Randomized CRISPR-Cas Transcriptional Perturbation Screening Reveals Protective Genes against Alpha-Synuclein Toxicity.

The genome-wide perturbation of transcriptional networks with CRISPR-Cas technology has primarily involved systematic and targeted gene modulation. Here, we developed PRISM (Perturbing Regulatory Interactions by Synthetic Modulators), a screening platform that uses randomized CRISPR-Cas transcription factors (crisprTFs) to globally perturb transcriptional networks. By applying PRISM to a yeast model of Parkinson's disease (PD), we identified guide RNAs (gRNAs) that modulate transcriptional networks and protect cells from alpha-synuclein (αSyn) toxicity. One gRNA identified in this screen outperformed the most protective suppressors of αSyn toxicity reported previously, highlighting PRISM's ability to identify modulators of important phenotypes. Gene expression profiling revealed genes differentially modulated by this strong protective gRNA that rescued yeast from αSyn toxicity when overexpressed. Human homologs of top-ranked hits protected against αSyn-induced cell death in a human neuronal PD model. Thus, high-throughput and unbiased perturbation of transcriptional networks via randomized crisprTFs can reveal complex biological phenotypes and effective disease modulators.

Clinical and methylomic features of spinal meningiomas.

PURPOSE: The objective of our study was to analyze methylomic and clinical features of a cohort of spinal meningiomas (SMs) resected at our institution. METHODS: This is a retrospective study of patients undergoing SM resection at our institution between 2010 and 2023. Clinical and radiographic characteristics were reviewed and analyzed with standard statistical methods. A Partitioning Around Medoids approach was used to cluster SMs with methylation data in a combined cohort from our institution and a publicly available dataset by methylation profiles. Clinical variables and pathway analyses were compared for the resulting clusters. RESULTS: Sixty-five SMs were resected in 53 patients with median radiographic follow-up of 34 months. Forty-six (87%) patients were female. The median age at surgery was 65 years and median tumor diameter was 1.9 cm. The five-year progression-free survival rate was 90%, with subtotal resection being associated with recurrence or progression (p = .017). SMs clustered into hypermethylation, intermediate methylation, and hypomethylation subgroups. Tumors in the hypermethylated subgroup were associated with higher WHO grade (p = .046) and higher risk histological subtypes (p <.001), while tumors in the hypomethylated subgroup were least likely to present with copy-number loss in chromosome 22q (p <.0001). SMs classified as immune-enriched under a previously developed intracranial meningioma classifier did not have increased leukocyte fractions or hypomethylation of genes typically hypomethylated in immune-enriched tumors. CONCLUSION: SMs are more benign than their intracranial counterparts, and gross-total resection results in long term PFS. Methylation profiling identifies subgroups with differences in clinical variables.

Association of mental health diagnosis with race and all-cause mortality after a cancer diagnosis: Large-scale analysis of electronic health record data.

BACKGROUND: Disparity in mental health care among cancer patients remains understudied. METHODS: A large, retrospective, single tertiary-care institution cohort study was conducted based on deidentified electronic health record data of 54,852 adult cancer patients without prior mental health diagnosis (MHD) diagnosed at the University of California, San Francisco between January 2012 and September 2019. The exposure of interest was early-onset MHD with or without psychotropic medication (PM) within 12 months of cancer diagnosis and primary outcome was all-cause mortality. RESULTS: There were 8.2% of patients who received a new MHD at a median of 197 days (interquartile range, 61-553) after incident cancer diagnosis; 31.0% received a PM prescription; and 3.7% a mental health-related visit (MHRV). There were 62.6% of patients who were non-Hispanic White (NHW), 10.8% were Asian, 9.8% were Hispanic, and 3.8% were Black. Compared with NHWs, minority cancer patients had reduced adjusted odds of MHDs, PM prescriptions, and MHRVs, particularly for generalized anxiety (Asian odds ratio [OR], 0.66, 95% CI, 0.55-0.78; Black OR, 0.60, 95% CI, 0.45-0.79; Hispanic OR, 0.72, 95% CI, 0.61-0.85) and selective serotonin-reuptake inhibitors (Asian OR, 0.43, 95% CI, 0.37-0.50; Black OR, 0.51, 95% CI, 0.40-0.61; Hispanic OR, 0.79, 95% CI, 0.70-0.89). New early MHD with PM was associated with elevated all-cause mortality (12-24 months: hazard ratio [HR], 1.43, 95% CI, 1.25-1.64) that waned by 24 to 36 months (HR, 1.18, 95% CI, 0.95-1.45). CONCLUSIONS: New mental health diagnosis with PM was a marker of early mortality among cancer patients. Minority cancer patients were less likely to receive documentation of MHDs or treatment, which may represent missed opportunities to identify and treat cancer-related mental health conditions.

