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Rapid eye movement (REM) sleep is an important component of the natural sleep/wake cycle, yet the mechanisms that regulate REM sleep remain incompletely understood. Cholinergic neurons in the mesopontine tegmentum have been implicated in REM sleep regulation, but lesions of this area have had varying effects on REM sleep. Therefore, this study aimed to clarify the role of cholinergic neurons in the pedunculopontine tegmentum (PPT) and laterodorsal tegmentum (LDT) in REM sleep generation. Selective optogenetic activation of cholinergic neurons in the PPT or LDT during non-REM (NREM) sleep increased the number of REM sleep episodes and did not change REM sleep episode duration. Activation of cholinergic neurons in the PPT or LDT during NREM sleep was sufficient to induce REM sleep.

CRISPR interference (CRISPRi) enables programmable, reversible, and titratable repression of gene expression (knockdown) in mammalian cells. Initial CRISPRi-mediated genetic screens have showcased the potential to address basic questions in cell biology, genetics, and biotechnology, but wider deployment of CRISPRi screening has been constrained by the large size of single guide RNA (sgRNA) libraries and challenges in generating cell models with consistent CRISPRi-mediated knockdown. Here, we present next-generation CRISPRi sgRNA libraries and effector expression constructs that enable strong and consistent knockdown across mammalian cell models. First, we combine empirical sgRNA selection with a dual-sgRNA library design to generate an ultra-compact (1–3 elements per gene), highly active CRISPRi sgRNA library. Next, we compare CRISPRi effectors to show that the recently published Zim3-dCas9 provides an excellent balance between strong on-target knockdown and minimal non-specific effects on cell growth or the transcriptome. Finally, we engineer a suite of cell lines with stable expression of Zim3-dCas9 and robust on-target knockdown. Our results and publicly available reagents establish best practices for CRISPRi genetic screening.

TDP-43 mislocalization and pathology occurs across a range of neurodegenerative diseases, but the pathways that modulate TDP-43 in neurons are not well understood. We generated a Halo-TDP-43 knock-in human induced pluripotent stem cell (iPSC) line and performed a genome-wide CRISPR interference FACS-based screen to identify modifiers of TDP-43 levels in neurons. A meta-analysis of our screen and publicly available screens identified both specific hits and pathways present across multiple screens, the latter likely responsible for generic protein level maintenance. We identified BORC, a complex required for anterograde lysosome transport, as a specific modifier of TDP-43 protein, but not mRNA, levels in neurons. BORC loss led to longer half-life of TDP-43 and other proteins, suggesting lysosome location is required for proper protein turnover. As such, lysosome location and function are crucial for maintaining TDP-43 protein levels in neurons.

Modifier genes are believed to account for the clinical variability observed in many Mendelian disorders, but their identification remains challenging due to the limited availability of genomics data from large patient cohorts. Here, we present GENDULF (GENetic moDULators identiFication), one of the first methods to facilitate prediction of disease modifiers using healthy and diseased tissue gene expression data. GENDULF is designed for monogenic diseases in which the mechanism is loss of function leading to reduced expression of the mutated gene. When applied to cystic fibrosis, GENDULF successfully identifies multiple, previously established disease modifiers, including EHF , SLC6A14 , and CLCA1 . It is then utilized in spinal muscular atrophy (SMA) and predicts U2AF1 as a modifier whose low expression correlates with higher SMN2 pre‐mRNA exon 7 retention. Indeed, knockdown of U2AF1 in SMA patient‐derived cells leads to increased full‐length SMN2 transcript and SMN protein expression. Taking advantage of the increasing availability of transcriptomic data, GENDULF is a novel addition to existing strategies for prediction of genetic disease modifiers, providing insights into disease pathogenesis and uncovering novel therapeutic targets. SYNOPSIS GENDULF predicts modifiers of loss‐of‐function monogenetic diseases using healthy and disease gene expression data. Application to cystic fibrosis (CF) and spinal muscular atrophy (SMA) identifies established CF modifiers and a new putative modifier of SMA, U2AF1 . GENDULF is a novel algorithm that identifies genetic modifiers for monogenetic diseases from healthy and disease gene expression data, by detecting patterns of co‐expression that are uniquely observed in healthy tissues. GENDULF may be used to provide a list of candidates for large‐scale analysis or may be incorporated with other approaches or a knowledge‐based step to yield a small list of candidates for small‐scale experimental evaluation. Different applications are demonstrated for CF, where the performance is estimated against previously established modifiers, and for SMA where it is used to uncover a new modifier, U2AF1 . Graphical Abstract GENDULF predicts modifiers of loss‐of‐function monogenetic diseases using healthy and disease gene expression data. Application to cystic fibrosis (CF) and spinal muscular atrophy (SMA) identifies established CF modifiers and a new putative modifier of SMA, U2AF1 .

