Molecular Brain

Tackling developmental changes in long-term potentiation (LTP) expression during adolescence is crucial to understand disease susceptibility in neurodevelopmental disorders, epileptogenesis or drug abuse. This paper investigated the alterations in the resting phosphorylation state of synaptic proteins essential for synaptic transmission and hippocampal LTP expression from weaning (3 weeks) to adulthood (12 weeks). Synaptic AMPA GluA1 and GluA2 subunit levels increased, yet to different extents, as the GluA1/GluA2 ratio also increased. Conversely, GluA1 phosphorylation in both Ser831 and Ser845 progressively decreased from weaning to adulthood, suggesting an enhanced availability of these sites for activity-dependent phosphorylation. In accordance, LTP induced by different theta-burst stimulation (TBS) intensities in the CA1 area of rat hippocampal slices enhanced gradually in this developmental period. In contrast, basal phosphorylation of GluN1, GluN2B and CaMKII increased during adolescence. Altogether, these findings suggest that alterations in AMPA receptor subunit composition and basal phosphorylation are crucial for the maturation of hippocampal LTP during adolescence, while a mild enhancement in synaptic CaMKII levels may further provide the necessary structural support to LTP expression and stability. Given the reported involvement of GluA1 phosphorylation changes in epileptogenesis and neurodevelopmental disorders, these findings provide important insights into hippocampal synaptic plasticity in normal and altered brain development and epileptogenesis.

Infantile amnesia refers to the inability to recall early-life experiences, despite their lasting influence on adult behavior. Recent evidence suggests that memory traces formed during infancy may persist in a silent engram state. However, whether and how these silent engram cells contribute to adult memory formation remains unclear. To address this, we examined whether experiences during infancy affect adult memory formation using contextual fear conditioning in mice. Consistent with previous studies, we observed infantile amnesia 30 days later. Despite amnesia, these mice exhibited memory enhancement upon retraining as adults, suggesting that silent infantile engrams influence adult memory. Notably, this effect was context-specific. Using a cellular tagging system and ablation approaches, we found that infantile engram cells in the infralimbic cortex (IL) were crucial for this memory enhancement. Overall, these findings demonstrate that infant engram cells in the IL are re-recruited into adult memory traces, providing a neural mechanism by which early-life experiences shape adult memory formation through relearning.

The cerebellar nuclei (CN) has demonstrated its influence on cognitive behavior via the cerebello-cortico circuit, yet the role of CN critical period mechanisms and how they may influence cognitive behavior, such as parvalbumin (PV) expressing interneurons enwrapped by perineuronal nets (PNNs), is still unclear. Therefore, we investigated the role of the lateral CN (LCN) PV cell calcium activity while animals performed a visual discrimination touchscreen cognitive task. All animals received the PV cell calcium indicator GCaMP6f at postnatal day 21 (P21). We targeted the LCN critical period by manipulating neural activity in male mice using the inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) from postnatal day 21 to 35 or by injecting an Hapln1-AAV vector to selectively target LCN PNN development. After animals completed the visual discrimination task, cerebellar tissue was collected for viral recovery and antibody staining for PNN components, Hapln1 and aggrecan. Results revealed DREADD animals showed improved reversal learning, an increase in calcium response to learning-related activity and altered PNN expression (Hapln1 and aggrecan). Hapln1 treated animals displayed a decrease in final day acquisition performance, lower reversal performance compared to DREADD groups, a decrease in reversal calcium learning-related activity, and an increase in PNN expression (Hapln1). Together, these data provide further evidence of LCN mechanisms associated with learning as well as the importance of understanding region-specific critical periods of plasticity.

