A chromosome 16p13.11 microduplication causes hyperactivity through dysregulation of miR-484/protocadherin-19 signaling

Concurrent de novo MACF1 mutation and inherited 16p13.11 microduplication in a preterm newborn with hypotonia, joint hyperlaxity and multiple congenital malformations: a case report

BACKGROUND

The MACF1 gene, found on chromosome 1p34.3, is vital for controlling cytoskeleton dynamics, cell movement, growth, and differentiation. It consists of 101 exons, spanning over 270 kb. The 16p13.11 microduplication syndrome results from the duplication of 16p13.11 chromosome copies and is associated with various neurodevelopmental and physiological abnormalities. Both MACF1 and 16p13.11 microduplication have significant impacts on neural development, potentially leading to nerve damage or neurological diseases. This study presents a unique case of a patient simultaneously experiencing a de novo MACF1 mutation and a hereditary 16p13.11 microduplication, which has not been reported previously.

CASE PRESENTATION

In this report, we describe a Chinese preterm newborn girl exhibiting the typical characteristics of 16.13.11 microduplication syndrome. These features include developmental delay, respiratory issues, feeding problems, muscle weakness, excessive joint movement, and multiple congenital abnormalities. Through whole-exome sequencing, we identified a disease-causing mutation in the MACF1 gene (c.15266T > C / p. Met5089Thr). Additionally, after microarray analysis, we confirmed the presence of a 16p13.11 microduplication (chr16:14,916,289 - 16,315,688), which was inherited from the mother.

CONCLUSIONS

The patient's clinical presentation, marked by muscle weakness and multiple birth defects, may be attributed to both the de novo MACF1 mutation and the 16p13.11 duplication, which could have further amplified her severe symptoms. Genetic testing for individuals with complex clinical manifestations can offer valuable insights for diagnosis and serve as a reference for genetic counseling for both patients and their families.

Neuronal network activity and connectivity are impaired in a conditional knockout mouse model with PCDH19 mosaic expression

Mutations in PCDH19 gene, which encodes protocadherin-19 (PCDH19), cause Developmental and Epileptic Encephalopathy 9 (DEE9). Heterogeneous loss of PCDH19 expression in neurons is considered a key determinant of the disorder; however, how PCDH19 mosaic expression affects neuronal network activity and circuits is largely unclear. Here, we show that the hippocampus of Pcdh19 mosaic mice is characterized by structural and functional synaptic defects and by the presence of PCDH19-negative hyperexcitable neurons. Furthermore, global reduction of network firing rate and increased neuronal synchronization have been observed in different limbic system areas. Finally, network activity analysis in freely behaving mice revealed a decrease in excitatory/inhibitory ratio and functional hyperconnectivity within the limbic system of Pcdh19 mosaic mice. Altogether, these results indicate that altered PCDH19 expression profoundly affects circuit wiring and functioning, and provide new key to interpret DEE9 pathogenesis.

Fetal Brain-Derived Exosomal miRNAs from Maternal Blood: Potential Diagnostic Biomarkers for Fetal Alcohol Spectrum Disorders (FASDs)

Fetal alcohol spectrum disorders (FASDs) are leading causes of neurodevelopmental disability but cannot be diagnosed early in utero. Because several microRNAs (miRNAs) are implicated in other neurological and neurodevelopmental disorders, the effects of EtOH exposure on the expression of these miRNAs and their target genes and pathways were assessed. In women who drank alcohol (EtOH) during pregnancy and non-drinking controls, matched individually for fetal sex and gestational age, the levels of miRNAs in fetal brain-derived exosomes (FB-Es) isolated from the mothers' serum correlated well with the contents of the corresponding fetal brain tissues obtained after voluntary pregnancy termination. In six EtOH-exposed cases and six matched controls, the levels of fetal brain and maternal serum miRNAs were quantified on the array by qRT-PCR. In FB-Es from 10 EtOH-exposed cases and 10 controls, selected miRNAs were quantified by ddPCR. Protein levels were quantified by ELISA. There were significant EtOH-associated reductions in the expression of several miRNAs, including miR-9 and its downstream neuronal targets BDNF, REST, Synapsin, and Sonic hedgehog. In 20 paired cases, reductions in FB-E miR-9 levels correlated strongly with reductions in fetal eye diameter, a prominent feature of FASDs. Thus, FB-E miR-9 levels might serve as a biomarker to predict FASDs in at-risk fetuses.

Characterization of exosomal microRNAs in preterm infants fed with breast milk and infant formula

Breastfeeding not only reduces infection-related morbidity, but also increases growth of preterm infants. Advantages of breast milk (BM) for preterm infants are significant. They continue to be studied. However, because not all preterm infants can receive breastfeeding, bovine-based infant formula (IF) is used as an alternative, which may increase the risk of several preterm complications. Exosomes isolated from biofluids are emerging as biomarkers in research of various diseases. Here, we characterized miRNA contents of exosomes in urine and serum samples of preterm infants who were BM and IF fed and performed transcriptomic analysis of small RNA libraries. We identified significantly up-regulated 6 miRNAs and 10 miRNAs, respectively. Gene Ontology (GO) analysis revealed that target genes of these miRNAs might participate in neuronal development, immunity modulation, detoxification of reactive oxygen species, and transmembrane exchange. Our data suggest that exosome-based systemic screening for preterm infants with breastfeeding might be a screening tool for identifying target molecules involved in therapy for preterm infants in neonatal intensive care unit (NICU) and for future application as nutraceutical formulations or pharmaceuticals.

Copy Number Variations in Neuropsychiatric Disorders

Neuropsychiatric disorders are complex conditions that represent a significant global health burden with complex and multifactorial etiologies. Technological advances in recent years have improved our understanding of the genetic architecture of the major neuropsychiatric disorders and the genetic loci involved. Previous studies mainly investigated genome-wide significant SNPs to elucidate the cross-disorder and disorder-specific genetic basis of neuropsychiatric disorders. Although copy number variations represent a major source of genetic variations, they are known risk factors in developing a variety of human disorders, including certain neuropsychiatric diseases. In this review, we demonstrate the current understanding of CNVs contributing to liability for schizophrenia, bipolar disorder, and major depressive disorder.

Prenatal Chromosomal Microarray Analysis: Does Increased Resolution Equal Increased Yield?

Chromosomal microarray analysis (CMA) is considered a first-tier test for patients with developmental disabilities and congenital anomalies and is also routinely applied in prenatal diagnosis. The current consensus size cut-off for reporting copy number variants (CNVs) in the prenatal setting ranges from 200 Kb to 400 Kb, with the intention of minimizing the impact of variants of uncertain significance (VUS). Very limited data are currently available on the application of higher resolution platforms prenatally. The aim of this study is to investigate the feasibility and impact of applying high-resolution CMA in the prenatal setting. To that end, we report on the outcomes of applying CMA with a size cut-off of 20 Kb in 250 prenatal samples and discuss the findings and diagnostic yield and also provide follow-up for cases with variants of uncertain significance. Overall, 19.6% (49) showed one or more chromosomal abnormalities, with the findings classified as Pathogenic (P) or Likely Pathogenic (LP) in 15.6% and as VUS in 4%. When excluding the cases with known familial aberrations, the diagnostic yield was 12%. The smallest aberration detected was a 32 Kb duplication of the 16p11.2 region. In conclusion, this study demonstrates that prenatal diagnosis with a high-resolution aCGH platform can reliably detect smaller CNVs that are often associated with neurodevelopmental phenotypes while providing an increased diagnostic yield, regardless of the indication for testing, with only a marginal increase in the VUS incidence. Thus, it can be an important tool in the prenatal setting.

