SLITRK1 binds 14-3-3 and regulates neurite outgrowth in a phosphorylation-dependent manner

The genetics of trichotillomania and excoriation disorder: A systematic review

BACKGROUND

Trichotillomania (TTM) and excoriation disorder (ED) are impairing obsessive-compulsive related disorders that are common in the general population and for which there are no clear first-line medications, highlighting the need to better understand the underlying biology of these disorders to inform treatments. Given the importance of genetics in obsessive-compulsive disorder (OCD), evaluating genetic factors underlying TTM and ED may advance knowledge about the pathophysiology of these body-focused repetitive behaviors.

AIM

In this systematic review, we summarize the available evidence on the genetics of TTM and ED and highlight gaps in the field warranting further research.

METHOD

We systematically searched Embase, PsycInfo, PubMed, Medline, Scopus, and Web of Science for original studies in genetic epidemiology (family or twin studies) and molecular genetics (candidate gene and genome-wide) published up to June 2023.

RESULTS

Of the 3536 records identified, 109 studies were included in this review. These studies indicated that genetic factors play an important role in the development of TTM and ED, some of which may be shared across the OCD spectrum, but there are no known high-confidence specific genetic risk factors for either TTM or ED.

CONCLUSIONS

Our review underscores the need for additional genome-wide research conducted on the genetics of TTM and ED, for instance, genome-wide association and whole-genome/whole-exome DNA sequencing studies. Recent advances in genomics have led to the discovery of risk genes in several psychiatric disorders, including related conditions such as OCD, but to date, TTM and ED have remained understudied.

14-3-3 protein augments the protein stability of phosphorylated spastin and promotes the recovery of spinal cord injury through its agonist intervention

Axon regeneration is abortive in the central nervous system following injury. Orchestrating microtubule dynamics has emerged as a promising approach to improve axonal regeneration. The microtubule severing enzyme spastin is essential for axonal development and regeneration through remodeling of microtubule arrangement. To date, however, little is known regarding the mechanisms underlying spastin action in neural regeneration after spinal cord injury. Here, we use glutathione transferase pulldown and immunoprecipitation assays to demonstrate that 14-3-3 interacts with spastin, both in vivo and in vitro, via spastin Ser233 phosphorylation. Moreover, we show that 14-3-3 protects spastin from degradation by inhibiting the ubiquitination pathway and upregulates the spastin-dependent severing ability. Furthermore, the 14-3-3 agonist Fusicoccin (FC-A) promotes neurite outgrowth and regeneration in vitro which needs spastin activation. Western blot and immunofluorescence results revealed that 14-3-3 protein is upregulated in the neuronal compartment after spinal cord injury in vivo. In addition, administration of FC-A not only promotes locomotor recovery, but also nerve regeneration following spinal cord injury in both contusion and lateral hemisection models; however, the application of spastin inhibitor spastazoline successfully reverses these phenomena. Taken together, these results indicate that 14-3-3 is a molecular switch that regulates spastin protein levels, and the small molecule 14-3-3 agonist FC-A effectively mediates the recovery of spinal cord injury in mice which requires spastin participation.

Pivotal Role of Slitrk1 in Adult Striatal Cholinergic Neurons in Mice: Implication in Tourette Syndrome

OBJECTIVE

The SLIT and NTRK-like 1 (SLITRK1) gene mutation and striatal cholinergic interneurons (ChIs) loss are associated with Tourette syndrome (TS). ChIs comprise only 1 to 2% of striatal neurons but project widely throughout the stratum to impact various striatal neurotransmission, including TS-related dopaminergic transmission. Here, we link striatal Slitrk1, ChI function, and dopaminergic transmission and their associations with TS-like tic behaviors.

METHODS

Slitrk1-KD mice were induced by bilaterally injecting Slitrk1 siRNA into their dorsal striatum. Control mice received scrambled siRNA injection. Their TS-like tic behaviors, prepulse inhibition, sensory-motor function and dopamine-related behaviors were compared. We also compared dopamine and ACh levels in microdialysates, Slitrk protein and dopamine transporter levels, and numbers of Slitrk-positive ChIs and activated ChIs in the striatum between two mouse groups, and electrophysiological properties between Slitrk-positive and Slitrk-negative striatal ChIs.

RESULTS

Slitrk1-KD mice exhibit TS-like haloperidol-sensitive stereotypic tic behaviors, impaired prepulse inhibition, and delayed sensorimotor response compared with the control group. These TS-like characteristics correlate with lower striatal Slitrk1 protein levels, fewer Slitrk1-containing ChIs, and fewer activated ChIs in Slitrk1-KD mice. Based on their electrophysiological properties, Slitrk1-negative ChIs are less excitable than Slitrk1-positive ChIs. Slitrk1-KD mice have lower evoked acetylcholine and dopamine levels, higher tonic dopamine levels, and downregulated dopamine transporters in the striatum, increased apomorphine-induced climbing behaviors, and impaired methamphetamine-induced hyperlocomotion compared with controls.

INTERPRETATION

Slitrk1 is pivotal in maintaining striatal ChIs activity and subsequent dopaminergic transmission for normal motor functioning. Furthermore, conditional striatal Slitrk1-KD mice may serve as a translational modality with aspects of TS phenomenology. ANN NEUROL 2023.

Developmental control of noradrenergic system by SLITRK1 and its implications in the pathophysiology of neuropsychiatric disorders

SLITRK1 is a neuronal transmembrane protein with neurite development-and synaptic formation-controlling abilities. Several rare variants of SLITRK1 have been identified and implicated in the pathogenesis of Tourette's syndrome, trichotillomania, and obsessive-compulsive disorder, which can be collectively referred to as obsessive-compulsive-spectrum disorders. Recent studies have reported a possible association between bipolar disorder and schizophrenia, including a revertant of modern human-specific amino acid residues. Although the mechanisms underlying SLITRK1-associated neuropsychiatric disorders are yet to be fully clarified, rodent studies may provide some noteworthy clues. Slitrk1-deficient mice show neonatal dysregulation of the noradrenergic system, and later, anxiety-like behaviors that can be attenuated by an alpha 2 noradrenergic receptor agonist. The noradrenergic abnormality is characterized by the excessive growth of noradrenergic fibers and increased noradrenaline content in the medial prefrontal cortex, concomitant with enlarged serotonergic varicosities. Slitrk1 has both cell-autonomous and cell-non-autonomous functions in controlling noradrenergic fiber development, and partly alters Sema3a-mediated neurite control. These findings suggest that transiently enhanced noradrenergic signaling during the neonatal stage could cause neuroplasticity associated with neuropsychiatric disorders. Studies adopting noradrenergic signal perturbation via pharmacological or genetic means support this hypothesis. Thus, Slitrk1 is a potential candidate genetic linkage between the neonatal noradrenergic signaling and the pathophysiology of neuropsychiatric disorders involving anxiety-like or depression-like behaviors.

