Screening of human LPHN3 for variants with a potential impact on ADHD susceptibility

Genome-wide association study of delay discounting in Heterogeneous Stock rats

Delay discounting refers to the behavioral tendency to devalue rewards as a function of their delay in receipt. Heightened delay discounting has been associated with substance use disorders and multiple co-occurring psychopathologies. Human and animal genetic studies have established that delay discounting is heritable, but only a few associated genes have been identified. We aimed to identify novel genetic loci associated with delay discounting through a genome-wide association study (GWAS) using Heterogeneous Stock (HS) rats, a genetically diverse outbred population derived from eight inbred founder strains. We assessed delay discounting in 650 male and female HS rats using an adjusting amount procedure in which rats chose between smaller immediate sucrose rewards or a larger reward at various delays. Preference switch points were calculated and both exponential and hyperbolic functions were fitted to these indifference points. Area under the curve (AUC) and the discounting parameter k of both functions were used as delay discounting measures. GWAS for AUC, exponential k, and one indifference point identified significant loci on chromosomes 20 and 14. The gene Slc35f1, which encodes a member of the solute carrier family, was the sole gene within the chromosome 20 locus. That locus also contained an eQTL for Slc35f1, suggesting that heritable differences in the expression might be responsible for the association with behavior. Adgrl3, which encodes a latrophilin subfamily G-protein coupled receptor, was the sole gene within the chromosome 14 locus. These findings implicate novel genes in delay discounting and highlight the need for further exploration.

Brain exposure to SARS-CoV-2 virions perturbs synaptic homeostasis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with short- and long-term neurological complications. The variety of symptoms makes it difficult to unravel molecular mechanisms underlying neurological sequalae after coronavirus disease 2019 (COVID-19). Here we show that SARS-CoV-2 triggers the up-regulation of synaptic components and perturbs local electrical field potential. Using cerebral organoids, organotypic culture of human brain explants from individuals without COVID-19 and post-mortem brain samples from individuals with COVID-19, we find that neural cells are permissive to SARS-CoV-2 to a low extent. SARS-CoV-2 induces aberrant presynaptic morphology and increases expression of the synaptic components Bassoon, latrophilin-3 (LPHN3) and fibronectin leucine-rich transmembrane protein-3 (FLRT3). Furthermore, we find that LPHN3-agonist treatment with Stachel partially restored organoid electrical activity and reverted SARS-CoV-2-induced aberrant presynaptic morphology. Finally, we observe accumulation of relatively static virions at LPHN3-FLRT3 synapses, suggesting that local hindrance can contribute to synaptic perturbations. Together, our study provides molecular insights into SARS-CoV-2-brain interactions, which may contribute to COVID-19-related neurological disorders.

Genome-wide association study of delay discounting in Heterogenous Stock rats

Delay discounting refers to the behavioral tendency to devalue rewards as a function of their delay in receipt. Heightened delay discounting has been associated with substance use disorders, as well as multiple co-occurring psychopathologies. Genetic studies in humans and animal models have established that delay discounting is a heritable trait, but only a few specific genes have been associated with delay discounting. Here, we aimed to identify novel genetic loci associated with delay discounting through a genome-wide association study (GWAS) using Heterogenous Stock rats, a genetically diverse outbred population derived from eight inbred founder strains. We assessed delay discounting in 650 male and female rats using an adjusting amount procedure in which rats chose between smaller immediate sucrose rewards or a larger reward at variable delays. Preference switch points were calculated for each rat and both exponential and hyperbolic functions were fitted to these indifference points. Area under the curve (AUC) and the discounting parameter k of both functions were used as delay discounting measures. GWAS for AUC, exponential k, and indifference points for a short delay identified significant loci on chromosomes 20 and 14. The gene Slc35f1, which encodes a member of the solute carrier family of nucleoside sugar transporters, was the only gene within the chromosome 20 locus. That locus also contained an eQTL for Slc35f1, suggesting that heritable differences in the expression of that gene might be responsible for the association with behavior. The gene Adgrl3, which encodes a member of the latrophilin family of G-protein coupled receptors, was the only gene within the chromosome 14 locus. These findings implicate novel genes in delay discounting and highlight the need for further exploration.

Context-dependent requirement of G protein coupling for Latrophilin-2 in target selection of hippocampal axons

The formation of neural circuits requires extensive interactions of cell-surface proteins to guide axons to their correct target neurons. Trans-cellular interactions of the adhesion G protein-coupled receptor latrophilin-2 (Lphn2) with its partner teneurin-3 instruct the precise assembly of hippocampal networks by reciprocal repulsion. Lphn2 acts as a repulsive receptor in distal CA1 neurons to direct their axons to the proximal subiculum, and as a repulsive ligand in the proximal subiculum to direct proximal CA1 axons to the distal subiculum. It remains unclear if Lphn2-mediated intracellular signaling is required for its role in either context. Here, we show that Lphn2 couples to Gα12/13 in heterologous cells; this coupling is increased by constitutive exposure of the tethered agonist. Specific mutations of Lphn2's tethered agonist region disrupt its G protein coupling and autoproteolytic cleavage, whereas mutating the autoproteolytic cleavage site alone prevents cleavage but preserves a functional tethered agonist. Using an in vivo misexpression assay, we demonstrate that wild-type Lphn2 misdirects proximal CA1 axons to the proximal subiculum and that Lphn2 tethered agonist activity is required for its role as a repulsive receptor in axons. By contrast, neither tethered agonist activity nor autoproteolysis were necessary for Lphn2's role as a repulsive ligand in the subiculum target neurons. Thus, tethered agonist activity is required for Lphn2-mediated neural circuit assembly in a context-dependent manner.

Adhesion G protein-coupled receptors: structure, signaling, physiology, and pathophysiology

Adhesion G protein-coupled receptors (AGPCRs) are a family of 33 receptors in humans exhibiting a conserved general structure but diverse expression patterns and physiological functions. The large NH2 termini characteristic of AGPCRs confer unique properties to each receptor and possess a variety of distinct domains that can bind to a diverse array of extracellular proteins and components of the extracellular matrix. The traditional view of AGPCRs, as implied by their name, is that their core function is the mediation of adhesion. In recent years, though, many surprising advances have been made regarding AGPCR signaling mechanisms, activation by mechanosensory forces, and stimulation by small-molecule ligands such as steroid hormones and bioactive lipids. Thus, a new view of AGPCRs has begun to emerge in which these receptors are seen as massive signaling platforms that are crucial for the integration of adhesive, mechanosensory, and chemical stimuli. This review article describes the recent advances that have led to this new understanding of AGPCR function and also discusses new insights into the physiological actions of these receptors as well as their roles in human disease.

ADGRL3 genomic variation implicated in neurogenesis and ADHD links functional effects to the incretin polypeptide GIP

Attention deficit/hyperactivity disorder (ADHD) is the most common childhood neurodevelopmental disorder. Single nucleotide polymorphisms (SNPs) in the Adhesion G Protein-Coupled Receptor L3 (ADGRL3) gene are associated with increased susceptibility to developing ADHD worldwide. However, the effect of ADGRL3 non-synonymous SNPs (nsSNPs) on the ADGRL3 protein function is vastly unknown. Using several bioinformatics tools to evaluate the impact of mutations, we found that nsSNPs rs35106420, rs61747658, and rs734644, previously reported to be associated and in linkage with ADHD in disparate populations from the world over, are predicted as pathogenic variants. Docking analysis of rs35106420, harbored in the ADGLR3-hormone receptor domain (HRM, a common extracellular domain of the secretin-like GPCRs family), showed that HRM interacts with the Glucose-dependent insulinotropic polypeptide (GIP), part of the incretin hormones family. GIP has been linked to the pathogenesis of diabetes mellitus, and our analyses suggest a potential link to ADHD. Overall, the comprehensive application of bioinformatics tools showed that functional mutations in the ADGLR3 gene disrupt the standard and wild ADGRL3 structure, most likely affecting its metabolic regulation. Further in vitro experiments are granted to evaluate these in silico predictions of the ADGRL3-GIP interaction and dissect the complexity underlying the development of ADHD.