Expanding the phenotypic spectrum of Chromosome 16p13.11 microduplication: A multicentric analysis of 206 patients

INTRODUCTION

Recurrent chromosome 16p13.11 microduplication has been characterised in the literature as a cause of developmental delay, learning difficulties and behavioural abnormalities. It is a neurosusceptibility locus and has incomplete penetrance and variable expression. Other clinical features, such as cardiac abnormalities have also been reported. The duplicated region contains the MYH11 gene, which encodes the protein myosin-11 and is a component of the myosin heavy chain in smooth muscle. Recent literature has suggested 16p13.11 microduplication as one of the possible risk factors for thoracic aortic aneurysms and dissection (TAAD). Therefore, we studied the detailed phenotype of cases of chromosome 16p13.11 microduplication from seven centres in the United Kingdom (UK) to expand the phenotype, focusing on the cardiac abnormalities.

METHODS

All individuals with a chromosome 16p13.11 microduplication seen in Clinical Genetics prior to June 2017 in 6 centres (prior to 2018 in the seventh centre) were identified through the regional genetics laboratory databases. A Microsoft Excel® proforma was created and clinical data was collected retrospectively from clinical genetics databases from the seven genetics services in the UK. The data was collated and analysed collectively.

RESULTS

The majority of the individuals presented with (72%) developmental delay and (62%) behavioural abnormalities, in keeping with the published literature. 27% had some dysmorphic features, 14% had visual impairment and 8% had congenital cardiac abnormalities. Echocardiograms were performed in 50% of patients, and only 3.8% patients had aortic dilatation and no one had aortic dissection. 9.7% of patients were found to have a second genetic/chromosomal diagnosis, especially where there were additional phenotypic features.

CONCLUSION

16p13.11 microduplication is a neurosusceptibility locus and is associated with variable expression. It may be helpful to refer children with 16p13.11 microduplication for a cardiac review for congenital cardiac abnormalities and also for ophthalmological assessment. Further prospective studies with cardiac assessments are recommended in this cohort of patients to determine whether ongoing aortic surveillance is indicated. Guidelines about the frequency of surveillance are indicated, especially in individuals with normal cardiac findings. We also highlight the importance of considering a second diagnosis if the phenotype is inconsistent with that reported.

Decoding microRNAs in autism spectrum disorder

Autism spectrum disorder (ASD)-a congenital mental disorder accompanied by social dysfunction and stereotyped behaviors-has attracted a great deal of attention worldwide. A combination of genetic and environmental factors may determine the pathogenesis of ASD. Recent research of multiple ASD models indicates that microRNAs (miRNAs) play a central role at the onset and progression of ASD by repressing the translation of key mRNAs in neural development and functions. As such, miRNAs show great potential to serve as biomarkers for ASD diagnosis or prognosis and therapeutic targets for the treatment of ASD. In this review, we discuss the regulatory mechanisms by which miRNAs influence ASD phenotypes through various in vivo and in vitro models, including necropsy specimens, animal models, cellular models, and, in particular, induced pluripotent stem cells derived from patients with ASD. We then discuss the potential of miRNA-based therapeutic strategies for ASD currently being evaluated in preclinical studies.

16p13.11 microdeletion/microduplication in fetuses: investigation of associated ultrasound phenotypes, genetic anomalies, and pregnancy outcome follow-up

OBJECTIVES

16p13.11 microdeletion/microduplication are rare genetic diseases with incomplete penetrance, most of which have been reported in adults and children, with ultrasound phenotyping in fetuses rarely described. Here, we have analyzed prenatal ultrasound phenotypic characteristics associated with 16p13.11 microdeletion/microduplication, in order to improve the understanding, diagnosis and monitoring of this disease in the fetus.

METHODS

A total of 9000 pregnant women who underwent invasive prenatal diagnosis for karyotyping and SNP-array were retrospectively analyzed in tertiary referral institutions from October 2016 to January 2022.

RESULTS

SNP-array revealed that 20 fetuses had copy number variation (CNV) in the 16p13.11 region, out of which 5 had 16p13.11 microdeletion and the rest showed microduplication, along with different ultrasound phenotypes. Furthermore, 4/20 cases demonstrated structural abnormalities, while the remaining 16 cases were atypical in ultrasound. Taken together, 16p13.1 microdeletion was closely related to thickened nuchal translucency, while 16p13.11 microduplication was more closely associated with echogenic bowel. Only 5/15 fetuses were verified by pedigree, with one case of 16p13.11 microdeletion being de novo, and the other cases of 16p13.11 microduplication were inherited from one parent. In 4/20 cases, the pregnancy was terminated. Except for one case with short stature and another one who underwent lung cystadenoma surgery, no abnormalities were reported in the other cases during follow-up.

CONCLUSION

Fetuses with 16p13.11 microdeletion/microduplication had no characteristic phenotype of intrauterine ultrasound and was in good health after birth, thus providing a reference for the perinatal management of such cases.

Modifying PCDH19 levels affects cortical interneuron migration

PCDH19 is a transmembrane protein and member of the protocadherin family. It is encoded by the X-chromosome and more than 200 mutations have been linked to the neurodevelopmental PCDH-clustering epilepsy (PCDH19-CE) syndrome. A disturbed cell-cell contact that arises when random X-inactivation creates mosaic absence of PCDH19 has been proposed to cause the syndrome. Several studies have shown roles for PCDH19 in neuronal proliferation, migration, and synapse function, yet most of them have focused on cortical and hippocampal neurons. As epilepsy can also be caused by impaired interneuron migration, we studied the role of PCDH19 in cortical interneurons during embryogenesis. We show that cortical interneuron migration is affected by altering PCDH19 dosage by means of overexpression in brain slices and medial ganglionic eminence (MGE) explants. We also detect subtle defects when PCDH19 expression was reduced in MGE explants, suggesting that the dosage of PCDH19 is important for proper interneuron migration. We confirm this finding in vivo by showing a mild reduction in interneuron migration in heterozygote, but not in homozygote PCDH19 knockout animals. In addition, we provide evidence that subdomains of PCDH19 have a different impact on cell survival and interneuron migration. Intriguingly, we also observed domain-dependent differences in migration of the non-targeted cell population in explants, demonstrating a non-cell-autonomous effect of PCDH19 dosage changes. Overall, our findings suggest new roles for the extracellular and cytoplasmic domains of PCDH19 and support that cortical interneuron migration is dependent on balanced PCDH19 dosage.

Phenotypic Impact of Rare Potentially Damaging Copy Number Variation in Obsessive-Compulsive Disorder and Chronic Tic Disorders

BACKGROUND

Recent studies report an important-and previously underestimated-role of rare variation in risk of obsessive-compulsive disorder (OCD) and chronic tic disorders (CTD). Using data from a large epidemiological study, we evaluate the distribution of potentially damaging copy number variation (pdCNV) in OCD and CTD, examining associations between pdCNV and the phenotypes of probands, including a consideration of early- vs. late-diagnoses.

