Expanding allelic and phenotypic spectrum of ZC4H2-related disorder: A novel hypomorphic variant and high prevalence of tethered cord

ZC4H2 (MIM# 300897) is a nuclear factor involved in various cellular processes including proliferation and differentiation of neural stem cells, ventral spinal patterning and osteogenic and myogenic processes. Pathogenic variants in ZC4H2 have been associated with Wieacker-Wolff syndrome (MIM# 314580), an X-linked neurodevelopmental disorder characterized by arthrogryposis, development delay, hypotonia, feeding difficulties, poor growth, skeletal abnormalities, and dysmorphic features. Zebrafish zc4h2 null mutants recapitulated the human phenotype, showed complete loss of vsx2 expression in brain, and exhibited abnormal swimming and balance problems. Here we report 7 new patients (four males and three females) with ZC4H2-related disorder from six unrelated families. Four of the 6 ZC4H2 variants are novel: three missense variants, designated as c.142T>A (p.Tyr48Asn), c.558G>A (p.Met186Ile) and c.602C>T (p.Pro201Leu), and a nonsense variant, c.618C>A (p.Cys206*). Two variants were previously reported : a nonsense variant c.199C>T (p.Arg67*) and a splice site variant (c.225+5G>A). Five patients were on the severe spectrum of clinical findings, two of whom had early death. The male patient harboring the p.Met186Ile variant and the female patient that carries the p.Pro201Leu variant have a relatively mild phenotype. Of note, 4/7 patients had a tethered cord that required a surgical repair. We also demonstrate and discuss previously under-recognized phenotypic features including sleep apnea, arrhythmia, hypoglycemia, and unexpected early death. To study the effect of the missense variants, we performed microinjection of human ZC4H2 wild-type or variant mRNAs into zc4h2 null mutant zebrafish embryos. The p.Met186Ile mRNA variant was able to partially rescue vsx2 expression while p.Tyr48Asn and p.Pro201Leu mRNA variants were not. However, swimming and balance problems could not be rescued by any of these variants. These results suggest that the p.Met186Ile is a hypomorphic allele. Our work expands the genotypes and phenotypes associated with ZC4H2-related disorder and demonstrates that the zebrafish system is a reliable method to determine the pathogenicity of ZC4H2 variants.

Chx10+V2a interneurons in spinal motor regulation and spinal cord injury

Chx10-expressing V2a (Chx10+V2a) spinal interneurons play a large role in the excitatory drive of motoneurons. Chemogenetic ablation studies have demonstrated the essential nature of Chx10+V2a interneurons in the regulation of locomotor initiation, maintenance, alternation, speed, and rhythmicity. The role of Chx10+V2a interneurons in locomotion and autonomic nervous system regulation is thought to be robust, but their precise role in spinal motor regulation and spinal cord injury have not been fully explored. The present paper reviews the origin, characteristics, and functional roles of Chx10+V2a interneurons with an emphasis on their involvement in the pathogenesis of spinal cord injury. The diverse functional properties of these cells have only been substantiated by and are due in large part to their integration in a variety of diverse spinal circuits. Chx10+V2a interneurons play an integral role in conferring locomotion, which integrates various corticospinal, mechanosensory, and interneuron pathways. Moreover, accumulating evidence suggests that Chx10+V2a interneurons also play an important role in rhythmic patterning maintenance, left-right alternation of central pattern generation, and locomotor pattern generation in higher order mammals, likely conferring complex locomotion. Consequently, the latest research has focused on postinjury transplantation and noninvasive stimulation of Chx10+V2a interneurons as a therapeutic strategy, particularly in spinal cord injury. Finally, we review the latest preclinical study advances in laboratory derivation and stimulation/transplantation of these cells as a strategy for the treatment of spinal cord injury. The evidence supports that the Chx10+V2a interneurons act as a new therapeutic target for spinal cord injury. Future optimization strategies should focus on the viability, maturity, and functional integration of Chx10+V2a interneurons transplanted in spinal cord injury foci.

