Mutations in WDR4 as a new cause of Galloway-Mowat syndrome

WHAMM functions in kidney reabsorption and polymerizes actin to promote autophagosomal membrane closure and cargo sequestration

The actin cytoskeleton is essential for many functions of eukaryotic cells, but the factors that nucleate actin assembly are not well understood at the organismal level or in the context of disease. To explore the function of the actin nucleation factor WHAMM in mice, we examined how Whamm inactivation impacts kidney physiology and cellular proteostasis. We show that male WHAMM knockout mice excrete elevated levels of albumin, glucose, phosphate, and amino acids, and display structural abnormalities of the kidney proximal tubule, suggesting that WHAMM activity is important for nutrient reabsorption. In kidney tissue, the loss of WHAMM results in the accumulation of the lipidated autophagosomal membrane protein LC3, indicating an alteration in autophagy. In mouse fibroblasts and human proximal tubule cells, WHAMM and its binding partner the Arp2/3 complex control autophagic membrane closure and cargo receptor recruitment. These results reveal a role for WHAMM-mediated actin assembly in maintaining kidney function and promoting proper autophagosome membrane remodeling.

Mapping medically relevant RNA isoform diversity in the aged human frontal cortex with deep long-read RNA-seq

Determining whether the RNA isoforms from medically relevant genes have distinct functions could facilitate direct targeting of RNA isoforms for disease treatment. Here, as a step toward this goal for neurological diseases, we sequenced 12 postmortem, aged human frontal cortices (6 Alzheimer disease cases and 6 controls; 50% female) using one Oxford Nanopore PromethION flow cell per sample. We identified 1,917 medically relevant genes expressing multiple isoforms in the frontal cortex where 1,018 had multiple isoforms with different protein-coding sequences. Of these 1,018 genes, 57 are implicated in brain-related diseases including major depression, schizophrenia, Parkinson's disease and Alzheimer disease. Our study also uncovered 53 new RNA isoforms in medically relevant genes, including several where the new isoform was one of the most highly expressed for that gene. We also reported on five mitochondrially encoded, spliced RNA isoforms. We found 99 differentially expressed RNA isoforms between cases with Alzheimer disease and controls.

Small-Molecule Inhibitors of the m7G-RNA Writer METTL1

We discovered the first inhibitors of the m7G-RNA writer METTL1 by high-throughput docking and an enzymatic assay based on luminescence. Eleven compounds, which belong to three different chemotypes, show inhibitory activity in the range 40-300 μM. Two adenine derivatives identified by docking have very favorable ligand efficiency of 0.34 and 0.31 kcal/mol per non-hydrogen atom, respectively. Molecular dynamics simulations provide evidence that the inhibitors compete with the binding of the cosubstrate S-adenosyl methionine to METTL1. We also present a soakable crystal form that was used to determine the structure of the complex of METTL1 with sinefungin at a resolution of 1.85 Å.

Case Report: Novel compound heterozygous TPRKB variants cause Galloway-Mowat syndrome

Background

Galloway-Mowat syndrome (GAMOS) is a rare genetic disease characterized by early-onset nephrotic syndrome and microcephaly with central nervous system abnormalities. Pathogenic variants in genes encoding kinase, endopeptidase, and other proteins of small size (KEOPS) complex subunits cause GAMOS. The subunit TPRKB (TP53RK binding protein) has been reported in only two patients with GAMOS with homozygous missense variants.

Clinical report

Herein, we described a three-year-old male with GAMOS. He exhibited developmental delay, developmental regression, microcephaly, distinctive facial features, skeletal abnormalities, and epilepsy. Brain magnetic resonance imaging revealed progressive brain atrophy, delayed myelination, T2-hypointense signals in the thalamus, and multiple intracranial abnormal signals on diffusion-weighted imaging. He presented with relapsing nephrotic proteinuria exacerbated by upper respiratory tract infections and progressive renal function decline. Exome sequencing identified compound heterozygous missense and frameshift variants in TPRKB: c.224dup, p.(Ser76IlefsTer3) and c.247C>T, p.(Leu83Phe).

Conclusions

Our study supports that pathogenic TPRKB variants cause KEOPS complex-related GAMOS.

Applying Proteomics and Computational Approaches to Identify Novel Targets in Blast-Associated Post-Traumatic Epilepsy

Traumatic brain injury (TBI) can lead to post-traumatic epilepsy (PTE). Blast TBI (bTBI) found in Veterans presents with several complications, including cognitive and behavioral disturbances and PTE; however, the underlying mechanisms that drive the long-term sequelae are not well understood. Using an unbiased proteomics approach in a mouse model of repeated bTBI (rbTBI), this study addresses this gap in the knowledge. After rbTBI, mice were monitored using continuous, uninterrupted video-EEG for up to four months. Following this period, we collected cortex and hippocampus tissues from three groups of mice: those with post-traumatic epilepsy (PTE+), those without epilepsy (PTE-), and the control group (sham). Hundreds of differentially expressed proteins were identified in the cortex and hippocampus of PTE+ and PTE- relative to sham. Focusing on protein pathways unique to PTE+, pathways related to mitochondrial function, post-translational modifications, and transport were disrupted. Computational metabolic modeling using dysregulated protein expression predicted mitochondrial proton pump dysregulation, suggesting electron transport chain dysregulation in the epileptic tissue relative to PTE-. Finally, data mining enabled the identification of several novel and previously validated TBI and epilepsy biomarkers in our data set, many of which were found to already be targeted by drugs in various phases of clinical testing. These findings highlight novel proteins and protein pathways that may drive the chronic PTE sequelae following rbTBI.

Advances in brain epitranscriptomics research and translational opportunities

Various chemical modifications of all RNA transcripts, or epitranscriptomics, have emerged as crucial regulators of RNA metabolism, attracting significant interest from both basic and clinical researchers due to their diverse functions in biological processes and immense clinical potential as highlighted by the recent profound success of RNA modifications in improving COVID-19 mRNA vaccines. Rapid accumulation of evidence underscores the critical involvement of various RNA modifications in governing normal neural development and brain functions as well as pathogenesis of brain disorders. Here we provide an overview of RNA modifications and recent advancements in epitranscriptomic studies utilizing animal models to elucidate important roles of RNA modifications in regulating mammalian neurogenesis, gliogenesis, synaptic formation, and brain function. Moreover, we emphasize the pivotal involvement of RNA modifications and their regulators in the pathogenesis of various human brain disorders, encompassing neurodevelopmental disorders, brain tumors, psychiatric and neurodegenerative disorders. Furthermore, we discuss potential translational opportunities afforded by RNA modifications in combatting brain disorders, including their use as biomarkers, in the development of drugs or gene therapies targeting epitranscriptomic pathways, and in applications for mRNA-based vaccines and therapies. We also address current limitations and challenges hindering the widespread clinical application of epitranscriptomic research, along with the improvements necessary for future progress.

WHAMM functions in kidney reabsorption and polymerizes actin to promote autophagosomal membrane closure and cargo sequestration

The actin cytoskeleton is essential for many functions of eukaryotic cells, but the factors that nucleate actin assembly are not well understood at the organismal level or in the context of disease. To explore the function of the actin nucleation factor WHAMM in mice, we examined how Whamm inactivation impacts kidney physiology and cellular proteostasis. We show that male WHAMM knockout mice excrete elevated levels of albumin, glucose, phosphate, and amino acids, and display abnormalities of the kidney proximal tubule, suggesting that WHAMM activity is important for nutrient reabsorption. In kidney tissue, the loss of WHAMM results in the accumulation of the lipidated autophagosomal membrane protein LC3, indicating an alteration in autophagy. In mouse fibroblasts and human proximal tubule cells, WHAMM and its binding partner the Arp2/3 complex control autophagic membrane closure and cargo receptor recruitment. These results reveal a role for WHAMM-mediated actin assembly in maintaining kidney function and promoting proper autophagosome membrane remodeling.

