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Light adaptation enables the vertebrate visual system to operate over a wide range of ambient illumination. Regulation of phototransduction in photoreceptors is considered a major mechanism underlying light adaptation. However, various types of neurons and glial cells exist in the retina, and whether and how all retinal cells interact to adapt to light/dark conditions at the cellular and molecular levels requires systematic investigation. Therefore, we utilized single-cell RNA sequencing to dissect retinal cell-type-specific transcriptomes during light/dark adaptation in mice. The results demonstrated that, in addition to photoreceptors, other retinal cell types also showed dynamic molecular changes and specifically enriched signaling pathways under light/dark adaptation. Importantly, Müller glial cells (MGs) were identified as hub cells for intercellular interactions, displaying complex cell‒cell communication with other retinal cells. Furthermore, light increased the transcription of the deiodinase Dio2 in MGs, which converted thyroxine (T4) to active triiodothyronine (T3). Subsequently, light increased T3 levels and regulated mitochondrial respiration in retinal cells in response to light conditions. As cones specifically express the thyroid hormone receptor Thrb, they responded to the increase in T3 by adjusting light responsiveness. Loss of the expression of Dio2 specifically in MGs decreased the light responsive ability of cones. These results suggest that retinal cells display global transcriptional changes under light/dark adaptation and that MGs coordinate intercellular communication during light/dark adaptation via thyroid hormone signaling.

Retinitis pigmentosa (RP) is a form of inherited retinal degenerative diseases that ultimately involves the macula, which is present in primates but not in the rodents. Therefore, creating nonhuman primate (NHP) models of RP is of critical importance to study its mechanism of pathogenesis and to evaluate potential therapeutic options in the future. Here we applied adeno-associated virus (AAV)-delivered CRISPR/SaCas9 technology to knockout the RHO gene in the retinae of the adult rhesus macaque (Macaca mulatta) to investigate the hypothesis whether non-germline mutation of the RHO gene is sufficient to recapitulate RP. Through a series of studies, we were able to demonstrate successful somatic editing of the RHO gene and reduced RHO protein expression. More importantly, the mutant macaque retinae displayed clinical RP phenotypes, including photoreceptor degeneration, retinal thinning, abnormal rod subcellular structures, and reduced photoresponse. Therefore, we suggest somatic editing of the RHO gene is able to phenocopy RP, and the reduced time span in generating NHP mutant accelerates RP research and expands the utility of NHP model for human disease study.

Methyltransferase like 9 (Mettl9) is a member of the methyltransferase like protein family which is characterized by the presence of binding domains for S-adenosyl methionine, (SAM), a co-substrate for methylation reactions. Despite METTL9 is predicted to be a methyltransferase, its enzymatic activity, substrate specificities and biological functions are still poorly characterized. In this study, we revealed a tumor-promoting role for METTL9. We found that deletion of Mettl9 in tumor cells suppresses tumor growth and elicits potent anti-tumor immunity. Mechanistically, METTL9 is a N1-histidine methyltransferase which methylates the histidine residues of a x-His-x-His (xHxH) motif on the substrates. This motif is found extensively in zinc transporter families SLC39s and SLC30s, particularly in SLC39A7. Deletion of Mettl9 impairs cytoplasmic zinc homeostasis, resulting in an altered gene expression program with increased endoplasmic reticulum (ER) stress and reduced cell cycle. Mutation of key METTL9 catalyzed methylhistidine residues of SLC39A7 impairs cytoplasmic zinc homeostasis and affects cell growth as well. Notably, METTL9 expression is increased in some cancer types and its higher expression is associated with worse clinical outcomes, particularly in liver and pancreatic cancer. In summary, our work identified METTL9 as a potential new oncogene and its mediated methylation is of regulatory importance. Identifying selective and potent small-molecule inhibitors of METTL9 could thus represent novel therapeutic strategy for anti-proliferative cancer drugs.

Retinitis pigmentosa (RP) is a form of inherited retinal degenerative disease that ultimately involves the macula, which is present in primates but not in the rodents. Therefore, creating nonhuman primate (NHP) models of RP is of critical importance to study its mechanism of pathogenesis and to evaluate potential therapeutic options in the future. Here we applied adeno-associated virus (AAV)-delivered CRISPR/SaCas9 technology to knockout the RHO gene in the retinae of the adult rhesus macaque (Macaca mulatta) to investigate the hypothesis whether non-germline mutation of the RHO gene is sufficient to recapitulate RP. Through a series of studies, we were able to demonstrate successful somatic editing of the RHO gene and reduced RHO protein expression. More importantly, the mutant macaque retinae displayed clinical RP phenotypes, including photoreceptor degeneration, retinal thinning, abnormal rod subcellular structures, and reduced photoresponse. Therefore, we suggest somatic editing of the RHO gene is able to phenocopy RP, and the reduced time span in generating NHP mutant accelerates RP research and expands the utility of NHP model for human disease study.