Primary cilia, which are present in most brain cells, are essential for brain development and function. During early brain development, dysfunction of the primary cilia can lead to a broad spectrum of disorders, collectively termed ciliopathies, that include brain malformations and intellectual disability. Although the role of primary cilia in brain development is well-established, cilia-mediated signaling in mature neurons and the contribution of cilia to neuronal circuit function remain controversial. Using mouse genetic and behavioral studies, single-cell electrophysiology, and 2-photon imaging, we show that deletion of primary cilia from adult hippocampal neurons is not required for hippocampal circuit function or behavior. Chronic genetic deletion or acute laser ablation of primary cilia from mature pyramidal neurons in the CA1 or CA3 regions of the hippocampus did not affect neuronal excitability, basal synaptic transmission, or long-term synaptic plasticity at excitatory CA3-CA1 hippocampal synapses. Moreover, the loss of primary cilia did not affect hippocampal-dependent learning and memory or anxiety-like behaviors. These results challenge the prevailing view of cilia function in mature hippocampal neurons and suggest that neuronal cilia in the adult hippocampus do not serve as major signaling hubs for pathways essential for neuronal function or behavior.

Mutations in the syntaxin-binding protein 1 (STXBP1) gene, which encodes the presynaptic protein Munc18-1, cause a spectrum of severe epileptic encephalopathies and neurodevelopmental disorders, including Ohtahara syndrome, for which no curative treatment is currently available. Because the disease pathomechanism is thought to be driven by haploinsufficiency, restoring expression of the wild-type allele to physiological levels could provide therapeutic benefit. Here, we evaluated CRISPR-mediated transcriptional activation (CRISPR-ON), based on a dCas9-VPR transcriptional activator, as a strategy to upregulate endogenous Stxbp1 expression in a Stxbp1-haploinsufficient (Stxbp1+/-) mouse model. Screening of guide RNAs (gRNAs) targeting the Stxbp1 promoter in Neuro2A cells identified a multiplexed four-gRNA cassette that elevated Stxbp1 mRNA approximately six-fold. AAV-PHP.eB vectors co-expressing this 4xgRNA cassette and Cre recombinase under the EF1a promoter were administered intracerebroventricularly to neonatal Stxbp1+/-/dCas9-VPRfl/+ mice. CRISPR-ON treatment restored not only brain Stxbp1 mRNA but also Munc18-1 protein levels to those of wild-type controls. Electrocorticographic recordings revealed an approximately 50% reduction in the frequency of spike-wave discharges in CRISPR-ON-treated Stxbp1+/- mice compared with untreated Stxbp1+/- controls, and aggressive behavior in the resident-intruder test was also partially attenuated. In contrast, locomotor activity remained unaffected, indicating that CRISPR-ON treatment achieves selective rescue of disease-related phenotypes without inducing motor side effects. Together, these findings demonstrate that CRISPR-ON-mediated activation of endogenous Stxbp1 is a promising therapeutic strategy for STXBP1-related encephalopathies and support endogenous gene activation as a broadly applicable platform for haploinsufficiency disorders.

BackgroundsEarly-life environmental insults cause persistent neurodevelopmental abnormalities accompanied by transcriptional and epigenetic dysregulation despite removal of the original insult or postnatal intervention. However, transcriptomic and epigenomic responses to developmental insults and subsequent treatment during active neurodevelopment remain insufficiently characterized. Developmental iron deficiency (ID) provides a unique model for investigating this question because iron is an essential cofactor for TET DNA dioxygenases and developmental ID causes persistent behavioral and molecular alterations despite iron repletion. ResultsWe integrated the hippocampal transcriptome, DNA methylome (5mC), and hydroxymethylome (5hmC) in male rats at postnatal day 15 following developmental ID and postnatal iron treatment, using Oxford Nanopore sequencing for native DNA modification profiling. Developmental ID induced substantial transcriptional and epigenetic alterations associated with synaptic function, neurodevelopment, and neuroinflammation. Postnatal iron treatment induced a hierarchical response across molecular layers: while transcriptomic alterations largely normalized, 5mC showed only partial recovery, and 5hmC showed extensive de novo modifications. Recovered, persistent, and newly emerged epigenetic marks were associated with increasingly specialized biological functions, from broad neurodevelopmental processes to specific pathways. Furthermore, while 5mC enrichment was associated with transcriptionally suppressed pathways, 5hmC enrichment showed weaker coupling with concurrent transcriptomic activity, suggesting epigenetic poising rather than immediate transcriptional output. MergeOmics integration identified key driver genes showing post-treatment epigenetic regulation despite transcriptional recovery. ConclusionsMolecular recovery following developmental ID extends beyond transcriptomic normalization, involving persistent and extensive epigenetic remodeling. This study provides a framework for understanding molecular responses following early-life environmental insults and highlights the importance of delineating persistent regulatory reprogramming.