METHOD

The Obsessive-Compulsive Inventory-Revised (OCI-R) questionnaire was used to ascertain psychometric profiles of OCD probands. CNV were identified genome-wide using chromosomal microarray data.

RESULTS

For 993 OCD cases, 86 (9%) were identified as pdCNV carriers. The most frequent pdCNV found was at the 16p13.11 region. There was no significant association between pdCNV and the OCI-R total score. However, pdCNV was associated with Obsessing and Checking subscores. There was no significant difference in pdCNV frequency between early- vs. late-diagnosed OCD probands. Of the 217 CTD cases, 18 (8%) were identified as pdCNV carriers. CTD probands with pdCNV were significantly more likely to have co-occurring autism spectrum disorder (ASD).

CONCLUSIONS

pdCNV represents part of the risk architecture for OCD and CTD. If replicated, our findings suggest pdCNV impact some OCD symptoms. Genes within the 16p13.11 region are potential OCD risk genes.

AntimiR targeting of microRNA-134 reduces seizures in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a severe neurodevelopmental disorder featuring ataxia, cognitive impairment, and drug-resistant epilepsy. AS is caused by mutations or deletion of the maternal copy of the paternally imprinted UBE3A gene, with current precision therapy approaches focusing on re-expression of UBE3A. Certain phenotypes, however, are difficult to rescue beyond early development. Notably, a cluster of microRNA binding sites was reported in the untranslated Ube3a1 transcript, including for miR-134, suggesting that AS may be associated with microRNA dysregulation. Here, we report levels of miR-134 and key targets are normal in the hippocampus of mice carrying a maternal deletion of Ube3a (Ube3a ^m-/p+ ). Nevertheless, intracerebroventricular injection of an antimiR oligonucleotide inhibitor of miR-134 (Ant-134) reduced audiogenic seizure severity over multiple trials in 21- and 42-day-old AS mice. Interestingly, Ant-134 also improved distance traveled and center crossings of AS mice in the open-field test. Finally, we show that silencing miR-134 can upregulate targets of miR-134 in neurons differentiated from Angelman patient-derived induced pluripotent stem cells. These findings indicate that silencing miR-134 and possibly other microRNAs could be useful to treat clinically relevant phenotypes with a later developmental window in AS.

Novel Findings, Mini-Review and Dysmorphological Characterization of 16p13.11 Microduplication syndrome

The short arm of chromosome 16 and especially the region 16p13.11 is a chromosome region where many structural variants, especially deletions and duplications, can be observed. While deletions of this region are clinically well defined, duplications are rare, and so far, there is no established clinical consensus in regard with its clinical picture, and especially the dysmorphic perspective of the disease is far from being clear. A 5-year-and-2-month-old patient who presented with epilepsy, autism and late speech onset complaints, was evaluated in our genetics department. On physical examination unilateral preauricular skin tag and upslanting palpebral fissures were noted. Microarray analysis was performed and reported as ([hg19]: 16p13.11 (14.897.804-16.730.375) x3). The literature review revealed only a few reports about the syndrome, but some dysmorphological findings appear to recur in different reports, which enables a possible characterization. Dysmorphic findings were discussed.

miR-484: A Potential Biomarker in Health and Disease

Disorders of miR-484 expression are observed in cancer, different diseases or pathological states. There is accumulating evidence that miR-484 plays an essential role in the development as well as the regression of different diseases, and miR-484 has been reported as a key regulator of common cancer and non-cancer diseases. The miR-484 targets that have effects on inflammation, apoptosis and mitochondrial function include SMAD7, Fis1, YAP1 and BCL2L13. For cancer, identified targets include VEGFB, VEGFR2, MAP2, MMP14, HNF1A, TUSC5 and KLF12. The effects of miR-484 on these targets have been documented separately. Moreover, miR-484 is typically described as an oncosuppressor, but this claim is simplistic and one-sided. This review will combine relevant basic and clinical studies to find that miR-484 promotes tumorigenesis and metastasis in liver, prostate and lung tissues. It will provide a basis for the possible mechanisms of miR-484 in early tumor diagnosis, prognosis determination, disease assessment, and as a potential therapeutic target for tumors.

Modeling PCDH19-CE: From 2D Stem Cell Model to 3D Brain Organoids

PCDH19 clustering epilepsy (PCDH19-CE) is a genetic disease characterized by a heterogeneous phenotypic spectrum ranging from focal epilepsy with rare seizures and normal cognitive development to severe drug-resistant epilepsy associated with intellectual disability and autism. Unfortunately, little is known about the pathogenic mechanism underlying this disease and an effective treatment is lacking. Studies with zebrafish and murine models have provided insights on the function of PCDH19 during brain development and how its altered function causes the disease, but these models fail to reproduce the human phenotype. Induced pluripotent stem cell (iPSC) technology has provided a complementary experimental approach for investigating the pathogenic mechanisms implicated in PCDH19-CE during neurogenesis and studying the pathology in a more physiological three-dimensional (3D) environment through the development of brain organoids. We report on recent progress in the development of human brain organoids with a particular focus on how this 3D model may shed light on the pathomechanisms implicated in PCDH19-CE.

Genome-Wide Methylation Profiling in the Thalamus of Scrapie Sheep

Scrapie is a neurodegenerative disorder belonging to the group of transmissible spongiform encephalopathy (TSE). Scrapie occurs in sheep and goats, which are considered good natural animal models of these TSE. Changes in DNA methylation occur in the central nervous system (CNS) of patients suffering from prion-like neurodegenerative diseases, such as Alzheimer's disease. Nevertheless, potential DNA methylation alterations have not yet been investigated in the CNS of any prion disease model or naturally infected cases, neither in humans nor in animals. Genome-wide DNA methylation patterns were studied in the thalamus obtained from sheep naturally infected with scrapie at a clinical stage (n = 4) and from controls (n = 4) by performing a whole-genome bisulfite sequencing (WGBS) analysis. Ewes carried the scrapie-susceptible ARQ/ARQ PRNP genotype and were sacrificed at a similar age (4–6 years). Although the average genomic methylation levels were similar between the control and the scrapie animals, we identified 8,907 significant differentially methylated regions (DMRs) and 39 promoters (DMPs). Gene Ontology analysis revealed that hypomethylated DMRs were enriched in genes involved in transmembrane transport and cell adhesion, whereas hypermethylated DMRs were related to intracellular signal transduction genes. Moreover, genes highly expressed in specific types of CNS cells and those previously described to be differentially expressed in scrapie brains contained DMRs. Finally, a quantitative PCR (qPCR) validation indicated differences in the expression of five genes (PCDH19, SNCG, WDR45B, PEX1, and CABIN1) that matched the methylation changes observed in the genomic study. Altogether, these results suggest a potential regulatory role of DNA methylation in prion neuropathology.

Apoptotic protease activating factor-1 gene and MicroRNA-484: A possible interplay in relapsing remitting multiple sclerosis

BACKGROUND

Emerging evidence suggests that dysregulated apoptosis might be implicated in the pathogenesis of multiple sclerosis (MS). The aim of the current study was to evaluate the expression of Apoptotic protease activating factor-1 (APAF1) mRNA and its potential regulator miR-484 in relapsing remitting MS patients (RRMS) and to investigate their role as potential disease biomarkers.