RNF220 is an E3 ubiquitin ligase for AMPA receptors to regulate synaptic transmission

The accurate expression of postsynaptic AMPA receptors (AMPARs) is critical for information processing in the brain, and ubiquitination is a key regulator for this biological process. However, the roles of E3 ubiquitin ligases in the regulation of AMPARs are poorly understood. Here, we find that RNF220 directly interacts with AMPARs to meditate their polyubiquitination, and RNF220 knockout specifically increases AMPAR protein levels, thereby enhancing basal synaptic activity while impairing synaptic plasticity. Moreover, depending on its E3 ubiquitin ligase activity, RNF220 represses AMPAR-mediated excitatory synaptic responses and their neuronal surface expression. Furthermore, learning and memory are altered in forebrain RNF220-deficient mice. In addition, two neuropathology-related RNF220 variants fail to repress excitatory synaptic activity because of the incapability to regulate AMPAR ubiquitination due to their attenuated interaction. Together, we identify RNF220 as an E3 ubiquitin ligase for AMPARs and establish its substantial role in excitatory synaptic transmission and brain function.

Loss of Protein Function Causing Severe Phenotypes of Female-Restricted Wieacker Wolff Syndrome due to a Novel Nonsense Mutation in the ZC4H2 Gene

Pathogenic variants of zinc finger C4H2-type containing (ZC4H2) on the X chromosome cause a group of genetic diseases termed ZC4H2-associated rare disorders (ZARD), including Wieacker-Wolff Syndrome (WRWF) and Female-restricted Wieacker-Wolff Syndrome (WRWFFR). In the current study, a de novo c.352C>T (p.Gln118*) mutation in ZC4H2 (NM_018684.4) was identified in a female neonate born with severe arthrogryposis multiplex congenita (AMC) and Pierre-Robin sequence (cleft palate and micrognathia). Plasmids containing the wild-type (WT), mutant-type (MT) ZC4H2, or GFP report gene (N) were transfected in 293T cell lines, respectively. RT-qPCR and western blot analysis showed that ZC4H2 protein could not be detected in the 293T cells transfected with MT ZC4H2. The RNA seq results revealed that the expression profile of the MT group was similar to that of the N group but differed significantly from the WT group, indicating that the c.352C>T mutation resulted in the loss of function of ZC4H2. Differentially expressed genes (DEGs) enrichment analysis showed that c.352C>T mutation inhibited the expression levels of a series of genes involved in the oxidative phosphorylation pathway. Subsequently, expression levels of ZC4H2 were knocked down in neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs) by lentiviral-expressed small hairpin RNAs (shRNAs) against ZC4H2. The results also demonstrated that decreasing the expression of ZC4H2 significantly reduced the growth of NSCs by affecting the expression of genes related to the oxidative phosphorylation signaling pathway. Taken together, our results strongly suggest that ZC4H2 c.352C>T (p.Gln118*) mutation resulted in the loss of protein function and caused WRWFFR.

Modelling human placental villous development: designing cultures that reflect anatomy

The use of in vitro tools to study trophoblast differentiation and function is essential to improve understanding of normal and abnormal placental development. The relative accessibility of human placentae enables the use of primary trophoblasts and placental explants in a range of in vitro systems. Recent advances in stem cell models, three-dimensional organoid cultures, and organ-on-a-chip systems have further shed light on the complex microenvironment and cell-cell crosstalk involved in placental development. However, understanding each model's strengths and limitations, and which in vivo aspects of human placentation in vitro data acquired does, or does not, accurately reflect, is key to interpret findings appropriately. To help researchers use and design anatomically accurate culture models, this review both outlines our current understanding of placental development, and critically considers the range of established and emerging culture models used to study this, with a focus on those derived from primary tissue.