BACKGROUNDSpinal muscular atrophy (SMA) is caused by deficient expression of survival motor neuron (SMN) protein. New SMN-enhancing therapeutics are associated with variable clinical benefits. Limited knowledge of baseline and drug-induced SMN levels in disease-relevant tissues hinders efforts to optimize these treatments.METHODSSMN mRNA and protein levels were quantified in human tissues isolated during expedited autopsies.RESULTSSMN protein expression varied broadly among prenatal control spinal cord samples, but was restricted at relatively low levels in controls and SMA patients after 3 months of life. A 2.3-fold perinatal decrease in median SMN protein levels was not paralleled by comparable changes in SMN mRNA. In tissues isolated from nusinersen-treated SMA patients, antisense oligonucleotide (ASO) concentration and full-length (exon 7 including) SMN2 (SMN2-FL) mRNA level increases were highest in lumbar and thoracic spinal cord. An increased number of cells showed SMN immunolabeling in spinal cord of treated patients, but was not associated with an increase in whole-tissue SMN protein levels.CONCLUSIONSA normally occurring perinatal decrease in whole-tissue SMN protein levels supports efforts to initiate SMN-inducing therapies as soon after birth as possible. Limited ASO distribution to rostral spinal and brain regions in some patients likely limits clinical response of motor units in these regions for those patients. These results have important implications for optimizing treatment of SMA patients and warrant further investigations to enhance bioavailability of intrathecally administered ASOs.FUNDINGSMA Foundation, SMART, NIH (R01-NS096770, R01-NS062869), Ionis Pharmaceuticals, and PTC Therapeutics. Biogen provided support for absolute real-time RT-PCR.

The iPSC Neurodegenerative Disease Initiative (iNDI) is the largest-ever induced pluripotent stem cell (iPSC) genome engineering project, modeling over 100 ADRD mutations in high-quality isogenic human iPSCs. iNDI leverages unbiased CRISPRi screens as a powerful tool to identify fundamental mechanisms and modifiers of disease. However, current CRISPRi molecular tools are poorly optimized for use in iPSC-derived neurons (iNeurons). Here we develop a Cre-lox inducible CRISPRi system (CRISPRi-Cre), enabling gene knockdown upon Cre delivery to postmitotic iNeurons, and identification of neuron-specific, disease-relevant modifiers. We modified a plasmid carrying a potent Zim3-dCas9 transcriptional repressor to include a strong floxed STOP cassette upstream of the Zim3 start codon. We leveraged HaloTag-TDP43 and HaloTag-FUS iSPCs from the iNDI project paired with flow cytometry to validate leakiness and responsiveness to Cre in iPSCs and iNeurons treated with sgRNAs. We then performed a genome-wide CRISPRi survival screen in iNeurons to demonstrate broad functionality of this inducible CRISPRi system with over 20,000 sgRNAs. Finally, we use CRISPRi-Cre to identify neuron-specific regulators of neuronal activity in iNeurons. We demonstrate that in the absence of Cre, dCas9 is inactive. Delivery of lentivirus-Cre to iNeurons activates dCas9, resulting in potent gene knockdown. In genome-wide CRISPRi screens, we show that CRISPRi-Cre identifies many of the same hits observed in screens using constitutive-active dCas9, and importantly uncovers novel neuron-specific hits not identified in previous CRISPRi screens. Here, we developed a robust Cre-inducible CRISPRi system that enables post-mitotic gene knockdown in iPSC-derived neurons. Our CRISPRi screens identify neuron-specific hits, demonstrating the utility of our tool to help uncover disease-relevant mechanisms, modifiers, and potential therapeutic targets in relevant cell types.

Recently, an African ancestry-specific Parkinson disease (PD) risk signal was identified at the gene encoding glucocerebrosidase ( GBA1 ). This variant ( rs3115534 -G) is carried by ~50% of West African PD cases and imparts a dose-dependent increase in risk for disease. The risk variant has varied frequencies across African ancestry groups but is almost absent in European and Asian ancestry populations. GBA1 is a gene of high clinical and therapeutic interest. Damaging biallelic protein-coding variants cause Gaucher disease and monoallelic variants confer risk for PD and dementia with Lewy bodies, likely by reducing the function of glucocerebrosidase. Interestingly, the African ancestry-specific GBA1 risk variant is a noncoding variant, suggesting a different mechanism of action. Using full-length RNA transcript sequencing, we identified partial intron 8 expression in risk variant carriers (G) but not in nonvariant carriers (T). Antibodies targeting the N terminus of glucocerebrosidase showed that this intron-retained isoform is likely not protein coding and subsequent proteomics did not identify a shorter protein isoform, suggesting that the disease mechanism is RNA based. Clustered regularly interspaced short palindromic repeats editing of the reported index variant ( rs3115534 ) revealed that this is the sequence alteration responsible for driving the production of these transcripts containing intron 8. Follow-up analysis of this variant showed that it is in a key intronic branchpoint sequence and, therefore, has important implications in splicing and disease. In addition, when measuring glucocerebrosidase activity, we identified a dose-dependent reduction in risk variant carriers. Overall, we report the functional effect of a GBA1 noncoding risk variant, which acts by interfering with the splicing of functional GBA1 transcripts, resulting in reduced protein levels and reduced glucocerebrosidase activity. This understanding reveals a potential therapeutic target in an underserved and underrepresented population. Here, the authors describe a noncoding genetic variant in GBA1 specific to people of African ancestry that increases the risk of neurodegenerative diseases by interfering with the splicing of mRNA, resulting in lowered protein levels and activity.

