Abstract Biallelic variants in PYROXD1 are associated with a life limiting muscle and connective tissue disorder characterised by generalised muscle weakness, breathing and feeding difficulties, distal laxity, hypernasal speech, blue sclera and osteopenia. PYROXD1 encodes an oxidoreductase implicated in mitochondrial function and tRNA ligase activity. Herein we present the first comprehensive suite of mouse models designed to elucidate PYROXD1 redox functions and the underlying pathogenetic basis for PYROXD1 disorders. A LacZ reporter strain reveals ubiquitous expression of Pyroxd1, particularly in the developing head, eye, heart and skin. Complete knockout (KO) of Pyroxd1 resulted in embryonic lethality between ED4.5–E9.5, suggesting Pyroxd1 performs a unique function during embryogenesis that cannot be substituted by other redox enzymes. Skeletal muscle tissue-specific KO, or stage-specific tamoxifen-induced KO during gestation or post-weaning, were viable but not sustainable models. Tamoxifen-inducible KO cell lines derived from these models provide valuable tools for dissecting Pyroxd1 function. Homozygous mice harbouring the recurrent human variant NM_024854.5:c.464A > G;p.(N155S), termed Pyroxd1 N155S, phenocopied a severe PYROXD1 disorder, presenting from ~ 10 weeks of age with a progressive myopathy, myofibrillar disorganisation, decreased contractile strength, muscle hypotrophy and osteopenia. Conversely, homozygous Pyroxd1 N155G mice, created incidentally during CRISPR editing, were phenotypically normal and provide an important benign control. Proteomic analyses reveal distinct molecular signatures between acute Pyroxd1 KO and Pyroxd1 N155S models, highlighting differential effects of complete loss-of-function (KO) compared to partial enzymatic activity (N155S). Pyroxd1 activity is critical for numerous cell essential processes, including protein biosynthesis and turnover, tRNA ligase complex activity and the unfolded protein response, mitochondrial respiratory chain function (especially complex 1), with an implicated broader role in the exon-ligation step of pre-mRNA splicing. Together, these murine Pyroxd1 models establish an enabling platform for gaining mechanistic insight and guiding the path of future therapeutic development for PYROXD1 disorders.

Paediatric acute-onset neuropsychiatric syndrome (PANS) is a syndrome of infection-provoked abrupt-onset obsessive-compulsive disorder (OCD) or eating restriction. Based on the hypothesis that PANS is an epigenetic disorder of immune and brain function, a full-spectrum medicinal cannabinoid-rich low-THC cannabis (NTI164) was selected for its known epigenetic and immunomodulatory properties. This open-label trial of 14 children with chronic-relapsing PANS (mean age 12·1 years; range 4–17; 71 % male) investigated the safety and efficacy of 20 mg/kg/day NTI164 over 12 weeks. Clinical outcomes were assessed using gold standard tools. To define the biological effects of NTI164, blood samples were collected pre- and post-treatment for bulk and single-cell transcriptomics, proteomics, phosphoproteomics, and DNA methylation. NTI164 was well-tolerated, and 12 weeks of treatment decreased the mean Clinical Global Impression-Severity (CGI-S) score from 4·8 to 3·3 (p = 0·002). Significant improvements were observed in emotional regulation (RCADS-P, p < 0·0001), obsessive-compulsive disorder (CYBOCS-II, p = 0·0001), tics (YGTSS, p < 0·0001), attention-deficit hyperactivity disorder (Conner's, p = 0·028), and overall quality of life (EQ-5D-Y, p = 0·011). At baseline, the multi-omic approach revealed that leucocytes from patients with PANS had dysregulated epigenetic (chromatin structure, DNA methylation, histone modifications, transcription factors), ribosomal, mRNA processing, immune, and signalling pathways. These pathways were significantly modulated by NTI164 treatment. NTI164 shows promise as a disease-modifying therapeutic for PANS. Multi-omics reveal broad epigenetic and immune dysregulation in patients, which was modified by NTI164, presenting epigenetic machinery as a therapeutic target in PANS.