Identity-by-descent analysis of a large Tourette's syndrome pedigree from Costa Rica implicates genes involved in neuronal development and signal transduction

Tourette Syndrome (TS) is a heritable, early-onset neuropsychiatric disorder that typically begins in early childhood. Identifying rare genetic variants that make a significant contribution to risk in affected families may provide important insights into the molecular aetiology of this complex and heterogeneous syndrome. Here we present a whole-genome sequencing (WGS) analysis from the 11-generation pedigree (>500 individuals) of a densely affected Costa Rican family which shares ancestry from six founder pairs. By conducting an identity-by-descent (IBD) analysis using WGS data from 19 individuals from the extended pedigree we have identified putative risk haplotypes that were not seen in controls, and can be linked with four of the six founder pairs. Rare coding and non-coding variants present on the haplotypes and only seen in haplotype carriers show an enrichment in pathways such as regulation of locomotion and signal transduction, suggesting common mechanisms by which the haplotype-specific variants may be contributing to TS-risk in this pedigree. In particular we have identified a rare deleterious missense variation in RAPGEF1 on a chromosome 9 haplotype and two ultra-rare deleterious intronic variants in ERBB4 and IKZF2 on the same chromosome 2 haplotype. All three genes play a role in neurodevelopment. This study, using WGS data in a pedigree-based approach, shows the importance of investigating both coding and non-coding variants to identify genes that may contribute to disease risk. Together, the genes and variants identified on the IBD haplotypes represent biologically relevant targets for investigation in other pedigree and population-based TS data.

SLITRK1-mediated noradrenergic projection suppression in the neonatal prefrontal cortex

SLITRK1 is an obsessive-compulsive disorder spectrum-disorders-associated gene that encodes a neuronal transmembrane protein. Here we show that SLITRK1 suppresses noradrenergic projections in the neonatal prefrontal cortex, and SLITRK1 functions are impaired by SLITRK1 mutations in patients with schizophrenia (S330A, a revertant of Homo sapiens-specific residue) and bipolar disorder (A444S). Slitrk1-KO newborns exhibit abnormal vocalizations, and their prefrontal cortices show excessive noradrenergic neurites and reduced Semaphorin3A expression, which suppresses noradrenergic neurite outgrowth in vitro. Slitrk1 can bind Dynamin1 and L1 family proteins (Neurofascin and L1CAM), as well as suppress Semaphorin3A-induced endocytosis. Neurofascin-binding kinetics is altered in S330A and A444S mutations. Consistent with the increased obsessive-compulsive disorder prevalence in males in childhood, the prefrontal cortex of male Slitrk1-KO newborns show increased noradrenaline levels, and serotonergic varicosity size. This study further elucidates the role of noradrenaline in controlling the development of the obsessive-compulsive disorder-related neural circuit.

The Role of Protein Kinase CK2 in Development and Disease Progression: A Critical Review

Protein kinase CK2 (CK2) is a ubiquitous holoenzyme involved in a wide array of developmental processes. The involvement of CK2 in events such as neurogenesis, cardiogenesis, skeletogenesis, and spermatogenesis is essential for the viability of almost all organisms, and its role has been conserved throughout evolution. Further into adulthood, CK2 continues to function as a key regulator of pathways affecting crucial processes such as osteogenesis, adipogenesis, chondrogenesis, neuron differentiation, and the immune response. Due to its vast role in a multitude of pathways, aberrant functioning of this kinase leads to embryonic lethality and numerous diseases and disorders, including cancer and neurological disorders. As a result, CK2 is a popular target for interventions aiming to treat the aforementioned diseases. Specifically, two CK2 inhibitors, namely CX-4945 and CIBG-300, are in the early stages of clinical testing and exhibit promise for treating cancer and other disorders. Further, other researchers around the world are focusing on CK2 to treat bone disorders. This review summarizes the current understanding of CK2 in development, the structure of CK2, the targets and signaling pathways of CK2, the implication of CK2 in disease progression, and the recent therapeutics developed to inhibit the dysregulation of CK2 function in various diseases.

Potential Serum Biomarkers for Postoperative Neurocognitive Disorders Based on Proteomic Analysis of Cognitive-Related Brain Regions

Postoperative neurocognitive disorders (po-NCD), including postoperative delirium (POD) and delayed neurocognitive recovery (dNCR), are common in geriatric surgical patients. However, the ideal diagnostic biomarkers to predict individual risks of po-NCDs have not been identified. In this study, proteomic analysis was used to detect dysregulated proteins in three cognitive-related brain regions, the hippocampus, prefrontal cortex, and temporal lobe, of aged dNCR rats. The common affected proteins in these three brain regions were further verified by real-time polymerase chain reaction and western blotting. Furthermore, serum samples from aged rats with dNCR and elderly hip fracture patients with POD were also assessed with enzyme linked immunosorbent assays to investigate the biomarker potential of these dysregulated proteins. The increased expression levels of haptoglobin, caseinolytic protease (ClpP), and alpha-2 macroglobulin (A2M) as well as decreased expression levels of 14-3-3β/α and biliverdin reductase-A (BVR-A) were validated by proteomic analysis in the hippocampus, prefrontal cortex, and temporal lobe of aged dNCR rats. The increased expression of haptoglobin and decreased expression of 14-3-3β/α were further demonstrated in the three brain regions by western blotting. Moreover, increased levels of S100A6 and BVR-A in the hippocampus, S100A6 in the prefrontal cortex, and A2M in the temporal lobe were also observed. More intriguingly, both decreased serum 14-3-3β/α and increased A2M in geriatric POD patients as well as decreased serum ClpP in aged dNCR rats were verified. These results not only indicate potential diagnostic biomarkers for po-NCD but also provide directions for further pathological investigations.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier [ChiCTR1900027393].

Pathways to Parkinson's disease: a spotlight on 14-3-3 proteins

14-3-3s represent a family of highly conserved 30 kDa acidic proteins. 14-3-3s recognize and bind specific phospho-sequences on client partners and operate as molecular hubs to regulate their activity, localization, folding, degradation, and protein-protein interactions. 14-3-3s are also associated with the pathogenesis of several diseases, among which Parkinson's disease (PD). 14-3-3s are found within Lewy bodies (LBs) in PD patients, and their neuroprotective effects have been demonstrated in several animal models of PD. Notably, 14-3-3s interact with some of the major proteins known to be involved in the pathogenesis of PD. Here we first provide a detailed overview of the molecular composition and structural features of 14-3-3s, laying significant emphasis on their peculiar target-binding mechanisms. We then briefly describe the implication of 14-3-3s in the central nervous system and focus on their interaction with LRRK2, α-Synuclein, and Parkin, three of the major players in PD onset and progression. We finally discuss how different types of small molecules may interfere with 14-3-3s interactome, thus representing a valid strategy in the future of drug discovery.