Rnf220 is Implicated in the Dorsoventral Patterning of the Hindbrain Neural Tube in Mice

Rnf220 is reported to regulate the patterning of the ventral spinal neural tube in mice. The brainstem has divergent connections with peripheral and central targets and contains unique internal neuronal groups, but the role of Rnf220 in the early development of the hindbrain has not been explored. In this study, Nestin-Cre-mediated conditional knockout (Rnf220^Nestin CKO) mice were used to examine if Rnf220 is involved in the early morphogenesis of the hindbrain. Rnf220 showed restricted expression in the ventral half of ventricular zone (VZ) of the hindbrain at embryonic day (E) 10.5, and as development progressed, Rnf220-expressing cells were also present in the mantle zone outside the VZ at E12.5. In Rnf220^Nestin CKO embryos, alterations of progenitor domains in the ventral VZ were observed at E10.5. There were significant reductions of the p1 and p2 domains shown by expression of Dbx1, Olig2, and Nkx6.1, accompanied by a ventral expansion of the Dbx1⁺ p0 domain and a dorsal expansion of the Nkx2.2⁺ p3 domain. Different from the case in the spinal cord, the Olig2⁺ pMN (progenitors of somatic motor neuron) domain shifted and expanded dorsally. Notably, the total range of the ventral VZ and the extent of the dorsal tube were unchanged. In addition, the post-mitotic cells derived from their corresponding progenitor domain, including oligodendrocyte precursor cells (OPCs) and serotonergic neurons (5-HTNs), were also changed in the same trend as the progenitor domains do in the CKO embryos at E12.5. In summary, our data suggest similar functions of Rnf220 in the hindbrain dorsoventral (DV) patterning as in the spinal cord with different effects on the pMN domain. Our work also reveals novel roles of Rnf220 in the development of 5-HTNs and OPCs.

PSD-93 up-regulates the synaptic activity of corticotropin-releasing hormone neurons in the paraventricular nucleus in depression

Since the discovery of ketamine anti-depressant effects in last decade, it has effectively revitalized interest in investigating excitatory synapses hypothesis in the pathogenesis of depression. In the present study, we aimed to reveal the excitatory synaptic regulation of corticotropin-releasing hormone (CRH) neuron in the hypothalamus, which is the driving force in hypothalamic-pituitary-adrenal (HPA) axis regulation. This study constitutes the first observation of an increased density of PSD-93-CRH co-localized neurons in the hypothalamic paraventricular nucleus (PVN) of patients with major depression. PSD-93 overexpression in CRH neurons in the PVN induced depression-like behaviors in mice, accompanied by increased serum corticosterone level. PSD-93 knockdown relieved the depression-like phenotypes in a lipopolysaccharide (LPS)-induced depression model. Electrophysiological data showed that PSD-93 overexpression increased CRH neurons synaptic activity, while PSD-93 knockdown decreased CRH neurons synaptic activity. Furthermore, we found that LPS induced increased the release of glutamate from microglia to CRH neurons resulted in depression-like behaviors using fiber photometry recordings. Together, these results show that PSD-93 is involved in the pathogenesis of depression via increasing the synaptic activity of CRH neurons in the PVN, leading to the hyperactivity of the HPA axis that underlies depression-like behaviors.

The many faces of the E3 ubiquitin ligase, RNF220, in neural development and beyond

Ubiquitin modification plays important roles in many cellular processes that are fundamental for vertebrate embryo development, such as cell division, differentiation, and migration. Aberrant function or deregulation of ubiquitination enzymes can cause developmental disorders, cancer progression, and neurodegenerative diseases in humans. RING finger protein 220 (RNF220) is an evolutionarily conserved RING-type ubiquitin E3 ligase. Recent studies have revealed the roles and mechanisms of RNF220 and its partner protein, zinc finger C4H2-type containing protein (ZC4H2), in embryonic development and human diseases. Using mouse and zebrafish models, it has been shown that RNF220 regulates sonic hedgehog (Shh) signaling via Gli and embryonic ectoderm development (EED), a polycomb repressive complex 2 (PRC2) component, during ventral neural patterning and cerebellum development. In addition, RNF220 also regulates the development and functions of central noradrenergic and motor neurons in mice. By stabilizing β-catenin and signal transducer and activator of transcription 1 (STAT1), RNF220 is also involved in Wnt and interferon (IFN)-STAT1 signaling and thus the regulation of tumorigenesis and immune response, respectively. In humans, both RNF220 and ZC4H2 mutations have been reported to be associated with diseases accompanied by complicated neural defects. In this review, we summarize the current knowledge of RNF220 with special emphasis on its roles and mechanisms of action in signal transduction, vertebrate neural development, and related human disorders.