Radiotherapy for meningiomas.

Meningiomas are the most common primary central nervous system neoplasm. Despite promising recent progress in elucidating the genomic landscape and underlying biology of these histologically, molecularly, and clinically diverse tumors, the mainstays of meningioma treatment remain maximal safe resection and radiation therapy. The aim of this review of meningioma radiotherapy is to provide a concise summary of the history, current evidence, and future for application of radiotherapy in meningioma treatment.

Image-Guided Percutaneous Ablation of Adrenal Metastases: A Meta-Analysis of Efficacy and Safety.

PURPOSE: To evaluate the efficacy and safety of percutaneous ablation of adrenal metastases through a meta-analysis of various image-guided percutaneous ablation techniques. MATERIALS AND METHODS: A comprehensive literature search of PubMed and Embase databases was performed for studies evaluating the efficacy and/or safety of image-guided percutaneous ablation of adrenal metastases. A total of 37 studies published between 2009 and 2020 were analyzed, comprising a sample size of 959 patients. Proportion estimates of overall survival, local control, and toxicity were analyzed in a pooled meta-analysis. The pooled prevalence of adverse events after ablation was calculated based on common terminology criteria for adverse events (CTCAE) grading. RESULTS: Of the 959 included patients, 320 (33.3%) underwent radiofrequency ablation, 72 (7.5%) microwave ablation, 95 (9.9%) cryoablation, and 46 (4.8%) ethanol injections for treatment of adrenal metastases. The remaining 426 (44.4%) patients were from studies involving a mixture of the 4 listed percutaneous ablation techniques. The pooled 1-year local control rate was 80% (95% confidence interval [CI], 76%-83%). The pooled 1-year overall survival rate was 77% (95% CI, 70%-83%). The overall rate of severe adverse events after ablation (CTCAE grade 3 or higher) was 16.1%. The overall rate of low-grade adverse events after ablation (CTCAE grade 2 or lower) was 32.6%. Approximately 21.9% (n = 203) of patients experienced intraprocedural hypertensive crises, the majority of which were reversed with antihypertensive medications. CONCLUSIONS: This study demonstrates that image-guided percutaneous ablation can be effective in achieving acceptable short- to mid-term local tumor control and overall survival with a moderate safety profile.

Efficacy and safety of magnetic resonance-guided focused ultrasound for the treatment of painful bone metastases: a systematic review and meta-analysis.

OBJECTIVE: To report the safety and efficacy of magnetic resonance-guided focused ultrasound (MRgFUS) in the treatment of painful bone metastases through a systematic review and meta-analysis of pain scores before and after MRgFUS treatment and post-treatment adverse events. MATERIALS AND METHODS: A comprehensive literature search of PubMed and Embase databases was performed for studies evaluating the efficacy and/or safety of MRgFUS. The mean difference of pain scores (10-point visual analogue scale or numerical rating scale) between baseline and 1-month/3-month pain scores was collected and analyzed in a pooled meta-analysis. Post-treatment adverse events based on the Common Terminology Criteria for Adverse Events (CTCAE) grading were recorded and the pooled prevalence was calculated. RESULTS: A total of 33 studies published between 2007 and 2019 were collected, resulting in a total sample size of 1082 patients. The majority of the studies were prospective with a reported follow-up period of 3 months. The pooled proportion of patients that achieved pain relief from MRgFUS (complete response or partial response [≥ 2-point improvement of pain score]) was 79% (95% CI 73-83%). The pooled 1-month and 3-month mean difference in pain score were - 3.8 (95% CI - 4.3; - 3.3) and - 4.4 (95% CI - 5.0; - 3.7), respectively. The overall rate of high-grade (CTCAE grade 3 or higher) and low-grade (CTCAE grade 2 or lower) MRgFUS-related adverse events were 0.9% and 5.9%, respectively. CONCLUSION: MRgFUS is an effective procedure that is able to provide significant pain palliation for patients with symptomatic bone metastases with a favorable safety profile.