Using deep long-read RNAseq in Alzheimer's disease brain to assess medical relevance of RNA isoform diversity

Due to alternative splicing, human protein-coding genes average over eight RNA isoforms, resulting in nearly four distinct protein coding sequences per gene. Long-read RNAseq (IsoSeq) enables more accurate quantification of isoforms, shedding light on their specific roles. To assess the medical relevance of measuring RNA isoform expression, we sequenced 12 aged human frontal cortices (6 Alzheimer's disease cases and 6 controls; 50% female) using one Oxford Nanopore PromethION flow cell per sample. Our study uncovered 53 new high-confidence RNA isoforms in medically relevant genes, including several where the new isoform was one of the most highly expressed for that gene. Specific examples include WDR4 (61%; microcephaly), MYL3 (44%; hypertrophic cardiomyopathy), and MTHFS (25%; major depression, schizophrenia, bipolar disorder). Other notable genes with new high-confidence isoforms include CPLX2 (10%; schizophrenia, epilepsy) and MAOB (9%; targeted for Parkinson's disease treatment). We identified 1,917 medically relevant genes expressing multiple isoforms in human frontal cortex, where 1,018 had multiple isoforms with different protein coding sequences, demonstrating the need to better understand how individual isoforms from a single gene body are involved in human health and disease, if at all. Exactly 98 of the 1,917 genes are implicated in brain-related diseases, including Alzheimer's disease genes such as APP (Aβ precursor protein; five), MAPT (tau protein; four), and BIN1 (eight). As proof of concept, we also found 99 differentially expressed RNA isoforms between Alzheimer's cases and controls, despite the genes themselves not exhibiting differential expression. Our findings highlight the significant knowledge gaps in RNA isoform diversity and their medical relevance. Deep long-read RNA sequencing will be necessary going forward to fully comprehend the medical relevance of individual isoforms for a "single" gene.

Mettl1-mediated internal m7G methylation of Sptbn2 mRNA elicits neurogenesis and anti-alzheimer's disease

BACKGROUND

N7-methylguanosine (m7G) is one of the most conserved modifications in nucleosides impacting mRNA export, splicing, and translation. However, the precise function and molecular mechanism of internal mRNA m7G methylation in adult hippocampal neurogenesis and neurogenesis-related Alzheimer's disease (AD) remain unknown.

RESULTS

We profiled the dynamic Mettl1/Wdr4 expressions and m7G modification during neuronal differentiation of neural stem cells (NSCs) in vitro and in vivo. Adult hippocampal neurogenesis and its molecular mechanisms were examined by morphology, biochemical methods and biological sequencing. The translation efficiency of mRNA was detected by polysome profiling. The stability of Sptbn2 mRNA was constructed by RNA stability assay. APPswe/PS1ΔE9 (APP/PS1) double transgenic mice were used as model of AD. Morris water maze was used to detect the cognitive function.

METHODS

We found that m7G methyltransferase complex Mettl1/Wdr4 as well as m7G was significantly elevated in neurons. Functionally, silencing Mettl1 in neural stem cells (NSCs) markedly decreased m7G modification, neuronal genesis and proliferation in addition to increasing gliogenesis, while forced expression of Mettl1 facilitated neuronal differentiation and proliferation. Mechanistically, the m7G modification of Sptbn2 mRNA by Mettl1 enhanced its stability and translation, which promoted neurogenesis. Importantly, genetic defciency of Mettl1 reduced hippocampal neurogenesis and spatial memory in the adult mice. Furthermore, Mettl1 overexpression in the hippocampus of APP/PS1 mice rescued neurogenesis and behavioral defects.

CONCLUSION

Our findings unravel the pivotal role of internal mRNA m7G modification in Sptbn2-mediated neurogenesis, and highlight Mettl3 regulation of neurogenesis as a novel therapeutic target in AD treatment.

RNA modification: mechanisms and therapeutic targets

RNA modifications are dynamic and reversible chemical modifications on substrate RNA that are regulated by specific modifying enzymes. They play important roles in the regulation of many biological processes in various diseases, such as the development of cancer and other diseases. With the help of advanced sequencing technologies, the role of RNA modifications has caught increasing attention in human diseases in scientific research. In this review, we briefly summarized the basic mechanisms of several common RNA modifications, including m6A, m5C, m1A, m7G, Ψ, A-to-I editing and ac4C. Importantly, we discussed their potential functions in human diseases, including cancer, neurological disorders, cardiovascular diseases, metabolic diseases, genetic and developmental diseases, as well as immune disorders. Through the "writing-erasing-reading" mechanisms, RNA modifications regulate the stability, translation, and localization of pivotal disease-related mRNAs to manipulate disease development. Moreover, we also highlighted in this review all currently available RNA-modifier-targeting small molecular inhibitors or activators, most of which are designed against m6A-related enzymes, such as METTL3, FTO and ALKBH5. This review provides clues for potential clinical therapy as well as future study directions in the RNA modification field. More in-depth studies on RNA modifications, their roles in human diseases and further development of their inhibitors or activators are needed for a thorough understanding of epitranscriptomics as well as diagnosis, treatment, and prognosis of human diseases.

Targeting N7-methylguanosine tRNA modification blocks hepatocellular carcinoma metastasis after insufficient radiofrequency ablation

Radiofrequency heat ablation is an ideal radical treatment for hepatocellular carcinoma (HCC). However, insufficient radiofrequency ablation (IRFA) could lead to high recurrence of HCC. N7-methylguanosine (m7G) on tRNAs, an evolutionally conservative modification in mammals and yeast, modulates heat stress responses and tumor progression, while its function in HCC recurrence after IRFA remains unknown. Here, we found that IRFA significantly upregulates the level of m7G tRNA modification and its methyltransferase complex components METTL1/WDR4 in multiple systems including HCC patient-derived xenograft (PDX) mouse, patients' HCC tissues, sublethal-heat-treated models of HCC cell lines, and organoids. Functionally, gain-/loss-of-function assays showed that METTL1-mediated m7G tRNA modification promotes HCC metastasis under sublethal heat exposure both in vitro and in vivo. Mechanistically, we found that METTL1 and m7G tRNA modification enhance the translation of SLUG/SNAIL in a codon frequency-dependent manner under sublethal heat stress. Overexpression of SLUG/SNAIL rescued the malignant potency of METTL1 knockdown HCC cells after sublethal heat exposure. Our study uncovers the key functions of m7G tRNA modification in heat stress responses and HCC recurrence after IRFA, providing molecular basis for targeting METTL1-m7G-SLUG/SNAIL axis to prevent HCC metastasis after radiofrequency heat ablation treatment.

WDR4 gene polymorphisms and Wilms tumor susceptibility in Chinese children: A five-center case-control study

Wilms tumor is the most common embryonal renal malignancy in children. WDR4 is an indispensable noncatalytic subunit of the RNA N7-methylguanosine (m7G) methyltransferase complex and plays an essential role in tumorigenesis. However, the relationship between polymorphisms in the WDR4 gene and susceptibility to Wilms tumor remains to be fully investigated. We performed a large case-control study involving 414 patients and 1199 cancer-free controls to investigate whether single nucleotide polymorphisms (SNPs) in the WDR4 gene are associated with Wilms tumor susceptibility. WDR4 gene polymorphisms (rs2156315 C > T, rs2156316 C > G, rs6586250 C > T, rs15736 G > A, and rs2248490 C > G) were genotyped using the TaqMan assay. In addition, unconditioned logistic regression analysis was performed, odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the association between WDR4 gene SNPs and Wilms tumor susceptibility as well as the strength of the associations. We found that only the rs6586250 C>T polymorphism was significantly associated with an increased risk of Wilms tumor (adjusted OR=2.99, 95% CI = 1.28-6.97, P = 0.011 for the rs6586250 TT genotype; adjusted OR=3.08, 95% CI = 1.33-7.17, P = 0.009 for the rs6586250 CC/CT genotype). Furthermore, the stratification analysis revealed that patients with the rs6586250 TT genotype and carriers with 1-5 risk genotypes exhibited statistically significant associations with increased Wilms tumor risk in specific subgroups. However, the rs2156315 CT/TT genotype was identified as having a protective effect against Wilms tumor in the age >18 months subgroup compared with the rs2156315 CC genotype. In brief, our study demonstrated that the rs6586250 C > T polymorphism of the WDR4 gene was significantly associated with Wilms tumor. This finding may contribute to the understanding of the genetic mechanism of Wilms tumor.