Latrophilin-3 heterozygous versus homozygous mutations in Sprague Dawley rats: Effects on egocentric and allocentric memory and locomotor activity

Latrophilin-3 (LPHN3) is a brain specific G-protein coupled receptor associated with increased risk of attention deficit hyperactivity disorder (ADHD) and cognitive deficits. CRISPR/Cas9 was used to generate a constitutive knockout (KO) rat of Lphn3 by deleting exon 3, based on human data that LPHN3 variants are associated with some cases of ADHD. Lphn3 KO rats are hyperactive with an attenuated response to ADHD medication and have cognitive deficits. Here, we tested KO, heterozygous (HET), and wildtype (WT) rats to determine if there was a gene-dosage effect. We tested the rats in home-cage activity starting at postnatal day (P)35 and P50, followed by tests of egocentric learning (Cincinnati water maze [CWM]), spatial learning (Morris water maze [MWM]), working memory (radial water maze [RWM]), incidental learning (novel object recognition [NOR]), acoustic startle response (ASR) habituation, tactile startle response (TSR) habituation, prepulse modification of acoustic startle, shuttle-box passive avoidance, conditioned freezing, and a mirror image version of the CWM. KO and HET rats were hyperactive. KO and HET rats had egocentric (CWM) and spatial deficits (MWM), increased startle response, and KO rats showed less conditioned freezing on contextual and cued memory; there were no effects on working memory (RWM) or passive avoidance. The selective gene-dosage effect in Lphn3 HET rats indicates that Lphn3 exhibits dominate expression on functions where it is most abundantly expressed (striatum, hippocampus) but not on behaviors mediated by regions of low expression. The data add further evidence to the impact of this synaptic protein on brain function and behavior.

ADGRL1 haploinsufficiency causes a variable spectrum of neurodevelopmental disorders in humans and alters synaptic activity and behavior in a mouse model

ADGRL1 (latrophilin 1), a well-characterized adhesion G protein-coupled receptor, has been implicated in synaptic development, maturation, and activity. However, the role of ADGRL1 in human disease has been elusive. Here, we describe ten individuals with variable neurodevelopmental features including developmental delay, intellectual disability, attention deficit hyperactivity and autism spectrum disorders, and epilepsy, all heterozygous for variants in ADGRL1. In vitro, human ADGRL1 variants expressed in neuroblastoma cells showed faulty ligand-induced regulation of intracellular Ca²⁺ influx, consistent with haploinsufficiency. In vivo, Adgrl1 was knocked out in mice and studied on two genetic backgrounds. On a non-permissive background, mice carrying a heterozygous Adgrl1 null allele exhibited neurological and developmental abnormalities, while homozygous mice were non-viable. On a permissive background, knockout animals were also born at sub-Mendelian ratios, but many Adgrl1 null mice survived gestation and reached adulthood. Adgrl1^-/- mice demonstrated stereotypic behaviors, sexual dysfunction, bimodal extremes of locomotion, augmented startle reflex, and attenuated pre-pulse inhibition, which responded to risperidone. Ex vivo synaptic preparations displayed increased spontaneous exocytosis of dopamine, acetylcholine, and glutamate, but Adgrl1^-/- neurons formed synapses in vitro poorly. Overall, our findings demonstrate that ADGRL1 haploinsufficiency leads to consistent developmental, neurological, and behavioral abnormalities in mice and humans.

Thwarting of Lphn3 Functions in Cell Motility and Signaling by Cancer-Related GAIN Domain Somatic Mutations

Cancer progression relies on cellular transition states accompanied by changes in the functionality of adhesion molecules. The gene for adhesion G protein-coupled receptor latrophilin-3 (aGPCR Lphn3 or ADGRL3) is targeted by tumor-specific somatic mutations predominantly affecting the conserved GAIN domain where most aGPCRs are cleaved. However, it is unclear how these GAIN domain-altering mutations impact Lphn3 function. Here, we studied Lphn3 cancer-related mutations as a proxy for revealing unknown GAIN domain functions. We found that while intra-GAIN cleavage efficiency was unaltered, most mutations produced a ligand-specific impairment of Lphn3 intercellular adhesion profile paralleled by an increase in cell-matrix actin-dependent contact structures for cells expressing the select S810L mutation. Aberrant remodeling of the intermediate filament vimentin, which was found to coincide with Lphn3-induced modification of nuclear morphology, had less impact on the nuclei of S810L expressing cells. Notoriously, receptor signaling through G13 protein was deficient for all variants bearing non-homologous amino acid substitutions, including the S810L variant. Analysis of cell migration paradigms revealed a non-cell-autonomous impairment in collective cell migration indistinctly of Lphn3 or its cancer-related variants expression, while cell-autonomous motility was potentiated in the presence of Lphn3, but this effect was abolished in S810L GAIN mutant-expressing cells. These data identify the GAIN domain as an important regulator of Lphn3-dependent cell motility, thus furthering our understanding of cellular and molecular events linking Lphn3 genetic somatic mutations to cancer-relevant pathogenesis mechanisms.

Convergent selective signaling impairment exposes the pathogenicity of latrophilin-3 missense variants linked to inheritable ADHD susceptibility

Latrophilin-3 (Lphn3; also known as ADGRL3) is a member of the adhesion G Protein Coupled Receptor subfamily, which participates in the stabilization and maintenance of neuronal networks by mediating intercellular adhesion through heterophilic interactions with transmembrane ligands. Polymorphisms modifying the Lphn3 gene are associated with attention-deficit/hyperactivity disorder (ADHD) in children and its persistence into adulthood. How these genetic alterations affect receptor function remains unknown. Here, we conducted the functional validation of distinct ADHD-related Lphn3 variants bearing mutations in the receptor's adhesion motif-containing extracellular region. We found that all variants tested disrupted the ability of Lphn3 to stabilize intercellular adhesion in a manner that was distinct between ligands classes, but which did not depend on ligand-receptor interaction parameters, thus pointing to altered intrinsic receptor signaling properties. Using G protein signaling biosensors, we determined that Lphn3 couples to Gαi1, Gαi2, Gαs, Gαq, and Gα13. However, all ADHD-related receptor variants consistently lacked intrinsic as well as ligand-dependent Gα13 coupling efficiency while maintaining unaltered coupling to Gαi, Gαs, and Gαq. Consistent with these alterations, actin remodeling functions as well as actin-relevant RhoA signaling normally displayed by the constitutively active Lphn3 receptor were impeded by select receptor variants, thus supporting additional signaling defects. Taken together, our data point to Gα13 selective signaling impairments as representing a disease-relevant pathogenicity pathway that can be inherited through Lphn3 gene polymorphisms. This study highlights the intricate interplay between Lphn3 GPCR functions and the actin cytoskeleton in modulating neurodevelopmental cues related to ADHD etiology.

Review of rodent models of attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a polygenic neurodevelopmental disorder that affects 8-12 % of children and >4 % of adults. Environmental factors are believed to interact with genetic predispositions to increase susceptibility to ADHD. No existing rodent model captures all aspects of ADHD, but several show promise. The main genetic models are the spontaneous hypertensive rat, dopamine transporter knock-out (KO) mice, dopamine receptor subtype KO mice, Snap-25 KO mice, guanylyl cyclase-c KO mice, and latrophilin-3 KO mice and rats. Environmental factors thought to contribute to ADHD include ethanol, nicotine, PCBs, lead (Pb), ionizing irradiation, 6-hydroxydopamine, neonatal hypoxia, some pesticides, and organic pollutants. Model validation criteria are outlined, and current genetic models evaluated against these criteria. Future research should explore induced multiple gene KOs given that ADHD is polygenic and epigenetic contributions. Furthermore, genetic models should be combined with environmental agents to test for interactions.

