Abstract Inherited primary arrhythmia syndromes (IPAS) are genetic heart diseases associated with an elevated risk of sudden cardiac death, particularly in young individuals. Modelling these rare and serious conditions is essential to elucidate their mechanisms and to identify new treatments. Most genes involved in IPAS (e.g., congenital long‐QT syndrome, catecholaminergic polymorphic ventricular tachycardia, calcium‐release deficiency syndrome, Andersen‐Tawil syndrome, Timothy syndrome, calmodulinopathies, and short‐QT syndrome) are conserved in Caenorhabditis elegans , a model organism that offers powerful genetic tools for precise gene manipulation, including knock‐in, knock‐out, and knock‐down approaches. In vivo studies in C. elegans can be used to characterize the consequences of genetic variants (at molecular, cellular, tissue, and behavioural scales), to identify new regulatory proteins, and to perform drug testing. Here we summarize the characteristics of human IPAS and highlight the accumulating evidence that supports the utility of C. elegans as a simple yet powerful in vivo model for these diseases, capable of filling the gap between in vitro studies and complex transgenic animal models. image

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ABSTRACT During myogenesis, myocyte fusion leads to the formation of multinucleated muscle fibers, but how exactly this process is initiated remains poorly understood. Here, we performed single-cell RNA-sequencing on mouse somites from E9.5-E11.5 embryos, revealing multiple differentiation states during primary myogenesis. Among these, we identified two unexpected myocyte populations: one expressing both myomaker (Mymk) and myomixer (Mymx) (termed Mc1) and another expressing only Mymk (termed Mc2). Fluorescence in situ hybridization demonstrated that both populations are mononucleated and co-exist within the same somites, with only Mc1 persisting during secondary myogenesis. Lineage tracing using Mymx:Cre; RosaTdT mice demonstrated that the Mc2 cells arise from the Mc1. Mechanistically, we show that Mef2 and Rxr factors positively and negatively regulate Mymx expression, respectively. Additionally, RXRG interacts with MYOD1 and MYOG, modulating their transcriptional activity in luciferase assays. Collectively, our findings uncover two populations among the myocytes that drive primary and secondary fiber formation, challenging the traditional view of vertebrate muscle precursor homogeneity.

Abstract Small conductance Ca2+-activated K+ channels (SK channels) are widely expressed in the central nervous system, where they play a crucial role in modulating neuronal excitability. Recent studies have identified missense variants in the genes encoding SK2 and SK3 channels as the cause of two rare neurodevelopmental disorders: NEDMAB and ZLS3, respectively. Here, we used Caenorhabditis elegans as an in vivo model to investigate the functional consequences of these patient variants. The C. elegans orthologue KCNL-1 regulates neuronal and muscle excitability in the egg-laying system, a well-characterized model circuit. To visualize KCNL-1 expression and localization, we generated a fluorescent translational reporter at the endogenous kcnl-1 locus. We then introduced eight point mutations corresponding to pathogenic variants reported in NEDMAB or ZLS3 patients. Our study confirmed the molecular pathogenicity of the ZLS3-associated mutations, revealing a gain-of-function effect that led to increased in utero egg retention, likely due to electrical silencing of the egg-laying circuitry. NEDMAB mutations exhibited more complex phenotypic effects. Most caused a loss-of-function phenotype, indistinguishable from null mutants, while one displayed a clear gain-of-function effect. Additionally, a subset of NEDMAB variants altered KCNL-1 localization, suggesting an impairment in channel biosynthesis, trafficking or stability. These findings provide new insights into the molecular mechanisms underlying NEDMAB and ZLS3 physiopathology, enhancing our understanding of SK channel dysfunction in human disease. Moreover, they establish C. elegans as a robust and cost-effective in vivo model for rapid functional validation of new SK channel mutations, paving the way for future investigations.

In brief SLIT1 has recently been shown to regulate ovarian follicle development and female fertility. In this study, we elucidate SLIT1’s intracellular signaling mechanisms and transcriptional targets and further show that it acts in a redundant manner with SLIT2 in granulosa cells. Abstract Recent evidence has suggested that Slit1 regulates female fertility by acting on ovarian granulosa cells to antagonize gonadotropin-induced AKT signaling and luteinizing hormone (LH)-stimulated gene expression and to promote apoptosis and follicular atresia. We sought to further define the mechanisms of Slit1 action and verify its potential functional redundancy with Slit2 and Slit3. RNA-seq analyses of cultured granulosa cells treated with SLIT1 showed that SLIT1 upregulated 612 and downregulated 601 genes, which were determined to be involved in processes including cell metabolism, reproduction and development. Although Slit1 has been previously identified as a potential antagonist of LH action, RNA-seq analyses showed that exogenous SLIT1 antagonized the effect of LH on only 14.7% of its target genes. Analyses of gonadotropin-induced signaling cascades in granulosa cells showed that SLIT1 antagonizes follicle-stimulating hormone (FSH)- (but not LH-) induced FOXO1 phosphorylation. Analyses of mRNA levels of Slit1 target genes in granulosa cells treated with exogenous SLIT2 and SLIT3 showed SLIT2 (but not SLIT3) to be able to regulate most genes in a manner similar to SLIT1. Likewise, SLIT2 was able to antagonize FSH-stimulated AKT and FOXO1 signaling (and LH-stimulated AKT signaling), whereas SLIT3 could not. As for SLIT1, SLIT2 was also able to induce granulosa cells apoptosis in vitro. Loss of the SLIT receptor Robo1 did not inhibit the ability of SLIT1 or SLIT2 to antagonize AKT/FOXO1 signaling, suggesting that it does not function as their sole receptor. Together these findings suggest that Slit1 and Slit2 share common functions and mechanisms of action in the ovary.