When N7-methyladenosine modification meets cancer: Emerging frontiers and promising therapeutic opportunities

N⁷-methylguanosine (m⁷G) methylation, one of the most common RNA modifications in eukaryotes, has recently gained considerable attention. The biological functions of m⁷G modification in RNAs, including tRNA, rRNA, mRNA, and miRNA, remain largely unknown in human diseases. Owing to rapid advances in high-throughput technologies, increasing evidence suggests that m⁷G modification plays a critical role in cancer initiation and progression. As m⁷G modification and hallmarks of cancer are inextricably linked together, targeting m⁷G regulators may provide new possibilities for future cancer diagnoses and potential intervention targets. This review summarizes various detection methods for m⁷G modification, recent advances in m⁷G modification and tumor biology regarding their interplay and regulatory mechanisms. We conclude with an outlook on the future of diagnosing and treating m⁷G-related diseases.

Branching out in different directions: Emerging cellular functions for the Arp2/3 complex and WASP-family actin nucleation factors

The actin cytoskeleton impacts practically every function of a eukaryotic cell. Historically, the best-characterized cytoskeletal activities are in cell morphogenesis, motility, and division. The structural and dynamic properties of the actin cytoskeleton are also crucial for establishing, maintaining, and changing the organization of membrane-bound organelles and other intracellular structures. Such activities are important in nearly all animal cells and tissues, although distinct anatomical regions and physiological systems rely on different regulatory factors. Recent work indicates that the Arp2/3 complex, a broadly expressed actin nucleator, drives actin assembly during several intracellular stress response pathways. These newly described Arp2/3-mediated cytoskeletal rearrangements are coordinated by members of the Wiskott-Aldrich Syndrome Protein (WASP) family of actin nucleation-promoting factors. Thus, the Arp2/3 complex and WASP-family proteins are emerging as crucial players in cytoplasmic and nuclear activities including autophagy, apoptosis, chromatin dynamics, and DNA repair. Characterizations of the functions of the actin assembly machinery in such stress response mechanisms are advancing our understanding of both normal and pathogenic processes, and hold great promise for providing insights into organismal development and interventions for disease.

[Neurological disorders and hereditary podocytopathies: Some fascinating pathophysiological overlaps]

Genetic studies of hereditary steroid resistant nephrotic syndrome (SRNS) have identified more than 60 genes involved in the development of single-gene, isolated or syndromic forms of hereditary podocytoapthies. Sometimes, syndromic SRNS is associated with neurological disorders. Over the past decades, various studies have established links between the podocyte, an epithelial glomerular cell involved in the renal filtration barrier, and neuronal cells, both morphologically (slit diaphragm and synapse) and functionally (signaling platforms). Variants of genes encoding proteins expressed in different compartments of the podocyte and neurons are responsible for phenotypes associating renal lesions with proteinuria to central and/or peripheral neurological disorders. In this review, we aim to focus on genetic syndromes associating proteinuria and neurological disease and to present the latest advances in the description of these neuro-renal disorders.

Diagnosis delay a family of Galloway-Mowat Syndrome caused by a classical splicing mutation of Lage3

BACKGROUND

Galloway-Mowat syndrome (GAMOS) is a group of rare hereditary diseases by the combination of early onset steroid-resistant nephrotic syndrome (SRNS) and microcephaly with brain anomalies caused by WDR73, LAGE3, OSGEP, TP53RK, TPRKB, GON7, WDR4 or NUP133 mutations.

CASE PRESENTATION

We present the clinical and genetic features of a two-year-old boy with early nephrotic syndrome, microcephaly, growth retardation hypotonia and hypothyroidism. Genetic testing showed the presence of a canonical-splice mutation in the LAGE3 gene (NM_006014: c.188 + 1C > T). A total of nine female members of the family carried the variant. Seven male members died prematurely, and three of them suffered from nephrotic syndrome, which is consistent with the x-linked gene map of the disease. The overall symptoms of the disease due to the LAGE3 mutation were mild compared to other pathogenic genes.

CONCLUSION

As far as we know, this is the largest family case of GAMOS2 caused by LAGE3 mutation found so far. We also compared other subtypes of GAMOS. Due to the heterogeneity of the renal phenotype, regular proteinuria screening is recommended for all patients diagnosed with GAMOS.

M7G-related molecular subtypes can predict the prognosis and correlate with immunotherapy and chemotherapy responses in bladder cancer patients

BACKGROUND

N7-methylguanosine (m7G) is closely associated with tumor prognosis and immune response in many cancer types. The correlation between m7G and bladder cancer (BC) needs further study. We aimed to orchestrate molecular subtypes and identify key genes for BC from the perspective of m7G.

METHODS

RNA-seq and clinical data of BC patients were extracted from TCGA and GSE13507 datasets. The patients were subtyped by "ConsensusClusterPlus" and "limma." The clusters were validated by the Kaplan‒Meier curves, univariable and multivariate Cox regression models, the concordance index, and calibration curves. The immunotherapy response was evaluated by immune checkpoints, immune infiltration, TIDE score, and IMvigor210 cohort. Genomics of Drug Sensitivity in Cancer was utilized to predict the chemotherapy response between the clusters.

RESULTS

The m7G-related cluster was ultimately established by EIF4G1, NUDT11, NUDT10, and CCNB1. The independent prognostic value of the m7G-related cluster was validated by the TCGA and GSE13507 datasets. The cluster was involved in immune-associated pathways, such as neutrophil degranulation, antigen processing cross-presentation, and signaling by interleukins pathways. Meanwhile, cluster 2 was positively correlated with many immune checkpoints, such as CD274, CTLA4, HAVCR2, LAG3, PDCD1, and PDCD1LG2. The cluster 2 was significantly correlated with a higher TIDE score than the cluster 1. Furthermore, in the IMvigor210 cohort, patients in the cluster 1 had a higher response rate than those in the cluster 2. Patients in the cluster 2 were sensitive to many chemotherapies.

CONCLUSIONS

We successfully determined molecular subtypes and identified key genes for BC from the perspective of m7G, thereby providing a roadmap for the evolution of immunotherapy and precision medicine.

Association of RNA m7G Modification Gene Polymorphisms with Pediatric Glioma Risk

Glioma stemming from glial cells of the central nervous system (CNS) is one of the leading causes of cancer death in childhood. The genetic predisposition of glioma is not fully understood. METTL1-WDR4 methyltransferase complex is implicated in tumorigenesis by catalyzing N7-methylguanosine (m⁷G) modification of RNA. This study is aimed at determining the association of glioma risk with three polymorphisms (rs2291617, rs10877013, and rs10877012) in METTL1 and five polymorphisms (rs2156315 rs2156316, rs6586250, rs15736, and rs2248490) in WDR4 gene in children of Chinese Han. We enrolled 314 cases and 380 controls from three independent hospitals. Genotypes of these polymorphisms were determined using the TaqMan assay. We found the WDR4 gene rs15736 was significantly associated with reduced glioma risk (GA/AA vs. GG: adjusted odds ratio = 0.63, 95%confidence interval = 0.42 - 0.94, P = 0.023) out of the eight studied polymorphisms. Stratified analyses showed that the association of rs15736 with the risk of glioma remained significant in children aged 60 months or older, girls, the subgroups with astrocytic tumors, or grade I + II glioma. We also found the combined effects of five WDR4 gene polymorphisms on glioma risk. Finally, expression quantitative trait locus (eQTL) analyses elucidated that the rs15736 polymorphism was related to the expression level of WDR4 and neighboring gene cystathionine-beta-synthase (CBS). Our finding provided evidence of a causal association between WDR4 gene polymorphisms and glioma susceptibility in Chinese Han children.

Wdr4 promotes cerebellar development and locomotion through Arhgap17-mediated Rac1 activation

Patients with mutations of WDR4, a substrate adaptor of the CUL4 E3 ligase complex, develop cerebellar atrophy and gait phenotypes. However, the underlying mechanisms remain unexplored. Here, we identify a crucial role of Wdr4 in cerebellar development. Wdr4 deficiency in granule neuron progenitors (GNPs) not only reduces foliation and the sizes of external and internal granular layers but also compromises Purkinje neuron organization and the size of the molecular layer, leading to locomotion defects. Mechanistically, Wdr4 supports the proliferation of GNPs by preventing their cell cycle exit. This effect is mediated by Wdr4-induced ubiquitination and degradation of Arhgap17, thereby activating Rac1 to facilitate cell cycle progression. Disease-associated Wdr4 variants, however, cannot provide GNP cell cycle maintenance. Our study identifies Wdr4 as a previously unappreciated participant in cerebellar development and locomotion, providing potential insights into treatment strategies for diseases with WDR4 mutations, such as primordial dwarfism and Galloway-Mowat syndrome.