α-Synuclein has been extensively studied for its role in Parkinson's disease, however its native function remains unclear. Several lines of evidence suggest it modulates presynaptic function. As many presynaptic proteins have their functions regulated by phosphorylation, we sought to determine whether α-synuclein, a known phosphoprotein, might similarly have phospho-dependent roles. We identified two residues in α-synuclein, Ser42 and Thr81, that undergo activity-dependent phosphorylation in response to neuronal depolarisation. We employed a molecular replacement strategy, introducing α-synuclein phosphovariants into neuronal cultures from α-synuclein knockout (KO) mice (of either sex), and revealed that ablating phosphorylation at Thr81 altered the subcellular distribution of synaptobrevin-2/VAMP2, a crucial fusogenic vesicular SNARE protein and known binding partner of α-synuclein. Ablating phosphorylation of α-synuclein at Thr81 specifically accelerated endocytic retrieval of synaptobrevin-2 during stimulation without impacting global endocytosis, evoked exocytosis, or the size of the recycling pool. Conversely, mimicking phosphorylation at Thr81 augmented post-stimulation retrieval of synaptobrevin-2. This suggests that activity-dependent phosphorylation of Thr81 modulates the trafficking of synaptobrevin-2 to direct its retrieval via different endocytic pathways, thereby impacting presynaptic functionality and plasticity. Significance statement The presynaptic proteins α-synuclein has been extensively studied for its role in Parkinson's disease, however its native function remains unclear. As many presynaptic proteins have their functions regulated by phosphorylation, we sought to determine whether α-synuclein, a known phosphoprotein, might similarly have phospho-dependent roles. We identified two residues in α-synuclein, Ser42 and Thr81, that undergo activity-dependent phosphorylation Mimicking or ablating phosphorylation of α-synuclein at Thr81 specifically and differentially altered retrieval of synaptobrevin-2 without impacting global endocytosis, evoked exocytosis, or the size of the recycling pool. This suggests that activity-dependent phosphorylation of Thr81 modulates the trafficking of synaptobrevin-2 to direct its retrieval via different endocytic pathways, thereby impacting presynaptic functionality and plasticity.

This study investigated how cumulative environmental exposures influence offspring behaviour and inflammation-related molecular signatures in the brain and peripheral immune system. A novel "triple-hit" mouse model was developed using C57Bl/6JAusB mice (N = 70), combining preconceptual social stress, antenatal high-fat diet, and a postnatal immune challenge (poly(I:C), 10 mg/kg). At 12 weeks, offspring underwent behavioural tests relevant to neurodevelopmental disorders (NDDs), including the Elevated Plus Maze, 3-Chamber Social Preference, Self-Grooming, and Marble Burying. A composite NDD-risk index was calculated. Single-cell RNA sequencing (scRNA-seq) and bulk proteomics were performed on male triple-hit offspring to identify differentially expressed genes and proteins associated with inflammatory pathways. Male triple-hit offspring showed elevated NDD-related behavioural risk and social deficits, not observed in females. scRNA-seq revealed altered inflammatory and ribosomal pathways in brain glia and peripheral immune cells. Proteomic analysis showed decreased abundance of proteins involved in inflammation, translation, chromatin remodelling, and synaptic function in both brain and blood. Combined environmental stressors may drive male-specific behavioural and inflammatory changes relevant to NDDs. The identification of overlapping inflammatory signatures in brain and peripheral immune cells supports a role for shared immune mechanisms in brain–immune axis dysfunction. However, these pathway-level findings should be interpreted as preliminary hypotheses and warrant independent validation to confirm their mechanistic significance.