Protein kinase CK2: a potential therapeutic target for diverse human diseases

CK2 is a constitutively active Ser/Thr protein kinase, which phosphorylates hundreds of substrates, controls several signaling pathways, and is implicated in a plethora of human diseases. Its best documented role is in cancer, where it regulates practically all malignant hallmarks. Other well-known functions of CK2 are in human infections; in particular, several viruses exploit host cell CK2 for their life cycle. Very recently, also SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has been found to enhance CK2 activity and to induce the phosphorylation of several CK2 substrates (either viral and host proteins). CK2 is also considered an emerging target for neurological diseases, inflammation and autoimmune disorders, diverse ophthalmic pathologies, diabetes, and obesity. In addition, CK2 activity has been associated with cardiovascular diseases, as cardiac ischemia-reperfusion injury, atherosclerosis, and cardiac hypertrophy. The hypothesis of considering CK2 inhibition for cystic fibrosis therapies has been also entertained for many years. Moreover, psychiatric disorders and syndromes due to CK2 mutations have been recently identified. On these bases, CK2 is emerging as an increasingly attractive target in various fields of human medicine, with the advantage that several very specific and effective inhibitors are already available. Here, we review the literature on CK2 implication in different human pathologies and evaluate its potential as a pharmacological target in the light of the most recent findings.

Proper synaptic adhesion signaling in the control of neural circuit architecture and brain function

Trans-synaptic cell-adhesion molecules are critical for governing various stages of synapse development and specifying neural circuit properties via the formation of multifarious signaling pathways. Recent studies have pinpointed the putative roles of trans-synaptic cell-adhesion molecules in mediating various cognitive functions. Here, we review the literature on the roles of a diverse group of central synaptic organizers, including neurexins (Nrxns), leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs), and their associated binding proteins, in regulating properties of specific type of synapses and neural circuits. In addition, we highlight the findings that aberrant synaptic adhesion signaling leads to alterations in the structures, transmission, and plasticity of specific synapses across diverse brain areas. These results seem to suggest that proper trans-synaptic signaling pathways by Nrxns, LAR-RPTPs, and their interacting network is likely to constitute central molecular complexes that form the basis for cognitive functions, and that these complexes are heterogeneously and complexly disrupted in many neuropsychiatric and neurodevelopmental disorders.

14-3-3 mitigates alpha-synuclein aggregation and toxicity in the in vivo preformed fibril model

Alpha-synuclein (αsyn) is the key component of proteinaceous aggregates termed Lewy Bodies that pathologically define a group of disorders known as synucleinopathies, including Parkinson's Disease (PD) and Dementia with Lewy Bodies. αSyn is hypothesized to misfold and spread throughout the brain in a prion-like fashion. Transmission of αsyn necessitates the release of misfolded αsyn from one cell and the uptake of that αsyn by another, in which it can template the misfolding of endogenous αsyn upon cell internalization. 14-3-3 proteins are a family of highly expressed brain proteins that are neuroprotective in multiple PD models. We have previously shown that 14-3-3θ acts as a chaperone to reduce αsyn aggregation, cell-to-cell transmission, and neurotoxicity in the in vitro pre-formed fibril (PFF) model. In this study, we expanded our studies to test the impact of 14-3-3s on αsyn toxicity in the in vivo αsyn PFF model. We used both transgenic expression models and adenovirus associated virus (AAV)-mediated expression to examine whether 14-3-3 manipulation impacts behavioral deficits, αsyn aggregation, and neuronal counts in the PFF model. 14-3-3θ transgene overexpression in cortical and amygdala regions rescued social dominance deficits induced by PFFs at 6 months post injection, whereas 14-3-3 inhibition by transgene expression of the competitive 14-3-3 peptide inhibitor difopein in the cortex and amygdala accelerated social dominance deficits. The behavioral rescue by 14-3-3θ overexpression was associated with delayed αsyn aggregation induced by PFFs in these brain regions. Conversely, 14-3-3 inhibition by difopein in the cortex and amygdala accelerated αsyn aggregation and reduction in NECAB1-positive neuron counts induced by PFFs. 14-3-3θ overexpression by AAV in the substantia nigra (SN) also delayed αsyn aggregation in the SN and partially rescued PFF-induced reduction in tyrosine hydroxylase (TH)-positive dopaminergic cells in the SN. 14-3-3 inhibition in the SN accelerated nigral αsyn aggregation and enhanced PFF-induced reduction in TH-positive dopaminergic cells. These data indicate a neuroprotective role for 14-3-3θ against αsyn toxicity in vivo.

Synaptic organizer: Slitrks and type IIa receptor protein tyrosine phosphatases

Slit-like and Trk-like (Slitrk) family members are leucine-rich repeat (LRR)-containing neuronal transmembrane proteins. Slitrks have been highlighted as key synapse organizers at neuronal synapses through interactions with specific members of the presynaptic type IIa receptor protein tyrosine phosphatase (RPTP) family. Recent structural studies on type IIa RPTP/Slitrk1 complexes have unveiled molecular insights into their binding selectivity and have established the role of higher-order receptor clustering in their synaptogenic activity. Here, we will discuss key structural aspects of Slitrk interactions with type IIa RPTP family members, the biological roles of Slitrks in neurons, and our current knowledge of SLITRK mutations in human diseases.

14-3-3 Proteins Reduce Cell-to-Cell Transfer and Propagation of Pathogenic α-Synuclein

α-Synuclein (αsyn) is the key protein that forms neuronal aggregates in the neurodegenerative disorders Parkinson's disease (PD) and dementia with Lewy bodies. Recent evidence points to the prion-like spread of αsyn from one brain region to another. Propagation of αsyn is likely dependent on release, uptake, and misfolding. Under normal circumstances, this highly expressed brain protein functions normally without promoting pathology, yet the underlying endogenous mechanisms that prevent αsyn spread are not understood. 14-3-3 proteins are highly expressed brain proteins that have chaperone function and regulate protein trafficking. In this study, we investigated the potential role of the 14-3-3 proteins in the regulation of αsyn spread using two models of αsyn spread. In a paracrine αsyn model, 14-3-3θ promoted release of αsyn complexed with 14-3-3θ. Despite higher amounts of released αsyn, extracellular αsyn showed reduced oligomerization and seeding capability, reduced internalization, and reduced toxicity in primary mixed-gender mouse neurons. 14-3-3 inhibition reduced the amount of αsyn released, yet released αsyn was more toxic and demonstrated increased oligomerization, seeding capability, and internalization. In the preformed fibril model, 14-3-3 θ reduced αsyn aggregation and neuronal death, whereas 14-3-3 inhibition enhanced αsyn aggregation and neuronal death in primary mouse neurons. 14-3-3s blocked αsyn spread to distal chamber neurons not exposed directly to fibrils in multichamber, microfluidic devices. These findings point to 14-3-3s as a direct regulator of αsyn propagation, and suggest that dysfunction of 14-3-3 function may promote αsyn pathology in PD and related synucleinopathies.SIGNIFICANCE STATEMENT Transfer of misfolded aggregates of α-synuclein from one brain region to another is implicated in the pathogenesis of Parkinson's disease and other synucleinopathies. This process is dependent on active release, internalization, and misfolding of α-synuclein. 14-3-3 proteins are highly expressed chaperone proteins that interact with α-synuclein and regulate protein trafficking. We used two different models in which toxicity is associated with cell-to-cell transfer of α-synuclein to test whether 14-3-3s impact α-synuclein toxicity. We demonstrate that 14-3-3θ reduces α-synuclein transfer and toxicity by inhibiting oligomerization, seeding capability, and internalization of α-synuclein, whereas 14-3-3 inhibition accelerates the transfer and toxicity of α-synuclein in these models. Dysfunction of 14-3-3 function may be a critical mechanism by which α-synuclein propagation occurs in disease.