Abstract Nicotinic acetylcholine receptors are widely expressed in the peripheral and central nervous systems. Mutations in acetylcholine receptor-subunit genes have been associated with neuromuscular diseases, such as arthrogryposis multiplex congenita (AMC) and epilepsy. We report a patient with arthrogryposis, severe muscle weakness and neurodevelopmental delay. During his first year of life, he developed therapy-refractory epilepsy. Using whole-exome sequencing, we identified the compound pathogenic variants c. 875G>A (p. Cys292Tyr) and c. 959delA (p. Gln320Argfs*25) in the cysteine-rich with epidermal growth factor-like domain protein 1 gene (CRELD1, NM_001077415.3). Recently, functional studies have shown that CRELD1 is a membrane-associated endoplasmic reticulum-resident protein disulphide isomerase that acts as a maturation enhancer of AChR biogenesis, thereby controlling the abundance of functional receptors at the cell surface. To test pathogenicity, we took advantage of the genetics and extremely rapid genome editing in Caenorhabditis elegans. We were able to model these heterozygous variants and observed a decrease in AChRs at the neuromuscular junction. Hence, our study identifies compound heterozygous CRELD1 variants responsible for a rare neurodevelopmental disorder characterized by arthrogryposis, muscle weakness and epilepsy.

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Abstract Myogenesis in amniotes occurs in two waves. Primary myotubes express slow myosin (often with fast myosin) and likely act as scaffolds for secondary myotubes, which express only fast myosin. The embryonic origins and relationships of these lineages, and their connection to satellite cells, remain unknown. Here, we combine a TCF-LEF/β-catenin signaling reporter with precise in vivo electroporation in avian embryos to trace limb muscle progenitors from early migration to fetal stages. We identify two distinct progenitor populations that coexist from the onset: reporter-positive cells give rise exclusively to primary myotubes, while reporter-negative cells generate secondary myotubes and satellite cells. We also reveal a previously unrecognized role for TCF-LEF/β-catenin signaling in spatially organizing the primary lineage via Cxcr4-mediated control of myoblast migration. These findings redefine the developmental origin of myogenic lineages, resolve a longstanding question in muscle biology, and provide a molecular framework for investigating how muscle fiber diversity emerges and how distinct lineages contribute to the functional specialization of skeletal muscle.

Abstract Muscle regeneration is impaired with aging, due to both intrinsic defects of muscle stem cells (MuSCs) and alterations of their niche. Here, we monitor the cells constituting the MuSC niche over time in young and old regenerating mouse muscle. Aging alters the expansion of all niche cells, with prominent phenotypes in macrophages that show impaired resolution of inflammation. RNA sequencing of FACS-isolated mononucleated cells uncovers specific profiles and kinetics of genes and molecular pathways in old versus young muscle cells, indicating that each cell type responds to aging in a specific manner. Moreover, we show that macrophages have an altered expression of Selenoprotein P (Sepp1). Macrophage-specific deletion of Sepp1 is sufficient to impair the acquisition of their restorative profile and causes inefficient skeletal muscle regeneration. When transplanted in aged mice, bone marrow from young WT mice, but not Sepp1-KOs, restores muscle regeneration. This work provides a unique resource to study MuSC niche aging, reveals that niche cell aging is asynchronous and establishes the antioxidant Selenoprotein P as a driver of age-related decline of muscle regeneration.

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Nicotine exposure elicits diverse behavioral changes, yet the underlying neural pathways and molecular mechanisms remain incompletely understood. Here, we demonstrate that chronic nicotine exposure markedly increases both the initiation and duration of reversals in Caenorhabditis elegans. Strikingly, these reversals were tightly coupled with the rhythmic body contractions of the defecation motor program (DMP). Through pharmacological, genetic, in situ electrophysiological, and calcium imaging analyses, we show that nicotine enhances the activity of the AVA interneuron via selective upregulation of ACR-16, a nicotinic ACh receptor critical for nicotine-induced motor coupling. Ablation of touch receptor neurons (TRNs) or inhibition of TRNs-mediated mechanosensation completely abolished this coupling. Furthermore, optogenetic activation of TRNs in nicotine-treated animals evoked stronger AVA depolarization, and nicotine amplified gentle touch-evoked reversals. Together, these findings reveal a potential interoceptive effect of nicotine mediated by sensitization of the TRNs-AVA mechanosensory pathway, providing new insight into the neural and molecular basis of nicotine’s modulation of sensory-motor coupling.