Patient iPSC-derived cerebral organoids are a leading human model of Alzheimers disease, yet their proteome has never been benchmarked against human disease. Clinical cohorts now nominate thousands of biomarkers and drug targets across three proteomic platforms, and whether patient organoids capture these candidates is unknown. Here, we profile AD and control cerebral organoids containing neurons, astrocytes, and microglia on the three platforms driving clinical discovery, mass spectrometry, SomaScan, and Olink, in both conditioned media and lysate. Benchmarked against 121 studies and clinical cohorts of over 17,000 plasma, CSF, and cortex samples, patient organoids detect almost every nominated candidate and reproduce the disease-associated change in roughly one in four of the most reproducible. This convergence spans plasma, CSF, and cortex, and extends to synaptic, mitochondrial, and proteostatic biology. We provide the first multi-platform reference proteome of a patient-derived AD model, establishing it as a translationally relevant system for studying AD.

Paediatric Acute-Onset Neuropsychiatric Syndrome (PANS) is characterised by abrupt onset obsessive compulsive disorder and regression in neurodevelopmental skills, triggered by infection or stress. Whether PANS is a distinct entity or part of a neurodevelopmental spectrum is uncertain, and its pathophysiology remains unclear. We show that children with PANS (n = 32) and other non-PANS (n = 68) neurodevelopmental disorders (total n = 100) have higher reported early childhood infections and a loss of previously acquired developmental skills compared to neurotypical controls (n = 58). Children with PANS have normal routine immune testing, however bulk RNA-sequencing (PANS n = 20 vs controls n = 15) revealed upregulated pathways in ribosomal biogenesis and RNA methyltransferases, and downregulated pathways in diverse cellular functions such as mitochondrial activity, cell signalling, endocytosis, and immune responses. Single-cell RNA-sequencing (PANS n = 2 vs controls n = 2) confirmed these findings but showed heterogeneity across immune cell types. Toll-like receptor stimulation assay using peripheral blood mononuclear cells revealed reduced TNF and interleukin-6 responses in PANS patients (n = 7) compared to controls (n = 7). RNA sequencing before and after intravenous immunoglobulin treatment in PANS patients (n = 9 vs controls n = 10) revealed reversal of the dysregulated ribosomal, epigenetic, and cell signaling pathways. Given the central role of the immune system in synaptic pruning and neurodevelopment, these insights provide rationale for novel epigenetic and immune modulating therapies to optimize neurodevelopmental trajectories and minimize neuropsychiatric impairment in PANS.

Nuclear filamentous actin (F-actin) is emerging as a key regulator of genome stability[1][1]–[6][2]. During replication stress, transient bursts of nuclear actin assembly in S-phase promote fork remodelling and repair[3][3],[4][4], but how these bursts are initiated, regulated, and whether nuclear F-actin also act on DNA lesions inherited across cell cycles, remains unknown. Here, we show that replication stress induces nuclear actin assembly at liquid-liquid phase-separated (LLPS) promyelocytic leukaemia nuclear bodies (PML NBs), driven by the actin-binding protein Anillin. Although best known as a cytokinesis factor, Anillin localises to PML NBs in interphase, where it concentrates monomeric actin (G-actin) and establishes a favourable environment for spontaneous actin assembly. Filament growth within these condensates remodels PML NB morphology and composition, releasing sequestered AKT into the nucleoplasm. AKT is subsequently phosphorylated and activated, and this nuclear AKT activity is required to regulate 53BP1 nuclear bodies in G1. These protective LLPS compartments shield under-replicated DNA inherited from the stressed S-phase until the following S-phase. This prevents premature engagement by aberrant repair pathways that would otherwise generate toxic intermediates and culminate in mitotic failure. Together, these findings define a condensate-to-filament pathway in which nuclear F-actin dynamically reorganises phase-separated compartments to safeguard genome stability across cell cycles. ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-1 [2]: #ref-6 [3]: #ref-3 [4]: #ref-4