A Switch and Wave of Neuronal Activity in the Cerebral Cortex During the First Second of Conscious Perception.

Conscious perception occurs within less than 1 s. To study events on this time scale we used direct electrical recordings from the human cerebral cortex during a conscious visual perception task. Faces were presented at individually titrated visual threshold for 9 subjects while measuring broadband 40-115 Hz gamma power in a total of 1621 intracranial electrodes widely distributed in both hemispheres. Surface maps and k-means clustering analysis showed initial activation of visual cortex for both perceived and non-perceived stimuli. However, only stimuli reported as perceived then elicited a forward-sweeping wave of activity throughout the cerebral cortex accompanied by large-scale network switching. Specifically, a monophasic wave of broadband gamma activation moves through bilateral association cortex at a rate of approximately 150 mm/s and eventually reenters visual cortex for perceived but not for non-perceived stimuli. Meanwhile, the default mode network and the initial visual cortex and higher association cortex networks are switched off for the duration of conscious stimulus processing. Based on these findings, we propose a new "switch-and-wave" model for the processing of consciously perceived stimuli. These findings are important for understanding normal conscious perception and may also shed light on its vulnerability to disruption by brain disorders.

Factors Associated with Osteoid Osteoma Recurrence after CT-Guided Radiofrequency Ablation.

PURPOSE: To identify clinical and imaging variables associated with symptomatic recurrence of osteoid osteomas (OOs) treated with computerized tomography (CT)-guided radiofrequency (RF) ablation. MATERIALS AND METHODS: Seventy-one patients treated with the use of CT-guided RF ablation for OO at a single institution from July 2005 to May 2018 were included in this retrospective cohort analysis. Clinical data, including patient age, sex, race, and clinical outcomes, were collected from institutional electronic health records and telephone follow-up. Imaging variables regarding tumor characteristics were gathered from imaging reports and a blinded review of preprocedural images by an experienced musculoskeletal radiologist. Logistic regression, Cox proportional hazards, and Kaplan-Meier analyses were used to identify variables that are significantly associated with symptomatic recurrence, which was defined as pain occurring > 2 weeks after RF ablation. RESULTS: Ten patients (14.1%) experienced symptomatic recurrence at a median of 21.5 months after RF ablation. Univariable logistic regression classified young age (≤ 13 years), female sex, maximum tumor length, and "eccentricity index" (EI) ≥ 3 as predictive variables significantly associated with symptomatic recurrence. Multivariable logistic regression identified female sex and EI ≥ 3 to be significant predictors for symptomatic recurrence. A multivariable proportional hazards Cox regression of time to recurrence revealed EI ≥ 3 to be the only significant predictor of symptomatic recurrence. CONCLUSIONS: Female patients with OOs with an EI ≥ 3 have a greater risk of symptomatic recurrence following RF ablation. The EI is a useful tool to identify OOs with elongated 3-dimensional morphology, which may warrant more extensive ablation.

Salvage therapy outcomes for atypical meningioma.

Atypical menginomas demonstrate increased clinical aggressiveness characterized by recurrence and diminished survival. The optimal management of atypical meningioma in the recurrent setting is especially not well defined. To characterize outcomes following salvage treatment of recurrent atypical meningioma and to identify risk factors for further recurrence. Retrospective chart review was performed on 65 patients who underwent salvage treatment of atypical meningioma at a single institution. Data were analyzed using the Kaplan-Meier method and Cox proportional hazards modeling. Sixty-five patients with recurrent atypical meningioma and median imaging follow-up of 4.0 years (range 1.9-6.6 years) underwent 62 surgeries and 114 radiation treatments (RT) for salvage therapy. Salvage modality was surgery (21%), surgery/RT (25%), or RT alone (54%), associated with 2 year local freedom from recurrence (LFFR) of 36, 59, and 73%, respectively (P = 0.01). Twenty percent of patients experienced CTCAE grade ≥ 3 toxicity with salvage therapy. Thirty-nine percent of patients experienced ≥ 3 recurrences. The median disease-free survival intervals after first and second salvage treatments were 2.9 and 1.3 years, respectively. On univariate Cox analysis, prior subtotal resection, prior RT, tumor diameter > 2.5 cm, and multifocal local recurrence were associated with recurrence after salvage therapy. On multivariate logistic regression, only multifocal local recurrence was associated with further recurrence. Recurrent atypical meningioma is clinically and pathologically more aggressive than primary atypical meningioma, and the likelihood of durable local control with salvage therapy is lower. Future efforts should identify patients at risk of recurrence, and aggressive upfront treatment should be employed.