Novel TP53RK variants cause varied clinical features of Galloway-Mowat syndrome without nephrotic syndrome in three unrelated Chinese patients

Objectives

Galloway-Mowat syndrome-4 (GAMOS4) is a very rare renal-neurological disease caused by TP53RK gene mutations. GAMOS4 is characterized by early-onset nephrotic syndrome, microcephaly, and brain anomalies. To date, only nine GAMOS4 cases with detailed clinical data (caused by eight deleterious variants in TP53RK) have been reported. This study aimed to examine the clinical and genetic characteristics of three unrelated GAMOS4 patients with TP53RK gene compound heterozygous mutations.

Methods

Whole-exome sequencing (WES) was used to identify four novel TP53RK variants in three unrelated Chinese children. Clinical characteristics such as biochemical parameters and image findings of patients were also evaluated. Furthermore, four studies of GAMOS4 patients with TP53RK variants were reviewed. In addition, clinical and genetic features were described after a retrospective analysis of clinical symptoms, laboratory data, and genetic test results.

Results

The three patients showed facial abnormalities, developmental delays, microcephaly, and aberrant cerebral imaging. Furthermore, patient 1 had slight proteinuria, while patient 2 had epilepsy. However, none of the individuals had nephrotic syndrome, and all were alive for more than 3 years of age. This is the first study to assess four variants in the TP53RK gene (NM_033550.4: c.15_16dup/p.A6Efs*29, c.745A > G/p.R249G, c.185G > A/p.R62H, and c.335A > G/p.Y112C).

Conclusion

The clinical characteristics of the three children with TP53RK mutations are significantly different from the known GAMOS4 traits, including early nephrotic syndrome and mortality mainly occurring in the first year of life. This study provides insights into the pathogenic TP53RK gene mutation spectrum and clinical phenotypes of GAMOS4.

Structural basis of regulated m7G tRNA modification by METTL1-WDR4

Chemical modifications of RNA have key roles in many biological processes1-3. N7-methylguanosine (m7G) is required for integrity and stability of a large subset of tRNAs4-7. The methyltransferase 1-WD repeat-containing protein 4 (METTL1-WDR4) complex is the methyltransferase that modifies G46 in the variable loop of certain tRNAs, and its dysregulation drives tumorigenesis in numerous cancer types8-14. Mutations in WDR4 cause human developmental phenotypes including microcephaly15-17. How METTL1-WDR4 modifies tRNA substrates and is regulated remains elusive18. Here we show,  through structural, biochemical and cellular studies of human METTL1-WDR4, that WDR4 serves as a scaffold for METTL1 and the tRNA T-arm. Upon tRNA binding, the αC region of METTL1 transforms into a helix, which together with the α6 helix secures both ends of the tRNA variable loop. Unexpectedly, we find that the predicted disordered N-terminal region of METTL1 is part of the catalytic pocket and essential for methyltransferase activity. Furthermore, we reveal that S27 phosphorylation in the METTL1 N-terminal region inhibits methyltransferase activity by locally disrupting the catalytic centre. Our results provide a molecular understanding of tRNA substrate recognition and phosphorylation-mediated regulation of METTL1-WDR4, and reveal the presumed disordered N-terminal region of METTL1 as a nexus of methyltransferase activity.

Conservation and Diversification of tRNA t6A-Modifying Enzymes across the Three Domains of Life

The universal N⁶-threonylcarbamoyladenosine (t⁶A) modification occurs at position 37 of tRNAs that decipher codons starting with adenosine. Mechanistically, t⁶A stabilizes structural configurations of the anticodon stem loop, promotes anticodon–codon pairing and safeguards the translational fidelity. The biosynthesis of tRNA t⁶A is co-catalyzed by two universally conserved protein families of TsaC/Sua5 (COG0009) and TsaD/Kae1/Qri7 (COG0533). Enzymatically, TsaC/Sua5 protein utilizes the substrates of L-threonine, HCO₃⁻/CO₂ and ATP to synthesize an intermediate L-threonylcarbamoyladenylate, of which the threonylcarbamoyl-moiety is subsequently transferred onto the A37 of substrate tRNAs by the TsaD–TsaB –TsaE complex in bacteria or by the KEOPS complex in archaea and eukaryotic cytoplasm, whereas Qri7/OSGEPL1 protein functions on its own in mitochondria. Depletion of tRNA t⁶A interferes with protein homeostasis and gravely affects the life of unicellular organisms and the fitness of higher eukaryotes. Pathogenic mutations of YRDC, OSGEPL1 and KEOPS are implicated in a number of human mitochondrial and neurological diseases, including autosomal recessive Galloway–Mowat syndrome. The molecular mechanisms underscoring both the biosynthesis and cellular roles of tRNA t⁶A are presently not well elucidated. This review summarizes current mechanistic understandings of the catalysis, regulation and disease implications of tRNA t⁶A-biosynthetic machineries of three kingdoms of life, with a special focus on delineating the structure–function relationship from perspectives of conservation and diversity.

tRNA dysregulation and disease

tRNAs are key adaptor molecules that decipher the genetic code during translation of mRNAs in protein synthesis. In contrast to the traditional view of tRNAs as ubiquitously expressed housekeeping molecules, awareness is now growing that tRNA-encoding genes display tissue-specific and cell type-specific patterns of expression, and that tRNA gene expression and function are both dynamically regulated by post-transcriptional RNA modifications. Moreover, dysregulation of tRNAs, mediated by alterations in either their abundance or function, can have deleterious consequences that contribute to several distinct human diseases, including neurological disorders and cancer. Accumulating evidence shows that reprogramming of mRNA translation through altered tRNA activity can drive pathological processes in a codon-dependent manner. This Review considers the emerging evidence in support of the precise control of functional tRNA levels as an important regulatory mechanism that coordinates mRNA translation and protein expression in physiological cell homeostasis, and highlights key examples of human diseases that are linked directly to tRNA dysregulation.

The epitranscriptome in ageing and stress resistance: A systematic review

Modifications of RNA, collectively called the "epitranscriptome", might provide novel biomarkers and innovative targets for interventions in geroscience but are just beginning to be studied in the context of ageing and stress resistance. RNA modifications modulate gene expression by affecting translation initiation and speed, miRNA binding, RNA stability, and RNA degradation. Nonetheless, the precise underlying molecular mechanisms and physiological consequences of most alterations of the epitranscriptome are still only poorly understood. We here systematically review different types of modifications of rRNA, tRNA and mRNA, the methodology to analyze them, current challenges in the field, and human disease associations. Furthermore, we compiled evidence for a connection between individual enzymes, which install RNA modifications, and lifespan in yeast, worm and fly. We also included resistance to different stressors and competitive fitness as search criteria for genes potentially relevant to ageing. Promising candidates identified by this approach include RCM1/NSUN5, RRP8, and F33A8.4/ZCCHC4 that introduce base methylations in rRNA, the methyltransferases DNMT2 and TRM9/ALKBH8, as well as factors involved in the thiolation or A to I editing in tRNA, and finally the m⁶A machinery for mRNA.

METTL1 promotes neuroblastoma development through m7G tRNA modification and selective oncogenic gene translation

Background

Neuroblastoma (NBL) is the most common extra-cranial solid tumour in childhood, with prognosis ranging from spontaneous remission to high risk for rapid and fatal progression. Despite existing therapy approaches, the 5-year event-free survival (EFS) for patients with advanced NBL remains below 30%, emphasizing urgent necessary for novel therapeutic strategies. Studies have shown that epigenetic disorders play an essential role in the pathogenesis of NBL. However, the function and mechanism of N7-methylguanosine (m⁷G) methyltransferase in NBL remains unknown.

Methods

The expression levels of m⁷G tRNA methyltransferase Methyltransferase-like 1 (METTL1) were analyzed by querying the Gene Expression Omnibus (GEO) database and further confirmed by immunohistochemistry (IHC) assay. Kaplan-Meier, univariate and multivariate cox hazard analysis were performed to reveal the prognostic role of METTL1. Cell function assays were performed to evaluate how METTL1 works in proliferation, apoptosis and migration in cell lines and xenograft mouse models. The role of METTL1 on mRNA translation activity of NBL cells was measured using puromycin intake assay and polysome profiling assay. The m⁷G modified tRNAs were identified by tRNA reduction and cleavage sequencing (TRAC-seq). Ribosome nascent-chain complex-bound mRNA sequencing (RNC-seq) was utilized to identify the variation of gene translation efficiency (TE). Analyzed the codon frequency decoded by m⁷G tRNA to clarify the translation regulation and mechanism of m⁷G modification in NBL.