Environmental exposures across critical developmental windows can significantly influence brain development and contribute to the pathogenesis of neurodevelopmental disorders (NDDs). Emerging clinical evidence suggests that cumulative environmental factors during early development result in more pronounced disease phenotypes in offspring. Here, we developed a triple-hit model using C57Bl/6JAusb mice to examine the cumulative effects of antenatal social stress, antenatal chronic high-fat diet consumption, and postnatal poly(I:C) exposure on neurodevelopmental outcomes in offspring. Male triple-hit offspring displayed autism-like social deficits and an overall increased susceptibility to neurodevelopmental behavioural alterations in adulthood compared to male non-stressed controls. Conversely, these behavioural changes were not observed amongst female triple-hit offspring. Single-cell RNA (scRNA) transcriptomic and bulk proteomic sequencing were performed in male triple-hit offspring across peripheral blood immune cells and brain tissue. scRNA sequencing in microglia, astrocytes, and oligodendrocytes revealed dysregulation in critical glial cell processes, ribosomal functions, and chromatin remodelling. Similar functional themes were observed across peripheral blood macrophages, neutrophils, and naive B cells - displaying immune and ribosomal dysregulation at the transcriptional level. Proteomics pathway enrichment analyses revealed significantly reduced protein abundance in ribosomal biogenesis, translation, and chromatin remodelling functions in both peripheral blood immune cells and brain tissue. We also observed synaptic dysfunction in the blood and brain proteome. Overall, using our unique triple-hit model, we demonstrate that multiple early life environmental exposures drive NDD-associated behaviours in a sex-specific manner; and is associated with overlapping central and peripheral molecular mechanisms that have clinical relevance to NDD pathogenesis. ### Competing Interest Statement The authors have declared no competing interest.

The intraneuronal aggregation of tau is a key driver of pathogenesis in tauopathies such as Alzheimer’s disease. Passive immunotherapy is a promising strategy for targeting tau, with several tau-specific antibodies having demonstrated the ability to reduce tau pathology and improve behavioural deficits in tau transgenic mouse models. Despite preclinical promise, however, conventional antibodies have limited access to the cell cytoplasm where tau pathology itself originates and accumulates to cause downstream neuronal dysfunction. As such, conventional antibodies are typically limited to targeting extracellular tau, failing to address the primary site of tau pathogenesis. This challenge can be overcome by intracellular antibodies or intrabodies, small antibody fragments that can be expressed within cells to target intracellular antigens like tau. Here, we have generated a single-chain variable fragment derived from the N-terminal tau-specific antibody, RNJ1, and investigated its potential as an intrabody to reduce tau pathology and restore neuronal function in a tau transgenic mouse model. The RNJ1 intrabody successfully engaged intracellular tau and reduced total tau and phosphorylated tau inclusions in brains of tau transgenic mice. Furthermore, treatment with the RNJ1 intrabody in female tau transgenic mice induced restoration of various protein pathways important for cellular homeostasis, thus promoting the restoration of neuronal function. Our findings underscore the therapeutic utility of targeting intracellular tau in disease, providing novel insights into the potential mechanisms by which intrabodies ameliorate tau pathology. ### Competing Interest Statement Ashley J. van Waardenberg is founder of i-Synapse. The authors declare no other competing interests. National Health and Medical Research Council, https://ror.org/011kf5r70, APP2000968 National Foundation for Medical Research and Innovation Bethlehem Griffiths Research Foundation, https://ror.org/04zp96367