Induction of glia-to-neuron conversion is a promising regenerative strategy for treating brain injuries and neurodegenerative diseases. Previous studies have suggested that NeuroD1 can induce microglia-to-neuron cross-lineage conversion. However, it remains highly controversial. To conclusively determine whether NeuroD1 can convert microglia into neurons, we used genetic fate mapping to track the cell fate of microglia ectopically expressing NeuroD1. Furthermore, we performed two-photon imaging to trace the fate of the NeuroD1-expressing microglia. Our findings revealed that cells ectopically expressing NeuroD1 are bona fide microglia, not neurons, regardless of injury preconditioning. Additionally, NeuroD1 overexpression in microglia did not promote brain injury recovery, and the microglial identity remained intact. These results provide solid evidence that NeuroD1 cannot convert microglia into neurons. Our study underscores the necessity of lineage-tracing and cell fate mapping strategies to verify glia-to-neuron conversion, highlighting the importance of rigorous validation in regenerative research.

The processes by which epileptic insults precipitate the molecular, cellular, and network alterations in the brain that lead to epilepsy are poorly understood. We previously discovered that after status epilepticus (SE - an epilepsy inducing severe bout of seizures) the H3K27 methylase Enhancer of Zeste Homolog 2 (EZH2) is robustly induced and drives repression of genes. Both systemic pharmacological inhibition of EZH2 and deletion of EZH2 in neurons exacerbates epilepsy progression, suggesting that acute EZH2 induction may exert a net protective effect against disease progression chronically. However, the mechanisms underlying EZH2-mediated control of the putative protective and pathological pathways in disease progression are still unknown. To interrogate the mechanisms of EZH2 function post-SE, we used bulk CUT&RUN- sequencing against H3K27me3 in tandem with bulk RNA-sequencing in hippocampi of naive and 4d. post-SE mice to profile epigenomic and transcriptomic changes. Differential peak analysis showed that H3K27me3 was enriched both at loci pre-marked by H3K27me3 in the naive hippocampus as well as in loci that were de novo methylated after SE, consistent with the SE-dependent induction of EZH2 protein levels. Multi-omic integration of CUT&RUN and RNA-seq data revealed a module of genes that were coordinately H3K27me3 enriched, transcriptionally repressed, and annotated to ontological terms involved in neuronal signaling and network excitability. This result suggests that EZH2 induction may function in part to control network excitability after injury. To test this, we treated mice acutely post-SE with the EZH2 inhibitor UNC1999 and found that EZH2 inhibition attenuated H3K27me3 induction and dampened repression of target network excitability genes in response to SE. Functionally, UNC1999 treatment significantly increased seizure probability acutely and exacerbated disease severity in the chronic period. Taken together, these results suggest that EZH2 induction after injury may function to maintain network excitability to lower seizure probability acutely to protect against disease progression.