A novel environment-evoked transcriptional signature predicts reactivity in single dentate granule neurons

Activity-induced remodeling of neuronal circuits is critical for memory formation. This process relies in part on transcription, but neither the rate of activity nor baseline transcription is equal across neuronal cell types. In this study, we isolated mouse hippocampal populations with different activity levels and used single nucleus RNA-seq to compare their transcriptional responses to activation. One hour after novel environment exposure, sparsely active dentate granule (DG) neurons had a much stronger transcriptional response compared to more highly active CA1 pyramidal cells and vasoactive intestinal polypeptide (VIP) interneurons. Activity continued to impact transcription in DG neurons up to 5 h, with increased heterogeneity. By re-exposing the mice to the same environment, we identified a unique transcriptional signature that selects DG neurons for reactivation upon re-exposure to the same environment. These results link transcriptional heterogeneity to functional heterogeneity and identify a transcriptional correlate of memory encoding in individual DG neurons.

Single nuclei RNA-seq has been used to characterize transcriptional signature of environment-related activity in cells of the dentate gyrus. Here the authors use this approach to show that whether a neuron will be reactivated in response to re-exposure to a previous environment can be predicted by its transcriptional signature.

Progress in Genetic Studies of Tourette's Syndrome

Tourette's Syndrome (TS) is a complex disorder characterized by repetitive, sudden, and involuntary movements or vocalizations, called tics. Tics usually appear in childhood, and their severity varies over time. In addition to frequent tics, people with TS are at risk for associated problems including attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), anxiety, depression, and problems with sleep. TS occurs in most populations and ethnic groups worldwide, and it is more common in males than in females. Previous family and twin studies have shown that the majority of cases of TS are inherited. TS was previously thought to have an autosomal dominant pattern of inheritance. However, several decades of research have shown that this is unlikely the case. Instead TS most likely results from a variety of genetic and environmental factors, not changes in a single gene. In the past decade, there has been a rapid development of innovative genetic technologies and methodologies, as well as significant progresses in genetic studies of psychiatric disorders. In this review, we will briefly summarize previous genetic epidemiological studies of TS and related disorders. We will also review previous genetic studies based on genome-wide linkage analyses and candidate gene association studies to comment on problems of previous methodological and strategic issues. Our main purpose for this review will be to summarize the new genetic discoveries of TS based on novel genetic methods and strategies, such as genome-wide association studies (GWASs), whole exome sequencing (WES) and whole genome sequencing (WGS). We will also compare the new genetic discoveries of TS with other major psychiatric disorders in order to understand the current status of TS genetics and its relationship with other psychiatric disorders.

Pediatric Autoimmune Disorders Associated with Streptococcal Infections and Tourette's Syndrome in Preclinical Studies

Accumulating evidence suggests that Tourette's Syndrome (TS) - a multifactorial pediatric disorder characterized by the recurrent exhibition of motor tics and/or vocal utterances - can partly depend on immune dysregulation provoked by early repeated streptococcal infections. The natural and adaptive antibody-mediated reaction to streptococcus has been proposed to potentially turn into a pathological autoimmune response in vulnerable individuals. Specifically, in conditions of increased permeability of the blood brain barrier (BBB), streptococcus-induced antibodies have been proposed to: (i) reach neuronal targets located in brain areas responsible for motion control; and (ii) contribute to the exhibition of symptoms. This theoretical framework is supported by indirect evidence indicating that a subset of TS patients exhibit elevated streptococcal antibody titers upon tic relapses. A systematic evaluation of this hypothesis entails preclinical studies providing a proof of concept of the aforementioned pathological sequelae. These studies shall rest upon individuals characterized by a vulnerable immune system, repeatedly exposed to streptococcus, and carefully screened for phenotypes isomorphic to the pathological signs of TS observed in patients. Preclinical animal models may thus constitute an informative, useful tool upon which conducting targeted, hypothesis-driven experiments. In the present review we discuss the available evidence in preclinical models in support of the link between TS and pediatric autoimmune neuropsychiatric disorders associated with streptococcus infections (PANDAS), and the existing gaps that future research shall bridge. Specifically, we report recent preclinical evidence indicating that the immune responses to repeated streptococcal immunizations relate to the occurrence of behavioral and neurological phenotypes reminiscent of TS. By the same token, we discuss the limitations of these studies: limited evidence of behavioral phenotypes isomorphic to tics and scarce knowledge about the immunological phenomena favoring the transition from natural adaptive immunity to pathological outcomes.

Slitrk1 is localized to excitatory synapses and promotes their development

Following the migration of the axonal growth cone to its target area, the initial axo-dendritic contact needs to be transformed into a functional synapse. This multi-step process relies on overlapping but distinct combinations of molecules that confer synaptic identity. Slitrk molecules are transmembrane proteins that are highly expressed in the central nervous system. We found that two members of the Slitrk family, Slitrk1 and Slitrk2, can regulate synapse formation between hippocampal neurons. Slitrk1 is enriched in postsynaptic fractions and is localized to excitatory synapses. Overexpression of Slitrk1 and Slitrk2 in hippocampal neurons increased the number of synaptic contacts on these neurons. Furthermore, decreased expression of Slitrk1 in hippocampal neurons led to a reduction in the number of excitatory, but not inhibitory, synapses formed in hippocampal neuron cultures. In addition, we demonstrate that different leucine rich repeat domains of the extracellular region of Slitrk1 are necessary to mediate interactions with Slitrk binding partners of the LAR receptor protein tyrosine phosphatase family, and to promote dimerization of Slitrk1. Altogether, our results demonstrate that Slitrk family proteins regulate synapse formation.