ZC4H2 stabilizes RNF220 to pattern ventral spinal cord through modulating Shh/Gli signaling

ZC4H2 encodes a C4H2 type zinc-finger nuclear factor, the mutation of which has been associated with disorders with various clinical phenotypes in human, including developmental delay, intellectual disability and dystonia. ZC4H2 has been suggested to regulate spinal cord patterning in zebrafish as a co-factor for RNF220, an ubiquitin E3 ligase involved in Gli signaling. Here we showed that ZC4H2 and RNF220 knockout animals phenocopy each other in spinal patterning in both mouse and zebrafish, with mispatterned progenitor and neuronal domains in the ventral spinal cord. We showed evidence that ZC4H2 is required for the stability of RNF220 and also proper Gli ubiquitination and signaling in vivo. Our data provides new insights into the possible etiology of the neurodevelopmental impairments observed in ZC4H2-associated syndromes.

Neuromuscular and Neuroendocrinological Features Associated With ZC4H2-Related Arthrogryposis Multiplex Congenita in a Sicilian Family: A Case Report

Wieacker-Wolff syndrome (WWS) is an X-linked Arthrogryposis Multiplex Congenita (AMC) disorder associated with broad neurodevelopmental impairment. The genetic basis of WWS lies in hemizygous pathogenic variants in ZC4H2, encoding a C4H2 type zinc-finger nuclear factor abundantly expressed in the developing human brain. The main clinical features described in WWS families carrying ZC4H2 pathogenic variants encompass having a short stature, microcephaly, birth respiratory distress, arthrogryposis, hypotonia, distal muscle weakness, and broad neurodevelopmental delay. We hereby report a Sicilian family with a boy clinically diagnosed with WWS and genetically investigated with exome sequencing (ES), leading to the identification of a c.593G>A (p. R198Q) hemizygous pathogenic variant in the ZC4H2 gene. During the first year of life, the onset of central hypoadrenalism led to recurrent hypoglycemic events, which likely contributed to seizure susceptibility. Also, muscle biopsy studies confirmed a pathology of the muscle tissue and revealed peculiar abnormalities of the neuromuscular junction. In conclusion, we expand the phenotypic spectrum of the WWS-related neurodevelopmental disorders and discuss the role of ZC4H2 in the context of the potential neuroendocrinological and neuromuscular features associated with this condition.

Exosomal miR-486-5p derived from human placental microvascular endothelial cells regulates proliferation and invasion of trophoblasts via targeting IGF1

Preeclampsia (PE) is a serious complication of pregnancy. Exosomes are known to be upregulated in PE. In this study, we sought to investigate the effect of miR-486-5p from human placental microvascular endothelial cells, on the function of trophoblast cells. To investigate the function of human placental microvascular endothelial cell (HPVEC)-derived exosomes on trophoblast cells, HPVECs were treated with hypoxia/reoxygenation (H/R). The separation efficiency of exosomes was determined by transmission electron microscopy, nanosight and Western blot. Cell Counting Kit-8, EdU staining, wound-healing, and transwell assay were performed to detect the effect of exosomally transferred miR-486-5p inhibitor on proliferation, migration and invasion of trophoblast cells. MiRDB and dual-luciferase report assay were used to find the target of miR-486-5p. Our data revealed that miR-486-5p was significantly upregulated in H/R-treated HPVEC-Exo, and miR-486-5p was enriched in HPVEC-Exo. miR-486-5p inhibitor carried by HPVEC-Exo significantly inhibited the proliferation, migration and invasion of trophoblast cells. Insulin-like growth factor 1 (IGF1) was found to be the target of miR-486-5p, and IGF1 overexpression notably reversed the effect of miR-486-5p inhibitor from HPVEC-Exo on trophoblast cell function. In summary, H/R-treated HPVEC-derived exosomally expressing miR-486-5p inhibitor significantly inhibited the proliferation, migration and invasion of trophoblast cells via downregulation of IGF1. The findings from the present study may be useful in the development of treatments for PE.

Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness

Leukodystrophies are a heterogeneous group of rare inherited disorders that involve preferentially the white matter of the central nervous system (CNS). These conditions are characterized by a primary glial cell and myelin sheath pathology of variable etiology, which causes secondary axonal degeneration, generally emerging with disease progression. Whole exome sequencing performed in 5 large consanguineous nuclear families allowed to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness. We report on two homozygous missense variants (p.R363Q and p.R365Q) in the ubiquitin E3 ligase RNF220 as the cause underlying a novel form of leukodystrophy with ataxia and sensorineural deafness having fibrotic cardiomyopathy and hepatopathy as associated features, in seven consanguineous families. Mass spectrometry analysis identified lamin B1 as RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1. We demonstrate that RNF220 silencing in Drosophila melanogaster specifically affects proper localization of lamin Dm0, the fly lamin B1 orthologue, promotes its aggregation, and causes a neurodegenerative phenotype, strongly supporting the functional link between RNF220 and lamin B1. Finally, we demonstrate that RNF220 plays a crucial role in the maintenance of nuclear morphology: mutations primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies. Overall, our data identify RNF220 as a gene implicated in leukodystrophy with ataxia and sensorineural deafness, and document a critical role of RNF220 in the regulation of nuclear lamina. Our findings provide further evidence on the direct link between nuclear lamina dysfunction and neurodegeneration.

Cross-Disorder Analysis of De Novo Variants Increases the Power of Prioritising Candidate Genes

De novo variants (DNVs) are critical to the treatment of neurodevelopmental disorders (NDDs). However, effectively identifying candidate genes in small cohorts is challenging in most NDDs because of high genetic heterogeneity. We hypothesised that integrating DNVs from multiple NDDs with genetic similarity can significantly increase the possibility of prioritising the candidate gene. We catalogued 66,186 coding DNVs in 50,028 individuals with nine types of NDDs in cohorts with sizes spanning from 118 to 31,260 from Gene4Denovo database to validate this hypothesis. Interestingly, we found that integrated DNVs can effectively increase the number of prioritised candidate genes for each disorder. We identified 654 candidate genes including 481 shared candidate genes carrying putative functional variants in at least two disorders. Notably, 13.51% (65/481) of shared candidate genes were prioritised only via integrated analysis including 44.62% (29/65) genes validated in recent large cohort studies. Moreover, we estimated that more novel candidate genes will be prioritised with the increase in cohort size, in particular for some disorders with high putative functional DNVs per individual. In conclusion, integrated DNVs may increase the power of prioritising candidate genes, which is important for NDDs with small cohort size.

Haploinsufficiency of the TDP43 ubiquitin E3 ligase RNF220 leads to ALS-like motor neuron defects in the mouse

TDP43 pathology is seen in a large majority of amyotrophic lateral sclerosis (ALS) cases, suggesting a central pathogenic role of this regulatory protein. Clarifying the molecular mechanism controlling TDP43 stability and subcellular location might provide important insights into ALS therapy. The ubiquitin E3 ligase RNF220 is involved in different neural developmental processes through various molecular targets in the mouse. Here, we report that the RNF220^+/− mice showed progressively decreasing mobility to different extents, some of which developed typical ALS pathological characteristics in spinal motor neurons, including TDP43 cytoplasmic accumulation, atrocytosis, muscle denervation, and atrophy. Mechanistically, RNF220 interacts with TDP43 in vitro and in vivo and promotes its polyubiquitination and proteasomal degradation. In conclusion, we propose that RNF220 might be a modifier of TDP43 function in vivo and contribute to TDP43 pathology in neurodegenerative disease like ALS.

