The m⁶A reader YTHDF2 is a negative regulator for dendrite development and maintenance of retinal ganglion cells

Abstract

The precise control of growth and maintenance of the retinal ganglion cell (RGC) dendrite arborization is critical for normal visual functions in mammals. However, the underlying mechanisms remain elusive. Here we find that the m6A reader YTHDF2 is highly expressed in the mouse RGCs. Conditional knockout (cKO) of Ythdf2 in the retina leads to increased RGC dendrite branching, resulting in more synapses in the inner plexiform layer. Interestingly, the Ythdf2 cKO mice show improved visual acuity compared with control mice. We further demonstrate that Ythdf2 cKO in the retina protects RGCs from dendrite degeneration caused by the experimental acute glaucoma model. We identify the m6A-modified YTHDF2 target transcripts which mediate these effects. This study reveals mechanisms by which YTHDF2 restricts RGC dendrite development and maintenance. YTHDF2 and its target mRNAs might be valuable in developing new treatment approaches for glaucomatous eyes.

m6A regulation of cortical and retinal neurogenesis is mediated by the redundant m6A readers YTHDFs

“…Immunostaining of Brn3a, AP2a and PKCa on the retinal vertical sections showed that generation of retinal ganglion cells, amacrine cells, or bipolar cells was not affected in the Ythdf1 scKO retinas at P6 and P15 (Figures S4B-S4F). These results and our previous findings (Niu et al, 2022) together suggest that knockout of Ythdf1 or Ythdf2 alone does not affect retinal neurogenesis.…”

“…Gene Ontology (GO) analysis of those target mRNAs revealed enrichment of genes related to regulation of nervous system development, regulation of neuron differentiation, regulation of neurogenesis et al (Figures 7B,S7A,and S7B), which is consistent with the redundant functions of YTHDF1 and YTHDF2 in mediating m 6 A regulation of cortical neurogenesis. We have previously shown that anti-YTHDF2 RIP-seq in mouse retina identified 1638 mRNAs (Niu et al, 2022). We also carried out anti-YTHDF1 RIP-seq in mouse retina and identified 2969 mRNAs (Figure 7C and Table S2).…”

“…Conditional knockout of Ythdf1 in dorsal spinal commissural neurons impaired translation of Robo3.1 mRNA, and disturbed commissural axon guidance (Zhuang et al, 2019). Conditional knockout of Ythdf2 in retinal ganglion cells (RGCs) increased RGC dendrite branching and improved visual acuity (Niu et al, 2022). Thus, the m 6 A readers YTHDFs have sequential functions in neuronal development, initially mediating m 6 A modification in neurogenesis redundantly, and then exerting unique and specific roles to regulate axon and dendrite development of postmitotic neurons.…”

“…We generated Ythdf1 and Ythdf2 single conditional knockouts in retina using Six3-cre: Six3cre +/À , Ythdf1 fl/fl (Ythdf1 scKO) and Six3-cre +/À ,Ythdf2 fl/fl (Ythdf2 scKO). We have previously shown that although retinal ganglion cell dendrite branching increases, retinal neurogenesis is not affected in the Ythdf2 scKO (Niu et al, 2022).…”

“…Next, we wanted to identify which readers mediate m 6 A functions in retinal neurogenesis. We first focused on YTHDF1 and YTHDF2 which are expressed in the developing retinas (Niu et al, 2022) (control retinas in Figure S4A). We generated Ythdf1 and Ythdf2 single conditional knockouts in retina using Six3-cre: Six3cre +/À , Ythdf1 fl/fl (Ythdf1 scKO) and Six3-cre +/À ,Ythdf2 fl/fl (Ythdf2 scKO).…”