Results

This study found that METTL1 were significantly up-regulated in advanced NBL, which acted as an independent risk factor and predicted poor prognosis. Further in NBL cell lines and BALB/c-nu female mice, we found METTL1 played a crucial role in promoting NBL progression. Furthermore, m⁷G profiling and translation analysis revealed downregulation of METTL1 would inhibit puromycin intake efficiency of NBL cells, indicating that METTL1 did count crucially in regulation of NBL cell translation. With all tRNAs with m⁷G modification identified in NBL cells, knockdown of METTL1 would significantly reduce the levels of both m⁷G modification and m⁷G tRNAs expressions. Result of RNC-seq shew there were 339 overlapped genes with impaired translation in NBL cells upon METTL1 knockdown. Further analysis revealed these genes contained higher frequency of codons decoded by m⁷G-modified tRNAs and were enriched in oncogenic pathways.

Conclusion

This study revealed the critical role and mechanism of METTL1-mediated tRNA m⁷G modification in regulating NBL progression, providing new insights for developing therapeutic approaches for NBL patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40364-022-00414-z.

The role of RNA modification in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly mortal type of primary liver cancer. Abnormal epigenetic modifications are present in HCC, and RNA modification is dynamic and reversible and is a key post-transcriptional regulator. With the in-depth study of post-transcriptional modifications, RNA modifications are aberrantly expressed in human cancers. Moreover, the regulators of RNA modifications can be used as potential targets for cancer therapy. In RNA modifications, N6-methyladenosine (m6A), N7-methylguanosine (m7G), and 5-methylcytosine (m5C) and their regulators have important regulatory roles in HCC progression and represent potential novel biomarkers for the confirmation of diagnosis and treatment of HCC. This review focuses on RNA modifications in HCC and the roles and mechanisms of m6A, m7G, m5C, N1-methyladenosine (m1A), N3-methylcytosine (m3C), and pseudouridine (ψ) on its development and maintenance. The potential therapeutic strategies of RNA modifications are elaborated for HCC.

The pattern of expression and prognostic value of key regulators for m7G RNA methylation in hepatocellular carcinoma

N7-methylguanosine (m7G) modification on internal RNA positions plays a vital role in several biological processes. Recent research shows m7G modification is associated with multiple cancers. However, in hepatocellular carcinoma (HCC), its implications remain to be determined. In this place, we need to interrogate the mRNA patterns for 29 key regulators of m7G RNA modification and assess their prognostic value in HCC. Initial, the details from The Cancer Genome Atlas (TCGA) database concerning transcribed gene data and clinical information of HCC patients were inspected systematically. Second, according to the mRNA profiles of 29 m7G RNA methylation regulators, two clusters (named 1 and 2, respectively) were identified by consensus clustering. Furthermore, robust risk signature for seven m7G RNA modification regulators was constructed. Last, we used the Gene Expression Omnibus (GEO) dataset to validate the prognostic associations of the seven-gene risk signature. We figured out that 24/29 key regulators of m7G RNA modification varied remarkably in their grades of expression between the HCC and the adjacent tumor control tissues. Cluster one compared with cluster two had a substandard prognosis and was also positively correlated with T classification (T), pathological stage, and vital status (fustat) significantly. Consensus clustering results suggested the expression pattern of m7G RNA modification regulators was correlated with the malignancy of HCC strongly. In addition, cluster one was extensively enriched in metabolic-related pathways. Seven optimal genes (METTL1, WDR4, NSUN2, EIF4E, EIF4E2, NCBP1, and NCBP2) were selected to establish the risk model for HCC. Indicating by further analyses and validation, the prognostic model has fine anticipating command and this probability signature might be a self supporting presage factor for HCC. Finally, a new prognostic nomogram based on age, gender, pathological stage, histological grade, and prospects were established to forecast the prognosis of HCC patients accurately. In essence, we detected association of HCC severity and expression levels of m7G RNA modification regulators, and developed a risk score model for predicting prognosis of HCC patients’ progression.

Integrating basic science with translational research: the 13th International Podocyte Conference 2021

The 13th International Podocyte Conference was held in Manchester, UK, and online from July 28 to 30, 2021. Originally planned for 2020, this biannual meeting was postponed by a year because of the coronavirus disease 2019 (COVID-19) pandemic and proceeded as an innovative hybrid meeting. In addition to in-person attendance, online registration was offered, and this attracted 490 conference registrations in total. As a Podocyte Conference first, a day for early-career researchers was introduced. This premeeting included talks from graduate students and postdoctoral researchers. It gave early career researchers the opportunity to ask a panel, comprising academic leaders and journal editors, about career pathways and the future for podocyte research. The main meeting over 3 days included a keynote talk and 4 focused sessions each day incorporating invited talks, followed by selected abstract presentations, and an open panel discussion. The conference concluded with a Patient Day, which brought together patients, clinicians, researchers, and industry representatives. The Patient Day was an interactive and diverse day. As well as updates on improving diagnosis and potential new therapies, the Patient Day included a PodoArt competition, exercise and cooking classes with practical nutrition advice, and inspirational stories from patients and family members. This review summarizes the exciting science presented during the 13th International Podocyte Conference and demonstrates the resilience of researchers during a global pandemic.

Genomic, Proteomic, and Phenotypic Spectrum of Novel O-Sialoglycoprotein Endopeptidase Variant in Four Affected Individuals With Galloway-Mowat Syndrome

Galloway-Mowat syndrome is a rare autosomal recessive disease characterized by a unique combination of renal and neurological manifestations, including early-onset steroid-resistant nephrotic syndrome, microcephaly, psychomotor delay, and gyral abnormalities of the brain. Most patients die during early childhood. Here, we identified a novel homozygous O-sialoglycoprotein endopeptidase (OSGEP) variant, NM_017807.3:c.973C>G (p.Arg325Gly), in four affected individuals in an extended consanguineous family from Saudi Arabia. We have described the detailed clinical characterization, brain imaging results, and muscle biopsy findings. The described phenotype varied from embryonic lethality to early pregnancy loss or death at the age of 9. Renal disease is often the cause of death. Protein modeling of this OSGEP variant confirmed its pathogenicity. In addition, proteomic analysis of the affected patients proposed a link between the KEOPS complex function and human pathology and suggested potential pathogenic mechanisms.

The potential role of N7-methylguanosine (m7G) in cancer

N⁷-methylguanosine (m7G), one of the most prevalent RNA modifications, has recently attracted significant attention. The m7G modification actively participates in biological and pathological functions by affecting the metabolism of various RNA molecules, including messenger RNA, ribosomal RNA, microRNA, and transfer RNA. Increasing evidence indicates a critical role for m7G in human disease development, especially cancer, and aberrant m7G levels are closely associated with tumorigenesis and progression via regulation of the expression of multiple oncogenes and tumor suppressor genes. Currently, the underlying molecular mechanisms of m7G modification in cancer are not comprehensively understood. Here, we review the current knowledge regarding the potential function of m7G modifications in cancer and discuss future m7G-related diagnostic and therapeutic strategies.

Galloway-Mowat Syndrome Type 3 Caused by OSGEP Gene Variants: A Case Report and Literature Review

BACKGROUND

Galloway-Mowat syndrome type 3 (GAMOS3) is an extremely rare and severe autosomal-recessive disease characterized by early-onset nephrotic syndrome (NS), microcephaly and neurological impairment. Reported GAMOS cases have gradually increased since pathogenic OSGEP variants were identified as the aetiology in 2017.

METHODS

Using whole-exome sequencing and a data analysis process established by Children's Hospital of Fudan University, the clinical and molecular features of 3 infants with OSGEP mutations were summarized. Literature regarding the clinical features of GAMOS3 caused by OSGEP variants was reviewed.