Systematic analysis to identify transcriptome-wide dysregulation of Alzheimer's disease in genes and isoforms

Alzheimer's disease (AD) is one of the most common neurodegeneration diseases caused by multiple factors. The mechanistic insight of AD remains limited. To disclose molecular mechanisms of AD, many studies have been proposed from transcriptome analyses. However, no analysis across multiple levels of transcription has been conducted to discover co-expression networks of AD. We performed gene-level and isoform-level analyses of RNA sequencing (RNA-seq) data from 544 brain tissues of AD patients, mild cognitive impaired (MCI) patients, and healthy controls. Gene and isoform levels of co-expression modules were constructed by RNA-seq data. The associations of modules with AD were evaluated by integrating cognitive scores of patients, Genome-wide association studies (GWAS), alternative splicing analysis, and dementia-related genes expressed in brain tissues. Totally, 29 co-expression modules were found with expressions significantly correlated with the cognitive scores. Among them, two isoform modules were enriched with AD-associated SNPs and genes whose mRNA splicing displayed significant alteration in relation to AD disease. These two modules were further found enriched with dementia-related genes expressed in four brain regions of 125 AD patients. Analyzing expressions of these two modules revealed expressions of 39 isoforms (corresponding to 35 genes) significantly correlated with cognitive scores of AD patients, in which 38 isoforms were significantly up-regulated in AD patients comparing to controls, and 33 isoforms (corresponding to 29 genes) were not reported as AD-related previously. Employing the co-expression modules and the drug-induced gene expression data from Connectivity Map (CMAP), 12 drugs were predicted as significant in restoring the gene expression of AD patients towards health, which include nine drugs reported for relieving AD. In comparison, four of the top 12 significant drugs were known for relieving AD if the drug prediction was performed by the genes expressed significantly different in AD and healthy controls. Analysis of multiple levels of the transcriptomic organization is useful in suggesting AD-related co-expression networks and discovering drugs.

Foxd4l1.1 negatively regulates transcription of neural repressor ventx1.1 during neuroectoderm formation in Xenopus embryos

Neuroectoderm formation is the first step in development of a proper nervous system for vertebrates. The developmental decision to form a non-neural ectoderm versus a neural one involves the regulation of BMP signaling, first reported many decades ago. However, the precise regulatory mechanism by which this is accomplished has not been fully elucidated, particularly for transcriptional regulation of certain key transcription factors. BMP4 inhibition is a required step in eliciting neuroectoderm from ectoderm and Foxd4l1.1 is one of the earliest neural genes highly expressed in the neuroectoderm and conserved across vertebrates, including humans. In this work, we focused on how Foxd4l1.1 downregulates the neural repressive pathway. Foxd4l1.1 inhibited BMP4/Smad1 signaling and triggered neuroectoderm formation in animal cap explants of Xenopus embryos. Foxd4l1.1 directly bound within the promoter of endogenous neural repressor ventx1.1 and inhibited ventx1.1 transcription. Foxd4l1.1 also physically interacted with Xbra in the nucleus and inhibited Xbra-induced ventx1.1 transcription. In addition, Foxd4l1.1 also reduced nuclear localization of Smad1 to inhibit Smad1-mediated ventx1.1 transcription. Foxd4l1.1 reduced the direct binding of Xbra and Smad1 on ventx1.1 promoter regions to block Xbra/Smad1-induced synergistic activation of ventx1.1 transcription. Collectively, Foxd4l1.1 negatively regulates transcription of a neural repressor ventx1.1 by multiple mechanisms in its exclusively occupied territory of neuroectoderm, and thus leading to primary neurogenesis. In conjunction with the results of our previous findings that ventx1.1 directly represses foxd4l1.1, the reciprocal repression of ventx1.1 and foxd4l1.1 is significant in at least in part specifying the mechanism for the non-neural versus neural ectoderm fate determination in Xenopus embryos.