A novel role for the ADHD risk gene latrophilin-3 in learning and memory in Lphn3 knockout rats

Latrophilins (LPHNs) are adhesion G protein-coupled receptors with three isoforms but only LPHN3 is brain specific (caudate, prefrontal cortex, dentate, amygdala, and cerebellum). Variants of LPHN3 are associated with ADHD. Null mutations of Lphn3 in rat, mouse, zebrafish, and Drosophila result in hyperactivity, but its role in learning and memory (L&M) is largely unknown. Using our Lphn3 knockout (KO) rats we examined the cognitive abilities, long-term potentiation (LTP) in CA1, NMDA receptor expression, and neurohistology from heterozygous breeding pairs. KO rats were impaired in egocentric L&M in the Cincinnati water maze, spatial L&M and cognitive flexibility in the Morris water maze (MWM), with no effects on conditioned freezing, novel object recognition, or temporal order recognition. KO-associated locomotor hyperactivity had no effect on swim speed. KO rats had reduced early-LTP but not late-LTP and had reduced hippocampal NMDA-NR1 expression. In a second experiment, KO rats responded to a light prepulse prior to an acoustic startle pulse, reflecting visual signal detection. In a third experiment, KO rats given extra MWM pretraining and hidden platform overtraining showed no evidence of reaching WT rats' levels of learning. Nissl histology revealed no structural abnormalities in KO rats. LPHN3 has a selective effect on egocentric and allocentric L&M without effects on conditioned freezing or recognition memory.

ADGRL3, FGF1 and DRD4: Linkage and Association with Working Memory and Perceptual Organization Candidate Endophenotypes in ADHD

Attention deficit hyperactivity disorder (ADHD) is a highly heritable neurobehavioral disorder that affects children worldwide, with detrimental long-term consequences in affected individuals. ADHD-affected patients display visual-motor and visuospatial abilities and skills that depart from those exhibited by non-affected individuals and struggle with perceptual organization, which might partially explain impulsive responses. Endophenotypes (quantifiable or dimensional constructs that are closely related to the root cause of the disease) might provide a more powerful and objective framework for dissecting the underlying neurobiology of ADHD than that of categories offered by the syndromic classification. In here, we explore the potential presence of the linkage and association of single-nucleotide polymorphisms (SNPs), harbored in genes implicated in the etiology of ADHD (ADGRL3, DRD4, and FGF1), with cognitive endophenotypes related to working memory and perceptual organization in 113 nuclear families. These families were ascertained from a geographical area of the Caribbean coast, in the north of Colombia, where the community is characterized by its ethnic diversity and differential gene pool. We found a significant association and linkage of markers ADGRL3-rs1565902, DRD4-rs916457 and FGF1-rs2282794 to neuropsychological tasks outlining working memory and perceptual organization such as performance in the digits forward and backward, arithmetic, similarities, the completion of figures and the assembly of objects. Our results provide strong support to understand ADHD as a combination of working memory and perceptual organization deficits and highlight the importance of the genetic background shaping the neurobiology, clinical complexity, and physiopathology of ADHD. Further, this study supplements new information regarding an ethnically diverse community with a vast African American contribution, where ADHD studies are scarce.

Latrophilin-3 disruption: Effects on brain and behavior

Latrophilin-3 (LPHN3), a G-protein-coupled receptor belonging to the adhesion subfamily, is a regulator of synaptic function and maintenance in brain regions that mediate locomotor activity, attention, and memory for location and path. Variants of LPHN3 are associated with increased risk for attention deficit hyperactivity disorder (ADHD) in some patients. Here we review the role of LPHN3 in the central nervous system (CNS). We describe synaptic localization of LPHN3, its trans-synaptic binding partners, links to neurodevelopmental disorders, animal models of Lphn3 disruption in different species, and evidence that LPHN3 is involved in cognition as well as activity and attention. The evidence shows that LPHN3 plays a more significant role in neuroplasticity than previously appreciated.

Adhesion G protein-coupled receptor L3 gene variants: Statistically significant association observed in the male Indo-caucasoid Attention deficit hyperactivity disorder probands

Primary symptoms of Attention Deficit Hyperactivity Disorder (ADHD) are age inappropriate inattention, hyperactivity and impulsivity. Caucasoid individuals showed increased susceptibility to ADHD and disruptive behaviour in presence of Adhesion G-protein-coupled receptor L3 (ADGRL3) gene variants. We investigated ADGRL3 rs1868790, rs6551665, rs2345039 in Indo-Caucasoid families with ADHD probands (N = 249) and controls (N = 350). Behavioural traits, executive function, and IQ of probands were measured through Conner's Parent Rating Scale-Revised, Parental Account of Children's Symptoms, Barkley Deficit in Executive Functioning-Child & Adolescent Scale, and Wechsler Intelligence Scale for Children-III respectively. After obtaining informed written consent, peripheral blood was collected for genomic DNA isolation and target sites were analyzed by PCR based methods or TaqMan assay. Case-control analysis showed higher frequency of rs2345039 'C' allele, 'CC' genotype and A-A-C haplotype in the ADHD probands, principally due to higher occurrence of the 'C' allele and A-A-C haplotype in the male probands (P < 0.05). Mother of the probands also showed higher occurrence of the 'C' allele and "CC" genotype (P < 0.01). Executive function was better in presence of rs2345039 "GG" (P = 0.04) while IQ score was higher in presence of rs6551665 "AA" (P = 0.06). Linkage disequilibrium between rs6551665 and rs2345039 was stronger in the ADHD cases, chiefly in the male probands. Multifactor dimensionality reduction analysis showed strong interaction between rs6551665 and rs2345039 in the male probands while in the female probands rs1868790 and rs6551665 revealed non-linear interaction. Based on these observations, we infer that ADGRL3 may have a role in the aetiology of ADHD in this population warranting further in depth investigation.

Mechanisms of adhesion G protein-coupled receptor activation

Adhesion G protein-coupled receptors (AGPCRs) are a thirty-three-member subfamily of Class B GPCRs that control a wide array of physiological processes and are implicated in disease. AGPCRs uniquely contain large, self-proteolyzing extracellular regions that range from hundreds to thousands of residues in length. AGPCR autoproteolysis occurs within the extracellular GPCR autoproteolysis-inducing (GAIN) domain that is proximal to the N terminus of the G protein-coupling seven-transmembrane-spanning bundle. GAIN domain-mediated self-cleavage is constitutive and produces two-fragment holoreceptors that remain bound at the cell surface. It has been of recent interest to understand how AGPCRs are activated in relation to their two-fragment topologies. Dissociation of the AGPCR fragments stimulates G protein signaling through the action of the tethered-peptide agonist stalk that is occluded within the GAIN domain in the holoreceptor form. AGPCRs can also signal independently of fragment dissociation, and a few receptors possess GAIN domains incapable of self-proteolysis. This has resulted in complex theories as to how these receptors are activated in vivo, complicating pharmacological advances. Currently, there is no existing structure of an activated AGPCR to support any of the theories. Further confounding AGPCR research is that many of the receptors remain orphans and lack identified activating ligands. In this review, we provide a detailed layout of the current theorized modes of AGPCR activation with discussion of potential parallels to mechanisms used by other GPCR classes. We provide a classification means for the ligands that have been identified and discuss how these ligands may activate AGPCRs in physiological contexts.

Enhanced Transient Striatal Dopamine Release and Reuptake in Lphn3 Knockout Rats

Latrophilin-3 (LPHN3) is an adhesion G protein coupled receptor involved in regulating neuroplasticity. Variants of LPHN3 are associated with increased risk of attention-deficit hyperactivity disorder. Data from mouse, zebrafish, Drosophila, and rat show that disruption of LPHN3 results in hyperactivity, and in the Sprague-Dawley Lphn3 knockout rat, exhibit deficits in learning and memory and changes in dopamine (DA) markers in the neostriatum. To determine the effects of Lphn3 deletion on DA neurotransmission, we compared the concentration, duration, and frequency of DA transients in KO and wild-type rats using fast-scan cyclic voltammetry in brain slices. Lphn3 KO rats showed higher release of DA, and the duration and interevent time were markedly decreased compared with wild-type rats. The data demonstrate that LPHN3 plays a heretofore unrecognized role in DA signaling and may represent a new target for small molecule regulation of DA neurotransmission with translational implications.

Structural Basis of Teneurin-Latrophilin Interaction in Repulsive Guidance of Migrating Neurons

Teneurins are ancient metazoan cell adhesion receptors that control brain development and neuronal wiring in higher animals. The extracellular C terminus binds the adhesion GPCR Latrophilin, forming a trans-cellular complex with synaptogenic functions. However, Teneurins, Latrophilins, and FLRT proteins are also expressed during murine cortical cell migration at earlier developmental stages. Here, we present crystal structures of Teneurin-Latrophilin complexes that reveal how the lectin and olfactomedin domains of Latrophilin bind across a spiraling beta-barrel domain of Teneurin, the YD shell. We couple structure-based protein engineering to biophysical analysis, cell migration assays, and in utero electroporation experiments to probe the importance of the interaction in cortical neuron migration. We show that binding of Latrophilins to Teneurins and FLRTs directs the migration of neurons using a contact repulsion-dependent mechanism. The effect is observed with cell bodies and small neurites rather than their processes. The results exemplify how a structure-encoded synaptogenic protein complex is also used for repulsive cell guidance.