RESULTS

Thirty-seven individuals (3 from this study) from 34 families were included. Twenty-two different OSGEP variants were identified. The c.740G>A (p.Arg247Gln) variant in OSGEP was detected in 15 families (44%), all from Asia. Most affected individuals (including patients I and II in this study) showed a typical phenotype, including microcephaly (92%) with brain anomalies (97%), developmental delay (81%), congenital NS (54%), and craniofacial (94%) and skeletal dysmorphism (84%). Renal manifestations varied from proteinuria (94%, median onset = 1.5 months) to NS (83%) and end-stage renal disease (48%, 11 months) during follow-up. Patients with congenital NS had a lower survival probability (median survival time = 3 months) than those without congenital NS (78 months) (P < 0.01, log-rank test).

CONCLUSION

GAMOS3 is a progressive renal-neurological syndrome with a poor prognosis, especially with congenital NS. Microcephaly with dysmorphic features are vital clues to further evaluate renal impairment and brain anomalies. Timely molecular diagnosis is crucial for clinical decision-making, appropriate treatment and genetic counselling.

METTL1 promotes hepatocarcinogenesis via m7 G tRNA modification-dependent translation control

BACKGROUND

N7 -methylguanosine (m7 G) modification is one of the most common transfer RNA (tRNA) modifications in humans. The precise function and molecular mechanism of m7 G tRNA modification in hepatocellular carcinoma (HCC) remain poorly understood.

METHODS

The prognostic value and expression level of m7 G tRNA methyltransferase complex components methyltransferase-like protein-1 (METTL1) and WD repeat domain 4 (WDR4) in HCC were evaluated using clinical samples and TCGA data. The biological functions and mechanisms of m7 G tRNA modification in HCC progression were studied in vitro and in vivo using cell culture, xenograft model, knockin and knockout mouse models. The m7 G reduction and cleavage sequencing (TRAC-seq), polysome profiling and polyribosome-associated mRNA sequencing methods were used to study the levels of m7 G tRNA modification, tRNA expression and mRNA translation efficiency.

RESULTS

The levels of METTL1 and WDR4 are elevated in HCC and associated with advanced tumour stages and poor patient survival. Functionally, silencing METTL1 or WDR4 inhibits HCC cell proliferation, migration and invasion, while forced expression of wild-type METTL1 but not its catalytic dead mutant promotes HCC progression. Knockdown of METTL1 reduces m7 G tRNA modification and decreases m7 G-modified tRNA expression in HCC cells. Mechanistically, METTL1-mediated tRNA m7 G modification promotes the translation of target mRNAs with higher frequencies of m7 G-related codons. Furthermore, in vivo studies with Mettl1 knockin and conditional knockout mice reveal the essential physiological function of Mettl1 in hepatocarcinogenesis using hydrodynamics transfection HCC model.

CONCLUSIONS

Our work reveals new insights into the role of the misregulated tRNA modifications in liver cancer and provides molecular basis for HCC diagnosis and treatment.

Neurological involvement in monogenic podocytopathies

Genetic studies of hereditary nephrotic syndrome (NS) have identified more than 50 genes that, if mutated, are responsible for monogenic forms of steroid-resistant NS (SRNS), either isolated or syndromic. Most of these genes encode proteins expressed in the podocyte with various functions such as transcription factors, mitochondrial proteins, or enzymes, but mainly structural proteins of the slit diaphragm (SD) as well as cytoskeletal binding and regulator proteins. Syndromic NS is sometimes associated with neurological features. Over recent decades, various studies have established links between the physiology of podocytes and neurons, both morphologically (slit diaphragm and synapse) and functionally (signaling platforms). Variants in genes expressed in different compartments of the podocyte and neurons are responsible for phenotypes associating kidney lesions with proteinuria (mainly Focal and Segmental Glomerulosclerosis (FSGS) or Diffuse Mesangial Sclerosis (DMS)) and central and/or peripheral neurological disorders. The Galloway-Mowat syndrome (GAMOS, OMIM#251300) associates neurological defects, microcephaly, and proteinuria and is caused by variants in genes encoding proteins of various functions (microtubule cytoskeleton regulation (WDR73), regulation of protein synthesis via transfer RNAs (KEOPS and WDR4 complexes)). Pierson syndrome (OMIM#609049) associating congenital nephrotic syndrome and central neurological and ophthalmological anomalies is secondary to variants in LAMB2, involved in glomerular and ocular basement membranes. Finally, Charcot-Marie-Tooth-FSGS (OMIM#614455) combines peripheral sensory-motor neuropathy and proteinuria and arises from INF2 variants, resulting in cytoskeletal polymerization defects. This review focuses on genetic syndromes associating nephrotic range proteinuria and neurological involvement and provides the latest advances in the description of these neuro-renal disorders.

Novel variants in OSGEP leading to Galloway-Mowat syndrome by altering its subcellular localization

Galloway-Mowat syndrome (GAMOS) is an extremely rare clinically heterogeneous autosomal or X-linked inherited recessive disease characterized by early-onset steroid-resistant nephrotic syndrome (SRNS), microcephaly and neurological impairment. In this study, two siblings mainly presenting with decreased head circumference, hypotonia, gross motor delay, and dysmorphic features were initially detected without pathogenic variants by karyotyping, SNP-array and WES. After a 3 year's follow-up, the proband manifested additional proteinuria, hematuria and "deeper sulci" with a sign of brain atrophy. By reanalysis on the proband's previous WES data, two novel compound heterozygous variants of OSGEP (c.133dupA; c.608C > T) were identified. Furthermore, functional studies showed that the variants reduced the expression of OSGEP protein and activated the DNA damage response (DDR) signaling in the lymphoblastoid cell lines (LCLs) obtained from the patient. The analysis of protein localization with confocal microscopy revealed that the EGFP-tagged/HA-tagged mutant OSGEP proteins were abnormal aggregation or retained inside the cytosol, respectively. Our study not only expanded the pathogenic variant spectrum of OSGEP but also carried on regular follow-up for kidney involvement and established a strategy for evaluation on the function of mutant OSGFP by subcellular localization assay.

Galloway-Mowat syndrome: New insights from bioinformatics and expression during Xenopus embryogenesis

Galloway-Mowat syndrome (GAMOS) is a rare developmental disease. Patients suffer from congenital brain anomalies combined with renal abnormalities often resulting in an early-onset steroid-resistant nephrotic syndrome. The etiology of GAMOS has a heterogeneous genetic contribution. Mutations in more than 10 different genes have been reported in GAMOS patients. Among these are mutations in four genes encoding members of the human KEOPS (kinase, endopeptidase and other proteins of small size) complex, including OSGEP, TP53RK, TPRKB and LAGE3. Until now, these components have been functionally mainly investigated in bacteria, eukarya and archaea and in humans in the context of the discovery of its role in GAMOS, but the KEOPS complex members' expression and function during embryogenesis in vertebrates is still unknown. In this study, in silico analysis showed that both gene localization and the protein sequences of the three core KEOPS complex members Osgep, Tp53rk and Tprkb are highly conserved across different species including Xenopus laevis. In addition, we examined the spatio-temporal expression pattern of osgep, tp53rk and tprkb using RT-PCR and whole mount in situ hybridization approaches during early Xenopus development. We observed that all three genes were expressed during early embryogenesis and enriched in tissues and organs affected in GAMOS. More precisely, KEOPS complex genes are expressed in the pronephros, but also in neural tissue such as the developing brain, eye and cranial cartilage. These findings suggest that the KEOPS complex plays an important role during vertebrate embryonic development.

m7G tRNA modification reveals new secrets in the translational regulation of cancer development

Orellana et al. (2021) and Dai et al. (2021) demonstrate that increased m7G modification of a subset of tRNAs by the METTL1/WDR4 complex stabilizes these mRNAs against decay, increases translation efficiency, reduces ribosome pausing, is associated with poor survival in human cancers, and is directly transforming.

METTL1/WDR4 mediated m7G tRNA modifications and m7G codon usage promote mRNA translation and lung cancer progression

Mis-regulated epigenetic modifications in RNAs are associated with human cancers. The transfer RNAs (tRNAs) are the most heavily modified RNA species in cells, however, little is known about the functions of tRNA modifications in cancers. In this study, we uncovered that the expression levels of tRNA N⁷-methylguanosine (m⁷G) methyltransferase complex components METTL1 and WDR4 are significantly elevated in human lung cancer samples and negatively associated with patient prognosis. Impaired m⁷G tRNA modification upon METTL1/WDR4 depletion resulted in decreased cell proliferation, colony formation, cell invasion and impaired tumorigenic capacities of lung cancer cells in vitro and in vivo. Moreover, gain-of-function and mutagenesis experiments revealed that METTL1 promoted lung cancer growth and invasion through regulation of m⁷G tRNA modifications. Profiling of tRNA methylation and mRNA translation revealed that highly translated mRNAs have higher frequencies of m⁷G tRNA decoded codons and knockdown of METTL1 resulted in decreased translation of mRNAs with higher frequencies of m⁷G tRNA codons, suggesting that tRNA modifications and codon usage play essential function in mRNA translation regulation. Our data uncovered novel insights on mRNA translation regulation through tRNA modifications and the corresponding mRNA codon compositions in lung cancer, providing new molecular basis underlying lung cancer progression.