Long-term depression (LTD) is a form of synaptic plasticity implicated in tasks involving the modification or elimination of previously learned information. While glial glutamate transporters can control the strength of synaptic plasticity, much less is known about the contribution of the neuronal glutamate transporter EAAT3 in controlling hippocampal LTD and learning processes. Here, we report that overexpression of EAAT3 in principal neurons, but not in GABAergic interneurons, impairs heterosynaptic GABAergic synaptic plasticity (iLTD) and homosynaptic excitatory LTD in the hippocampus. LTD impairments can be reversed by inhibiting EAAT3 or by a brief exogenous activation of mGluR during LTD induction, suggesting that, by limiting glutamate spillover between neighboring synapses, EAAT3 contributes to setting the strength of different forms of hippocampal LTD. Moreover, mice overexpressing EAAT3 in principal neurons, but not in GABAergic interneurons, display impaired reversal learning, a phenotype that can be rescued by blocking EAAT3 in vivo. Together, these findings reveal that, by controlling the strength of hippocampal LTD, EAAT3 contributes to cognitive flexibility required for processing new information.

Heterozygous de novo missense mutations in the EEF1A2 gene encoding translation elongation factor eEF1A2 result in neurodevelopmental disorders, typically characterised by early onset epilepsy and intellectual disability (ID). The E122K mutation is the most commonly reported missense mutation and is amongst the more severe in terms of epilepsy and ID. Here we made use of a recently developed mouse model which recapitulates the E122K mutation to examine how mutations in EEF1A2 might disrupt neuronal gene expression. Primary neurons from mutant mice and transfected HEK293T cells were used to examine effects on global protein synthesis. In contrast to previous reports, we were unable to detect a change in global protein synthesis using either of two different assay systems. TRAP-seq and mass spectrometry were then employed to study the effects of the mutation on the translatome and proteome respectively. These analyses revealed perturbation of expression of a subset of genes, with a slight skew towards downregulation, particularly for longer transcripts. Further analysis indicated a down regulation of proteins involved in synaptic function in both the translatomic and proteomic datasets.

Nearly five decades ago, it was first observed that long-term memory consolidation requires waves of transcriptional activity and protein synthesis, with the first two waves occurring within hours after learning. While numerous studies have examined the effects of protein synthesis inhibitors, the contribution of epigenetic mechanisms in these waves remains poorly understood. Here, we aimed to determine the role of HDAC3, a key modulator of memory, in these two phases of gene expression, as well as its functional link with the transcription factor NF-{kappa}B, one of its deacetylation targets, and a critical player in memory formation. Pharmacological inhibition of HDAC3 with RGFP966, either immediately or 6 hours after training, enhanced memory persistence in the NOR task in mice. Conversely, inhibition of NF-kB with BAY 11-7082 impaired memory at the same time points. Moreover, RGFP966 injection increased the nuclear proportion of NF-{kappa}B in the CA1 region of the hippocampus, suggesting a functional link between HDAC3 activity and NF-{kappa}B nuclear translocation. To our knowledge, this study provides the first in vivo evidence of this relationship during memory consolidation, extending previous findings from cell culture and electrophysiological studies in brain slices.

Fos-expressing neuronal ensembles in nucleus accumbens (NAc) are selectively activated by drug-associated cues and shown to play a causal role in drug-cue memories. Many unique molecular and cellular alterations have been identified in these ensembles and thought to be components of an engram encoding the memory; however, spine morphology alterations on these ensembles have rarely been examined. Here, we examined alterations of identified spine types on Fos-expressing neurons in NAc core that were selectively activated by drug-associated cues during cocaine relapse. We combined Fos immunolabeling along with viral-based sparse GFP labeling to identify Fos-positive and Fos-negative neurons with distinguishable dendrites and quantified spine composition, densities and interspine intervals (ISIs) for all spine types, and head and neck diameters of mushroom spines. ISIs and head and neck diameters of mushroom spines were altered on Fos-positive (versus Fos-negative) neurons activated during cue-induced cocaine relapse. Critically, these alterations were not found on Fos-positive neurons activated by exposure to a novel context on relapse test day, despite having identical cocaine self-administration histories. Based on previous work, this suggests these alterations were not simply due to acute activation of a randomly selected set of neurons on test day, but rather they were altered specifically on neurons selectively activated during cocaine self-administration training and then reactivated during relapse. Stubby spines and immature spines, including filopodia and thin spines, were not altered. Altogether, these mushroom spine alterations describe a unique spine morphology signature for a drug-cue memory in NAc neuronal ensembles selectively activated during cocaine relapse.