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Crystal structures reveal binding site for Latrophilin on the Teneurin YD shell

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A ternary Latrophilin-Teneurin-FLRT complex forms in vitro and in vivo

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Latrophilin controls cortical migration by binding to Teneurins and FLRTs

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Latrophilin elicits repulsion of cortical cell bodies/small neurites but not axons

Latrophilin's Social Protein Network

Latrophilins (LPHNs) are adhesion GPCRs that are originally discovered as spider's toxin receptors, but are now known to be involved in brain development and linked to several neuronal and non-neuronal disorders. Latrophilins act in conjunction with other cell adhesion molecules and may play a leading role in its network organization. Here, we focus on the main protein partners of latrophilins, namely teneurins, FLRTs and contactins and summarize their respective temporal and spatial expression patterns, links to neurodevelopmental disorders as well as their structural characteristics. We discuss how more recent insights into the separate cell biological functions of these proteins shed light on the central role of latrophilins in this network. We postulate that latrophilins control the refinement of synaptic properties of specific subtypes of neurons, requiring discrete combinations of proteins.

Latrophilins: A Neuro-Centric View of an Evolutionary Conserved Adhesion G Protein-Coupled Receptor Subfamily

The adhesion G protein-coupled receptors latrophilins have been in the limelight for more than 20 years since their discovery as calcium-independent receptors for α-latrotoxin, a spider venom toxin with potent activity directed at neurotransmitter release from a variety of synapse types. Latrophilins are highly expressed in the nervous system. Although a substantial amount of studies has been conducted to describe the role of latrophilins in the toxin-mediated action, the recent identification of endogenous ligands for these receptors helped confirm their function as mediators of adhesion events. Here we hypothesize a role for latrophilins in inter-neuronal contacts and the formation of neuronal networks and we review the most recent information on their role in neurons. We explore molecular, cellular and behavioral aspects related to latrophilin adhesion function in mice, zebrafish, Drosophila melanogaster and Caenorhabditis elegans, in physiological and pathophysiological conditions, including autism spectrum, bipolar, attention deficit and hyperactivity and substance use disorders.

Knockout of latrophilin-3 in Sprague-Dawley rats causes hyperactivity, hyper-reactivity, under-response to amphetamine, and disrupted dopamine markers

Attention deficit hyperactivity disorder is a pervasive developmental disorder characterized by inattention, impulsivity, and hyperactivity and is 75-90% heritable. Latrophilin-3 (LPHN3; or ADGRL(3)) is associated with a subtype of ADHD, but how it translates to symptoms is unknown. LPHN3 is a synaptic adhesion G protein coupled receptor that binds to fibronectin leucine rich transmembrane protein 3 and teneurin-3 (FLRT3 and TEN-3). We created a null mutation of Lphn3 (KO) in Sprague-Dawley rats using CRISPR/Cas9 to delete exon-3. The KO rats had no effects on reproduction or survival but reduced growth. KO females showed catch-up weight gain whereas KO males did not. We tested WT and KO littermates for home-cage activity, anxiety-like behavior, acoustic startle response, and activity after amphetamine challenge. Expression of Lphn3-related genes, monoamines, and receptors were determined. Lphn3 KO rats showed persistent hyperactivity, increased acoustic startle, reduced activity in response to amphetamine relative to baseline, and female-specific reduced anxiety-like behavior. Expression of Lphn1, Lphn2, and Flrt3 by qPCR and their protein products by western-blot analysis showed no compensatory upregulation. Striatal tyrosine hydroxylase, aromatic L-amino acid decarboxylase (AADC), and the dopamine transporter were increased and dopamine D1 receptor (DRD1) and dopamine- and cAMP-regulated neuronal phosphoprotein (DARPP-32) decreased with no changes in DRD2, DRD4, vesicular monoamine transporter-2, N-methyl-d-aspartate (NMDA)-NR1, -NR2A, or -NR2B. LPHN3 is expressed in many brain regions but its function is largely unknown. Data from human, mouse, zebrafish, Drosophila and our new Lphn3 KO rat data collectively show that its disruption is significantly correlated with hyperactivity and associated striatal changes in dopamine markers.

Olfactomedin domain-containing proteins: evolution, functional divergence, expression patterns and damaging SNPs

Olfactomedin domain-containing proteins appear to facilitate neurodevelopment, cell adhesion, intercellular interactions, and protein-protein interactions, and the disruption of their expression will lead to dramatic developmental perturbations and lethality. The aim of the present work was to study how these genes evolved in metazoans and diverged after their duplication as well as to characterize their expression profiles and detrimental mutations. We conducted an exhaustive survey of olfactomedin domain-containing genes in genomic databases, identifying 235 olfactomedin-like (OLF) proteins in 29 representative species covering all the main metazoan lineages. Phylogenetic analyses allowed us to define nine different subfamilies of OLF genes, and subfamily IX, which specifically includes two immunoglobulin domains, was identified for the first time in arthropods. Functional divergence analysis suggested that the function of this arthropod-specific OLF subfamily might have diverged from that of other subfamilies. Expression pattern analysis of OLF genes in humans and rats showed that human OLF genes tended to be highly expressed in the brain, while rat OLF genes were inclined to be expressed in the ovary and brain. We used the SIFT and PolyPhen servers in dbNSFP to distinguish deleterious mutations from neutral mutations for each member of the OLF gene family. The results showed that OLFML2B contains the most destructive SNPs (up to 61), while none of the mutations in OLFM2, OLFM4 and LPHN2 were predicted to be harmful. Taken together, these findings may not only enhance understanding of the phylogenetic relationships of the OLF family but also aid future studies on OLF protein regulation of nervous system development and immune function.

ADGRL3 rs6551665 as a Common Vulnerability Factor Underlying Attention-Deficit/Hyperactivity Disorder and Autism Spectrum Disorder

Neurodevelopmental disorders are prevalent, frequently occur in comorbidity and share substantial genetic correlation. Previous evidence has suggested a role for the ADGRL3 gene in Attention-Deficit/Hyperactivity Disorder (ADHD) susceptibility in several samples. Considering ADGRL3 functionality in central nervous system development and its previous association with neurodevelopmental disorders, we aimed to assess ADGRL3 influence in early-onset ADHD (before 7 years of age) and Autism Spectrum Disorder (ASD). The sample comprises 187 men diagnosed with early-onset ADHD, 135 boys diagnosed with ASD and 468 male blood donors. We tested the association of an ADGRL3 variant (rs6551665) with both early-onset ADHD and ASD susceptibility. We observed significant associations between ADGRL3-rs6551665 on ADHD and ASD susceptibilities; we found that G-carriers were at increased risk of ADHD and ASD, in accordance with previous studies. The overall evidence from the literature, corroborated by our results, suggests that ADGRL3 might be involved in brain development, and genetic modifications related to it might be part of a shared vulnerability factor associated with the underlying neurobiology of neurodevelopmental disorders such as ADHD and ASD.

Pharmacological analysis of zebrafish lphn3.1 morphant larvae suggests that saturated dopaminergic signaling could underlie the ADHD-like locomotor hyperactivity

Polymorphisms in the gene coding for the adhesion G-protein coupled receptor LPHN3 are a risk factor for attention-deficit/hyperactivity disorder (ADHD). Transient down-regulation of latrophilin3.1 (lphn3.1), the zebrafish LPHN3 homologue, causes hyperactivity. Zebrafish injected with a lphn3.1-specific morpholino are hyperactive and display an impairment in dopaminergic neuron development. In the present study we used lphn3.1 morphants to further characterize the changes to dopaminergic signaling that trigger hyperactivity. We applied dopamine agonists (Apomorphine, Quinpirole, SKF-38393) and antagonists (Haloperidol, Eticlopride, SCH-23390) to Lphn3.1 morpholino-injected or control-injected animals. The percentage of change in locomotor activity was then determined at three different time periods (10-20 min, 30-40 min and 60-70 min). Our results show that drugs targeting dopamine receptors appear to elicit similar effects on locomotion in zebrafish larvae and mammals. In addition, we observed that lphn3.1 morphants have an overall hyposensitivity to dopamine agonists and antagonists compared to control fish. These results are compatible with a model whereby dopaminergic neurotransmission is saturated in lphn3.1 morphants.