METHODS

After Bioinformatic analysis was conducted and revealed miR-484 involvement in the regulation of APAF-1 gene expression. Reverse Transcription-quantitative Real-Time PCR (RT-qPCR) was performed to detect the expression levels of APAF-1 and miR-484 in the peripheral blood mononuclear cells (PBMCs) of 34 RRMS patients recruited from the MS clinic of kasr al ainy hospital- faculty of medicine-Egypt and 34 healthy controls.

RESULTS

APAF-1 mRNA was significantly downregulated in patients whereas miR-484 expression was upregulated compared to controls (p < 0.01). Sensitivity and specificity of APAF-1 and miR-484 to diagnose MS was (85.3%, 76.5%) and (88.2% and 86.7%) respectively.

CONCLUSION

APAF-1 and miR-484 could play a role as potential MS diagnostic biomarkers. However, absence of a control group of patients with other inflammatory diseases in our study warrants further research to corroborate our findings.

16p13.11 deletion variants associated with neuropsychiatric disorders cause morphological and synaptic changes in induced pluripotent stem cell-derived neurons

16p13.11 copy number variants (CNVs) have been associated with autism, schizophrenia, psychosis, intellectual disability, and epilepsy. The majority of 16p13.11 deletions or duplications occur within three well-defined intervals, and despite growing knowledge of the functions of individual genes within these intervals, the molecular mechanisms that underlie commonly observed clinical phenotypes remain largely unknown. Patient-derived, induced pluripotent stem cells (iPSCs) provide a platform for investigating the morphological, electrophysiological, and gene-expression changes that result from 16p13.11 CNVs in human-derived neurons. Patient derived iPSCs with varying sizes of 16p13.11 deletions and familial controls were differentiated into cortical neurons for phenotypic analysis. High-content imaging and morphological analysis of patient-derived neurons demonstrated an increase in neurite branching in patients compared with controls. Whole-transcriptome sequencing revealed expression level changes in neuron development and synaptic-related gene families, suggesting a defect in synapse formation. Subsequent quantification of synapse number demonstrated increased numbers of synapses on neurons derived from early-onset patients compared to controls. The identification of common phenotypes among neurons derived from patients with overlapping 16p13.11 deletions will further assist in ascertaining common pathways and targets that could be utilized for screening drug candidates. These studies can help to improve future treatment options and clinical outcomes for 16p13.11 deletion patients.

Cellular and Behavioral Characterization of Pcdh19 Mutant Mice: subtle Molecular Changes, Increased Exploratory Behavior and an Impact of Social Environment

Mutations in the X-linked cell adhesion protein PCDH19 lead to seizures, cognitive impairment, and other behavioral comorbidities when present in a mosaic pattern. Neither the molecular mechanisms underpinning this disorder nor the function of PCDH19 itself are well understood. By combining RNA in situ hybridization with immunohistochemistry and analyzing single-cell RNA sequencing datasets, we reveal Pcdh19 expression in cortical interneurons and provide a first account of the subtypes of neurons expressing Pcdh19/PCDH19, both in the mouse and the human cortex. Our quantitative analysis of the Pcdh19 mutant mouse exposes subtle changes in cortical layer composition, with no major alterations of the main axonal tracts. In addition, Pcdh19 mutant animals, particularly females, display preweaning behavioral changes, including reduced anxiety and increased exploratory behavior. Importantly, our experiments also reveal an effect of the social environment on the behavior of wild-type littermates of Pcdh19 mutant mice, which show alterations when compared with wild-type animals not housed with mutants.

δ-Protocadherins regulate neural progenitor cell division by antagonizing Ryk and Wnt/β-catenin signaling

The division of neural progenitor cells provides the cellular substrate from which the nervous system is sculpted during development. The δ-protocadherin family of homophilic cell adhesion molecules is essential for the development of the vertebrate nervous system and is implicated in an array of neurodevelopmental disorders. We show that lesions in any of six, individual δ-protocadherins increases cell divisions of neural progenitors in the hindbrain. This increase is due to mis-regulation of Wnt/β-catenin signaling, as this pathway is upregulated in δ-protocadherin mutants and inhibition of this pathway blocks the increase in cell division. Furthermore, the δ-protocadherins can be present in complex with the Wnt receptor Ryk, and Ryk is required for the increased proliferation in protocadherin mutants. Thus, δ-protocadherins are novel regulators of Wnt/β-catenin signaling that may control the development of neural circuits by defining a molecular code for the identity of neural progenitor cells and differentially regulating their proliferation.

Development of neuronal circuits: From synaptogenesis to synapse plasticity

Optimal brain function critically hinges on the remarkably precise interconnections made among millions of neurons. These specialized interconnected neuronal junctions, termed synapses, are used for neuronal communication, whence the presynaptic neurons releases a specific neurotransmitter, which then binds to the appropriate protein receptor on the membrane of the postsynaptic neuron, activating and eliciting a response in this connected neuron. In this chapter, we discuss how synapses form and are modified as the brain matures. Genetic programs control most of the wiring in the brain, from allowing axons to choose where to target their synapses, to determining synapse identity. However, the final map of neuronal connectivity in the brain crucially relies on incoming sensory information during early childhood to strengthen and refine the preexisting synapses thus allowing both nature and nurture to shape the final structure and function of the nervous system (Fig. 5.1). Finally, we discuss how advances in the knowledge of basic mechanisms governing synapse formation and plasticity can shed light on the pathophysiology of neurodevelopmental disorders.

Dissecting the Role of PCDH19 in Clustering Epilepsy by Exploiting Patient-Specific Models of Neurogenesis

PCDH19-related epilepsy is a rare genetic disease caused by defective function of PCDH19, a calcium-dependent cell–cell adhesion protein of the cadherin superfamily. This disorder is characterized by a heterogeneous phenotypic spectrum, with partial and generalized febrile convulsions that are gradually increasing in frequency. Developmental regression may occur during disease progression. Patients may present with intellectual disability (ID), behavioral problems, motor and language delay, and a low motor tone. In most cases, seizures are resistant to treatment, but their frequency decreases with age, and some patients may even become seizure-free. ID generally persists after seizure remission, making neurological abnormalities the main clinical issue in affected individuals. An effective treatment is lacking. In vitro studies using patient-derived induced pluripotent stem cells (iPSCs) reported accelerated neural differentiation as a major endophenotype associated with PCDH19 mutations. By using this in vitro model system, we show that accelerated in vitro neurogenesis is associated with a defect in the cell division plane at the neural progenitors stage. We also provide evidence that altered PCDH19 function affects proper mitotic spindle orientation. Our findings identify an altered equilibrium between symmetric versus asymmetric cell division as a previously unrecognized mechanism contributing to the pathogenesis of this rare epileptic encephalopathy.

miR-484 is associated with disease recurrence and promotes migration in prostate cancer

BACKGROUND: microRNAs (miRs) regulate the expression of protein-coding genes and play key roles in various biological processes, including development and immunity. However, dysregulation of miR expression is also involved in disease biology, including cancer.

METHODS: We utilized The Cancer Genome Atlas (TCGA) and other publicly available databases for miRs and mRNA expression in prostate cancer, selected miR-484 and investigated its role in prostate cancer biology and disease progression using in vitro studies.