Mutations in phosphatase and tensin homolog (PTEN) drive unregulated activation of the phosphatidylinositol-3-kinase (PI3K) pathway, resulting in neuronal hypertrophy, and are strongly associated with autism spectrum disorder (ASD). Several PTEN mutations alter subcellular localization, yet how localization governs PTEN function in developing neurons remains unclear. Although PTEN has been reported broadly distributed throughout neurons, here, live imaging of HaloTagged PTEN reveals dynamically regulated localization, suggesting spatial control of its signaling. We then used retroviral-mediated genetic manipulation to delete endogenous Pten in developing hippocampal neurons while simultaneously expressing PTEN fused to defined localization motifs, allowing us to directly test how subcellular targeting regulates neuronal morphology. Loss of Pten produces neurons characterized by enlarged somata, more elaborate dendritic arbors, and increased spine density, length, and head area. Nuclear-excluded PTEN fully rescued these phenotypes, whereas targeting PTEN to filopodia via fusion to the FBAR domain of srGAP3 or to the postsynaptic density via Homer1C corrected or corrected all morphological abnormalities in PTEN-deficient neurons and simplified dendritic arborization compared to wild-type. In contrast, nuclear-localized PTEN produced only partial rescue, normalizing soma size and spine head area but not dendritic complexity or spine density. These findings indicate that PTEN acts locally to restrain growth and structural connectivity, whereas regulation of spine head size can be mediated by PTEN both inside and outside the nucleus, potentially through transcriptional or splicing-dependent mechanisms. Together, our results identify subcellular localization as a critical determinant of PTEN function and reveal spatially distinct mechanisms through which PTEN sculpts neuronal development.

ADGRD1 (GPR133) is an orphan adhesion G protein-coupled receptor (aGPCR) that primarily signals through Gs to regulate intracellular cAMP levels and is increasingly recognized for its roles across multiple tissues, including the central nervous system. Its conserved expression in neural tissues, the presence of splice variants in the fetal brain, and its structural similarity to other aGPCRs all suggest that it might play important roles in the organization of neural circuits. Recent studies have identified a wide range of extracellular, membrane- associated, and intracellular interacting partners, highlighting the receptors ability to integrate diverse signals. In this study, we explored the consequences of Adgrd1 deficiency in mice using behavioral, electrophysiological, and transcriptomic approaches. Adgrd1-null mice showed reduced nest-building behavior and decreased exploratory drive, while motor coordination and recognition memory remained largely intact. Electrophysiological recordings indicated a trend toward impaired long-term potentiation. These mice also exhibit increased susceptibility to kainate-induced excitotoxicity. RNA-seq analysis revealed coordinated changes in genes associated with inhibitory signaling, extracellular matrix organization, and cytoskeletal regulation, pointing to a shift toward reduced synaptic stabilization and increased hippocampal vulnerability. Altogether, these results suggest that Adgrd1 plays a key role in maintaining hippocampal resilience and regulating motivational behaviors through integrated molecular and circuit-level mechanisms.