RNF220 promotes the proliferation of leukaemic cells and reduces the degradation of the Cyclin D1 protein through USP22

Ring finger proteins contain a characteristic ring finger motif and perform a wide range of biological functions in living organisms. These genes are abnormally expressed in many cancers. We found that the expression level of Ring finger protein 220 (RNF220) was negatively correlated with the disease-free survival (DFS) and overall survival (OS) of acute myeloid leukaemia (AML) patients. Moreover, the mRNA level of this gene is significantly higher in the bone marrow cells of AML patients than in the mobilized peripheral blood haematopoietic stem cells of healthy donors. The overexpression of RNF220 promotes the proliferation of AML cells and accelerates the transition from G1 phase to S phase. Increased protein levels and decreased ubiquitylation levels of Cyclin D1 were observed in the nuclei of cells overexpressing RNF220 compared to those of control cells. The protein level of USP22 was also increased in cells overexpressing RNF220. RNF220 cannot enhance the stability of the Cyclin D1 protein without increased expression of the USP22 protein. Our study provided proof of principle to show that RNF220 promotes stabilization of the Cyclin D1 protein via USP22.

RNF220 mediates K63-linked polyubiquitination of STAT1 and promotes host defense

STAT1 is a master regulator that orchestrates type 1 and 2 interferon (IFN)-induced IFN-stimulated gene (ISG) expression. The mechanisms by which STAT1 is phosphorylated and activated upon IFN signaling remain elusive. Our work demonstrated that ubiquitination of STAT1 mediated by the E3 ligase RNF220 contributed significantly to STAT1 activation and innate immune responses. Rnf220 gene deficiency resulted in the downregulation of IFN signaling and decreased expression of ISGs in response to type 1 and 2 IFNs stimulation and Acinetobacter baumannii and HSV-1 infection. Mechanistically, RNF220 interacted with STAT1 and mediated the K63-linked polyubiquitination of STAT1 at residue K110, which promoted the interaction between STAT1 and the kinase JAK1. The expression of RNF220 was induced by pathogenic infection and IFN signaling. RNF220 promoted STAT1 ubiquitination and phosphorylation through a positive feedback loop. RNF220 haploinsufficiency impaired IFN signaling, and RNF220-defective mice were more susceptible to A. baumannii and HSV-1 infection than WT mice. Our work offers novel insights into the mechanisms of STAT1 modulation and provides potential therapeutic targets against bacterial and viral infection and inflammatory diseases.

Loss of ZC4H2 and RNF220 Inhibits Neural Stem Cell Proliferation and Promotes Neuronal Differentiation

The ubiquitin E3 ligase RNF220 and its co-factor ZC4H2 are required for multiple neural developmental processes through different targets, including spinal cord patterning and the development of the cerebellum and the locus coeruleus. Here, we explored the effects of loss of ZC4H2 and RNF220 on the proliferation and differentiation of neural stem cells (NSCs) derived from mouse embryonic cortex. We showed that loss of either ZC4H2 or RNF220 inhibits the proliferation and promotes the differentiation abilities of NSCs in vitro. RNA-Seq profiling revealed 132 and 433 differentially expressed genes in the ZC4H2^−/− and RNF220^−/− NSCs, compared to wild type (WT) NSCs, respectively. Specifically, Cend1, a key regulator of cell cycle exit and differentiation of neuronal precursors, was found to be upregulated in both ZC4H2^−/− and RNF220^−/− NSCs at the mRNA and protein levels. The targets of Cend1, such as CyclinD1, Notch1 and Hes1, were downregulated both in ZC4H2^−/− and RNF220^−/− NSCs, whereas p53 and p21 were elevated. ZC4H2^−/− and RNF220^−/− NSCs showed G0/G1 phase arrest compared to WT NSCs in cell cycle analysis. These results suggested that ZC4H2 and RNF220 are likely involved in the regulation of neural stem cell proliferation and differentiation through Cend1.