Astrocyte scar formation aids central nervous system axon regeneration

Transected axons fail to regrow in the mature central nervous system. Astrocytic scars are widely regarded as causal in this failure. Here, using three genetically targeted loss-of-function manipulations in adult mice, we show that preventing astrocyte scar formation, attenuating scar-forming astrocytes, or ablating chronic astrocytic scars all failed to result in spontaneous regrowth of transected corticospinal, sensory or serotonergic axons through severe spinal cord injury (SCI) lesions. By contrast, sustained local delivery via hydrogel depots of required axon-specific growth factors not present in SCI lesions, plus growth-activating priming injuries, stimulated robust, laminin-dependent sensory axon regrowth past scar-forming astrocytes and inhibitory molecules in SCI lesions. Preventing astrocytic scar formation significantly reduced this stimulated axon regrowth. RNA sequencing revealed that astrocytes and non-astrocyte cells in SCI lesions express multiple axon-growth-supporting molecules. Our findings show that contrary to the prevailing dogma, astrocyte scar formation aids rather than prevents central nervous system axon regeneration.

14-3-3 Proteins regulate mutant LRRK2 kinase activity and neurite shortening

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common known cause of inherited Parkinson's disease (PD), and LRRK2 is a risk factor for idiopathic PD. How LRRK2 function is regulated is not well understood. Recently, the highly conserved 14-3-3 proteins, which play a key role in many cellular functions including cell death, have been shown to interact with LRRK2. In this study, we investigated whether 14-3-3s can regulate mutant LRRK2-induced neurite shortening and kinase activity. In the presence of 14-3-3θ overexpression, neurite length of primary neurons from BAC transgenic G2019S-LRRK2 mice returned back to wild-type levels. Similarly, 14-3-3θ overexpression reversed neurite shortening in neuronal cultures from BAC transgenic R1441G-LRRK2 mice. Conversely, inhibition of 14-3-3s by the pan-14-3-3 inhibitor difopein or dominant-negative 14-3-3θ further reduced neurite length in G2019S-LRRK2 cultures. Since G2019S-LRRK2 toxicity is likely mediated through increased kinase activity, we examined 14-3-3θ's effects on LRRK2 kinase activity. 14-3-3θ overexpression reduced the kinase activity of G2019S-LRRK2, while difopein promoted the kinase activity of G2019S-LRRK2. The ability of 14-3-3θ to reduce LRRK2 kinase activity required direct binding of 14-3-3θ with LRRK2. The potentiation of neurite shortening by difopein in G2019S-LRRK2 neurons was reversed by LRRK2 kinase inhibitors. Taken together, we conclude that 14-3-3θ can regulate LRRK2 and reduce the toxicity of mutant LRRK2 through a reduction of kinase activity.

14-3-3 inhibition promotes dopaminergic neuron loss and 14-3-3θ overexpression promotes recovery in the MPTP mouse model of Parkinson's disease

14-3-3s are a highly conserved protein family that plays important roles in cell survival and interact with several proteins implicated in Parkinson's disease (PD). Disruption of 14-3-3 expression and function has been implicated in the pathogenesis of PD. We have previously shown that increasing the expression level of 14-3-3θ is protective against rotenone and 1-methyl-4-phenylpyridinium (MPP(+)) in cultured cells. Here, we extend our studies to examine the effects of 14-3-3s in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We first investigated whether targeted nigral 14-3-3θ overexpression mediated by adeno-associated virus offers neuroprotection against MPTP-induced toxicity. 14-3-3θ overexpression using this approach did not reduce MPTP-induced dopaminergic cell loss in the substantia nigra nor the depletion of dopamine (DA) and its metabolites in the striatum at three weeks after MPTP administration. However, 14-3-3θ-overexpressing mice showed a later partial recovery in striatal DA metabolites at eight weeks after MPTP administration compared to controls, suggesting that 14-3-3θ overexpression may help in the functional recovery of those dopaminergic neurons that survive. Conversely, we investigated whether disrupting 14-3-3 function in transgenic mice expressing the pan 14-3-3 inhibitor difopein exacerbates MPTP-induced toxicity. We found that difopein expression promoted dopaminergic cell loss in response to MPTP treatment. Together, these findings suggest that 14-3-3θ overexpression promotes recovery of DA metabolites whereas 14-3-3 inhibition exacerbates neuron loss in the MPTP mouse model of PD.

The Tourette International Collaborative Genetics (TIC Genetics) study, finding the genes causing Tourette syndrome: objectives and methods

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by recurrent motor and vocal tics, often accompanied by obsessive-compulsive disorder and/or attention-deficit/hyperactivity disorder. While the evidence for a genetic contribution is strong, its exact nature has yet to be clarified fully. There is now mounting evidence that the genetic risks for TS include both common and rare variants and may involve complex multigenic inheritance or, in rare cases, a single major gene. Based on recent progress in many other common disorders with apparently similar genetic architectures, it is clear that large patient cohorts and open-access repositories will be essential to further advance the field. To that end, the large multicenter Tourette International Collaborative Genetics (TIC Genetics) study was established. The goal of the TIC Genetics study is to undertake a comprehensive gene discovery effort, focusing both on familial genetic variants with large effects within multiply affected pedigrees and on de novo mutations ascertained through the analysis of apparently simplex parent-child trios with non-familial tics. The clinical data and biomaterials (DNA, transformed cell lines, RNA) are part of a sharing repository located within the National Institute for Mental Health Center for Collaborative Genomics Research on Mental Disorders, USA, and will be made available to the broad scientific community. This resource will ultimately facilitate better understanding of the pathophysiology of TS and related disorders and the development of novel therapies. Here, we describe the objectives and methods of the TIC Genetics study as a reference for future studies from our group and to facilitate collaboration between genetics consortia in the field of TS.

IgLON cell adhesion molecules are shed from the cell surface of cortical neurons to promote neuronal growth

Matrix metalloproteinases and a disintegrin and metalloproteinases are members of the zinc endopeptidases, which cleave components of the extracellular matrix as well as cell surface proteins resulting in degradation or release of biologically active fragments. Surface ectodomain shedding affects numerous biological processes, including survival, axon outgrowth, axon guidance, and synaptogenesis. In this study, we evaluated the role of metalloproteinases in regulating cortical neurite growth. We found that treatment of mature cortical neurons with pan-metalloproteinase inhibitors or with tissue inhibitors of metalloproteinase-3 reduced neurite outgrowth. Through mass spectrometry, we characterized the metalloproteinase-sensitive cell surface proteome of mature cortical neurons. Members of the IgLON family of glycosylphosphatidylinositol-anchored neural cell adhesion molecules were identified and validated as proteins that were shed from the surface of mature cortical neurons in a metalloproteinase-dependent manner. Introduction of two members of the IgLON family, neurotrimin and NEGR1, in early embryonic neurons was sufficient to confer sensitivity to metalloproteinase inhibitors in neurite outgrowth assays. Outgrowth experiments on immobilized IgLON proteins revealed a role for all IgLON family members in promoting neurite extension from cortical neurons. Together, our findings support a role for metalloproteinase-dependent shedding of IgLON family members in regulating neurite outgrowth from mature cortical neurons.

Porcine SLITRK1: Molecular cloning and characterization

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Molecular cloning of the porcine SLITRK1 gene is reported.