ABSTRACT Forty first-trimester human hearts were studied to lay groundwork for further studies of the mechanisms underlying congenital heart defects. We first sampled 49,227 cardiac nuclei from three fetuses at 8.6, 9.0, and 10.7 post-conceptional weeks (pcw) for single-nucleus RNA sequencing, enabling the distinction of six classes comprising 21 cell types. Improved resolution led to the identification of previously unappreciated cardiomyocyte populations and minority autonomic and lymphatic endothelial transcriptomes, among others. After integration with 5-7 pcw heart single-cell RNA-sequencing data, we identified a human cardiomyofibroblast progenitor preceding the diversification of cardiomyocyte and stromal lineages. Spatial transcriptomic analysis (six Visium sections from two additional hearts) was aided by deconvolution, and key spatial markers validated on sectioned and whole hearts in two- and three-dimensional space and over time. Altogether, anatomical-positional features, including innervation, conduction and subdomains of the atrioventricular septum, translate latent molecular identity into specialized cardiac functions. This atlas adds unprecedented spatial and temporal resolution to the characterization of human-specific aspects of early heart formation.

ABSTRACTSkeletal muscle repair is primarily driven by muscle stem cells (MuSCs) that regenerate damaged myofibers. The differentiation process of MuSCs into differentiated myofibers, known as adult myogenesis, is tightly regulated by various transcription factors, which involve precise spatio‐temporal gene expression patterns. Epigenetic factors play an important role in this regulation, as they modulate gene expression to maintain the balance between the different myogenic states. Histone lysine methyltransferases KMT sare key epigenetic regulators, with the SUV39 family being of particular interest for their role in gene repression via H3K9 methylation. This family comprises SUV39H1, SUV39H2, SETDB1, SETDB2, G9A, and GLP. While the functions of SUV39 family members have been well characterized during development in embryonic stem cells and in disease contexts such as cancer, their functions in adult stem cell populations, especially in MuSCs, are still not fully understood. Recent studies shed new light on how the SUV39 family influences muscle biology, particularly in regulating MuSCs fate and adult myogenesis. These enzymes are critical for maintaining the epigenetic landscape essential for effective muscle repair, as they regulate the transition between different myogenic states and ensure coordinated gene expression during regeneration. Here, we present a comprehensive overview of the functions of the SUV39 KMTs family in skeletal muscle biology, emphasizing their role in adult myogenesis and exploring the broader implications for muscle regeneration and related diseases.

Murine pancreatic endocrinogenesis has been extensively studied, but human data remain scarce due to limited sample availability. Here, we first built a large collection of human embryonic and fetal pancreases covering the first trimester of pregnancy to explore human endocrinogenesis. Using an experimental pipeline combining in toto staining, tissue clearing, and light-sheet fluorescence microscopy, we show that insulin-, glucagon-, and somatostatin-positive cells appear simultaneously at Carnegie stage (CS) 16. This contrasts with rodents, in which glucagon-positive cells appear first, followed by insulin-positive and, finally, somatostatin-positive cells and highlights interspecies differences. We also detected bihormonal endocrine cells in 7 of 9 human pancreases between CS16 and CS18, which were no longer detected at later stages. We observed that cell distribution within human fetal islets resembles adult mouse islets, with a core of β-cells surrounded by α- and δ-cells, differing from a more complex arrangement in adult human islets. This, in connection with the small size of human fetal islets when compared with adult islets, suggests that adult human islets may form by fusion of preexisting islets, in contrast to the mouse fission model. Together, our study provides a detailed and comprehensive description of the spatiotemporal dynamics of human pancreatic endocrinogenesis. Article Highlights Data on human pancreas development are limited and derived from two-dimensional staining. We overcome this using in toto staining, tissue clearing, and light-sheet imaging. We sought to understand when and where endocrine cells first emerge and how they cluster. First, endocrine cell types appear simultaneously, and early pancreases contain bihormonal cells. There are morphometric differences between fetal and adult islets. We propose a mechanism of adult islet formation by fusion: a new base to reconstitute in vitro islet neogenesis.

Abstract Habituating to the constant stimuli in the environment is a critical learning process conserved across species. We use a larval zebrafish visual response to sudden darkness as a model for studying habituation learning, where zebrafish reduce their responses to repeated stimulations. In this paradigm, treatment with estradiol strongly increases learning rate, resulting in more strongly suppressed responses. We used mutant lines for the estrogen receptors (ERs)—esr1, esr2a, esr2b, gper1—in an attempt to identify the receptor(s) mediating these effects. These experiments failed to identify a necessary receptor (or combination of receptors). Surprisingly, esr1, esr2a, and gper1 mutants showed weak but consistent increases in habituation, indicating that these receptors suppress habituation learning. These experiments demonstrate that estradiol is a complex modulator of learning in our model, where the learning-promoting effects are mediated by an unidentified estradiol target, and the classical estrogen receptors act in competition to subtly suppress learning.