Brain imaging genetics in ADHD and beyond - Mapping pathways from gene to disorder at different levels of complexity

Attention-deficit/hyperactivity disorder (ADHD) is a common and often persistent neurodevelopmental disorder. Beyond gene-finding, neurobiological parameters, such as brain structure, connectivity, and function, have been used to link genetic variation to ADHD symptomatology. We performed a systematic review of brain imaging genetics studies involving 62 ADHD candidate genes in childhood and adult ADHD cohorts. Fifty-one eligible research articles described studies of 13 ADHD candidate genes. Almost exclusively, single genetic variants were studied, mostly focussing on dopamine-related genes. While promising results have been reported, imaging genetics studies are thus far hampered by methodological differences in study design and analysis methodology, as well as limited sample sizes. Beyond reviewing imaging genetics studies, we also discuss the need for complementary approaches at multiple levels of biological complexity and emphasize the importance of combining and integrating findings across levels for a better understanding of biological pathways from gene to disease. These may include multi-modal imaging genetics studies, bioinformatic analyses, and functional analyses of cell and animal models.

An Ultraconserved Brain-Specific Enhancer Within ADGRL3 (LPHN3) Underpins Attention-Deficit/Hyperactivity Disorder Susceptibility

BACKGROUND

Genetic factors predispose individuals to attention-deficit/hyperactivity disorder (ADHD). Previous studies have reported linkage and association to ADHD of gene variants within ADGRL3. In this study, we functionally analyzed noncoding variants in this gene as likely pathological contributors.

METHODS

In silico, in vitro, and in vivo approaches were used to identify and characterize evolutionary conserved elements within the ADGRL3 linkage region (~207 Kb). Family-based genetic analyses of 838 individuals (372 affected and 466 unaffected patients) identified ADHD-associated single nucleotide polymorphisms harbored in some of these conserved elements. Luciferase assays and zebrafish green fluorescent protein transgenesis tested conserved elements for transcriptional enhancer activity. Electromobility shift assays were used to verify transcription factor-binding disruption by ADHD risk alleles.

RESULTS

An ultraconserved element was discovered (evolutionary conserved region 47) that functions as a transcriptional enhancer. A three-variant ADHD risk haplotype in evolutionary conserved region 47, formed by rs17226398, rs56038622, and rs2271338, reduced enhancer activity by 40% in neuroblastoma and astrocytoma cells (p_Bonferroni < .0001). This enhancer also drove green fluorescent protein expression in the zebrafish brain in a tissue-specific manner, sharing aspects of endogenous ADGRL3 expression. The rs2271338 risk allele disrupts binding of YY1 transcription factor, an important factor in the development and function of the central nervous system. Expression quantitative trait loci analysis of postmortem human brain tissues revealed an association between rs2271338 and reduced ADGRL3 expression in the thalamus.

CONCLUSIONS

These results uncover the first functional evidence of common noncoding variants with potential implications for the pathology of ADHD.

Structural Perspectives on Axon Guidance

Axon guidance relies on a combinatorial code of receptor and ligand interactions that direct adhesive/attractive and repulsive cellular responses. Recent structural data have revealed many of the molecular mechanisms that govern these interactions and enabled the design of sophisticated mutant tools to dissect their biological functions. Here, we discuss the structure/function relationships of four major classes of guidance cues (ephrins, semaphorins, slits, netrins) and examples of morphogens (Wnt, Shh) and of cell adhesion molecules (FLRT). These cell signaling systems rely on specific modes of receptor-ligand binding that are determined by selective binding sites; however, defined structure-encoded receptor promiscuity also enables cross talk between different receptor/ligand families and can also involve extracellular matrix components. A picture emerges in which a multitude of highly context-dependent structural assemblies determines the finely tuned cellular behavior required for nervous system development.

ADGRL3 (LPHN3) variants are associated with a refined phenotype of ADHD in the MTA study

Background

ADHD is the most common neuropsychiatric condition affecting individuals of all ages. Long‐term outcomes of affected individuals and association with severe comorbidities as SUD or conduct disorders are the main concern. Genetic associations have been extensively described. Multiple studies show that intronic variants harbored in the ADGRL3 (LPHN3) gene are associated with ADHD, especially associated with poor outcomes.

Methods

In this study, we evaluated this association in the Multimodal Treatment Study of children with ADHD (MTA), initiated as a 14‐month randomized clinical trial of 579 children diagnosed with DSM‐IV ADHD‐Combined Type (ADHD‐C), that transitioned to a 16‐year prospective observational follow‐up, and 289 classmates added at the 2‐year assessment to serve as a local normative comparison group (LNCG). Diagnostic evaluations at entry were based on the Diagnostic Interview Schedule for Children‐Parent (DISC‐P), which was repeated at several points over the years. For an add‐on genetic study, blood samples were collected from 232 in the MTA group and 139 in the LNCG.

Results

For the 205 MTA participants, 14.6% retained the DISC‐P diagnosis of ADHD‐C in adolescence. For 127 LNCG participants, 88.2% remained undiagnosed by the DISC‐P. We genotyped 15 polymorphic SNP markers harbored in the ADGRL3 gene, and compared allele frequencies for the 30 cases with continued diagnosis of ADHD‐C in adolescence to the other participants. Replication of the association of rs2345039 ADGRL3 variant was observed (P value = 0.004, FDR corrected = 0.03; Odds ratio = 2.25, upper CI 1.28–3.97).

Conclusion

The detection of susceptibility conferred by ADGRL3 variants in the extreme phenotype of continued diagnosis of ADHD‐C from childhood to adolescence provides additional support that the association of ADGRL3 and ADHD is not spurious. Exploring genetic effects in longitudinal cohorts, in which refined, age‐dependent phenotypes are documented, is crucial to understand the natural history of ADHD.

Super-complexes of adhesion GPCRs and neural guidance receptors

Latrophilin adhesion-GPCRs (Lphn1–3 or ADGRL1–3) and Unc5 cell guidance receptors (Unc5A–D) interact with FLRT proteins (FLRT1–3), thereby promoting cell adhesion and repulsion, respectively. How the three proteins interact and function simultaneously is poorly understood. We show that Unc5D interacts with FLRT2 in cis, controlling cell adhesion in response to externally presented Lphn3. The ectodomains of the three proteins bind cooperatively. Crystal structures of the ternary complex formed by the extracellular domains reveal that Lphn3 dimerizes when bound to FLRT2:Unc5, resulting in a stoichiometry of 1:1:2 (FLRT2:Unc5D:Lphn3). This 1:1:2 complex further dimerizes to form a larger ‘super-complex' (2:2:4), using a previously undescribed binding motif in the Unc5D TSP1 domain. Molecular dynamics simulations, point-directed mutagenesis and mass spectrometry demonstrate the stability and molecular properties of these complexes. Our data exemplify how receptors increase their functional repertoire by forming different context-dependent higher-order complexes.

FLRT proteins are known to interact with Lphns and Unc5s, mediating cell adhesion and repulsion respectively. Here the authors use crystallography, native mass spectrometry, molecular dynamics simulations and cell-based assays to show that these three proteins form large super-complexes with functions distinct from their smaller subcomplexes.