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A SLITRK1 transcript variant encoding a truncated protein was identified.

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The SLITRK1 transcript was exclusively expressed in brain tissues.

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There was low methylation of both the SLITRK1 gene body and its promoter.

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SLITRK1 was mapped to pig chromosome 11.

The membrane protein SLITRK1 functions as a developmentally regulated stimulator of neurite outgrowth and variants in this gene have been implicated in Tourette syndrome. In the current study we have cloned and characterized the porcine SLITRK1 gene. The genomic organization of SLITRK1 lacks introns, as does its human and mouse counterparts. RT-PCR cloning revealed two SLITRK1 transcripts: a full-length mRNA and a transcript variant that results in a truncated protein. The encoded SLITRK1 protein, consisting of 695 amino acids, displays a very high homology to human SLITRK1 (99%). The porcine SLITRK1 gene is expressed exclusively in brain tissues.

The Inheritance of Tourette Disorder: A review

Georges Gilles de la Tourette, in describing the syndrome that now bears his name, observed that the condition aggregated within families. Over the last three decades, numerous studies have confirmed this observation, and demonstrated that familial clustering is due in part to genetic factors. Recent studies are beginning to provide clues about the underlying genetic mechanisms important for the manifestation of some cases of Tourette Disorder (TD). Evidence has come from different study designs, such as nuclear families, twins, multigenerational families, and case-control samples, together examining the broad spectrum of genetic variation including cytogenetic abnormalities, copy number variants, genome-wide association of common variants, and sequencing studies targeting rare and/or de novo variation. Each of these classes of genetic variation holds promise for identifying the causative genes and biological pathways contributing to this paradigmatic neuropsychiatric disorder.

Animal models of tic disorders: a translational perspective

Tics are repetitive, sudden movements and/or vocalizations, typically enacted as maladaptive responses to intrusive premonitory urges. The most severe tic disorder, Tourette syndrome (TS), is a childhood-onset condition featuring multiple motor and at least one phonic tic for a duration longer than 1 year. The pharmacological treatment of TS is mainly based on antipsychotic agents; while these drugs are often effective in reducing tic severity and frequency, their therapeutic compliance is limited by serious motor and cognitive side effects. The identification of novel therapeutic targets and development of better treatments for tic disorders is conditional on the development of animal models with high translational validity. In addition, these experimental tools can prove extremely useful to test hypotheses on the etiology and neurobiological bases of TS and related conditions. In recent years, the translational value of these animal models has been enhanced, thanks to a significant re-organization of our conceptual framework of neuropsychiatric disorders, with a greater focus on endophenotypes and quantitative indices, rather than qualitative descriptors. Given the complex and multifactorial nature of TS and other tic disorders, the selection of animal models that can appropriately capture specific symptomatic aspects of these conditions can pose significant theoretical and methodological challenges. In this article, we will review the state of the art on the available animal models of tic disorders, based on genetic mutations, environmental interventions as well as pharmacological manipulations. Furthermore, we will outline emerging lines of translational research showing how some of these experimental preparations have led to significant progress in the identification of novel therapeutic targets for tic disorders.

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.

Neural cell adhesion molecules belonging to the family of leucine-rich repeat proteins

Leucine-rich repeats (LRRs) are motifs that form protein-ligand interaction domains. There are approximately 140 human genes encoding proteins with extracellular LRRs. These encode cell adhesion molecules (CAMs), proteoglycans, G-protein-coupled receptors, and other types of receptors. Here we give a brief description of 36 proteins with extracellular LRRs that all can be characterized as CAMs or putative CAMs expressed in the nervous system. The proteins are involved in multiple biological processes in the nervous system including the proliferation and survival of cells, neuritogenesis, axon guidance, fasciculation, myelination, and the formation and maintenance of synapses. Moreover, the proteins are functionally implicated in multiple diseases including cancer, hearing impairment, glaucoma, Alzheimer's disease, multiple sclerosis, Parkinson's disease, autism spectrum disorders, schizophrenia, and obsessive-compulsive disorders. Thus, LRR-containing CAMs constitute a large group of proteins of pivotal importance for the development, maintenance, and regeneration of the nervous system.

Sequence analysis of SLITRK1 for var321 in Danish patients with Tourette syndrome and review of the literature

Tourette syndrome (TS) is a complex neuropsychiatric disorder characterized by multiple motor and vocal tics and is often accompanied by comorbidities such as attention deficit hyperactivity disorder and obsessive-compulsive disorder. The complex etiology of TS and its co-occurrence with other disorders impedes linking genetic changes with disease segregation. One of the few genes that has been linked to TS is the SLITRK1 (Slit and Trk-like 1) gene, where four variations have been suggested as possible disease-associated changes. One of these variations, which has been reported in six unrelated TS patients, was a noncoding variant (var321) at the 3'-untranslated region of SLITRK1 within a conserved binding site for microRNA has-mir-189. To elucidate the potential role of var321 in disease pathogenesis, a cohort of 112 deeply phenotyped Danish TS patients was investigated for this variation. We could not detect var321 in the present cohort, suggesting that this is not a common variant among Danish TS patients.

Slitrk gene duplication and expression in the developing zebrafish nervous system

BACKGROUND

The Slitrk family of leucine-rich repeat (LRR) transmembrane proteins bears structural similarity to the Slits and the Trk receptor families, which exert well-established roles in directing nervous system development. Slitrks are less well understood, although they are highly expressed in the developing vertebrate nervous system. Moreover, slitrk variants are associated with several sensory and neuropsychiatric disorders, including myopia, deafness, obsessive-compulsive disorder (OCD), schizophrenia, and Tourette syndrome. Loss-of-function studies in mice show that Slitrks modulate neurite outgrowth and inhibitory synapse formation, although the molecular mechanisms of Slitrk function remain poorly characterized.

RESULTS

As a prelude to examining the functional roles of Slitrks, we identified eight slitrk orthologs in zebrafish and observed that seven of the eight orthologs were actively transcribed in the nervous system at embryonic, larval, and adult stages. Similar to previous findings in mice and humans, zebrafish slitrks exhibited unique but overlapping spatial and temporal expression patterns in the developing brain, retina, and spinal cord.

CONCLUSIONS

Zebrafish express Slitrks in the developing central nervous system at times and locations important to neuronal morphogenesis and synaptogenesis. Future studies will use zebrafish as a convenient, cost-effective model organism to characterize the functional roles of Slitrks in nervous system development.