BackgroundKabuki syndrome (KS) is a genetic disorder caused by DNA mutations in KMT2D, a lysine methyltransferase that methylates histones and other proteins, and therefore modifies chromatin structure and subsequent gene expression. Ketones, derived from the ketogenic diet, are histone deacetylase inhibitors that can ‘open’ chromatin and encourage gene expression. Preclinical studies have shown that the ketogenic diet rescues hippocampal memory neurogenesis in mice with KS via the epigenetic effects of ketones.MethodsSingle-cell RNA sequencing and mass spectrometry-based proteomics were used to explore molecular mechanisms of disease in individuals with KS (n = 4) versus controls (n = 4).FindingsPathway enrichment analysis indicated that loss of function mutations in KMT2D are associated with ribosomal protein dysregulation at an RNA and protein level in individuals with KS (FDR <0.05). Cellular proteomics also identified immune dysregulation and increased abundance of other lysine modification and histone binding proteins, representing a potential compensatory mechanism. A 12-year-old boy with KS, suffering from recurrent episodes of cognitive decline, exhibited improved cognitive function and neuropsychological assessment performance after 12 months on the ketogenic diet, with concomitant improvement in transcriptomic ribosomal protein dysregulation.InterpretationOur data reveals that lysine methyltransferase deficiency is associated with ribosomal protein dysfunction, with secondary immune dysregulation. Diet and the production of bioactive molecules such as ketone bodies serve as a significant environmental factor that can induce epigenetic changes and improve clinical outcomes. Integrating transcriptomic, proteomic, and clinical data can define mechanisms of disease and treatment effects in individuals with neurodevelopmental disorders.FundingThis study was supported by the Dale NHMRC Investigator Grant (APP1193648) (R.D), Petre Foundation (R.D), and The Sydney Children’s Hospital Foundation/Kids Research Early and Mid-Career Researcher Grant (E.T).

The microtubule-associated protein Tau is a driver of neuronal dysfunction in Alzheimer's disease and other tauopathies. In this process, Tau initially undergoes subtle changes to its abundance, subcellular localisation and a vast array of post-translational modifications including phosphorylation, that progressively result in the protein's somatodendritic accumulation and dysregulation of multiple Tau-dependent cellular processes. Given the various loss- and gain-of-functions of Tau in disease and the brain-wide changes in the proteome that characterise tauopathies, we asked whether targeting Tau would restore the alterations in proteostasis observed in disease. Therefore, by phage display, we generated a novel pan-Tau antibody, RNJ1, that preferentially binds human Tau and neutralises proteopathic seeding activity in multiple cell lines, and benchmarked it against a clinically tested pan-Tau antibody, HJ8.5 (murine version of tilavonemab). We then evaluated both antibodies, alone and in combination, in the K3 tauopathy mouse model, showing reduced Tau pathology and improvements in neuronal function following 14 weekly treatments, without obtaining synergy for the combination. These effects were more pronounced in female mice. To investigate the molecular mechanisms contributing to improvements in neuronal function, we employed quantitative proteomics, phosphoproteomics and kinase prediction analysis to first establish alterations in K3 mice relative to WT controls at the proteome level. In female K3 mice, we found 342 differentially abundant proteins, which are predominantly involved in metabolic and microtubule-associated processes, strengthening previously reported findings of defects in several functional domains in multiple tauopathy models. We next asked whether antibody-mediated Tau target engagement indirectly affects levels of deregulated proteins in the K3 model. Importantly, both immunotherapies, in particular RNJ1, induced abundance shifts towards a restoration to wild-type levels (proteostasis). A total of 257 of 342 (∼75%) proteins altered in K3 were closer in abundance to WT levels after RNJ1 treatment, and 73% after HJ8.5 treatment. However, the magnitude of these changes was less pronounced than that observed with RNJ1, as reflected by a far smaller number of differentially abundant proteins. Furthermore, analysis of the phosphoproteome showed an even stronger restoration effect with RNJ1, with ∼82% of altered phosphopeptides in K3 showing a shift to WT levels, and 75% with HJ8.5. Gene set over-representation analysis (ORA) further confirmed that proteins undergoing restoration are involved in biological pathways affected in K3 mice. Together, our study suggests that a Tau immunotherapy-induced restoration of proteostasis links target engagement and treatment efficacy.