AbstractImmune checkpoint inhibitors (ICIs) have revolutionized cancer therapy, and the association with immune-related adverse events (irAEs) is well-established. However, cerebellar irAEs are poorly defined and their relationship with paraneoplastic disorders remains unclear. Our aim was (i) to characterize cerebellar irAE; (ii) to compare it with paraneoplastic cerebellar ataxia (PCA). We performed a multicenter, retrospective, cohort study of patients developing new-onset, immune-mediated, isolated/predominant cerebellar dysfunction after ICI administration. In addition, a systematic review following PRISMA guidelines was performed. Cerebellar irAE cases were compared with a consecutive cohort of patients with PCA. Overall, 35 patients were included, of whom 12 were original cases (males: 25/35 (71%), median age: 65 [range: 20–82]). The most frequent tumor was non-small cell lung cancer (12/35, 34%). Anti-PD1 were adopted in 19/35 (54%). Symptoms developed at a median of 11 weeks after ICI onset. Neuronal antibodies were detected in 15/31 patients tested (48%). Cerebrospinal fluid was inflammatory in 25/30 (83%). Magnetic resonance imaging showed cerebellar hyperintensities in 8/35 (23%). Immunotherapy was applied in 33/35 cases (94%), and most patients improved with residual disability (16/35, 46%). When compared with a series of PCA (n = 15), the cerebellar irAE group was significantly more associated with male sex, lung cancer (rather than gynecological/breast cancers), isolated ataxia, and a better outcome. We provide a detailed characterization of cerebellar irAE. Compared to PCA, differences exist in terms of tumor association, clinical features, and outcome. Clinical presentation-antibody-tumor triad in the ICI group only partially reflects the associations described in paraneoplastic disorders.

Abstract Objectives To investigate the association between human leukocyte antigen (HLA) and paraneoplastic neurological syndromes (PNS) with Hu antibodies, and potential specificities according to clinical presentation and cancer status. Methods HLA genotypes at four-digit resolution were imputed from available genome-wide association data. Allele carrier frequencies were compared between patients (whole cohort, n = 100, and according to clinical presentation and cancer status) and matched healthy controls (n = 508) using logistic regression controlled by the three main principal components. Results The clinical presentation of 100 anti-Hu patients involved the central nervous system (28, 28%), the peripheral nervous system (36, 36%) or both combined (36, 36%). Cancer diagnosis was certain in 75 (75%). HLA association analyses revealed that anti-Hu PNS patients were more frequently carriers of DQA1*05:01 (39% vs. 19%, OR = 2.8 [1.74–4.49]), DQB1*02:01 (39% vs. 18%, OR = 2.88 [1.79–4.64]) and DRB1*03:01 (41% vs. 19%, OR = 2.92 [1.80–4.73]) than healthy controls. Remarkably, such DR3 ~ DQ2 association was absent in patients with pure central involvement, but more specific to those manifesting with peripheral involvement: DQA1*05:01 (OR = 3.12 [1.48–6.60]), DQB1*02:01 (OR = 3.35 [1.57–7.15]) and DRB1*03:01 (OR = 3.62 [1.64–7.97]); being even stronger in cases with sensory neuropathy, DQA1*05:01 (OR = 4.41 [1.89–10.33]), DQB1*02:01 (OR = 4.85 [2.04–11.53]) and DRB1*03:01 (OR = 5.79 [2.28–14.74]). Similarly, DR3 ~ DQ2 association was only observed in patients with cancer. Discussion Patients with anti-Hu PNS show different HLA profiles according to clinical presentation and, probably, cancer status, suggesting pathophysiological differences.

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Abstract Anti-IgLON5 disease is a rare and likely underdiagnosed subtype of autoimmune encephalitis. The disease displays a heterogeneous phenotype that includes sleep, movement and bulbar-associated dysfunction. The presence of IgLON5-antibodies in CSF/serum, together with a strong association with HLA-DRB1*10:01∼DQB1*05:01, supports an autoimmune basis. In this study, a multicentric human leukocyte antigen (HLA) study of 87 anti-IgLON5 patients revealed a stronger association with HLA-DQ than HLA-DR. Specifically, we identified a predisposing rank-wise association with HLA-DQA1*01:05∼DQB1*05:01, HLA-DQA1*01:01∼DQB1*05:01 and HLA-DQA1*01:04∼DQB1*05:03 in 85% of patients. HLA sequences and binding cores for these three DQ heterodimers were similar, unlike those of linked DRB1 alleles, supporting a causal link to HLA-DQ. This association was further reflected in an increasingly later age of onset across each genotype group, with a delay of up to 11 years, while HLA-DQ-dosage dependent effects were also suggested by reduced risk in the presence of non-predisposing DQ1 alleles. The functional relevance of the observed HLA-DQ molecules was studied with competition binding assays. These proof-of-concept experiments revealed preferential binding of IgLON5 in a post-translationally modified, but not native, state to all three risk-associated HLA-DQ receptors. Further, a deamidated peptide from the Ig2-domain of IgLON5 activated T cells in two patients, compared with one control carrying HLA-DQA1*01:05∼DQB1*05:01. Taken together, these data support a HLA-DQ-mediated T-cell response to IgLON5 as a potentially key step in the initiation of autoimmunity in this disease.