Characterization of SLITRK1 variation in obsessive-compulsive disorder

Obsessive compulsive disorder (OCD) is a syndrome characterized by recurrent and intrusive thoughts and ritualistic behaviors or mental acts that a person feels compelled to perform. Twin studies, family studies, and segregation analyses provide compelling evidence that OCD has a strong genetic component. The SLITRK1 gene encodes a developmentally regulated stimulator of neurite outgrowth and previous studies have implicated rare variants in this gene in disorders in the OC spectrum, specifically Tourette syndrome (TS) and trichotillomania (TTM). The objective of the current study was to evaluate rare genetic variation in SLITRK1 in risk for OCD and to functionally characterize associated coding variants. We sequenced SLITRK1 coding exons in 381 individuals with OCD as well as in 356 control samples and identified three novel variants in seven individuals. We found that the combined mutation load in OCD relative to controls was significant (p = 0.036). We identified a missense N400I change in an individual with OCD, which was not found in more than 1000 control samples (P<0.05). In addition, we showed the the N400I variant failed to enhance neurite outgrowth in primary neuronal cultures, in contrast to wildtype SLITRK1, which enhanced neurite outgrowth in this assay. These important functional differences in the N400I variant, as compared to the wildtype SLITRK1 sequence, may contribute to OCD and OC spectrum symptoms. A synonymous L63L change identified in an individual with OCD and an additional missense change, T418S, was found in four individuals with OCD and in one individual without an OCD spectrum disorder. Examination of additional samples will help assess the role of rare SLITRK1 variation in OCD and in related psychiatric illness.

Theoretical and practical considerations behind the use of laboratory animals for the study of Tourette syndrome

In the present manuscript we review a substantial body of literature describing several pre-clinical animal models designed and developed with the purpose of investigating the biological determinants of Tourette syndrome (TS). In order to map the animal models onto the theoretical background upon which they have been devised, we first define phenomenological and etiological aspects of TS and then match this information to the available pre-clinical models. Thus, we first describe the characteristic symptoms exhibited by TS patients and then a series of hypotheses attempting to identify the multifactorial causes of TS. With respect to the former, we detail the phenomenology of abnormal repetitive behaviors (tics and stereotypies), obsessive-compulsive behaviors and aberrant sensory-motor gating. With respect to the latter, we describe both potential candidate vulnerability genes and environmental factors (difficult pregnancies, psychosocial stressors and infections). We then discuss how this evidence has been translated in pre-clinical research with respect to both dependent (symptoms) and independent (etiological factors) variables. Thus, while, on the one hand, we detail the methodologies adopted to measure abnormal repetitive and obsessive-compulsive behaviors, and sensory-motor gating, on the other hand, we describe genetic engineering studies and environmental modulations aimed at reproducing the proposed biological determinants in laboratory rodents. A special emphasis is placed upon "programming" events, occurring during critical stages of early development and exerting organizational delayed consequences. In the final section, we outline a heuristic model with the purpose of integrating clinical and pre-clinical evidence in the study of TS.

Slitrks control excitatory and inhibitory synapse formation with LAR receptor protein tyrosine phosphatases

The balance between excitatory and inhibitory synaptic inputs, which is governed by multiple synapse organizers, controls neural circuit functions and behaviors. Slit- and Trk-like proteins (Slitrks) are a family of synapse organizers, whose emerging synaptic roles are incompletely understood. Here, we report that Slitrks are enriched in postsynaptic densities in rat brains. Overexpression of Slitrks promoted synapse formation, whereas RNAi-mediated knockdown of Slitrks decreased synapse density. Intriguingly, Slitrks were required for both excitatory and inhibitory synapse formation in an isoform-dependent manner. Moreover, Slitrks required distinct members of the leukocyte antigen-related receptor protein tyrosine phosphatase (LAR-RPTP) family to trigger synapse formation. Protein tyrosine phosphatase σ (PTPσ), in particular, was specifically required for excitatory synaptic differentiation by Slitrks, whereas PTPδ was necessary for inhibitory synapse differentiation. Taken together, these data suggest that combinatorial interactions of Slitrks with LAR-RPTP family members maintain synapse formation to coordinate excitatory-inhibitory balance.

Animal models recapitulating the multifactorial origin of Tourette syndrome

Tourette Syndrome (TS) is a neurological disorder characterized by motor and phonic tics affecting approximately 1% of the pediatric population. Behavioral comorbidities often include obsessive-compulsive behavior and impaired attention. The neurobiological substrates associated with TS generally entail abnormalities in neurotransmitter circuitry regulating basal ganglia activity. The neurotransmitters most often associated with TS are dopamine, serotonin, and GABA. TS origin roots in genetic predisposing factors, and environmental variables favoring tic onset and exacerbation. Among the latter, repeated infections with group A beta-hemolytic Streptococcus and psychosocial stressors encountered during development have been proposed to constitute likely susceptibility factors. In this chapter, we describe how this clinical/epidemiological knowledge has been translated into animal models of TS. Specifically, we review several studies attempting to reproduce TS-like symptoms (tics and behavioral stereotypies) and comorbidities (impaired attention, increased locomotion, and perseverative responding) in laboratory rodents. Additionally, we discuss studies in which the genetic and environmental predisposing factors have been modeled in experimental subjects. Ultimately, we propose a unifying perspective recapitulating dependent and independent variables in the preclinical study of TS and discuss its potential theoretical and heuristic implications.

The leucine-rich repeat superfamily of synaptic adhesion molecules: LRRTMs and Slitrks

Synapses are asymmetric intercellular junctions connected by multiple synaptic cell adhesion molecules (CAMs). Synaptic CAMs function in various stages of synaptogenesis - the process of synapse creation - encompassing synapse formation, maturation, refinement, plasticity, and elimination. The list of synaptic CAMs has rapidly grown, although their precise functions of most CAMs at synapses remain incomplete. Members of an emerging class of transmembrane proteins containing leucine-rich repeat (LRR) domains have received considerable recent research attention. In this minireview, I discuss recent findings on LRR-containing synaptic CAMs that impact synapse development and circuit formation, focusing on two families of LRR synaptic CAMs: leucine-rich transmembrane proteins (LRRTMs) and Slit and Trk-like family (Slitrks). Their basic biochemical properties, proposed functions at synapses, physiological significances, and open questions are summarized.

Functional annotation of the human brain methylome identifies tissue-specific epigenetic variation across brain and blood

Background

Dynamic changes to the epigenome play a critical role in establishing and maintaining cellular phenotype during differentiation, but little is known about the normal methylomic differences that occur between functionally distinct areas of the brain. We characterized intra- and inter-individual methylomic variation across whole blood and multiple regions of the brain from multiple donors.

Results

Distinct tissue-specific patterns of DNA methylation were identified, with a highly significant over-representation of tissue-specific differentially methylated regions (TS-DMRs) observed at intragenic CpG islands and low CG density promoters. A large proportion of TS-DMRs were located near genes that are differentially expressed across brain regions. TS-DMRs were significantly enriched near genes involved in functional pathways related to neurodevelopment and neuronal differentiation, including BDNF, BMP4, CACNA1A, CACA1AF, EOMES, NGFR, NUMBL, PCDH9, SLIT1, SLITRK1 and SHANK3. Although between-tissue variation in DNA methylation was found to greatly exceed between-individual differences within any one tissue, we found that some inter-individual variation was reflected across brain and blood, indicating that peripheral tissues may have some utility in epidemiological studies of complex neurobiological phenotypes.