LPHN3 and attention-deficit/hyperactivity disorder: a susceptibility and pharmacogenetic study

Latrophilin 3 (LPHN3) is a brain-specific member of the G-protein coupled receptor family associated to both attention-deficit/hyperactivity disorder (ADHD) genetic susceptibility and methylphenidate (MPH) pharmacogenetics. Interactions of LPHN3 variants with variants harbored in the 11q chromosome improve the prediction of ADHD development and medication response. The aim of this study was to evaluate the role of LPHN3 variants in childhood ADHD susceptibility and treatment response in a naturalistic clinical cohort. The association between LPHN3 and ADHD was evaluated in 523 children and adolescents with ADHD and 132 controls. In the pharmacogenetic study, 172 children with ADHD were investigated. The primary outcome measure was the parent-rated Swanson, Nolan and Pelham Scale - version IV applied at baseline, first and third months of treatment with MPH. The results reported herein suggest the CGC haplotype derived from single nucleotide polymorphisms (SNPs) rs6813183, rs1355368 and rs734644 as an ADHD risk haplotype (P = 0.02, OR = 1.46). Although non-significant after multiple testing correction, its interaction with the 11q chromosome SNP rs965560 slightly increases risk (P = 0.03, OR = 1.55). Homozygous individuals for the CGC haplotype showed faster response to MPH treatment as a significant interaction effect between CGC haplotype and treatment over time was observed (P < 0.001). Homozygous individuals for the GT haplotype derived from SNPs rs6551665 and rs1947275 showed a nominally significant interaction with treatment over time (P = 0.04). Our findings replicate previous findings reporting that LPHN3 confers ADHD susceptibility, and moderates MPH treatment response in children and adolescents with ADHD.

Behavioral and transcriptomic profiling of mice null for Lphn3, a gene implicated in ADHD and addiction

Background

The Latrophilin 3 (LPHN3) gene (recently renamed Adhesion G protein‐coupled receptor L3 (ADGRL3)) has been linked to susceptibility to attention deficit/hyperactivity disorder (ADHD) and vulnerability to addiction. However, its role and function are not well understood as there are no known functional variants.

Methods

To characterize the function of this little known gene, we phenotyped Lphn3 null mice. We assessed motivation for food reward and working memory via instrumental responding tasks, motor coordination via rotarod, and depressive‐like behavior via forced swim. We also measured neurite outgrowth of primary hippocampal and cortical neuron cultures. Standard blood chemistries and blood counts were performed. Finally, we also evaluated the transcriptome in several brain regions.

Results

Behaviorally, loss of Lphn3 increases both reward motivation and activity levels. Lphn3 null mice display significantly greater instrumental responding for food than wild‐type mice, particularly under high response ratios, and swim incessantly during a forced swim assay. However, loss of Lphn3 does not interfere with working memory or motor coordination. Primary hippocampal and cortical neuron cultures demonstrate that null neurons display comparatively enhanced neurite outgrowth after 2 and 3 days in vitro. Standard blood chemistry panels reveal that nulls have low serum calcium levels. Finally, analysis of the transcriptome from prefrontal cortical, striatal, and hippocampal tissue at different developmental time points shows that loss of Lphn3 results in genotype‐dependent differential gene expression (DGE), particularly for cell adhesion molecules and calcium signaling proteins. Much of the DGE is attenuated with age, and is consistent with the idea that ADHD is associated with delayed cortical maturation.

Conclusions

Transcriptome changes likely affect neuron structure and function, leading to behavioral anomalies consistent with both ADHD and addiction phenotypes. The data should further motivate analyses of Lphn3 function in the developmental timing of altered gene expression and calcium signaling, and their effects on neuronal structure/function during development.

Adhesion GPCRs as Novel Actors in Neural and Glial Cell Functions: From Synaptogenesis to Myelination

Adhesion G-protein-coupled receptors (aGPCRs) are emerging as key regulators of nervous system development and health. aGPCRs can regulate many aspects of neural development, including cell signaling, cell-cell and cell-matrix interactions, and, potentially, mechanosensation. Here, we specifically focus on the roles of several aGPCRs in synapse biology, dendritogenesis, and myelinating glial cell development. The lessons learned from these examples may be extrapolated to other contexts in the nervous system and beyond.

International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G protein-coupled receptors

The Adhesion family forms a large branch of the pharmacologically important superfamily of G protein-coupled receptors (GPCRs). As Adhesion GPCRs increasingly receive attention from a wide spectrum of biomedical fields, the Adhesion GPCR Consortium, together with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification, proposes a unified nomenclature for Adhesion GPCRs. The new names have ADGR as common dominator followed by a letter and a number to denote each subfamily and subtype, respectively. The new names, with old and alternative names within parentheses, are: ADGRA1 (GPR123), ADGRA2 (GPR124), ADGRA3 (GPR125), ADGRB1 (BAI1), ADGRB2 (BAI2), ADGRB3 (BAI3), ADGRC1 (CELSR1), ADGRC2 (CELSR2), ADGRC3 (CELSR3), ADGRD1 (GPR133), ADGRD2 (GPR144), ADGRE1 (EMR1, F4/80), ADGRE2 (EMR2), ADGRE3 (EMR3), ADGRE4 (EMR4), ADGRE5 (CD97), ADGRF1 (GPR110), ADGRF2 (GPR111), ADGRF3 (GPR113), ADGRF4 (GPR115), ADGRF5 (GPR116, Ig-Hepta), ADGRG1 (GPR56), ADGRG2 (GPR64, HE6), ADGRG3 (GPR97), ADGRG4 (GPR112), ADGRG5 (GPR114), ADGRG6 (GPR126), ADGRG7 (GPR128), ADGRL1 (latrophilin-1, CIRL-1, CL1), ADGRL2 (latrophilin-2, CIRL-2, CL2), ADGRL3 (latrophilin-3, CIRL-3, CL3), ADGRL4 (ELTD1, ETL), and ADGRV1 (VLGR1, GPR98). This review covers all major biologic aspects of Adhesion GPCRs, including evolutionary origins, interaction partners, signaling, expression, physiologic functions, and therapeutic potential.

Structural and Mechanistic Insights into the Latrophilin3-FLRT3 Complex that Mediates Glutamatergic Synapse Development

Latrophilins (LPHNs) are adhesion-like G-protein-coupled receptors implicated in attention-deficit/hyperactivity disorder. Recently, LPHN3 was found to regulate excitatory synapse number through trans interactions with fibronectin leucine-rich repeat transmembrane 3 (FLRT3). By isothermal titration calorimetry, we determined that only the olfactomedin (OLF) domain of LPHN3 is necessary for FLRT3 association. By multi-crystal native single-wavelength anomalous diffraction phasing, we determined the crystal structure of the OLF domain. This structure is a five-bladed β propeller with a Ca(2+) ion bound in the central pore, which is capped by a mobile loop that allows the ion to exchange with the solvent. The crystal structure of the OLF/FLRT3 complex shows that LPHN3-OLF in the closed state binds with high affinity to the concave face of FLRT3-LRR with a combination of hydrophobic and charged residues. Our study provides structural and functional insights into the molecular mechanism underlying the contribution of LPHN3/FLRT3 to the development of glutamatergic synapses.

Structural Basis of Latrophilin-FLRT-UNC5 Interaction in Cell Adhesion

Fibronectin leucine-rich repeat transmembrane proteins (FLRTs) are cell-adhesion molecules with emerging functions in cortical development and synapse formation. Their extracellular regions interact with latrophilins (LPHNs) to mediate synapse development, and with Uncoordinated-5 (UNC5)/netrin receptors to control the migration of neurons in the developing cortex. Here, we present the crystal structures of FLRT3 in isolation and in complex with LPHN3. The LPHN3/FLRT3 structure reveals that LPHN3 binds to FLRT3 at a site distinct from UNC5. Structure-based mutations specifically disrupt LPHN3/FLRT3 binding, but do not disturb their interactions with other proteins or their cell-membrane localization. Thus, they can be used as molecular tools to dissect the functions of FLRTs and LPHNs in vivo. Our results suggest that UNC5 and LPHN3 can simultaneously bind to FLRT3, forming a trimeric complex, and that FLRT3 may form transsynaptic complexes with both LPHN3 and UNC5. These findings provide molecular insights for understanding the role of cell-adhesion proteins in synapse function.