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Abstract Encephalitis with antibodies to leucine-rich glioma-inactivated 1 (LGI1-Ab-E) is a common form of autoimmune encephalitis, presenting with seizures and neuropsychiatric changes, predominantly in older males. More than 90% of patients carry the human leukocyte antigen (HLA) class II allele, HLA-DRB1*07:01. However, this is also present in 25% of healthy controls. Therefore, we hypothesized the presence of additional genetic predispositions. In this genome-wide association study and meta-analysis, we studied a discovery cohort of 131 French LGI1-Ab-E and a validation cohort of 126 American, British and Irish LGI1-Ab-E patients, ancestry-matched to 2613 and 2538 European controls, respectively. Outside the known major HLA signal, we found two single nucleotide polymorphisms at genome-wide significance (P < 5 × 10−8), implicating PTPRD, a protein tyrosine phosphatase, and LINC00670, a non-protein coding RNA gene. Meta-analysis defined four additional non-HLA loci, including the protein coding COBL gene. Polygenic risk scores with and without HLA variants proposed a contribution of non-HLA loci. In silico network analyses suggested LGI1 and PTPRD-mediated interactions via the established receptors of LGI1, ADAM22 and ADAM23. Our results identify new genetic loci in LGI1-Ab-E. These findings present opportunities for mechanistic studies and offer potential markers of susceptibility, prognostics and therapeutic responses.

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ABSTRACT Terminal selectors are transcription factors that control neuronal identity by regulating expression of key effector molecules, such as neurotransmitter biosynthesis proteins and ion channels. Whether and how terminal selectors control neuronal connectivity is poorly understood. Here, we report that UNC-30 (PITX2/3), the terminal selector of GABA nerve cord motor neurons in Caenorhabditis elegans, is required for neurotransmitter receptor clustering, a hallmark of postsynaptic differentiation. Animals lacking unc-30 or madd-4B, the short isoform of the motor neuron-secreted synapse organizer madd-4 (punctin/ADAMTSL), display severe GABA receptor type A (GABAAR) clustering defects in postsynaptic muscle cells. Mechanistically, UNC-30 acts directly to induce and maintain transcription of madd-4B and GABA biosynthesis genes (e.g. unc-25/GAD, unc-47/VGAT). Hence, UNC-30 controls GABAA receptor clustering in postsynaptic muscle cells and GABA biosynthesis in presynaptic cells, transcriptionally coordinating two crucial processes for GABA neurotransmission. Further, we uncover multiple target genes and a dual role for UNC-30 as both an activator and a repressor of gene transcription. Our findings on UNC-30 function may contribute to our molecular understanding of human conditions, such as Axenfeld–Rieger syndrome, caused by PITX2 and PITX3 gene variants.

Abstract Background Fine characterization of gene expression patterns is crucial to understand many aspects of embryonic development. The chicken embryo is a well-established and valuable animal model for developmental biology. The period spanning from the third to sixth embryonic days (E3 to E6) is critical for many organ developments. Hybridization chain reaction RNA fluorescent in situ hybridization (HCR RNA-FISH) enables multiplex RNA detection in thick samples including embryos of various animal models. However, its use is limited by tissue opacity. Results We optimized HCR RNA-FISH protocol to efficiently label RNAs in whole mount chicken embryos from E3.5 to E5.5 and adapted it to ethyl cinnamate (ECi) tissue clearing. We show that light sheet imaging of HCR RNA-FISH after ECi clearing allows RNA expression analysis within embryonic tissues with good sensitivity and spatial resolution. Finally, whole mount immunofluorescence can be performed after HCR RNA-FISH enabling as exemplified to assay complex spatial relationships between axons and their environment or to monitor GFP electroporated neurons. Conclusions We could extend the use of HCR RNA-FISH to older chick embryos by optimizing HCR RNA-FISH and combining it with tissue clearing and 3D imaging. The integration of immunostaining makes possible to combine gene expression with classical cell markers, to correlate expressions with morphological differentiation and to depict gene expressions in gain or loss of function contexts. Altogether, this combined procedure further extends the potential of HCR RNA-FISH technique for chicken embryology.