Vitamin D3 (VD) deficiency is a global health concern, and its supplementation has been shown to alleviate inflammation and oxidative stress across numerous neurological disorders. However, the beneficial effect of this common nutraceutical in schizophrenia (SCZ) remains inadequately explored. The present study investigated the presupplementation effects of VD on positive and cognitive symptoms in a MK-801induced mouse model of SCZ. MK-801, a non-competitive NMDA receptor antagonist, is a widely used drug that mimics some of the psychotic symptoms associated with SCZ. The repeated administration of a single dose of MK-801 (0.5mg/kg; intraperitoneally) for two weeks produced hyperlocomotion, anxiety- like behavior, and working memory deficits in MK-801-induced SCZ-like mice. These behavioral abnormalities were significantly attenuated in VS5 mice (SCZ mice presupplemented with 500 IU/kg/day of VD). At the molecular level, VD rescued gene expression of major NMDA receptor subunits (NR1, NR2A, NR2B), 7 nicotinic acetylcholine receptors (7nAChRs), and neurotrophin factors (NGF and BDNF). A restoration of PSD-95 protein expression, accompanied by downregulation of calcineurin, was also observed in the prefrontal cortex (PFC) of VS5 mice, suggesting protective effects of VD on synaptic communication and function in SCZ. In vitro studies showed that calcitriol (1 M) treatment of HEK-293 T cells transfected with 7nAChRs potentiated the single-channel current amplitude and demonstrated a direct modulatory effect of this nutraceutical on 7nAChRs expression and function. In silico JASPAR analysis further identified putative Vitamin D response elements (VDREs) within the promoter regions of various target genes, supporting the genomic action of VD. Additionally, VD deficiency was observed in Indian SCZ patients, highlighting its potential clinical relevance. Together with our previous findings (Manjari et al., 2022, 2023), the present study also demonstrates anti-inflammatory, anti-cholinesterase, neurotrophic, and synaptic-enhancing effects of VD, deepening our understanding of the multifaceted neuroprotective effects of the "D3" neurosteroid in neuropsychiatric disorders such as SCZ. HighlightsO_LIVD presupplementation improves the behavioral deficits in MK-801 induced SCZ mice. C_LIO_LINutraceutical intervention normalizes the gene expression of major NMDARs subunits namely, NR1, NR2A, NR2B, in the PFC of SCZ mice. C_LIO_LIVD mediates a restoration in the expression and function of 7nAChRs in SCZ mice. C_LIO_LIVD exhibits neuroprotective, neurotrophic, synaptoprotective, anti-inflammatory and anti-acetylcholinesterase effects, highlighting its therapeutic potential in SCZ. C_LI

The hippocampal CA3 subfield is central to associative learning and memory consolidation. The principal cells of the CA3, pyramidal neurons, execute these functions by generating hypersynchronous bursts that feed forward to the CA1. Extensive recurrent collateral connections within the CA3 neuron population are crucial for the generation of this burst activity. Double C2 domain-containing protein (Doc2) and synaptotagmin 7 (Syt7) are high-affinity calcium sensors implicated in asynchronous synaptic vesicle (SV) release and in the exocytosis of dense-core vesicles (DCVs). Additionally, Doc2 is a sensor for miniature neurotransmission, whereas Syt7 is involved in synaptic facilitation and SV replenishment. Both Doc2 and Syt7 are expressed in the hippocampus, but their potential roles in spontaneous excitatory network activity remain unanswered. Using whole-cell recordings in disinhibited acute hippocampal slices obtained from juvenile Doc2- and Syt7- knockout (KO) mice (P15-21), we report increased CA3 burst generation without changes in spontaneous excitatory postsynaptic current (sEPSC) frequency or amplitude. Moreover, the intrinsic properties of CA3 pyramidal neurons, such as the resting membrane potential, firing rate and input resistance, are unchanged. We propose that this novel burst phenotype in Doc2- and Syt7- KO mice is unrelated to changes in SV release but might be mediated by changes in neuropeptide release from DCVs. Regardless of the underlying mechanisms, this work reveals that both proteins act to regulate network activity. The hippocampal CA3 subfield is central to associative learning and memory consolidation. The principal cells of the CA3, pyramidal neurons, execute these functions by generating hypersynchronous bursts that feed forward to the CA1. Extensive recurrent collateral connections within the CA3 neuron population are crucial for the generation of this burst activity. Double C2 domain-containing protein (Doc2) and synaptotagmin 7 (Syt7) are high-affinity calcium sensors implicated in asynchronous synaptic vesicle (SV) release and in the exocytosis of dense-core vesicles (DCVs). Additionally, Doc2 is a sensor for miniature neurotransmission, whereas Syt7 is involved in synaptic facilitation and SV replenishment. Both Doc2 and Syt7 are expressed in the hippocampus, but their potential roles in spontaneous excitatory network activity remain unanswered. Using whole-cell recordings in disinhibited acute hippocampal slices obtained from juvenile Doc2- and Syt7- knockout (KO) mice (P15-21), we report increased CA3 burst generation without changes in spontaneous excitatory postsynaptic current (sEPSC) frequency or amplitude. Moreover, the intrinsic properties of CA3 pyramidal neurons, such as the resting membrane potential, firing rate and input resistance, are unchanged. We propose that this novel burst phenotype in Doc2- and Syt7- KO mice is unrelated to changes in SV release but might be mediated by changes in neuropeptide release from DCVs. Regardless of the underlying mechanisms, this work reveals that both proteins act to regulate network activity.