Impaired Serotonergic Brainstem Function during and after Seizures.

Impaired breathing, cardiac function, and arousal during and after seizures are important causes of morbidity and mortality. Previous work suggests that these changes are associated with depressed brainstem function in the ictal and post-ictal periods. Lower brainstem serotonergic systems are postulated to play an important role in cardiorespiratory changes during and after seizures, whereas upper brainstem serotonergic and other systems regulate arousal. However, direct demonstration of seizure-associated neuronal activity changes in brainstem serotonergic regions has been lacking. Here, we performed multiunit and single-unit recordings from medullary raphe and midbrain dorsal raphe nuclei in an established rat seizure model while measuring changes in breathing rate and depth as well as heart rate. Serotonergic neurons were identified by immunohistochemistry. Respiratory rate, tidal volume, and minute ventilation were all significantly decreased during and after seizures in this model. We found that population firing of neurons in the medullary and midbrain raphe on multiunit recordings was significantly decreased during the ictal and post-ictal periods. Single-unit recordings from identified serotonergic neurons in the medullary raphe revealed highly consistently decreased firing during and after seizures. In contrast, firing of midbrain raphe serotonergic neurons was more variable, with a mixture of increases and decreases. The markedly suppressed firing of medullary serotonergic neurons supports their possible role in simultaneously impaired cardiorespiratory function in seizures. Decreased arousal likely arises from depressed population activity of several neuronal pools in the upper brainstem and forebrain. These findings have important implications for preventing morbidity and mortality in people living with epilepsy. SIGNIFICANCE STATEMENT: Seizures often cause impaired breathing, cardiac dysfunction, and loss of consciousness. The brainstem and, specifically, brainstem serotonin neurons are thought to play an important role in controlling breathing, cardiac function, and arousal. We used an established rat seizure model to study the overall neuronal activity in the brainstem as well as firing of specific serotonin neurons while measuring cardiorespiratory function. Our results demonstrated overall decreases in brainstem neuronal activity and marked downregulation of lower brainstem serotonin neuronal firing in association with decreased breathing and heart rate during and after seizures. These findings point the way toward new treatments to augment brainstem function and serotonin, aiming to prevent seizure complications and reduce morbidity and mortality in people living with epilepsy.

Role of the immune system in cardiac tissue damage and repair following myocardial infarction.

INTRODUCTION: The immune system plays a crucial role in the initiation, development, and resolution of inflammation following myocardial infarction (MI). The lack of oxygen and nutrients causes the death of cardiomyocytes and leads to the exposure of danger-associated molecular patterns that are recognized by the immune system to initiate inflammation. RESULTS: At the initial stage of post-MI inflammation, the immune system further damages cardiac tissue to clear cell debris. The excessive production of reactive oxygen species (ROS) by immune cells and the inability of the anti-oxidant system to neutralize ROS cause oxidative stress that further aggravates inflammation. On the other hand, the cells of both innate and adaptive immune system and their secreted factors are critically instrumental in the very dynamic and complex processes of regulating inflammation and mediating cardiac repair. CONCLUSIONS: It is important to decipher the balance between detrimental and beneficial effects of the immune system in MI. This enables us to identify better therapeutic targets for reducing the infarct size, sustaining the cardiac function, and minimizing the likelihood of heart failure. This review discusses the role of both innate and adaptive immune systems in cardiac tissue damage and repair in experimental models of MI.

Cognitive Decline, Body Mass Index, and Waist Circumference in Community-Dwelling Elderly Participants.

OBJECTIVE: The aim of this study was to explore the association of body mass index (BMI), waist circumference (WC), and BMI and WC changes over time with cognitive decline in a nationally representative sample. METHODS: A total of 5239 participants (≥65 years) were followed for 3 years as part of the National Health and Aging Trends Study. Cox proportional hazard regression was applied to model the risk of cognitive decline. RESULTS: BMI, after adjusting for WC and main confounders, was associated with reduced risk of cognitive decline (hazard ratio [HR] 0.97 for each unit BMI increase, 0.95-0.99). After stratifying by gender and age, this effect remained significant among females and young elders ≤80 years. A BMI decrease and WC increase >10% over the study period were associated with increased risk of cognitive decline (HR 1.98, 1.16-3.38; HR 1.30, 1.04-1.62, respectively). CONCLUSION: In the elderly individuals, lean mass, as measured by BMI adjusted for WC, was associated with reduced risk of cognitive decline. Loss of lean mass and gain of fat mass, as measured by WC adjusted for BMI, were associated with elevated risk of cognitive decline.