RESULTS: Our data mining efforts revealed that increased miR-484 in prostate tumors associates with early disease recurrence, while miR-484 expression in human prostate cancer cells enhances cancer cell mobility. Using RNAseq and bioinformatics, we identified candidate target genes of miR-484 and generated a list of potential tumor suppressors. One candidate in this list was PSMG1. We applied luciferase assays and immunoblotting to confirm that miR-484 directly targets PSMG1. Additional in vitro assays with cancer cell lines showed that PSMG1 knockdown rescued the reduction in mobility brought on by miR-484 inhibition, pointing toward the existence of a miR-484–PSMG1 axis in prostate cancer.

CONCLUSIONS: We hypothesize that miR-484 is an oncogene in the prostate that increases cancer cell mobility, with PSMG1 being a mir-484 target in this process.

microRNAs Mediated Regulation of the Ribosomal Proteins and its Consequences on the Global Translation of Proteins

Ribosomal proteins (RPs) are mostly derived from the energy-consuming enzyme families such as ATP-dependent RNA helicases, AAA-ATPases, GTPases and kinases, and are important structural components of the ribosome, which is a supramolecular ribonucleoprotein complex, composed of Ribosomal RNA (rRNA) and RPs, coordinates the translation and synthesis of proteins with the help of transfer RNA (tRNA) and other factors. Not all RPs are indispensable; in other words, the ribosome could be functional and could continue the translation of proteins instead of lacking in some of the RPs. However, the lack of many RPs could result in severe defects in the biogenesis of ribosomes, which could directly influence the overall translation processes and global expression of the proteins leading to the emergence of different diseases including cancer. While microRNAs (miRNAs) are small non-coding RNAs and one of the potent regulators of the post-transcriptional gene expression, miRNAs regulate gene expression by targeting the 3' untranslated region and/or coding region of the messenger RNAs (mRNAs), and by interacting with the 5' untranslated region, and eventually finetune the expression of approximately one-third of all mammalian genes. Herein, we highlighted the significance of miRNAs mediated regulation of RPs coding mRNAs in the global protein translation.

Right Place at the Right Time: How Changes in Protocadherins Affect Synaptic Connections Contributing to the Etiology of Neurodevelopmental Disorders

During brain development, neurons need to form the correct connections with one another in order to give rise to a functional neuronal circuitry. Mistakes during this process, leading to the formation of improper neuronal connectivity, can result in a number of brain abnormalities and impairments collectively referred to as neurodevelopmental disorders. Cell adhesion molecules (CAMs), present on the cell surface, take part in the neurodevelopmental process regulating migration and recognition of specific cells to form functional neuronal assemblies. Among CAMs, the members of the protocadherin (PCDH) group stand out because they are involved in cell adhesion, neurite initiation and outgrowth, axon pathfinding and fasciculation, and synapse formation and stabilization. Given the critical role of these macromolecules in the major neurodevelopmental processes, it is not surprising that clinical and basic research in the past two decades has identified several PCDH genes as responsible for a large fraction of neurodevelopmental disorders. In the present article, we review these findings with a focus on the non-clustered PCDH sub-group, discussing the proteins implicated in the main neurodevelopmental disorders.

Proximity-dependent Proteomics Reveals Extensive Interactions of Protocadherin-19 with Regulators of Rho GTPases and the Microtubule Cytoskeleton

Protocadherin-19 belongs to the cadherin family of cell surface receptors and has been shown to play essential roles in the development of the vertebrate nervous system. Mutations in human Protocadherin-19 (PCDH19) lead to PCDH19 Female-limited epilepsy (PCDH19 FLE) in humans, characterized by the early onset of epileptic seizures in children and a range of cognitive and behavioral problems in adults. Despite being considered the second most prevalent gene in epilepsy, very little is known about the intercellular pathways in which it participates. In order to characterize the protein complexes within which Pcdh19 functions, we generated Pcdh19-BioID fusion proteins and utilized proximity-dependent biotinylation to identify neighboring proteins. Proteomic identification and analysis revealed that the Pcdh19 interactome is enriched in proteins that regulate Rho family GTPases, microtubule binding proteins and proteins that regulate cell divisions. We cloned the centrosomal protein Nedd1 and the RacGEF Dock7 and verified their interactions with Pcdh19 in vitro. Our findings provide the first comprehensive insights into the interactome of Pcdh19, and provide a platform for future investigations into the cellular and molecular biology of this protein critical to the proper development of the nervous system.

Implications of germline copy-number variations in psychiatric disorders: review of large-scale genetic studies

Copy number variants (CNVs), defined as genome sequences of ≥50 bp that differ in copy number from that in a reference genome, are a common form of structural variation. Germline CNVs account for some of the missing heritability that single nucleotide polymorphisms could not account for. Recent technological advances have had a huge impact on CNV research. Microarray technology enables relatively low-cost, high-throughput, genome-wide measurements, and short-read sequencing technology enables the detection of short CNVs that cannot be detected by microarrays. As a result, large-scale genetic studies have been able to identify a variety of common and rare germline CNVs and their associations with diseases. Rare germline CNVs have been reported to be associated with neuropsychiatric disorders. In this review, we focused on germline CNVs and briefly described their functional characteristics, formation mechanisms, detection methods, related databases, and the latest findings. Finally, we introduced recent large-scale genetic studies to assess associations of CNVs with diseases, especially psychiatric disorders, and discussed the use of CNV-based animal models to investigate the molecular and cellular mechanisms underlying these disorders. The development and implementation of improved detection methods, such as long-read single-molecule sequencing, are expected to provide additional insight into the molecular basis of psychiatric disorders and other complex diseases, thus facilitating basic and clinical research on CNVs.

Circulating exosomal microRNAs in bipolar disorder

INTRODUCTION

Emerging evidence suggests central roles of miRNAs in the pathogenesis of bipolar disorder (BD). Exosomes are membrane-bound vesicles acting as "biological cargo carriers" of various types of molecules including microRNAs. In this study, we aimed to investigate circulating exosomal microRNAs as potential diagnostic biomarkers for BD.

METHODS

The exosomes were precipitated from plasma samples of patients with BD (n = 69; 15 depressed, 27 manic, 27 euthymic) and healthy controls (n = 41). Total RNA was extracted from the exosomes and the levels of miRNAs were assayed by qPCR. Dysregulated miRNAs were subjected to Kyoto Encyclopedia of Genes and Genomes" (KEGG) pathway analysis by DIANA-miRPath v3.0 to identify the predicted targets and the related pathways.

RESULTS

Thirteen miRNAs showed significant differences between patients with BD and healthy individuals; among these, MiR-484, -652-3p, -142-3p remained significantly downregulated and miR-185-5p remained significantly upregulated after accounting for multiple comparisons and adjustments for potential confounders. There were no significant alterations among different states of BD. The KEEG analysis of four dysregulated miRNAs highlighted several target pathways including PI3K/Akt signaling, fatty acid biosynthesis/metabolism, extracellular matrix and adhesion pathways.

CONCLUSION

Our findings suggest that dysregulation of miRNAs might be involved in the underlying pathophysiology of BD through several biological pathways; and highlight the importance of the exosomal miRNAs for biomarker research in BD. Further longitudinal studies may clarify the roles of exosomal miRNAs and their targets in the neurobiology of BD.