The Zinc-Finger Domain Containing Protein ZC4H2 Interacts with TRPV4, Enhancing Channel Activity and Turnover at the Plasma Membrane

The Ca²⁺-permeable Transient Receptor Potential channel vanilloid subfamily member 4 (TRPV4) is involved in a broad range of physiological processes, including the regulation of systemic osmotic pressure, bone resorption, vascular tone, and bladder function. Mutations in the TRPV4 gene are the cause of a spectrum of inherited diseases (or TRPV4-pathies), which include skeletal dysplasias, arthropathies, and neuropathies. There is little understanding of the pathophysiological mechanisms underlying these variable disease phenotypes, but it has been hypothesized that disease-causing mutations affect interaction with regulatory proteins. Here, we performed a mammalian protein-protein interaction trap (MAPPIT) screen to identify proteins that interact with the cytosolic N terminus of human TRPV4, a region containing the majority of disease-causing mutations. We discovered the zinc-finger domain-containing protein ZC4H2 as a TRPV4-interacting protein. In heterologous expression experiments, we found that ZC4H2 increases both the basal activity of human TRPV4 as well as Ca²⁺ responses evoked by ligands or hypotonic cell swelling. Using total internal reflection fluorescence (TIRF) microscopy, we further showed that ZC4H2 accelerates TRPV4 turnover at the plasma membrane. Overall, these data demonstrate that ZC4H2 is a positive modulator of TRPV4, and suggest a link between TRPV4 and ZC4H2-associated rare disorders, which have several neuromuscular symptoms in common with TRPV4-pathies.

Rnf220/Zc4h2-mediated monoubiquitylation of Phox2 is required for noradrenergic neuron development

Noradrenaline belongs to the monoamine system and is involved in cognition and emotional behaviors. Phox2a and Phox2b play essential but non-redundant roles during development of the locus coeruleus (LC), the main noradrenergic (NA) neuron center in the mammalian brain. The ubiquitin E3 ligase Rnf220 and its cofactor Zc4h2 participate in ventral neural tube patterning by modulating Shh/Gli signaling, and ZC4H2 mutation is associated with intellectual disability, although the mechanisms for this remain poorly understood. Here, we report that Zc4h2 and Rnf220 are required for the development of central NA neurons in the mouse brain. Both Zc4h2 and Rnf220 are expressed in developing LC-NA neurons. Although properly initiated at E10.5, the expression of genes associated with LC-NA neurons is not maintained at the later embryonic stages in mice with a deficiency of either Rnf220 or Zc4h2 In addition, we show that the Rnf220/Zc4h2 complex monoubiquitylates Phox2a/Phox2b, a process required for the full transcriptional activity of Phox2a/Phox2b. Our work reveals a role for Rnf220/Zc4h2 in regulating LC-NA neuron development, and this finding may be helpful for understanding the pathogenesis of ZC4H2 mutation-associated intellectual disability.

Establishing neuronal diversity in the spinal cord: a time and a place

The vertebrate spinal cord comprises multiple functionally distinct neuronal cell types arranged in characteristic positions. During development, these different types of neurons differentiate from transcriptionally distinct neural progenitors that are arrayed in discrete domains along the dorsal-ventral and anterior-posterior axes of the embryonic spinal cord. This organization arises in response to morphogen gradients acting upstream of a gene regulatory network, the architecture of which determines the spatial and temporal pattern of gene expression. In recent years, substantial progress has been made in deciphering the regulatory network that underlies the specification of distinct progenitor and neuronal cell identities. In this Review, we outline how distinct neuronal cell identities are established in response to spatial and temporal patterning systems, and outline novel experimental approaches to study the emergence and function of neuronal diversity in the spinal cord.