Structural basis of latrophilin-FLRT interaction

Latrophilins, receptors for spider venom α-latrotoxin, are adhesion type G-protein-coupled receptors with emerging functions in synapse development. The N-terminal region binds the endogenous cell adhesion molecule FLRT, a major regulator of cortical and synapse development. We present crystallographic data for the mouse Latrophilin3 lectin and olfactomedin-like (Olf) domains, thereby revealing the Olf β-propeller fold and conserved calcium-binding site. We locate the FLRT-Latrophilin binding surfaces by a combination of sequence conservation analysis, point mutagenesis, and surface plasmon resonance experiments. In stripe assays, we show that wild-type Latrophilin3 and its high-affinity interactor FLRT2, but not the binding-impaired mutants we generated, promote HeLa cell adhesion. In contrast, cortical neurons expressing endogenous FLRTs are repelled by wild-type Latrophilin3 and not by the binding-impaired mutant. Taken together, we present molecular level insights into Latrophilin structure, its FLRT-binding mechanism, and a role for Latrophilin and FLRT that goes beyond a simply adhesive interaction.

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The LPHN olfactomedin-like domain forms a five-bladed β propeller

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A conserved calcium-binding site is located at the center of the protein

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Latrophilin-FLRT binding depends on a conserved binding site

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Mutations in the binding site inhibit Latrophilin-FLRT signaling

Structural basis for misfolding in myocilin-associated glaucoma

Olfactomedin (OLF) domain-containing proteins play roles in fundamental cellular processes and have been implicated in disorders ranging from glaucoma, cancers and inflammatory bowel disorder, to attention deficit disorder and childhood obesity. We solved crystal structures of the OLF domain of myocilin (myoc-OLF), the best studied such domain to date. Mutations in myoc-OLF are causative in the autosomal dominant inherited form of the prevalent ocular disorder glaucoma. The structures reveal a new addition to the small family of five-bladed β-propellers. Propellers are most well known for their ability to act as hubs for protein-protein interactions, a function that seems most likely for myoc-OLF, but they can also act as enzymes. A calcium ion, sodium ion and glycerol molecule were identified within a central hydrophilic cavity that is accessible via movements of surface loop residues. By mapping familial glaucoma-associated lesions onto the myoc-OLF structure, three regions sensitive to aggregation have been identified, with direct applicability to differentiating between neutral and disease-causing non-synonymous mutations documented in the human population worldwide. Evolutionary analysis mapped onto the myoc-OLF structure reveals conserved and divergent regions for possible overlapping and distinctive functional protein-protein or protein-ligand interactions across the broader OLF domain family. While deciphering the specific normal biological functions, ligands and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, atomic detail structural knowledge of myoc-OLF is a valuable guide for understanding the implications of glaucoma-associated mutations and will help focus future studies of this biomedically important domain family.

Control of neural circuit formation by leucine-rich repeat proteins

The function of neural circuits depends on the precise connectivity between populations of neurons. Increasing evidence indicates that disruptions in excitatory or inhibitory synapse formation or function lead to excitation/inhibition (E/I) imbalances and contribute to neurodevelopmental and psychiatric disorders. Leucine-rich repeat (LRR)-containing surface proteins have emerged as key organizers of excitatory and inhibitory synapses. Distinct LRR proteins are expressed in different cell types and interact with key pre- and postsynaptic proteins. These protein interaction networks allow LRR proteins to coordinate pre- and postsynaptic elements during synapse formation and differentiation, pathway-specific synapse development, and synaptic plasticity. LRR proteins, therefore, play a critical role in organizing synaptic connections into functional neural circuits, and their dysfunction may contribute to neuropsychiatric disorders.

LPHN3, a presynaptic adhesion-GPCR implicated in ADHD, regulates the strength of neocortical layer 2/3 synaptic input to layer 5

Background

Latrophilins (LPHNs) are a small family of neuronal adhesion-GPCRs originally discovered as receptors for the black widow spider toxin α-latrotoxin. Mutations in LPHN3 have recently been identified as risk factors for attention deficit hyperactivity disorder (ADHD) in humans, but their physiological function has remained elusive. In this study, we tested two hypotheses regarding LPHN3 function: (1) LPHN3 regulates synaptic transmission by modulating probability of release; and (2) LPHN3 controls synapse development and the abundance of synapses.

Results

We manipulated LPHN3 expression in mouse layer 2/3 (L2/3) pyramidal neurons and examined the consequences on the L2/3 to L5 cortical microcircuit. Employing an optogenetic strategy combined with shRNA knockdown of LPHN3, we found that LPHN3 did not influence probability of release at synapses formed by L2/3 neurons onto L5 pyramidal cells. The strength of L2/3 afferent input to L5, however, was weakened by loss of LPHN3. Using Synaptophysin-GFP as an anatomical marker of presynaptic terminals, we found that the density of synapses formed by L2/3 axons in L5 was reduced when LPHN3 was lost. Finally, we investigated the structural organization of the extracellular domain of LPHN3. We used single particle negative stain electron microscopy to image the extracellular domain of LPHN3 and showed that the Olfactomedin and Lectin domains form a globular domain on an elongated stalk. Cell-based binding experiments with mutant proteins revealed that the Olfactomedin domain was required for binding to FLRT3, whereas both the Olfactomedin and Lectin domains were involved in binding to Teneurin 1. Mutant LPHN3 lacking the Olfactomedin domain was not capable of rescuing the deficit in presynaptic density following knockdown of endogenous LPHN3.

Conclusions

We find that LPHN3 regulates the number of synapses formed by L2/3 neurons in L5 and the strength of synaptic drive from the L2/3-L5 pathway. The Olfactomedin domain of LPHN3 is required for this effect on synapse number and binding to its postsynaptic ligand FLRT3. We propose that LPHN3 functions in synaptic development and is important in determining the connectivity rates between principal neurons in the cortex.

Genome-wide association study of patient-rated and clinician-rated global impression of severity during antipsychotic treatment

OBJECTIVE

To examine the unique and congruent findings between multiple raters in a genome-wide association study (GWAS) in the context of understanding individual differences in treatment response during antipsychotic therapy for schizophrenia.

MATERIALS AND METHODS

We performed GWAS to search for genetic variation affecting treatment response. The analysis sample included 738 patients with schizophrenia, successfully genotyped for ∼492k single nucleotide polymorphisms (SNPs) from the Clinical Antipsychotic Trial of Intervention Effectiveness. Outcomes included both clinician and patient report of illness severity on global impression scales, the clinical global impression severity scale and patient global impression, respectively. Our criterion for genome-wide significance was a prespecified threshold ensuring that, on average, only 10% of the significant findings are false discoveries.

RESULTS

Thirteen SNPs reached genome-wide significance. The top findings indicated three SNPs in PDE4D, 5q12.1 (P=4.2×10, 1.6×10, 1.8×10), mediating the effects of quetiapine on patient-reported severity and an additional three SNPs in TJP1, 15q13.1 (P=2.25×10, 4.86×10, 4.91×10), mediating the effects of risperidone on patient-reported severity. For clinician-reported severity, two SNPs in PPA2, 4q24 (P=3.68×10, 5.05×10), were found to reach genome-wide significance.

CONCLUSION

We found evidence of both a novel and a consistent association when examining the results from the patient and clinician ratings, suggesting that different raters may capture unique facets of schizophrenia. Although our findings require replication and functional validation, this study shows the potential of GWAS to discover genes that potentially mediate treatment response of antipsychotic medication.

Influence of a latrophilin 3 (LPHN3) risk haplotype on event-related potential measures of cognitive response control in attention-deficit hyperactivity disorder (ADHD)

Current research strategies have made great efforts to further elucidate the complex genetic architecture of attention-deficit hyperactivity disorder (ADHD). The present study examined the impact of an LPHN3 haplotype that has recently been associated with ADHD (Arcos-Burgos et al., 2010) on neural activity in a visual Go-NoGo task. Two hundred sixteen adult ADHD patients completed a Continuous Performance Test (CPT) while the ongoing EEG was simultaneously recorded. Results showed that patients carrying two copies of the LPHN3 risk haplotype (n=114) made more omission errors and had a more anterior Go-centroid of the P300 than patients carrying at least one LPHN3 non-risk haplotype (n=102). Accordingly, the NoGo-Anteriorization (NGA; topographical ERP difference of the Go- and NoGo-condition), a neurophysiological marker of prefrontal functioning, was reduced in the LPHN3 high risk group. However, in the NoGo-condition itself no marked differences attributable to the LPHN3 haplotype could be found. Our findings indicate that, within a sample of ADHD patients, the LPHN3 gene impacts behavioral and neurophysiological measures of cognitive response control. The results of our study further strengthen the concept of an LPHN3 risk haplotype for ADHD and support the usefulness of the endophenotype approach in psychiatric and psychological research.