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Cilia play critical roles in cell signal transduction and organ development. Defects in cilia function result in a variety of genetic disorders. Cep290 is an evolutionarily conserved ciliopathy protein that bridges the ciliary membrane and axoneme at the basal body (BB) and plays critical roles in the initiation of ciliogenesis and TZ assembly. How Cep290 is maintained at BB and whether axonemal and ciliary membrane localized cues converge to determine the localization of Cep290 remain unknown. Here, we report that the Cep131-Cep162 module near the axoneme and the Cby-Fam92 module close to the membrane synergistically control the BB localization of Cep290 and the subsequent initiation of ciliogenesis in Drosophila. Concurrent deletion of any protein of the Cep131-Cep162 module and of the Cby-Fam92 module leads to a complete loss of Cep290 from BB and blocks ciliogenesis at its initiation stage. Our results reveal that the first step of ciliogenesis strictly depends on cooperative and retroactive interactions between Cep131-Cep162, Cby-Fam92 and Cep290, which may contribute to the complex pathogenesis of Cep290-related ciliopathies.

AbstractCell polarity mechanisms allow the formation of specialized membrane domains with unique protein compositions, signalling properties, and functional characteristics. By analyzing the localization of potassium channels and proteins belonging to the dystrophin-associated protein complex, we reveal the existence of distinct planar-polarized membrane compartments at the surface of C. elegans muscle cells. We find that muscle polarity is controlled by a non-canonical Wnt signalling cascade involving the ligand EGL-20/Wnt, the receptor CAM-1/Ror, and the intracellular effector DSH-1/Dishevelled. Interestingly, classical planar cell polarity proteins are not required for this process. Using time-resolved protein degradation, we demonstrate that –while it is essentially in place by the end of embryogenesis– muscle polarity is a dynamic state, requiring continued presence of DSH-1 throughout post-embryonic life. Our results reveal the unsuspected complexity of the C. elegans muscle membrane and establish a genetically tractable model system to study cellular polarity and membrane compartmentalization in vivo.

AbstractAtaxia with anti-regulator of G-protein signaling 8 autoantibodies (RGS8-Abs) is an autoimmune disease recently described in four patients. The present study aimed to identify other patients with RGS8-Abs, describe their clinical features, including the link between RGS8-related autoimmune cerebellar ataxia (ACA) and cancer. Patients with RGS8-Abs were identified retrospectively in the biological collections of the French Reference Center for Paraneoplastic Neurological Syndrome and the University of California San Francisco Center for Encephalitis and Meningitis. Clinical data were collected, and cerebrospinal fluid, serum, and tumor pathological samples were retrieved to characterize the autoantibodies and the associated malignancies. Only three patients with RGS8-Abs were identified. All of them presented with a pure cerebellar ataxia of mild to severe course, unresponsive to current immunotherapy regimens for ACA. Two patients presented with a Hodgkin lymphoma of the rare specific subtype called nodular lymphocyte-predominant Hodgkin lymphoma, with very mild extension. Autoantibodies detected in all patients enriched the same epitope on the RGS8 protein, which is an intracellular protein physiologically expressed in Purkinje cells but also ectopically expressed specifically in lymphoma cells of patients with RGS8-related ACA. The present results and those of the four cases previously described suggest that RGS8-Abs define a new paraneoplastic neurological syndrome of extreme rarity found mostly in middle-aged males that associates pure cerebellar ataxia and a particular lymphoma specifically expressing the RGS8 antigen. As in other paraneoplastic ACA with intracellular antigen, the disease course is severe, and patients tend to exhibit a poor response to immune therapy.

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Abstract Background Herpes simplex virus encephalitis (HSE) frequently triggers secondary anti-N-methyl-d-aspartate receptor encephalitis (NMDARE), but markers predicting the occurrence of this entity (HSE-NMDARE) are lacking. Methods We conducted a retrospective description of patients with HSE-NMDARE diagnosed between July 2014 and August 2022 and compared them to both patients with regular forms of HSE and NMDARE. Results Among the 375 patients with NMDARE, 13 HSE-NMDARE were included. The median age was 19 years (0.5–73), 4/13 (31%) were children < 4 years old, and 7/13 (54%) were male. The median time between HSE and NMDARE onset was 30 days (21–46). During NMDARE, symptoms differed from HSE, including increased behavioral changes (92% vs 23%, p = 0.008), movements disorders (62% vs 0%, p = 0.013), and dysautonomia (54% vs 0%, p = 0.041). Compared to 21 patients with regular HSE, patients with HSE-NMDARE more often achieved severity-associated criteria on initial MRIs, with extensive lesions (11/11, 100% vs 10/21, 48%, p = 0.005) and bilateral diffusion-weighted imaging sequence abnormalities (9/10, 90% vs 6/21, 29%, p = 0.002). Compared to 198 patients with regular NMDARE, patients with HSE-NMDARE were more frequently males (7/13, 54% vs 43/198, 22%; p = 0.015) and children < 4 (4/13, 31% vs 14/198, 7%; p = 0.016), with a worse 12-month mRS (2[1–6] vs 1[0–6], p = 0.023). Conclusions Herein, patients with HSE-NMDARE have a poorer long-term prognosis than patients with regular NMDARE. We report a greater rate of severity-associated criteria on initial MRIs for HSE-NMDARE compared to regular HSE, which may help identify patients with higher risk of HSE-NMDARE.