High-resolution chromosomal microarray analysis for copy-number variations in high-functioning autism reveals large aberration typical for intellectual disability

Copy-number variants (CNVs), in particular rare, small and large ones (< 1% frequency) and those encompassing brain-related genes, have been shown to be associated with neurodevelopmental disorders like autism spectrum disorders (ASDs), attention deficit hyperactivity disorder (ADHD), and intellectual disability (ID). However, the vast majority of CNV findings lack specificity with respect to autistic or developmental-delay phenotypes. Therefore, the aim of the study was to investigate the size and frequency of CNVs in high-functioning ASD (HFA) without ID compared with a random population sample and with published findings in ASD and ID. To investigate the role of CNVs for the "core symptoms" of high-functioning autism, we included in the present exploratory study only patients with HFA without ID. The aim was to test whether HFA have similar large rare (> 1 Mb) CNVs as reported in ASD and ID. We performed high-resolution chromosomal microarray analysis in 108 children and adolescents with HFA without ID. There was no significant difference in the overall number of rare CNVs compared to 124 random population samples. However, patients with HFA carried significantly more frequently CNVs containing brain-related genes. Surprisingly, six HFA patients carried very large CNVs known to be typically present in ID. Our findings provide new evidence that not only small, but also large CNVs affecting several key genes contribute to the genetic etiology/risk of HFA without affecting their intellectual ability.

Novel and de novo mutation of PCDH19 in Girls Clustering Epilepsy

BACKGROUND

PCDH19 has become the second most relevant gene in epilepsy after SCN1A. Seizures often provoked by fever.

METHODS

We screened 152 children with fever-sensitive epilepsy for gene detection. Their clinical information was followed up.

RESULTS

We found eight PCDH19 point mutations (four novel and four reported) and one whole gene deletion in 10 female probands (seven sporadic cases and three family cases) who also had cluster seizures. The common clinical features of 16 patients in 10 families included fever-sensitive and cluster seizures, mainly focal or tonic-clonic seizures, and absence of status epilepticus, normal intelligence, or mild-to-moderate cognitive impairment, the onset age ranges from 5 months to 20 years. Only four patients had multiple or focal transient discharges in interictal EEG. Focal seizures originating in the frontal region were recorded in four patients, two from the parietal region, and one from the occipital region.

CONCLUSION

PCDH19 mutation can be inherited or de novo. The clinical spectrum of PCDH19 mutation includes PCDH19 Girls Clustering Epilepsy with or without mental retardation, psychosis, and asymptomatic male. The onset age of PCDH19 Girls Clustering Epilepsy can range from infancy to adulthood. Sisters in the same family may be sensitive to the same antiepileptic drugs. And our report expands the mutation spectrum of PCDH19 Girls Clustering Epilepsy.

Multiplane Calcium Imaging Reveals Disrupted Development of Network Topology in Zebrafish pcdh19 Mutants

Functional brain networks self-assemble during development, although the molecular basis of network assembly is poorly understood. Protocadherin-19 (pcdh19) is a homophilic cell adhesion molecule that is linked to neurodevelopmental disorders, and influences multiple cellular and developmental events in zebrafish. Although loss of PCDH19 in humans and model organisms leads to functional deficits, the underlying network defects remain unknown. Here, we employ multiplane, resonant-scanning in vivo two-photon calcium imaging of developing zebrafish, and use graph theory to characterize the development of resting state functional networks in both wild-type and pcdh19 mutant larvae. We find that the brain networks of pcdh19 mutants display enhanced clustering and an altered developmental trajectory of network assembly. Our results show that functional imaging and network analysis in zebrafish larvae is an effective approach for characterizing the developmental impact of lesions in genes of clinical interest.

Integrated Transcriptome Analysis of microRNA and mRNA in Mouse Skin Derived Precursors (SKPs) and SKP Derived Fibroblast (SFBs) by RNA-Seq

Background:

Skin-derived precursors (SKPs) display the characteristics of self-renewal and multilineage differentiation.

Objective:

The study aimed to explore the molecular mechanisms of mouse SKPs differentiation into SKP-derived fibroblasts (SFBs).

Methods:

We compared the microRNA (miRNA) profile in mouse SKPs and SFBs by RNA sequenc-ing. Real-time quantitative reverse transcription PCR (qRT-PCR) was performed to validate the miRNA expression. The integrated analysis of miRNA and mRNA expression data was performed to explore the potential crosstalk of miRNA-mRNA in SKP differentiation.

Results:

207 differentially expressed miRNAs and 835 miRNA target genes in the gene list of integrated mRNA expression profiling were identified. Gene Ontology (GO) enrichment analysis revealed that cell differentiation and cell proliferation process were significantly enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed the target genes were significantly most enriched in the cytokine-cytokine receptor interaction, cancer pathways and axon guidance signaling pathway. The most upregulated and downregulated target genes were involved in the Wnt, Notch, cytokine-cytokine receptor interaction, TGF-β, p53 and apoptotic signaling pathway. The miRNA-mRNA regulatory net-works and 507 miRNA-mRNA pairs were constructed. Seven miRNAs (miR-486-3p, miR-504-5p, miR-149-3p, miR-31-5p, miR-484, miR-328-5p and miR-22-5p) and their target genes Wnt4, Dlx2, Se-ma4f, Kit, Kitl, Inpp5d, Igfbp3, Prdm16, Sfn, Irf6 and Clu were identified as miRNA-mRNA crosstalk pairs.

Conclusion:

These genes and signaling pathways might control SKPs proliferation and SKPs differen-tiation into SFBs during the process of SKPs differentiation, which might promote the application of SKPs in the clinical treatment of skin-related diseases by regulating SKPs proliferation and SKPs differ-entiation.

Reversal of proliferation deficits caused by chromosome 16p13.11 microduplication through targeting NFκB signaling: an integrated study of patient-derived neuronal precursor cells, cerebral organoids and in vivo brain imaging

The molecular basis of how chromosome 16p13.11 microduplication leads to major psychiatric disorders is unknown. Here we have undertaken brain imaging of patients carrying microduplications in chromosome 16p13.11 and unaffected family controls, in parallel with iPS cell-derived cerebral organoid studies of the same patients. Patient MRI revealed reduced cortical volume, and corresponding iPSC studies showed neural precursor cell (NPC) proliferation abnormalities and reduced organoid size, with the NPCs therein displaying altered planes of cell division. Transcriptomic analyses of NPCs uncovered a deficit in the NFκB p65 pathway, confirmed by proteomics. Moreover, both pharmacological and genetic correction of this deficit rescued the proliferation abnormality. Thus, chromosome 16p13.11 microduplication disturbs the normal programme of NPC proliferation to reduce cortical thickness due to a correctable deficit in the NFκB signalling pathway. This is the first study demonstrating a biologically relevant, potentially ameliorable, signalling pathway underlying chromosome 16p13.11 microduplication syndrome in patient-derived neuronal precursor cells.

The female epilepsy protein PCDH19 is a new GABAAR-binding partner that regulates GABAergic transmission as well as migration and morphological maturation of hippocampal neurons

The PCDH19 gene (Xp22.1) encodes the cell-adhesion protein protocadherin-19 (PCDH19) and is responsible for a neurodevelopmental pathology characterized by female-limited epilepsy, cognitive impairment and autistic features, the pathogenic mechanisms of which remain to be elucidated. Here, we identified a new interaction between PCDH19 and GABAA receptor (GABAAR) alpha subunits in the rat brain. PCDH19 shRNA-mediated downregulation reduces GABAAR surface expression and affects the frequency and kinetics of miniature inhibitory postsynaptic currents (mIPSCs) in cultured hippocampal neurons. In vivo, PCDH19 downregulation impairs migration, orientation and dendritic arborization of CA1 hippocampal neurons and increases rat seizure susceptibility. In sum, these data indicate a role for PCDH19 in GABAergic transmission as well as migration and morphological maturation of neurons.