Toward developmental models of psychiatric disorders in zebrafish

Psychiatric disorders are a diverse set of diseases that affect all aspects of mental function including social interaction, thinking, feeling, and mood. Although psychiatric disorders place a large economic burden on society, the drugs available to treat them are often palliative with variable efficacy and intolerable side-effects. The development of novel drugs has been hindered by a lack of knowledge about the etiology of these diseases. It is thus necessary to further investigate psychiatric disorders using a combination of human molecular genetics, gene-by-environment studies, in vitro pharmacological and biochemistry experiments, animal models, and investigation of the non-biological basis of these diseases, such as environmental effects. Many psychiatric disorders, including autism spectrum disorder, attention-deficit/hyperactivity disorder, mental retardation, and schizophrenia can be triggered by alterations to neural development. The zebrafish is a popular model for developmental biology that is increasingly used to study human disease. Recent work has extended this approach to examine psychiatric disorders as well. However, since psychiatric disorders affect complex mental functions that might be human specific, it is not possible to fully model them in fish. In this review, I will propose that the suitability of zebrafish for developmental studies, and the genetic tools available to manipulate them, provide a powerful model to study the roles of genes that are linked to psychiatric disorders during neural development. The relative speed and ease of conducting experiments in zebrafish can be used to address two areas of future research: the contribution of environmental factors to disease onset, and screening for novel therapeutic compounds.

Dense-map genome scan for dyslexia supports loci at 4q13, 16p12, 17q22; suggests novel locus at 7q36

Analysis of genetic linkage to dyslexia was performed using 133,165 array-based SNPs genotyped in 718 persons from 101 dyslexia-affected families. Results showed five linkage peaks with lod scores >2.3 (4q13.1, 7q36.1-q36.2, 7q36.3, 16p12.1, and 17q22). Of these five regions, three have been previously implicated in dyslexia (4q13.1, 16p12.1, and 17q22), three have been implicated in attention-deficit hyperactivity disorder (ADHD, which highly co-occurs with dyslexia; 4q13.1, 7q36.3, 16p12.1) and four have been implicated in autism (a condition characterized by language deficits; 7q36.1-q36.2, 7q36.3, 16p12.1, and 17q22). These results highlight the reproducibility of dyslexia linkage signals, even without formally significant lod scores, and suggest dyslexia predisposing genes with relatively major effects and locus heterogeneity. The largest lod score (2.80) occurred at 17q22 within the MSI2 gene, involved in neuronal stem cell lineage proliferation. Interestingly, the 4q13.1 linkage peak (lod 2.34) occurred immediately upstream of the LPHN3 gene, recently reported both linked and associated with ADHD. Separate analyses of larger pedigrees revealed lods >2.3 at 1-3 regions per family; one family showed strong linkage (lod 2.9) to a known dyslexia locus (18p11) not detected in our overall data, demonstrating the value of analyzing single large pedigrees. Association analysis identified no SNPs with genome-wide significance, although a borderline significant SNP (P = 6 × 10(-7)) occurred at 5q35.1 near FGF18, involved in laminar positioning of cortical neurons during development. We conclude that dyslexia genes with relatively major effects exist, are detectable by linkage analysis despite genetic heterogeneity, and show substantial overlapping predisposition with ADHD and autism.

The ADHD-susceptibility gene lphn3.1 modulates dopaminergic neuron formation and locomotor activity during zebrafish development

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by inattention, hyperactivity, increased impulsivity and emotion dysregulation. Linkage analysis followed by fine-mapping identified variation in the gene coding for Latrophilin 3 (LPHN3), a putative adhesion-G protein-coupled receptor, as a risk factor for ADHD. In order to validate the link between LPHN3 and ADHD, and to understand the function of LPHN3 in the etiology of the disease, we examined its ortholog lphn3.1 during zebrafish development. Loss of lphn3.1 function causes a reduction and misplacement of dopamine-positive neurons in the ventral diencephalon and a hyperactive/impulsive motor phenotype. The behavioral phenotype can be rescued by the ADHD treatment drugs methylphenidate and atomoxetine. Together, our results implicate decreased Lphn3 activity in eliciting ADHD-like behavior, and demonstrate its correlated contribution to the development of the brain dopaminergic circuitry.

GWAS reveals new recessive loci associated with non-syndromic facial clefting

We have applied a GWAS to 40 consanguineous families segregating cases of non-syndromic cleft lip with or without cleft palate (NS CL/P) (a total of 160 affected and unaffected individuals) in order to trace potential recessive loci that confer susceptibility to this common facial malformation. Pedigree-based association test (PBAT) analyses reported nominal evidence of association and linkage over SNP markers located at 11q25 (rs4937877, P = 2.7 × 10(-6)), 19p12 (rs4324267, P = 1.6 × 10(-5)), 5q14.1 (rs4588572, P-value = 3.36 × 10(-5)), and 15q21.1 (rs4774497, P = 1.08 × 10(-4)). Using the Versatile Gene-Based Association Study to complement the PBAT results, we found clusters of markers located at chromosomes 19p12, 11q25, and 8p23.2 overcome the threshold for GWAS significance (P < 1 × 10(-7)). From this study, new recessive loci implicated in NS CL/P include: B3GAT1, GLB1L2, ZNF431, ZNF714, and CSMD1, even though the functional association with the genesis of NS CL/P remains to be elucidated. These results emphasize the importance of using homogeneous populations, phenotypes, and family structures for GWAS combined with gene-based association analyses, and should encourage. other researchers to evaluate these genes on independent patient samples affected by NS CL/P.

FLRT proteins are endogenous latrophilin ligands and regulate excitatory synapse development

Latrophilins (LPHNs) are a small family of G protein-coupled receptors known to mediate the massive synaptic exocytosis caused by the black widow spider venom α-latrotoxin, but their endogenous ligands and function remain unclear. Mutations in LPHN3 are strongly associated with attention deficit hyperactivity disorder, suggesting a role for latrophilins in human cognitive function. Using affinity chromatography and mass spectrometry, we identify the FLRT family of leucine-rich repeat transmembrane proteins as endogenous postsynaptic ligands for latrophilins. We demonstrate that the FLRT3 and LPHN3 ectodomains interact with high affinity in trans and that interference with this interaction using soluble recombinant LPHN3, LPHN3 shRNA, or FLRT3 shRNA reduces excitatory synapse density in cultured neurons. In addition, reducing FLRT3 levels with shRNA in vivo decreases afferent input strength and dendritic spine number in dentate granule cells. These observations indicate that LPHN3 and its ligand FLRT3 play an important role in glutamatergic synapse development.

Genetic regulation of Nrxn1 [corrected] expression: an integrative cross-species analysis of schizophrenia candidate genes

Neurexin 1 (NRXN1) is a large presynaptic transmembrane protein that has complex and variable patterns of expression in the brain. Sequence variants in NRXN1 are associated with differences in cognition, and with schizophrenia and autism. The murine Nrxn1 gene is also highly polymorphic and is associated with significant variation in expression that is under strong genetic control. Here, we use co-expression analysis, high coverage genomic sequence, and expression quantitative trait locus (eQTL) mapping to study the regulation of this gene in the brain. We profiled a family of 72 isogenic progeny strains of a cross between C57BL/6J and DBA/2J (the BXD family) using exon arrays and massively parallel RNA sequencing. Expression of most Nrxn1 exons have high genetic correlation (r>0.6) because of the segregation of a common trans eQTL on chromosome (Chr) 8 and a common cis eQTL on Chr 17. These two loci are also linked to murine phenotypes relevant to schizophrenia and to a novel human schizophrenia candidate gene with high neuronal expression (Pleckstrin and Sec7 domain containing 3). In both human and mice, NRXN1 is co-expressed with numerous synaptic and cell signaling genes, and known schizophrenia candidates. Cross-species co-expression and protein interaction network analyses identified glycogen synthase kinase 3 beta (GSK3B) as one of the most consistent and conserved covariates of NRXN1. By using the Molecular Genetics of Schizophrenia data set, we were able to test and confirm that markers in NRXN1 and GSK3B have epistatic interactions in human populations that can jointly modulate risk of schizophrenia.