Conclusions

This study reinforces the importance of DNA methylation in regulating cellular phenotype across tissues, and highlights genomic patterns of epigenetic variation across functionally distinct regions of the brain, providing a resource for the epigenetics and neuroscience research communities.

Slitrks as emerging candidate genes involved in neuropsychiatric disorders

Slitrks are a family of structurally related transmembrane proteins belonging to the leucine-rich repeat (LRR) superfamily. Six family members exist (Slitrk1-6) and all are highly expressed in the central nervous system (CNS). Slitrks have been implicated in mediating basic neuronal processes, ranging from neurite outgrowth and dendritic elaboration to neuronal survival. Recent studies in humans and genetic mouse models have led to the identification of Slitrks as candidate genes that might be involved in the development of neuropsychiatric conditions, such as obsessive compulsive spectrum disorders and schizophrenia. Although these system-level approaches have suggested that Slitrks play prominent roles in CNS development, key questions remain regarding the molecular mechanisms through which they mediate neuronal signaling and connectivity.

Genetic animal models of Tourette syndrome: The long and winding road from lab to clinic

Tourette syndrome (TS) is a disabling neuropsychiatric disorder characterised by persistent motor and vocal tics. TS is a highly comorbid state, hence, patients might experience anxiety, obsessions, compulsions, sleep abnormalities, depression, emotional liability, learning problems, and attention deficits in addition to tics. In spite of its complex heterogeneous genetic aetiology, recent studies highlighted a strong link between TS and genetic lesions in the HDC (L-histidine decarboxylase) gene, which encodes the enzyme that synthetises histamine, and the SLITRK1 (SLIT and TRK-like family member 1) gene, which encodes a transmembrane protein that was found to regulate neurite outgrowth. In addition to validating the contribution of a specific genetic aberration to the development of a particular pathology, animal models are crucial to dissect the function of disease-linked proteins, expose disease pathways through examination of genetic modifiers and discover as well as assess therapeutic strategies. Mice with a knockout of either Hdc or Slitrk1 exhibit anxiety and those lacking Hdc, display dopamine agonist-triggered stereotypic movements. However, the mouse knockouts do not spontaneously display tics, which are recognised as the hallmark of TS. In this review, we explore the features of the present genetic animal models of TS and identify reasons for their poor resemblance to the human condition. Importantly, we highlight ways forward aimed at developing a valuable genetic model of TS or a model that has good predictive validity in developing therapeutic drugs for the treatment of tics, hence potentially accelerating the arduous journey from lab to clinic.

Cyclin-dependent kinase 5-dependent phosphorylation of Pctaire1 regulates dendrite development

Pctaire1, a Cdk-related protein kinase, is prominently expressed in terminally differentiated tissues, including the brain and the testis. We have previously shown that Pctaire1 regulates neurotransmitter release through phosphorylation of NSF, and its kinase activity is regulated by the Cdk5-dependent phosphorylation at Serine-95 (Ser95). Nonetheless, the functional roles of Pctaire1 in neurons during development remained poorly understood. In this study, we found that Pctaire1 is expressed along neurites and is concentrated at the growth cones of early differentiating hippocampal neurons. Upon maturation of these neurons, Pctiare1 is expressed as puncta and co-localized with synaptic marker in dendrites. Phosphorylation of Pctaire1 at Ser95 increases upon neuronal differentiation, concurrent with the elevation in Cdk5 activity. Knockdown of Pctaire1 abolishes dendrite development, and more importantly, expression of Ser95 phosphorylation-deficient mutant of Pctaire1 also reduces dendrite complexity, suggesting that Cdk5 regulates Pctaire1 functions in differentiating neurons. Together, our findings demonstrate that Cdk5-dependent phosphorylation of Pctaire1 at Ser95 plays an important role in dendrite development.

The genetics of Tourette disorder

Tourette disorder (TD) is a childhood onset neuropsychiatric syndrome defined by persistent motor and vocal tics. Despite a long-standing consensus for a strong genetic contribution, the pace of discovery compared to other disorders of similar prevalence has been slow, due in part to a paucity of studies and both clinical heterogeneity and a complex genetic architecture. However, the potential for rapid progress is high. Recent rare variant findings have pointed to the importance of copy number variation, the overlap of risks among distinct diagnostic entities, the contribution of novel molecular mechanisms, and the value of family based studies. Finally, analysis of a cohort of sufficient size to identify common polymorphisms of plausible effect is underway, promising key information regarding the contribution of common alleles to TD.

The genetics of child psychiatric disorders: focus on autism and Tourette syndrome

Investigations into the genetics of child psychiatric disorders have finally begun to shed light on molecular and cellular mechanisms of psychopathology. The first strains of success in this notoriously difficult area of inquiry are the result of an increasingly sophisticated appreciation of the allelic architecture of common neuropsychiatric and neurodevelopmental disorders, the consolidation of large patient cohorts now beginning to reach sufficient size to power reliable studies, the emergence of genomic tools enabling comprehensive investigations of rare as well as common genetic variation, and advances in developmental neuroscience that are fueling the rapid translation of genetic findings.

Tourette syndrome: gene expression as a tool to discover drug targets

Gene expression microarrays are a high-throughput, cost-effective method for measuring the expression of all genes in a sample. By comparing the expression patterns of healthy controls to diseased subjects, the genetic regulatory pathways underlying and affected by the disease can be elucidated. Furthermore, dysregulated genes are possible candidates for pharmaceutical therapy. Here, we consider the possibility of applying this approach to Tourette syndrome. We also review current theories of Tourette syndrome etiology and pharmacology.

Binding of alphaII spectrin to 14-3-3beta is involved in NCAM-dependent neurite outgrowth

Members of the 14-3-3 protein family have been implicated in neuronal migration, synaptic plasticity and learning. Using affinity chromatography followed by mass spectrometry analysis, we show here that the cytoskeletal protein alphaII spectrin is a novel ligand of 14-3-3beta. We found that 14-3-3beta interacts with alphaII spectrin via the mode 2 14-3-3 binding motif RLIQS(1302)HP. Binding required phosphorylation of Ser(1302) by casein kinase II and was enhanced in the presence of calmodulin. Co-immunoprecipitation of alphaII spectrin and 14-3-3beta with the neural cell adhesion molecule NCAM suggested that the 14-3-3-spectrin-interaction affects NCAM function. Indeed, disruption of the 14-3-3beta/alphaII spectrin interaction by mutating Ser(1302) to Ala enhanced NCAM-dependent neurite outgrowth. Our results indicate that the phosphorylation-dependent interaction between 14-3-3beta and alphaII spectrin acts as a switch between positive and negative regulation of neurite outgrowth stimulated by NCAM, representing a novel and acute mechanism preventing uncontrolled elongation of neuronal processes.