A patient diagnosed with Galloway-Mowat syndrome presenting with a rod-cone functional anomaly with electronegative dark-adapted ERGs

PURPOSE

Galloway-Mowat syndrome (GAMOS) is a clinically heterogenous and rare condition classically described as the combination of nephrotic syndrome associated with brain anomaly and delays in development. It was first reported in the literature in 1968 by Galloway W.H and Mowat A.P. Reports of visual anomaly in these patients are generally limited to decreased visual acuity, nystagmus and optic nerve atrophy. To this day, little is known about retinal function in this disease. Therefore, the purpose of this case report is to reveal abnormal retinal function (including light-adapted and dark-adapted retinal function) in a female patient diagnosed with GAMOS due to mutation of the WDR73 gene.

METHODS

Complete dilated pediatric ophthalmic examination and ISCEV full field standard light (10 min of light adaptation; background light: 30 cd.m^-2; flash intensity: 3.0 cd.sec.m^-2) and dark-adapted (20 min of dark adaptation; flash intensities: 0.01, 3.0 and 10.0 cd.sec.m^-2) electroretinograms were performed on a 2-year-old female patient diagnosed with GAMOS due to a biallelic mutation in the WDR73 gene.

RESULTS

Ophthalmologic evaluation under anesthesia revealed normal appearing anterior segments. Significant bilateral optic nerve pallor was noted. Fundus examination appeared to be abnormal and demonstrated mid-peripheral whitish glistening appearance with possible gliosis. Retinoscopy revealed bilateral high myopia with a refractive error of -8.00 sphere in both eyes. ISCEV standard ERG revealed residual responses under light-adapted condition. Undetectable responses were obtained after 20 min of dark adaptation when using a dim flash (DA 0.01). However, when brighter flashes were used in a dark-adapted condition (DA 3.0 and DA 10.0), the ERGs were detectable, albeit abnormal in amplitudes and of electronegative morphology.

CONCLUSIONS

The results obtained showed significant retinal functional deficit affecting both the cone and the rod photoreceptor pathways, along with the inner retina, in a patient diagnosed with GAMOS due to biallelic mutations in the WDR73 gene. Our report is limited to one patient, and additional studies are needed to verify whether retinal functional anomalies, as measured by the full field electroretinogram, present a novel biomarker in all patients affected with GAMOS or only in patients with a mutation in the WDR73 gene. Given the evidence of retinal functional changes presented in this study, it is strongly suggested to include complete ophthalmic examination, retinal imaging, including OCT, and full field ERG testing in patients affected with GAMOS.

N7-Methylguanosine tRNA modification enhances oncogenic mRNA translation and promotes intrahepatic cholangiocarcinoma progression

Cancer cells selectively promote translation of specific oncogenic transcripts to facilitate cancer survival and progression, but the underlying mechanisms are poorly understood. Here, we find that N⁷-methylguanosine (m⁷G) tRNA modification and its methyltransferase complex components, METTL1 and WDR4, are significantly upregulated in intrahepatic cholangiocarcinoma (ICC) and associated with poor prognosis. We further reveal the critical role of METTL1/WDR4 in promoting ICC cell survival and progression using loss- and gain-of-function assays in vitro and in vivo. Mechanistically, m⁷G tRNA modification selectively regulates the translation of oncogenic transcripts, including cell-cycle and epidermal growth factor receptor (EGFR) pathway genes, in m⁷G-tRNA-decoded codon-frequency-dependent mechanisms. Moreover, using overexpression and knockout mouse models, we demonstrate the crucial oncogenic function of Mettl1-mediated m⁷G tRNA modification in promoting ICC tumorigenesis and progression in vivo. Our study uncovers the important physiological function and mechanism of METTL1-mediated m⁷G tRNA modification in the regulation of oncogenic mRNA translation and cancer progression.

Division of labor in epitranscriptomics: What have we learnt from the structures of eukaryotic and viral multimeric RNA methyltransferases?

The translation of an mRNA template into the corresponding protein is a highly complex and regulated choreography performed by ribosomes, tRNAs, and translation factors. Most RNAs involved in this process are decorated by multiple chemical modifications (known as epitranscriptomic marks) contributing to the efficiency, the fidelity, and the regulation of the mRNA translation process. Many of these epitranscriptomic marks are written by holoenzymes made of a catalytic subunit associated with an activating subunit. These holoenzymes play critical roles in cell development. Indeed, several mutations being identified in the genes encoding for those proteins are linked to human pathologies such as cancers and intellectual disorders for instance. This review describes the structural and functional properties of RNA methyltransferase holoenzymes, which when mutated often result in brain development pathologies. It illustrates how structurally different activating subunits contribute to the catalytic activity of these holoenzymes through common mechanistic trends that most likely apply to other classes of holoenzymes. This article is categorized under: RNA Processing > RNA Editing and Modification RNA Processing > Capping and 5' End Modifications.

Aging through an epitranscriptomic lens

The mechanistic causes of aging, the time-related decline in function and good health that leads to increased mortality, remain poorly understood. Here we propose that age-dependent alteration of the epitranscriptome, encompassing more than 150 chemically distinct post-transcriptional modifications or editing events, warrants exploration as an important modulator of aging. The epitranscriptome is a potent regulator of RNA function, diverse cellular processes and tissue regenerative capacity. To date, only a few studies link alterations in the epitranscriptome to molecular and physiological changes during aging; however, epitranscriptome dysfunction is associated with and underlies several age-associated pathologies, including cancer and neurodegenerative, cardiovascular and autoimmune diseases. For example, changes in RNA modifications (such as N⁶-methyladenosine and inosine) impact cardiac physiology and are linked to cardiac fibrosis. Although an uncharted research focus, mapping epitranscriptome alterations in the context of aging may elucidate novel predictors of both health and lifespan, and may identify therapeutic targets for attenuating aging and abrogating age-related diseases.

Disruption of pathways regulated by Integrator complex in Galloway-Mowat syndrome due to WDR73 mutations

Several studies have reported WDR73 mutations to be causative of Galloway–Mowat syndrome, a rare disorder characterised by the association of neurological defects and renal-glomerular disease. In this study, we demonstrate interaction of WDR73 with the INTS9 and INTS11 components of Integrator, a large multiprotein complex with various roles in RNA metabolism and transcriptional control. We implicate WDR73 in two Integrator-regulated cellular pathways; namely, the processing of uridylate-rich small nuclear RNAs (UsnRNA), and mediating the transcriptional response to epidermal growth factor stimulation. We also show that WDR73 suppression leads to altered expression of genes encoding cell cycle regulatory proteins. Altogether, our results suggest that a range of cellular pathways are perturbed by WDR73 loss-of-function, and support the consensus that proper regulation of UsnRNA maturation, transcription initiation and cell cycle control are all critical in maintaining the health of post-mitotic cells such as glomerular podocytes and neurons, and preventing degenerative disease.

Mutations in PRDM15 Are a Novel Cause of Galloway-Mowat Syndrome

BACKGROUND

Galloway-Mowat syndrome (GAMOS) is characterized by neurodevelopmental defects and a progressive nephropathy, which typically manifests as steroid-resistant nephrotic syndrome. The prognosis of GAMOS is poor, and the majority of children progress to renal failure. The discovery of monogenic causes of GAMOS has uncovered molecular pathways involved in the pathogenesis of disease.

METHODS

Homozygosity mapping, whole-exome sequencing, and linkage analysis were used to identify mutations in four families with a GAMOS-like phenotype, and high-throughput PCR technology was applied to 91 individuals with GAMOS and 816 individuals with isolated nephrotic syndrome. In vitro and in vivo studies determined the functional significance of the mutations identified.