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Abstract Background Herpes simplex virus encephalitis (HSE) frequently triggers secondary anti-N-methyl-d-aspartate receptor encephalitis (NMDARE), but markers predicting the occurrence of this entity (HSE-NMDARE) are lacking. Methods We conducted a retrospective description of patients with HSE-NMDARE diagnosed between July 2014 and August 2022 and compared them to both patients with regular forms of HSE and NMDARE. Results Among the 375 patients with NMDARE, 13 HSE-NMDARE were included. The median age was 19 years (0.5–73), 4/13 (31%) were children < 4 years old, and 7/13 (54%) were male. The median time between HSE and NMDARE onset was 30 days (21–46). During NMDARE, symptoms differed from HSE, including increased behavioral changes (92% vs 23%, p = 0.008), movements disorders (62% vs 0%, p = 0.013), and dysautonomia (54% vs 0%, p = 0.041). Compared to 21 patients with regular HSE, patients with HSE-NMDARE more often achieved severity-associated criteria on initial MRIs, with extensive lesions (11/11, 100% vs 10/21, 48%, p = 0.005) and bilateral diffusion-weighted imaging sequence abnormalities (9/10, 90% vs 6/21, 29%, p = 0.002). Compared to 198 patients with regular NMDARE, patients with HSE-NMDARE were more frequently males (7/13, 54% vs 43/198, 22%; p = 0.015) and children < 4 (4/13, 31% vs 14/198, 7%; p = 0.016), with a worse 12-month mRS (2[1–6] vs 1[0–6], p = 0.023). Conclusions Herein, patients with HSE-NMDARE have a poorer long-term prognosis than patients with regular NMDARE. We report a greater rate of severity-associated criteria on initial MRIs for HSE-NMDARE compared to regular HSE, which may help identify patients with higher risk of HSE-NMDARE.

IntroductionMononeuritis multiplex is frequently related to vasculitic neuropathy and has been reported only sporadically as an adverse event of immune checkpoint inhibitors.MethodsCase series of three patients with mononeuritis multiplex—all with mesothelioma—identified in the databases of two French clinical networks (French Reference Center for Paraneoplastic Neurological Syndromes, Lyon; OncoNeuroTox, Paris; January 2015–October 2022) set up to collect and investigate n-irAEs on a nationwide level.ResultsThree patients (male; median age 86 years; range 72–88 years) had pleural mesothelioma and received 10, 4, and 6 cycles, respectively, of first-line nivolumab plus ipilimumab combined therapy. In patient 1, the neurological symptoms involved the median nerves, and in the other two patients, there was a more diffuse distribution; the symptoms were severe (common terminology criteria for adverse events, CTCAE grade 3) in all patients. Nerve conduction studies indicated mononeuritis multiplex in all patients. Peripheral nerve biopsy demonstrated necrotizing vasculitis in patients 1 and 3 and marked IgA deposition without inflammatory lesions in patient 2. Immune checkpoint inhibitors were permanently withdrawn, and corticosteroids were administered to all patients, leading to complete symptom regression (CTCAE grade 0, patient 2) or partial improvement (CTCAE grade 2, patients 1 and 3). During steroid tapering, patient 1 experienced symptom recurrence and spreading to other nerve territories (CTCAE grade 3); he improved 3 months after rituximab and cyclophosphamide administration.DiscussionWe report the occurrence of mononeuritis multiplex, a very rare adverse event of immune checkpoint inhibitors, in the three patients with mesothelioma. Clinicians must be aware of this severe, yet treatable adverse event.

Abstract Leak potassium (K+) currents, conducted by two-pore domain K+ (K2P) channels, are critical for the stabilization of the membrane potential. The effect of K2P channels on motor rhythm remains enigmatic. We show here that the K2P TWK-40 contributes to the rhythmic defecation motor program (DMP) in Caenorhabditis elegans. Disrupting TWK-40 suppresses the expulsion defects of nlp-40 and aex-2 mutants. By contrast, a gain-of-function (gf) mutant of twk-40 significantly reduces the expulsion frequency per DMP cycle. In situ whole-cell patch clamping demonstrates that TWK-40 forms an outward current that hyperpolarize the resting membrane potential of dorsorectal ganglion ventral process B (DVB), an excitatory GABAergic motor neuron that activates expulsion muscle contraction. In addition, TWK-40 substantially contributes to the rhythmic activity of DVB. Specifically, DVB Ca2+ oscillations exhibit obvious defects in loss-of-function (lf) mutant of twk-40. Expression of TWK-40(gf) in DVB recapitulates the expulsion deficiency of the twk-40(gf) mutant, and inhibits DVB Ca2+ oscillations in both wild-type and twk-40(lf) animals. Moreover, DVB innervated enteric muscles also exhibit rhythmic Ca2+ defects in twk-40 mutants. In summary, these findings establish TWK-40 as a crucial neuronal stabilizer of DMP, linking leak K2P channels with rhythmic motor activity.

