Retinal Ganglion Cell Fate Induction by Ngn-Family Transcription Factors.

Purpose: Retinal ganglion cells (RGCs) are the projection neurons of the retina. Loss of RGCs is the cellular basis for vision loss in patients with glaucoma. Finding ways to regenerate RGCs will aid in the development of regenerative therapies for patients with glaucoma. The aim of this study was to examine the ability of Ngn-family transcription factors (TFs) to induce RGC regeneration through reprogramming in vitro and in vivo. Methods: In vitro, lentiviruses were used to deliver Ngn-TFs into mouse embryonic fibroblasts (MEFs). In vivo, mouse pup retina electroporation was used to deliver Ngn-TFs into late-stage retinal progenitor cells (RPCs). Immunofluorescence staining and RNA sequencing were used to examine cell fate reprogramming; patch-clamp recording was used to examine neuronal electrophysiologic functions. Results: In vitro, all three Ngn-TFs, Ngn1, Ngn2, and Ngn3, were able to work alone to reprogram MEFs into RGC-like neurons that resembled RGCs at the transcriptome level, exhibited typical neuronal membrane electrophysiologic properties, and formed functional synaptic communications with retinal neurons. In vivo, Ngn-TFs reprogrammed the differentiation-competent state of late-stage RPCs to generate RGCs. Conclusions: Ngn-TFs are effective in inducing an RGC-like fate both in vitro and in vivo and might be explored further in the future for glaucoma translational applications.

m6A epitranscriptomic modification regulates neural progenitor-to-glial cell transition in the retina.

N 6-methyladenosine (m6A) is the most prevalent mRNA internal modification and has been shown to regulate the development, physiology, and pathology of various tissues. However, the functions of the m6A epitranscriptome in the visual system remain unclear. In this study, using a retina-specific conditional knockout mouse model, we show that retinas deficient in Mettl3, the core component of the m6A methyltransferase complex, exhibit structural and functional abnormalities beginning at the end of retinogenesis. Immunohistological and single-cell RNA sequencing (scRNA-seq) analyses of retinogenesis processes reveal that retinal progenitor cells (RPCs) and Müller glial cells are the two cell types primarily affected by Mettl3 deficiency. Integrative analyses of scRNA-seq and MeRIP-seq data suggest that m6A fine-tunes the transcriptomic transition from RPCs to Müller cells by promoting the degradation of RPC transcripts, the disruption of which leads to abnormalities in late retinogenesis and likely compromises the glial functions of Müller cells. Overexpression of m6A-regulated RPC transcripts in late RPCs partially recapitulates the Mettl3-deficient retinal phenotype. Collectively, our study reveals an epitranscriptomic mechanism governing progenitor-to-glial cell transition during late retinogenesis, which is essential for the homeostasis of the mature retina. The mechanism revealed in this study might also apply to other nervous systems.

The retina is a layer in the eye that converts light into electrical signals, which allows us to see. It is a part of the central nervous system and is made of brain cells, such as neurons and supporting cells called glia. These supporting cells protect neurons, supply them with nutrients and maintain steady surrounding conditions. The retina shares many characteristics with other neural tissues, so it is useful for biologists to study these structures. One way for cells to control the activity of genes is by chemically modifying messenger RNA molecules. These alterations can affect various aspects of mRNA and the proteins that are ultimately produced. The most common mRNA modification, referred to as m⁶A, plays a key role in the development and healthy performance of various tissues. However, it is unclear whether m⁶A is involved in how glial cells in the retina develop. To address this question, Xin et al. studied the impact of blocking m⁶A in the retina of mice. These genetically modified mice displayed abnormalities as the retina developed. Analysis of the mRNA produced in single cells and the pattern of modifications revealed that m⁶A is involved in the development of glia. In particular, m⁶A helps to remove the mRNA associated with early-stage proto-glia, allowing the cells to mature and transition to their final form. The finding by Xin et al. that the m⁶A RNA modification is an essential part of retina development could help to understand eye diseases. In addition, this discovery may apply to other brain regions, and, in time, such work could lead to new treatments for neurodegenerative diseases.