RESULTS

Three biallelic variants of the transcriptional regulator PRDM15 were detected in six families with proteinuric kidney disease. Four families with a variant in the protein's zinc-finger (ZNF) domain have additional GAMOS-like features, including brain anomalies, cardiac defects, and skeletal defects. All variants destabilize the PRDM15 protein, and the ZNF variant additionally interferes with transcriptional activation. Morpholino oligonucleotide-mediated knockdown of Prdm15 in Xenopus embryos disrupted pronephric development. Human wild-type PRDM15 RNA rescued the disruption, but the three PRDM15 variants did not. Finally, CRISPR-mediated knockout of PRDM15 in human podocytes led to dysregulation of several renal developmental genes.

CONCLUSIONS

Variants in PRDM15 can cause either isolated nephrotic syndrome or a GAMOS-type syndrome on an allelic basis. PRDM15 regulates multiple developmental kidney genes, and is likely to play an essential role in renal development in humans.

Human transfer RNA modopathies: diseases caused by aberrations in transfer RNA modifications

tRNA molecules are post-transcriptionally modified by tRNA modification enzymes. Although composed of different chemistries, more than 40 types of human tRNA modifications play pivotal roles in protein synthesis by regulating tRNA structure and stability as well as decoding genetic information on mRNA. Many tRNA modifications are conserved among all three kingdoms of life, and aberrations in various human tRNA modification enzymes cause life-threatening diseases. Here, we describe the class of diseases and disorders caused by aberrations in tRNA modifications as 'tRNA modopathies'. Aberrations in over 50 tRNA modification enzymes are associated with tRNA modopathies, which most frequently manifest as dysfunctions of the brain and/or kidney, mitochondrial diseases, and cancer. However, the molecular mechanisms that link aberrant tRNA modifications to human diseases are largely unknown. In this review, we provide a comprehensive compilation of human tRNA modification functions, tRNA modification enzyme genes, and tRNA modopathies, and we summarize the elucidated pathogenic mechanisms underlying several tRNA modopathies. We will also discuss important questions that need to be addressed in order to understand the molecular pathogenesis of tRNA modopathies.

Expanding the phenotype of biallelic loss-of-function variants in the NSUN2 gene: Description of four individuals with juvenile cataract, chronic nephritis, or brain anomaly as novel complications

The NSUN2 gene encodes a tRNA cytosine methyltransferase that functions in the maturation of leucyl tRNA (Leu) (CAA) precursors, which is crucial for the anticodon-codon pairing and correct translation of mRNA. Biallelic loss of function variants in NSUN2 are known to cause moderate to severe intellectual disability. Microcephaly, postnatal growth retardation, and dysmorphic facial features are common complications in this genetic disorder, and delayed puberty is occasionally observed. Here, we report four individuals, two sets of siblings, with biallelic loss-of-function variants in the NSUN2 gene. The first set of siblings have compound heterozygous frameshift variants: c.546_547insCT, p.Met183Leufs*13; c.1583del, p.Pro528Hisfs*19, and the other siblings carry a homozygous frameshift variant: c.1269dup, p.Val424Cysfs*14. In addition to previously reported clinical features, the first set of siblings showed novel complications of juvenile cataract and chronic nephritis. The other siblings showed hypomyelination and simplified gyral pattern in neuroimaging. NSUN2-related intellectual disability is a very rare condition, and less than 20 cases have been reported previously. Juvenile cataract, chronic nephritis, and brain anomaly shown in the present patients have not been previously described. Our report suggests clinical diversity of NSUN2-related intellectual disability.

Genetic aspects of congenital nephrotic syndrome: a consensus statement from the ERKNet-ESPN inherited glomerulopathy working group

Congenital nephrotic syndrome (CNS) is a heterogeneous group of disorders presenting with massive proteinuria within the first 3 months of life almost inevitably leading to end-stage kidney disease. The Work Group for the European Reference Network for Kidney Diseases (ERKNet) and the European Society for Pediatric Nephrology (ESPN) has developed consensus statement on genetic aspects of CNS diagnosis and management. The presented expert opinion recommends genetic diagnostics as the key diagnostic test to be ordered already during the initial evaluation of the patient, discusses which phenotyping workup should be performed and presents known genotype-phenotype correlations.

WD40-Repeat Proteins in Ciliopathies and Congenital Disorders of Endocrine System

WD40-repeat (WDR)-containing proteins constitute an evolutionarily conserved large protein family with a broad range of biological functions. In human proteome, WDR makes up one of the most abundant protein-protein interaction domains. Members of the WDR protein family play important roles in nearly all major cellular signalling pathways. Mutations of WDR proteins have been associated with various human pathologies including neurological disorders, cancer, obesity, ciliopathies and endocrine disorders. This review provides an updated overview of the biological functions of WDR proteins and their mutations found in congenital disorders. We also highlight the significant role of WDR proteins in ciliopathies and endocrine disorders. The new insights may help develop therapeutic approaches targeting WDR motifs.

Hypomodified tRNA in evolutionarily distant yeasts can trigger rapid tRNA decay to activate the general amino acid control response, but with different consequences

All tRNAs are extensively modified, and modification deficiency often results in growth defects in the budding yeast Saccharomyces cerevisiae and neurological or other disorders in humans. In S. cerevisiae, lack of any of several tRNA body modifications results in rapid tRNA decay (RTD) of certain mature tRNAs by the 5'-3' exonucleases Rat1 and Xrn1. As tRNA quality control decay mechanisms are not extensively studied in other eukaryotes, we studied trm8Δ mutants in the evolutionarily distant fission yeast Schizosaccharomyces pombe, which lack 7-methylguanosine at G46 (m7G46) of their tRNAs. We report here that S. pombe trm8Δ mutants are temperature sensitive primarily due to decay of tRNATyr(GUA) and that spontaneous mutations in the RAT1 ortholog dhp1+ restored temperature resistance and prevented tRNA decay, demonstrating conservation of the RTD pathway. We also report for the first time evidence linking the RTD and the general amino acid control (GAAC) pathways, which we show in both S. pombe and S. cerevisiae. In S. pombe trm8Δ mutants, spontaneous GAAC mutations restored temperature resistance and tRNA levels, and the trm8Δ temperature sensitivity was precisely linked to GAAC activation due to tRNATyr(GUA) decay. Similarly, in the well-studied S. cerevisiae trm8Δ trm4Δ RTD mutant, temperature sensitivity was closely linked to GAAC activation due to tRNAVal(AAC) decay; however, in S. cerevisiae, GAAC mutations increased tRNA loss and exacerbated temperature sensitivity. A similar exacerbated growth defect occurred upon GAAC mutation in S. cerevisiae trm8Δ and other single modification mutants that triggered RTD. Thus, these results demonstrate a conserved GAAC activation coincident with RTD in S. pombe and S. cerevisiae, but an opposite impact of the GAAC response in the two organisms. We speculate that the RTD pathway and its regulation of the GAAC pathway is widely conserved in eukaryotes, extending to other mutants affecting tRNA body modifications.

Defects in t6A tRNA modification due to GON7 and YRDC mutations lead to Galloway-Mowat syndrome

N⁶-threonyl-carbamoylation of adenosine 37 of ANN-type tRNAs (t⁶A) is a universal modification essential for translational accuracy and efficiency. The t⁶A pathway uses two sequentially acting enzymes, YRDC and OSGEP, the latter being a subunit of the multiprotein KEOPS complex. We recently identified mutations in genes encoding four out of the five KEOPS subunits in children with Galloway-Mowat syndrome (GAMOS), a clinically heterogeneous autosomal recessive disease characterized by early-onset steroid-resistant nephrotic syndrome and microcephaly. Here we show that mutations in YRDC cause an extremely severe form of GAMOS whereas mutations in GON7, encoding the fifth KEOPS subunit, lead to a milder form of the disease. The crystal structure of the GON7/LAGE3/OSGEP subcomplex shows that the intrinsically disordered GON7 protein becomes partially structured upon binding to LAGE3. The structure and cellular characterization of GON7 suggest its involvement in the cellular stability and quaternary arrangement of the KEOPS complex.

The biosynthesis of N⁶-threonylcarbamoylated adenosine 37 in tRNA (t⁶A) involves the YRDC enzyme and the KEOPS complex. Here, the authors report mutations in YRDC and the KEOPS component GON7 in Galloway-Mowat syndrome and determine the crystal structure of a GON7-containg subcomplex that suggests a role in KEOPS complex stability.