AbstractHuman embryonic bone and joint formation is determined by coordinated differentiation of progenitors in the nascent skeleton. The cell states, epigenetic processes and key regulatory factors that underlie lineage commitment of these cells remain elusive. Here we applied paired transcriptional and epigenetic profiling of approximately 336,000 nucleus droplets and spatial transcriptomics to establish a multi-omic atlas of human embryonic joint and cranium development between 5 and 11 weeks after conception. Using combined modelling of transcriptional and epigenetic data, we characterized regionally distinct limb and cranial osteoprogenitor trajectories across the embryonic skeleton and further described regulatory networks that govern intramembranous and endochondral ossification. Spatial localization of cell clusters in our in situ sequencing data using a new tool, ISS-Patcher, revealed mechanisms of progenitor zonation during bone and joint formation. Through trajectory analysis, we predicted potential non-canonical cellular origins for human chondrocytes from Schwann cells. We also introduce SNP2Cell, a tool to link cell-type-specific regulatory networks to polygenic traits such as osteoarthritis. Using osteolineage trajectories characterized here, we simulated in silico perturbations of genes that cause monogenic craniosynostosis and implicate potential cell states and disease mechanisms. This work forms a detailed and dynamic regulatory atlas of bone and cartilage maturation and advances our fundamental understanding of cell-fate determination in human skeletal development.

Continuity of behaviors requires animals to make smooth transitions between mutually exclusive behavioral states. Neural principles that govern these transitions are not well understood. Caenorhabditis elegans spontaneously switch between two opposite motor states, forward and backward movement, a phenomenon thought to reflect the reciprocal inhibition between interneurons AVB and AVA. Here, we report that spontaneous locomotion and their corresponding motor circuits are not separately controlled. AVA and AVB are neither functionally equivalent nor strictly reciprocally inhibitory. AVA, but not AVB, maintains a depolarized membrane potential. While AVA phasically inhibits the forward promoting interneuron AVB at a fast timescale, it maintains a tonic, extrasynaptic excitation on AVB over the longer timescale. We propose that AVA, with tonic and phasic activity of opposite polarities on different timescales, acts as a master neuron to break the symmetry between the underlying forward and backward motor circuits. This master neuron model offers a parsimonious solution for sustained locomotion consisted of mutually exclusive motor states.

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Overactivation of the transforming growth factor-β (TGFβ) signaling in Duchenne muscular dystrophy (DMD) is a major hallmark of disease progression, leading to fibrosis and muscle dysfunction. Here, we investigated the role of SETDB1 (SET domain, bifurcated 1), a histone lysine methyltransferase involved in muscle differentiation. Our data show that, following TGFβ induction, SETDB1 accumulates in the nuclei of healthy myotubes while being already present in the nuclei of DMD myotubes where TGFβ signaling is constitutively activated. Transcriptomics revealed that depletion of SETDB1 in DMD myotubes leads to down-regulation of TGFβ target genes coding for secreted factors involved in extracellular matrix remodeling and inflammation. Consequently, SETDB1 silencing in DMD myotubes abrogates the deleterious effect of their secretome on myoblast differentiation by impairing myoblast pro-fibrotic response. Our findings indicate that SETDB1 potentiates the TGFβ–driven fibrotic response in DMD muscles, providing an additional axis for therapeutic intervention.

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Evolutionary transitions from egg laying (oviparity) to live birth (viviparity) are common across various taxa. Many species also exhibit genetic variation in egg-laying mode or display an intermediate mode with laid eggs containing embryos at various stages of development. Understanding the mechanistic basis and fitness consequences of such variation remains experimentally challenging. Here, we report highly variable intra-uterine egg retention across 316 Caenorhabditis elegans wild strains, some exhibiting strong retention, followed by internal hatching. We identify multiple evolutionary origins of such phenotypic extremes and pinpoint underlying candidate loci. Behavioral analysis and genetic manipulation indicates that this variation arises from genetic differences in the neuromodulatory architecture of the egg-laying circuitry. We provide experimental evidence that while strong egg retention can decrease maternal fitness due to in utero hatching, it may enhance offspring protection and confer a competitive advantage. Therefore, natural variation in C. elegans egg-laying behaviour can alter an apparent trade-off between different fitness components across generations. Our findings highlight underappreciated diversity in C. elegans egg-laying behavior and shed light on its fitness consequences. This behavioral variation offers a promising model to elucidate the molecular changes in a simple neural circuit underlying evolutionary shifts between alternative egg-laying modes in invertebrates.