Behavioral flexibility is crucial to animal survival in dynamic environments, and a failure to update actions in response to recent outcomes is a hallmark of many neuropsychiatric disorders. However, the cellular and circuit mechanisms in the brain that support behavioral flexibility remain poorly understood. Forms of short-term plasticity such as synaptic facilitation have been theorized to transiently maintain information in neural circuits, and flexibly modulate how circuits process information depending on recent activity. Despite theoretical support, there is no direct experimental evidence linking synaptic facilitation to flexible decision-making. Recently, the presynaptic calcium sensor Synaptotagmin-7 (Syt7) has been shown to be required for synaptic facilitation at many synapses in the mammalian brain. Here, we assess operant learning in male and female Syt7 KO mice to determine how facilitation contributes to learning both stable and dynamic reward contingencies. We find that Syt7 KO mice acquired stable contingencies similarly to wild-type controls. However, KO mice were impaired in learning dynamic contingencies, showed more perseverative responding, and were delayed in applying a new task rule to all trial types following reversal. Behavioral modeling revealed a reduced influence of recent trial history on decisions in KO mice compared to wild-type controls. The behavioral deficits could not be explained by differences in motivation or memory. These results suggest that synaptic facilitation supports adaptive decision-making and that disruptions of short-term plasticity impair animals ability to use recent outcomes to update behavior.

Seasonal breeding is a remarkable adaptive trait, but it constrains efficient production in the sheep industry. Recent studies have shown that seasonal breeding is associated with endogenous circannual rhythms, which are regulated in part by the circadian clock system. FBXL3, a pivotal component of the SCF (SKP1 - CUL1 - F-box) E3 ubiquitin ligase complex, is a known determinant of the mammalian circadian period. In this study, we identified a missense mutation, T183M, in FBXL3 through selective sweep analysis. The allele frequency of this mutation differed significantly between sheep breeds exhibiting year-round estrus and those showing seasonal breeding patterns. The association between the T183M mutation and seasonal breeding was further validated using an ovariectomized, estradiol-implanted sheep model. We then generated mice carrying the homologous T183M mutation and found that they exhibited significantly lengthened circadian periods, accompanied by reduced CRY1 expression and increased CLOCK expression. Co-immunoprecipitation assays confirmed that the mutation reduced the interaction between FBXL3 and CRY1. These findings demonstrate an evolutionarily conserved role of FBXL3 in the circadian clock system. We propose that the T183M mutation disrupts day-length recognition, thereby influencing seasonal estrus in sheep. Author summarySeasonal breeding limits sheep productivity and is regulated by circadian rhythms, yet the key genetic determinants remain poorly understood. Here, we identified an FBXL3 T183M missense mutation whose allele frequency differed markedly between year-round-estrous and seasonally breeding sheep, and validated its association with seasonal reproduction in a sheep population. Functional analyses in mutant mice showed that this variant lengthened the circadian period, disrupted the expression of core clock genes, and weakened the interaction between FBXL3 and CRY1. These findings suggest that the FBXL3 T183M variant impairs day-length perception, thereby modulating seasonal estrus in sheep. Our study reveals a conserved circadian mechanism underlying seasonal breeding and highlights FBXL3 T183M as a promising genetic target for improving reproductive performance in sheep.