To investigate the phosphorylation-based signaling and protein changes occurring early in epileptogenesis, the hippocampi of mice treated with pilocarpine were examined by quantitative mass spectrometry at 4 and 24 h post-status epilepticus at vast depth. Hundreds of posttranscriptional regulatory proteins were the major early targets of increased phosphorylation. At 24 h, many protein level changes were detected and the phosphoproteome continued to be perturbed. The major targets of decreased phosphorylation at 4 and 24 h were a subset of postsynaptic density scaffold proteins, ion channels, and neurotransmitter receptors. Many proteins targeted by dephosphorylation at 4 h also had decreased protein abundance at 24 h, indicating a phosphatase-mediated weakening of synapses. Increased translation was indicated by protein changes at 24 h. These observations, and many additional indicators within this multiomic resource, suggest that early epileptogenesis is characterized by signaling that stimulates both growth and a homeostatic response that weakens excitability.

Defining the molecular networks orchestrating human brain formation is crucial for understanding neurodevelopment and neurological disorders. Challenges in acquiring early brain tissue have incentivized the use of three-dimensional human pluripotent stem cell (hPSC)-derived neural organoids to recapitulate neurodevelopment. To elucidate the molecular programs that drive this highly dynamic process, here, we generate a comprehensive trans-omic map of the phosphoproteome, proteome, and transcriptome of the exit of pluripotency and neural differentiation toward human cerebral organoids (hCOs). These data reveal key phospho-signaling events and their convergence on transcriptional factors to regulate hCO formation. Comparative analysis with developing human and mouse embryos demonstrates the fidelity of our hCOs in modeling embryonic brain development. Finally, we demonstrate that biochemical modulation of AKT signaling can control hCO differentiation. Together, our data provide a comprehensive resource to study molecular controls in human embryonic brain development and provide a guide for the future development of hCO differentiation protocols.

Neuronal communication relies on the release of neurotransmitters from various populations of synaptic vesicles. Despite displaying vastly different release probabilities and mobilities, the reserve and recycling pool of vesicles co-exist within a single cluster suggesting that small synaptic biomolecular condensates could regulate their nanoscale distribution. Here, we performed a large-scale activity-dependent phosphoproteome analysis of hippocampal neurons in vitro and identified Tau as a highly phosphorylated and disordered candidate protein. Single-molecule super-resolution microscopy revealed that Tau undergoes liquid-liquid phase separation to generate presynaptic nanoclusters whose density and number are regulated by activity. This activity-dependent diffusion process allows Tau to translocate into the presynapse where it forms biomolecular condensates, to selectively control the mobility of recycling vesicles. Tau, therefore, forms presynaptic nano-biomolecular condensates that regulate the nanoscale organization of synaptic vesicles in an activity-dependent manner. Using single-molecule super-resolution microscopy, researchers revealed that Tau controls the recycling pool of synaptic vesicles in hippocampal neurons by forming nanoscale biomolecular condensates that are dynamically regulated by neuronal activity.

Understanding the molecular changes associated with the aged brain forms the basis for developing potential strategies for slowing cognitive decline associated with normal aging. Focusing on the hippocampus, a critical brain region involved in learning and memory, we employed tandem mass tag methodology to investigate global proteomic changes that occur in advanced-aged (20-month) versus young (3-month) C57BL/6 male mice. Our analysis revealed the upregulation of 236 proteins in the old hippocampal proteome, including those enriched within several age-related processes, such as the adaptive immune response and molecular metabolic pathways, whereas downregulated proteins (88 in total) are mainly involved in axonogenesis and growth cone-related processes. Categorizing proteins by cell-type enrichment in the brain identified a general upregulation of proteins preferentially expressed in microglia, astrocytes, and oligodendrocytes. In contrast, proteins with neuron-specific expression displayed an overall age-related downregulation. By integrating our proteomic with our previously published transcriptomic data, we discovered a mild but significant positive correlation between mRNA and protein expression changes in the aged hippocampus. Therefore, this proteomic data is a valuable additional resource for further understanding age-related molecular mechanisms.