The Role of Protocadherin 19 (PCDH19) in Neurodevelopment and in the Pathophysiology of Early Infantile Epileptic Encephalopathy-9 (EIEE9)

PCDH19 is considered one of the most clinically relevant genes in epilepsy, second only to SCN1A. To date about 150 mutations have been identified as causative for PCDH19-female epilepsy (also known as early infantile epileptic encephalopathy-9, EIEE9), which is characterized by early onset epilepsy, intellectual disabilities, and behavioral disturbances. Although little is known about the physiological role of PCDH19 and the pathogenic mechanisms that lead to EIEE9, in this review, we will present latest researches focused on these aspects, underlining protein expression, its known functions and the mechanisms by which the protein acts, with particular interest in PCDH19 extracellular and intracellular roles in neurons.

16p13.11 microduplication in 45 new patients: refined clinical significance and genotype-phenotype correlations

BACKGROUND

The clinical significance of 16p13.11 duplications remains controversial while frequently detected in patients with developmental delay (DD), intellectual deficiency (ID) or autism spectrum disorder (ASD). Previously reported patients were not or poorly characterised. The absence of consensual recommendations leads to interpretation discrepancy and makes genetic counselling challenging. This study aims to decipher the genotype-phenotype correlations to improve genetic counselling and patients' medical care.

METHODS

We retrospectively analysed data from 16 013 patients referred to 12 genetic centers for DD, ID or ASD, and who had a chromosomal microarray analysis. The referring geneticists of patients for whom a 16p13.11 duplication was detected were asked to complete a questionnaire for detailed clinical and genetic data for the patients and their parents.

RESULTS

Clinical features are mainly speech delay and learning disabilities followed by ASD. A significant risk of cardiovascular disease was noted. About 90% of the patients inherited the duplication from a parent. At least one out of four parents carrying the duplication displayed a similar phenotype to the propositus. Genotype-phenotype correlations show no impact of the size of the duplicated segment on the severity of the phenotype. However, NDE1 and miR-484 seem to have an essential role in the neurocognitive phenotype.

CONCLUSION

Our study shows that 16p13.11 microduplications are likely pathogenic when detected in the context of DD/ID/ASD and supports an essential role of NDE1 and miR-484 in the neurocognitive phenotype. Moreover, it suggests the need for cardiac evaluation and follow-up and a large study to evaluate the aortic disease risk.

Identification of MS-specific serum miRNAs in an international multicenter study

Objective

To identify circulating microRNAs (miRNAs) linked to disease, disease stage, and disability in MS across cohorts.

Methods

Samples were obtained from the Comprehensive Longitudinal Investigation of Multiple Sclerosis (CLIMB, Boston, MA), EPIC (San Francisco, CA), AMIR (Beirut, Lebanon) as part of the SUMMIT consortium, and Stockholm Prospective Assessment of Multiple Sclerosis (Stockholm, Sweden) cohorts. Serum miRNA expression was measured using locked nucleic acid–based quantitative PCR. Four groups were compared: (1) MS vs healthy control (HC), (2) relapsing-remitting (RR) vs HC, (3) secondary progressive (SP) vs HC, and (4) RR vs SP. A Wilcoxon rank-sum test was used for the comparisons. The association between each miRNA and the Expanded Disability Status Scale (EDSS) score was assessed using the Spearman correlation coefficient. For each comparison, the p values were corrected for multiple comparisons using the approach of Benjamini and Hochberg to control the false discovery rate.

Results

In the CLIMB cohort, 5 miRNAs (hsa-miR-484, hsa-miR-140-5p, hsa-miR-320a, hsa-miR-486-5p, and hsa-miR-320c) showed a significant difference between patients with MS and healthy individuals; among these, miR-484 remained significant after accounting for multiple comparisons (p = 0.01). When comparing RRMS with HCs, hsa-miR-484 showed a significant difference (p = 0.004) between the groups after accounting for multiple group comparisons. When SP and HC were compared, 6 miRNAs (hsa-miR-484, hsa-miR-140-5p, hsa-miR-142-5p, hsa-miR-320a, hsa-miR-320b, and hsa-miR-320c) remained significantly different after accounting for multiple comparisons. Disability correlation analysis with miRNA provided 4 miRNAs (hsa-miR-320a, hsa-miR-337-3p, hsa-miR-199a-5p, and hsa-miR-142-5p) that correlated with the EDSS during the internal reproducibility phase. Among these, hsa-miR-337-3p was the most statistically significant miRNA that negatively correlated with the EDSS in three of the MS cohorts tested.

Conclusions

These findings further confirm the use of circulating serum miRNAs as biomarkers to diagnose and monitor disease status in MS.

Classification of evidence

This study provides Class III evidence that levels of circulating miRNAs identify patients with MS.

The Cadherin Superfamily in Neural Circuit Assembly

The cadherin superfamily comprises a large, diverse collection of cell surface receptors that are expressed in the nervous system throughout development and have been shown to be essential for the proper assembly of the vertebrate nervous system. As our knowledge of each family member has grown, it has become increasingly clear that the functions of various cadherin subfamilies are intertwined: they can be present in the same protein complexes, impinge on the same developmental processes, and influence the same signaling pathways. This interconnectedness may illustrate a central way in which core developmental events are controlled to bring about the robust and precise assembly of neural circuitry.

The NDE1 genomic locus can affect treatment of psychiatric illness through gene expression changes related to microRNA-484

Genetic studies of familial schizophrenia in Finland have observed significant associations with a group of biologically related genes, DISC1, NDE1, NDEL1, PDE4B and PDE4D, the ‘DISC1 network’. Here, we use gene expression and psychoactive medication use data to study their biological consequences and potential treatment implications. Gene expression levels were determined in 64 individuals from 18 families, while prescription medication information has been collected over a 10-year period for 931 affected individuals. We demonstrate that the NDE1 SNP rs2242549 associates with significant changes in gene expression for 2908 probes (2542 genes), of which 794 probes (719 genes) were replicable. A significant number of the genes altered were predicted targets of microRNA-484 (p = 3.0 × 10⁻⁸), located on a non-coding exon of NDE1. Variants within the NDE1 locus also displayed significant genotype by gender interaction to early cessation of psychoactive medications metabolized by CYP2C19. Furthermore, we demonstrate that miR-484 can affect the expression of CYP2C19 in a cell culture system. Thus, variation at the NDE1 locus may alter risk of mental illness, in part through modification of miR-484, and such modification alters treatment response to specific psychoactive medications, leading to the potential for use of this locus in targeting treatment.