Background: Sleep problems are common in autism, emerge early in life and reduce quality of life, yet the mechanistic link between autism and poor sleep remains unclear. Human and rodent data indicate that difficulty falling asleep is a core feature of autistic insomnia, pointing to impaired responses to sleepiness as the underlying cause. We previously showed that adult mice carrying a mutation in the high-confidence autism gene Shank3 (Shank3{Delta}C) recapitulate this insomnia phenotype and struggle to respond to sleepiness after acute sleep deprivation. Here, we used Shank3{Delta}C mice to examine the molecular basis of sleepiness and how this autism-associated mutation alters it to inform understanding of sleep problems in autistic individuals. Methods: This study used RNA-sequencing and bioinformatics to identify molecular targets underlying the effect of the Shank3{Delta}C mutation on the molecular basis of sleepiness across development in male mice. We first compared cortical genome-wide gene expression following acute sleep deprivation and recovery sleep in adult wild-type (WT) and mutant mice. We then used polysomnography and RNA-sequencing to assess the response to increased sleepiness in WT and mutant mice at postnatal days 24 and 30. Results: The neurotypical response to acute sleep deprivation shifted from upregulating neuronal growth and development pathways at P24/P30 to upregulating DNA damage repair and neuronal activity-dependent transcription in adulthood. The Shank3{Delta}C mutation largely blocked recruitment of these pathways at P24 and in adulthood while paradoxically increasing the magnitude of the mutant response at P30. In addition, mutants consistently upregulated oxidative stress pathways linked to neurodegeneration and protein synthesis regardless of age, whereas WT animals downregulated these functions. Limitations: This study examined gene expression only in male mice, used a single autism rodent model, and averaged signals across mixed cortical cell types. Future work should include females, additional autism models, and single-cell approaches in additional brain regions to further characterize the cellular effects of sleep deprivation and autism-associated mutations. Conclusions: The Shank3{Delta}C mutation impairs the molecular accumulation of and response to sleepiness, both by elevating oxidative stress responses and by blocking the age-typical upregulation of pathways that differ between juveniles and adults.

Dysregulation of the delta-type glutamate receptor GluD1 and N-methyl-D-aspartate receptors (NMDARs) is implicated in neuropsychiatric disorders including schizophrenia and intellectual disability, and GluD1 modulates NMDAR response in hippocampal neurons. However, the precise mechanisms by which GluD1 influences specific NMDAR subtypes remain undefined, representing a critical gap given the reliance of synaptic plasticity and cognition on NMDAR composition. GluN2A- and GluN2B-containing NMDARs are essential for synaptic long-term potentiation (LTP) and contextual learning and memory. Here, we used CRISPR/Cas9 to generate GluD1 knockout (KO) in cultured hippocampal neurons and observed a selective decrease in GluN2B-containing NMDAR responses. In acute hippocampal slices, GluD1 KO similarly reduced GluN2B-containing NMDAR currents at ventral CA1[->]subiculum synapses and impaired LTP at these synapses. In vivo, region-specific GluD1 deficiency in the ventral subiculum disrupted long-term contextual memory, indicating a critical role for GluD1 in cognitive processes. These findings demonstrate that GluD1 is indispensable for preserving GluN2B-containing NMDAR function, synaptic plasticity, and memory, providing molecular insight into how GluD1 regulates NMDAR subtypes implicated in synaptic dysfunction in neuropsychiatric disorders. Understanding this mechanism will guide the development of therapeutic strategies that selectively target GluD1-dependent modulation of NMDAR subtypes in brain disease.