AbstractDysferlin is a Ca2+-activated lipid binding protein implicated in muscle membrane repair. Recessive variants in DYSF result in dysferlinopathy, a progressive muscular dystrophy. We showed previously that calpain cleavage within a motif encoded by alternatively spliced exon 40a releases a 72 kDa C-terminal minidysferlin recruited to injured sarcolemma. Herein we use CRISPR/Cas9 gene editing to knock out murine Dysf exon 40a, to specifically assess its role in membrane repair and development of dysferlinopathy. We created three Dysf exon 40a knockout (40aKO) mouse lines that each express different levels of dysferlin protein ranging from ~ 90%, ~ 50% and ~ 10–20% levels of wild-type. Histopathological analysis of skeletal muscles from all 12-month-old 40aKO lines showed virtual absence of dystrophic features and normal membrane repair capacity for all three 40aKO lines, as compared with dysferlin-null BLAJ mice. Further, lipidomic and proteomic analyses on 18wk old quadriceps show all three 40aKO lines are spared the profound lipidomic/proteomic imbalance that characterises dysferlin-deficient BLAJ muscles. Collective results indicate that membrane repair does not depend upon calpain cleavage within exon 40a and that ~ 10–20% of WT dysferlin protein expression is sufficient to maintain the muscle lipidome, proteome and membrane repair capacity to crucially prevent development of dysferlinopathy.

The blood-brain barrier (BBB) is a tightly and actively regulated vascular barrier. Answering fundamental biological and translational questions about the BBB with currently available approaches is hampered by a trade-off between accessibility and biological validity. We report an approach combining micropipette-based local perfusion of capillaries in acute brain slices with multiphoton microscopy. Micro-perfusion offers control over the luminal solution and allows application of molecules and drug delivery systems, whereas the bath solution defines the extracellular milieu in the brain parenchyma. Here we show, that this combination allows monitoring of BBB transport at the cellular level, visualization of BBB permeation of cells and molecules in real-time and resolves subcellular details of the neurovascular unit. In combination with electrophysiology, it permits comparison of drug effects on neuronal activity following luminal versus parenchymal application. We further apply micro-perfusion to the human and mouse BBB of epileptic hippocampi highlighting its utility for translational research and analysis of therapeutic strategies.

Stable function of networks requires that synapses adapt their strength to levels of neuronal activity, and failure to do so results in cognitive disorders. How such homeostatic regulation may be implemented in mammalian synapses remains poorly understood. Here we show that the phosphorylation status of several positions of the active-zone (AZ) protein RIM1 are relevant for synaptic glutamate release. Position RIMS1045 is necessary and sufficient for expression of silencing-induced homeostatic plasticity and is kept phosphorylated by serine arginine protein kinase 2 (SRPK2). SRPK2-induced upscaling of synaptic release leads to additional RIM1 nanoclusters and docked vesicles at the AZ and is not observed in the absence of RIM1 and occluded by RIMS1045E. Our data suggest that SRPK2 and RIM1 represent a presynaptic phosphosignaling hub that is involved in the homeostatic balance of synaptic coupling of neuronal networks.

Advances in the study of neurological conditions have been possible because of pluripotent stem cell technologies and organoids. Studies have described the generation of neural ectoderm-derived retinal and brain structures from pluripotent stem cells. However, the field is still troubled by technical challenges, including high culture costs and variability. Here, we describe a simple and economical protocol that reproducibly gives rise to the neural retina and cortical brain regions from confluent cultures of stem cells. The spontaneously generated cortical organoids are transcriptionally comparable with organoids generated by other methods. Furthermore, these organoids showed spontaneous functional network activity and proteomic analysis confirmed organoids maturity. The generation of retinal and brain organoids in close proximity enabled their mutual isolation. Suspension culture of this complex organoid system demonstrated the formation of nerve-like structures connecting retinal and brain organoids, which might facilitate the investigation of neurological diseases of the eye and brain.