Quantitative trait locus mapping and analysis of heritable variation in affiliative social behavior and co-occurring traits

Humans exhibit broad heterogeneity in affiliative social behavior. Twin and family studies show that individual differences in core dimensions of social behavior are heritable, yet there are knowledge gaps in understanding the underlying genetic and neurobiological mechanisms. Animal genetic reference panels (GRPs) provide a tractable strategy for examining the behavioral and genetic architecture of complex traits. Here, using males from 50 mouse strains from the BXD GRP, 4 domains of affiliative social behavior-social approach, social recognition, direct social interaction (DSI) (partner sniffing) and vocal communication-were examined in 2 widely used behavioral tasks-the 3-chamber and DSI tasks. There was continuous and broad variation in social and nonsocial traits, with moderate to high heritability of social approach sniff preference (0.31), ultrasonic vocalization (USV) count (0.39), partner sniffing (0.51), locomotor activity (0.54-0.66) and anxiety-like behavior (0.36). Principal component analysis shows that variation in social and nonsocial traits are attributable to 5 independent factors. Genome-wide mapping identified significant quantitative trait loci for USV count on chromosome (Chr) 18 and locomotor activity on Chr X, with suggestive loci and candidate quantitative trait genes identified for all traits with one notable exception-partner sniffing in the DSI task. The results show heritable variation in sociability, which is independent of variation in activity and anxiety-like traits. In addition, a highly heritable and ethological domain of affiliative sociability-partner sniffing-appears highly polygenic. These findings establish a basis for identifying functional natural variants, leading to a new understanding typical and atypical sociability.

PCDH19 regulation of neural progenitor cell differentiation suggests asynchrony of neurogenesis as a mechanism contributing to PCDH19 Girls Clustering Epilepsy

PCDH19-Girls Clustering Epilepsy (PCDH19-GCE) is a childhood epileptic encephalopathy characterised by a spectrum of neurodevelopmental problems. PCDH19-GCE is caused by heterozygous loss-of-function mutations in the X-chromosome gene, Protocadherin 19 (PCDH19) encoding a cell-cell adhesion molecule. Intriguingly, hemizygous males are generally unaffected. As PCDH19 is subjected to random X-inactivation, heterozygous females are comprised of a mosaic of cells expressing either the normal or mutant allele, which is thought to drive pathology. Despite being the second most prevalent monogeneic cause of epilepsy, little is known about the role of PCDH19 in brain development. In this study we show that PCDH19 is highly expressed in human neural stem and progenitor cells (NSPCs) and investigate its function in vitro in these cells of both mouse and human origin. Transcriptomic analysis of mouse NSPCs lacking Pcdh19 revealed changes to genes involved in regulation of neuronal differentiation, and we subsequently show that loss of Pcdh19 causes increased NSPC neurogenesis. We reprogramed human fibroblast cells harbouring a pathogenic PCDH19 mutation into human induced pluripotent stem cells (hiPSC) and employed neural differentiation of these to extend our studies into human NSPCs. As in mouse, loss of PCDH19 function caused increased neurogenesis, and furthermore, we show this is associated with a loss of human NSPC polarity. Overall our data suggests a conserved role for PCDH19 in regulating mammalian cortical neurogenesis and has implications for the pathogenesis of PCDH19-GCE. We propose that the difference in timing or "heterochrony" of neuronal cell production originating from PCDH19 wildtype and mutant NSPCs within the same individual may lead to downstream asynchronies and abnormalities in neuronal network formation, which in-part predispose the individual to network dysfunction and epileptic activity.

Regulation of neural circuit formation by protocadherins

The protocadherins (Pcdhs), which make up the most diverse group within the cadherin superfamily, were first discovered in the early 1990s. Data implicating the Pcdhs, including ~60 proteins encoded by the tandem Pcdha, Pcdhb, and Pcdhg gene clusters and another ~10 non-clustered Pcdhs, in the regulation of neural development have continually accumulated, with a significant expansion of the field over the past decade. Here, we review the many roles played by clustered and non-clustered Pcdhs in multiple steps important for the formation and function of neural circuits, including dendrite arborization, axon outgrowth and targeting, synaptogenesis, and synapse elimination. We further discuss studies implicating mutation or epigenetic dysregulation of Pcdh genes in a variety of human neurodevelopmental and neurological disorders. With recent structural modeling of Pcdh proteins, the prospects for uncovering molecular mechanisms of Pcdh extracellular and intracellular interactions, and their role in normal and disrupted neural circuit formation, are bright.

δ-Protocadherins: Organizers of neural circuit assembly

The δ-protocadherins comprise a small family of homophilic cell adhesion molecules within the larger cadherin superfamily. They are essential for neural development as mutations in these molecules give rise to human neurodevelopmental disorders, such as schizophrenia and epilepsy, and result in behavioral defects in animal models. Despite their importance to neural development, a detailed understanding of their mechanisms and the ways in which their loss leads to changes in neural function is lacking. However, recent results have begun to reveal roles for the δ-protocadherins in both regulation of neurogenesis and lineage-dependent circuit assembly, as well as in contact-dependent motility and selective axon fasciculation. These evolutionarily conserved mechanisms could have a profound impact on the robust assembly of the vertebrate nervous system. Future work should be focused on unraveling the molecular mechanisms of the δ-protocadherins and understanding how this family functions broadly to regulate neural development.

The RNA-binding protein MARF1 promotes cortical neurogenesis through its RNase activity domain

Cortical neurogenesis is a fundamental process of brain development that is spatiotemporally regulated by both intrinsic and extrinsic cues. Although recent evidence has highlighted the significance of transcription factors in cortical neurogenesis, little is known regarding the role of RNA-binding proteins (RBPs) in the post-transcriptional regulation of cortical neurogenesis. Here, we report that meiosis arrest female 1 (MARF1) is an RBP that is expressed during neuronal differentiation. Cortical neurons expressed the somatic form of MARF1 (sMARF1) but not the oocyte form (oMARF1). sMARF1 was enriched in embryonic brains, and its expression level decreased as brain development progressed. Overexpression of sMARF1 in E12.5 neuronal progenitor cells promoted neuronal differentiation, whereas sMARF1 knockdown decreased neuronal progenitor differentiation in vitro. We also examined the function of sMARF1 in vivo using an in utero electroporation technique. Overexpression of sMARF1 increased neuronal differentiation, whereas knockdown of sMARF1 inhibited differentiation in vivo. Moreover, using an RNase domain deletion mutant of sMARF1, we showed that the RNase domain is required for the effects of sMARF1 on cortical neurogenesis in vitro. Our results further elucidate the mechanisms of post-transcriptional regulation of cortical neurogenesis by RBPs.

Modeling Fragile X syndrome in neurogenesis: An unexpected phenotype and a novel tool for future therapies

FMRP is an RNA-binding protein involved in synaptic translation. Its absence causes a form of intellectual disability, the Fragile X syndrome (FXS). Small neuroanatomical abnormalities, present both in human and mouse FMRP-deficient brains, suggest a subtle critical role of this protein in neurogenesis. Stable depletion of FMRP has been obtained in a mouse embryonic stem cell line Fmr1 (shFmr1 ES) that does not display morphological alterations, but an abnormal expression of a subset of genes mainly involved in neuronal differentiation and maturation. Inducing the differentiation of shFmr1 ES cells into the neuronal lineage results in an accelerated generation of neural progenitors and neurons during the first steps of neurogenesis. This transient phenotype is due to an elevated level of the Amyloid Precursor Protein (APP), whose mRNA is a target of FMRP. APP is processed by the BACE-1 enzyme, producing the β-amyloid (Aβ) peptide accelerating neurogenesis by activating the expression of Ascll. Inhibition of the BACE-1 enzyme rescues the phenotype of shFmr1 ES cells. Here we discuss the importance of the shFmr1 ES line not only to understand the physiopathology of FXS but also as a tool to screen biomolecules for new FXS therapies.