Human myocardial pericytes: multipotent mesodermal precursors exhibiting cardiac specificity.

Perivascular mesenchymal precursor cells (i.e., pericytes) reside in skeletal muscle where they contribute to myofiber regeneration; however, the existence of similar microvessel-associated regenerative precursor cells in cardiac muscle has not yet been documented. We tested whether microvascular pericytes within human myocardium exhibit phenotypes and multipotency similar to their anatomically and developmentally distinct counterparts. Fetal and adult human heart pericytes (hHPs) express canonical pericyte markers in situ, including CD146, NG2, platelet-derived growth factor receptor (PDGFR) ß, PDGFRα, alpha-smooth muscle actin, and smooth muscle myosin heavy chain, but not CD117, CD133, and desmin, nor endothelial cell (EC) markers. hHPs were prospectively purified to homogeneity from ventricular myocardium by flow cytometry, based on a combination of positive- (CD146) and negative-selection (CD34, CD45, CD56, and CD117) cell lineage markers. Purified hHPs expanded in vitro were phenotypically similar to human skeletal muscle-derived pericytes (hSkMPs). hHPs express mesenchymal stem/stromal cell markers in situ and exhibited osteo-, chondro-, and adipogenic potentials but, importantly, no ability for skeletal myogenesis, diverging from pericytes of all other origins. hHPs supported network formation with/without ECs in Matrigel cultures; hHPs further stimulated angiogenic responses under hypoxia, markedly different from hSkMPs. The cardiomyogenic potential of hHPs was examined following 5-azacytidine treatment and neonatal cardiomyocyte coculture in vitro, and intramyocardial transplantation in vivo. Results indicated cardiomyocytic differentiation in a small fraction of hHPs. In conclusion, human myocardial pericytes share certain phenotypic and developmental similarities with their skeletal muscle homologs, yet exhibit different antigenic, myogenic, and angiogenic properties. This is the first example of an anatomical restriction in the developmental potential of pericytes as native mesenchymal stem cells.

Human bedside evaluation versus automatic responsiveness testing in epilepsy (ARTiE).

Evaluation of behavioral impairment during epileptic seizures is critical for medical decision making, including accurate diagnosis, recommendations for driving, and presurgical evaluation. We investigated the quality of behavioral testing during inpatient video-electroencephalography (EEG) monitoring at an established epilepsy center, and introduce a technical innovation that may improve clinical care. We retrospectively reviewed video-EEG data from 152 seizures in 33 adult or pediatric patients admitted for video-EEG monitoring. Behavioral testing with questions or commands was performed in only 50% of seizures ictally, 73% of seizures postictally, and 80% with either ictal or postictal testing combined. Furthermore, the questions or commands were highly inconsistent and were performed by nonmedical personnel in about one fourth of cases. In an effort to improve this situation we developed and here introduce Automatic Responsiveness Testing in Epilepsy (ARTiE), a series of video-recorded behavioral tasks automatically triggered to play in the patient's room by computerized seizure detection. In initial technical testing using prerecorded or live video-EEG data we found that ARTiE is initiated reliably by automatic seizure detection. With additional clinical testing we hope that ARTiE will succeed in providing comprehensive and reliable behavioral evaluation during seizures for people with epilepsy to greatly improve their clinical care.

Rhythmic 3-4Hz discharge is insufficient to produce cortical BOLD fMRI decreases in generalized seizures.

