolabeling for NFIA and NFIB closely matched patterns of expression revealed in different types of retinal neurons and glia, consistent with findings from scRNA-seq. In addition, we find expression of NFIA and NFIB through progenitors in the circumferential marginal zone at the far periphery of the retina. We find similar patterns of expression for NFIs in scRNA-seq databases for pig and monkey retinas. Patterns of expression of NFIA and NFIB were validated with immunofluorescence in pig and monkey retinas wherein these factors were predominantly detected in MG and a few types of inner retinal neurons. In summary, NFIA and NFIB are prominently expressed in developing chick retina and by mature neurons and glia in the retinas of chicks, pigs and monkeys. Although levels of NFIs are decreased in chick, in MGPCs these levels remain higher than those seen in neurogenic RPCs. We

Age- and cell cycle-related expression patterns of transcription factors and cell cycle regulators in Müller glia

“…Contrary to our expectation, Nfia expression was maintained in rat Müller glia during injury-induced proliferation and significantly increased in mouse Müller glia after cell cycle reentry in dissociated cultures. Our findings agree with the recent report that Nfia is highly expressed in Müller glia-derived proliferating progenitors in the chick retina 31 . Nfia, while critical for maintaining differentiation and quiescence of Müller glia 27 , may act to drive proliferation once Müller glia are reprogrammed to a proliferation-competent state.…”

“…This possibility is supported by the well-established anti-proliferative effects of NFI factors in the retina 27 , 30 . Alternatively, Nfia may promote glial cell fate and limit neurogenic potential of Müller glia as has been suggested previously in the chick retina 31 . Nfia, together with other NFI factors, plays a critical role in Müller glia specification during retinal development 30 .…”

“…These factors, like Pax6 and Vsx2, have been shown to promote quiescence of Müller glia after injury 27 . However, NFI factors are highly expressed in Müller glia-derived proliferating progenitors in the chick retina, arguing against the role of these factors in the induction of cell cycle exit 31 . Thus, again, the role of these factors may change once Müller glia reenter the cell cycle and dedifferentiate into progenitor-like cells.…”

Transcriptomic analysis reveals the dynamic changes of transcription factors during early development of chicken embryo

“…For instance, ZBTB16 regulates innate and innate-like lymphoid lineage development [ 81 , 82 ]. THRB and NFIA are both involved in retina and brain development [ 83 , 84 ]. However, a few studies have investigated the roles of ZBTB16 , THRB , NIFA or MKX in chicken.…”

Epigenetics and Degenerative Retinal Diseases: Prospects for New Therapeutic Approaches

“…There is also current interest in reprogramming Muller glia to provide a source of cells to replace those lost through disease. 64,65 As we better understand the epigenetic processes regulating the formation of cell types during normal development, we will be able to direct the differentiation of stem cells more efficiently into the cell types desired, and possibly produce cells more rapidly. Most of the studies published to date have focused on mapping the epigenetic changes during development (reviewed in Ref 66 …”