INTRODUCTION Variants of uncertain significance (VUS) surged with affordable genetic testing, posing challenges for determining pathogenicity. We examine the pathogenicity of a novel VUS P93S in Annexin A11 (ANXA11) – an amyotrophic lateral sclerosis/frontotemporal dementia‐associated gene – in a corticobasal syndrome kindred. Established ANXA11 mutations cause ANXA11 aggregation, altered lysosomal‐RNA granule co‐trafficking, and transactive response DNA binding protein of 43 kDa (TDP‐43) mis‐localization. METHODS We described the clinical presentation and explored the phenotypic diversity of ANXA11 variants. P93S's effect on ANXA11 function and TDP‐43 biology was characterized in induced pluripotent stem cell‐derived neurons alongside multiomic neuronal and microglial profiling. RESULTS ANXA11 mutations were linked to corticobasal syndrome cases. P93S led to decreased lysosome colocalization, neuritic RNA, and nuclear TDP‐43 with cryptic exon expression. Multiomic microglial signatures implicated immune dysregulation and interferon signaling pathways. DISCUSSION This study establishes ANXA11 P93S pathogenicity, broadens the phenotypic spectrum of ANXA11 mutations, underscores neuronal and microglial dysfunction in ANXA11 pathophysiology, and demonstrates the potential of cellular models to determine variant pathogenicity. Highlights ANXA11 P93S is a pathogenic variant. Corticobasal syndrome is part of the ANXA11 phenotypic spectrum. Hybridization chain reaction fluorescence in situ hybridization (HCR FISH) is a new tool for the detection of cryptic exons due to TDP‐43‐related loss of splicing regulation. Microglial ANXA11 and related immune pathways are important drivers of disease. Cellular models are powerful tools for adjudicating variants of uncertain significance.

The 5-year survival rate for patients with oral cancer remains at 50%, in large part due the high rate of post-treatment recurrence. In this study, we transfected epithelial-specific integrin αvβ6 and Fyn-kinase, a member of the Src-family kinases, into embryonic murine fibroblasts. In oral cancer, expression of αvβ6 is neo-expressed. Using a variety of in vitro assays, including cell migration and multicellular spheroid formation, we determined that these embryonic fibroblasts expressing αvβ6 and Fyn-kinase were able to acquire an epithelial phenotype. This is in direct contrast to human oral SCC, where expression of αvβ6 with Fyn-kinase promotes epithelial to mesenchymal transition. This demonstrates that signaling pathways can be species-specific.

Background The iPSC Neurodegenerative Disease Initiative (iNDI) is the largest‐ever induced pluripotent stem cell (iPSC) genome engineering project, modeling over 100 ADRD mutations in high‐quality isogenic human iPSCs. iNDI leverages unbiased CRISPRi screens as a powerful tool to identify fundamental mechanisms and modifiers of disease. However, current CRISPRi molecular tools are poorly optimized for use in iPSC‐derived neurons (iNeurons). Here we develop a Cre‐lox inducible CRISPRi system (CRISPRi‐Cre), enabling gene knockdown upon Cre delivery to postmitotic iNeurons, and identification of neuron‐specific, disease‐relevant modifiers. Method We modified a plasmid carrying a potent Zim3‐dCas9 transcriptional repressor to include a strong floxed STOP cassette upstream of the Zim3 start codon. We leveraged HaloTag‐TDP43 and HaloTag‐FUS iSPCs from the iNDI project paired with flow cytometry to validate leakiness and responsiveness to Cre in iPSCs and iNeurons treated with sgRNAs. We then performed a genome‐wide CRISPRi survival screen in iNeurons to demonstrate broad functionality of this inducible CRISPRi system with over 20,000 sgRNAs. Finally, we use CRISPRi‐Cre to identify neuron‐specific regulators of neuronal activity in iNeurons. Result We demonstrate that in the absence of Cre, dCas9 is inactive. Delivery of lentivirus‐Cre to iNeurons activates dCas9, resulting in potent gene knockdown. In genome‐wide CRISPRi screens, we show that CRISPRi‐Cre identifies many of the same hits observed in screens using constitutive‐active dCas9, and importantly uncovers novel neuron‐specific hits not identified in previous CRISPRi screens. Conclusion Here, we developed a robust Cre‐inducible CRISPRi system that enables post‐mitotic gene knockdown in iPSC‐derived neurons. Our CRISPRi screens identify neuron‐specific hits, demonstrating the utility of our tool to help uncover disease‐relevant mechanisms, modifiers, and potential therapeutic targets in relevant cell types.