Absence seizures are transient episodes of impaired consciousness accompanied by 3-4 Hz spike-wave discharge on electroencephalography (EEG). Human functional magnetic resonance imaging (fMRI) studies have demonstrated widespread cortical decreases in the blood oxygen-level dependent (BOLD) signal that may play an important role in the pathophysiology of these seizures. Animal models could provide an opportunity to investigate the fundamental mechanisms of these changes, however they have so far failed to consistently replicate the cortical fMRI decreases observed in human patients. This may be due to important differences between human seizures and animal models, including a lack of cortical development in rodents or differences in the frequencies of rodent (7-8 Hz) and human (3-4 Hz) spike-wave discharges. To examine the possible contributions of these differences, we developed a ferret model that exhibits 3-4 Hz spike-wave seizures in the presence of a sulcated cortex. Measurements of BOLD fMRI and simultaneous EEG demonstrated cortical fMRI increases during and following spike-wave seizures in ferrets. However unlike human patients, significant fMRI decreases were not observed. The lack of fMRI decreases was consistent across seizures of different durations, discharge frequencies, and anesthetic regimes, and using fMRI analysis models similar to human patients. In contrast, generalized tonic-clonic seizures under the same conditions elicited sustained postictal fMRI decreases, verifying that the lack of fMRI decreases with spike-wave was not due to technical factors. These findings demonstrate that 3-4 Hz spike-wave discharge in a sulcated animal model does not necessarily produce fMRI decreases, leaving the mechanism for this phenomenon open for further investigation.

Management and disease outcome of type I gastric neuroendocrine tumors: the Mount Sinai experience.

BACKGROUND AND AIM: The incidence of gastric neuroendocrine tumors (NETs) has increased tenfold since the 1970s. Our aim was to describe the clinicopathologic profile, management, and outcomes of type I gastric NETs at The Mount Sinai Hospital. METHODS: From existing databases of the Mount Sinai Division of Gastrointestinal Pathology and the Carcinoid Cancer Foundation, we identified 56 patients with type I gastric NETs seen at The Mount Sinai Hospital from 1993 to 2012. We generated a comprehensive dataset encompassing demographic, clinical, endoscopic, and pathologic factors. Survival information was determined from medical records and the Social Security Death Index. Tumor-node-metastasis staging was conducted, and tumors were graded based on mitotic counts and Ki67 index. RESULTS: Median NET size was 3.0 mm; 55.8 % displayed multifocal disease. Stages I, II, III, and IV disease were observed in 83.8, 10.8, 5.4, and 0 %, respectively. Tumors were either low (69.7 %) or intermediate (30.3 %) grade. Furthermore, 3.6 % of patients developed gastric dysplasia, and 5.5 % had gastric adenocarcinoma. Patients underwent endoscopy every 15 months, while 28.6 % underwent polypectomy, 32.7 % somatostatin therapy, and 46.4 % surgical resection. 5- and 10-year disease-specific survival was 100 %. CONCLUSIONS: Most patients received annual endoscopic surveillance, with a minority undergoing surgical resection, though outcomes remained excellent independent of therapeutic approach. We identified a very low but real rate of loco-regional spread, despite the generally indolent behavior of type I gastric NETs. Several patients demonstrated concurrent dysplasia or adenocarcinoma, underscoring the efficacy of regular endoscopic management not only for gastric NETs, but also for dysplasia and adenocarcinoma.

Long-range regulatory polymorphisms affecting a GABA receptor constitute a quantitative trait locus (QTL) for social behavior in Caenorhabditis elegans.

Aggregation is a social behavior that varies between and within species, providing a model to study the genetic basis of behavioral diversity. In the nematode Caenorhabditis elegans, aggregation is regulated by environmental context and by two neuromodulatory pathways, one dependent on the neuropeptide receptor NPR-1 and one dependent on the TGF-ß family protein DAF-7. To gain further insight into the genetic regulation of aggregation, we characterize natural variation underlying behavioral differences between two wild-type C. elegans strains, N2 and CB4856. Using quantitative genetic techniques, including a survey of chromosome substitution strains and QTL analysis of recombinant inbred lines, we identify three new QTLs affecting aggregation in addition to the two known N2 mutations in npr-1 and glb-5. Fine-mapping with near-isogenic lines localized one QTL, accounting for 5%-8% of the behavioral variance between N2 and CB4856, 3' to the transcript of the GABA neurotransmitter receptor gene exp-1. Quantitative complementation tests demonstrated that this QTL affects exp-1, identifying exp-1 and GABA signaling as new regulators of aggregation. exp-1 interacts genetically with the daf-7 TGF-ß pathway, which integrates food availability and population density, and exp-1 mutations affect the level of daf-7 expression. Our results add to growing evidence that genetic variation affecting neurotransmitter receptor genes is a source of natural behavioral variation.