SCRIB and PUF60 are primary drivers of the multisystemic phenotypes of the 8q24.3 copy-number variant

Spliceosome complex and neurodevelopmental disorders

Neurodevelopment requires complex spatiotemporal expression, which heavily relies on proper RNA splicing. The spliceosome is a ribonucleoprotein complex that removes introns from pre-mRNA, joins exons, and produces mature mRNA. Pathogenic variants in genes that code for spliceosome RNAs and proteins cause RNA mis-splicing and spliceosomopathies. Splicing defects during nervous system development upend the tightly controlled neurodevelopmental process, leading to neurodevelopmental disorders (NDDs). Despite the fact that the spliceosome is expressed in every cell, not all spliceosomopathies present as NDDs; spliceosomopathies are often tissue-specific in that a variant has a greater impact on certain cell lineages or cell types. Here we discuss spliceosomopathies whose presentations include NDDs and focus on spliceosome-coding genes.

Identification of a de novo PUF60 variant associated with craniofacial microsomia

Craniofacial microsomia (CFM), also known as the oculo-auriculo-vertebral spectrum, is a congenital disorder characterized by hypoplasia of the mandible and external ear due to tissue malformations originating from the first and second branchial arches. However, distinguishing it from other syndromes of branchial arch abnormalities is difficult, and causal variants remain unidentified in many cases. In this report, we performed an exome sequencing analysis of a Brazilian family with CFM. The proband was a 12-month-old boy with clinical findings consistent with the diagnostic criteria for CFM, including unilateral mandibular hypoplasia, microtia, and external auditory canal abnormalities. A heterozygous de novo nonsense variant (c.713C>G, p.S238*) in PUF60 was identified, which was predicted to be pathogenic in silico. PUF60 has been reported as a causal gene in Verheij syndrome, but not in CFM. Although the boy showed craniofacial abnormalities and developmental delay that overlapped with Verheij syndrome, the facial asymmetry with unilateral hypoplasia of the mandible observed in this case did not match the previously reported phenotypes of PUF60 variants. Our findings expand the phenotypic range of PUF60 variants that cover CFM and Verheij syndrome.

PUF60 loss-of-function with normal cognition should be considered in the differential diagnosis of Klippel-Feil syndrome

Klippel-Feil syndrome (KFS) has a genetically heterogeneous phenotype with six known genes, exhibiting both autosomal dominant and autosomal recessive inheritance patterns. PUF60 is a nucleic acid-binding protein, which is involved in a number of nuclear processes, including pre-mRNA splicing, apoptosis, and transcription regulation. Pathogenic variants in this gene have been described in Verheij syndrome due to either 8q24.3 microdeletion or PUF60 single-nucleotide variants. PUF60-associated conditions usually include intellectual disability, among other findings, some overlapping KFS; however, PUF60 is not classically referred to as a KFS gene. Here, we describe a 6-year-old female patient with clinically diagnosed KFS and normal cognition, who harbors a heterozygous de novo variant in the PUF60 gene (c.1179del, p.Ile394Serfs*7). This is a novel frameshift variant, which is predicted to result in a premature stop codon. Clinically, our patient demonstrates a pattern of malformations that matches reported cases of PUF60 variants; however, unlike most others, she has no clear learning difficulties. In light of these findings, we propose that PUF60 should be considered in the differential diagnosis of KFS and that normal cognition should not exclude its testing.

Novel PUF60 variant suggesting an interaction between Verheij and Cornelia de Lange syndrome: phenotype description and review of the literature

Verheij syndrome [VRJS; OMIM 615583] is a rare autosomal dominant neurodevelopmental disorder characterized by distinct clinical features, including growth retardation, intellectual disability, cardiac, and renal anomalies. VRJS is caused by deletions of chromosome 8q24.3 or pathogenic variants in the PUF60 gene. Recently, pathogenic PUF60 variants have been reported in some individuals with VRJS, contributing to the variability in the clinical presentation and severity of the condition. PUF60 encodes a protein involved in regulating gene expression and cellular growth. In this report, we describe a new case of VRJS with developmental delay, cardiac-, and renal abnormalities, caused by a heterozygous pathogenic PUF60 variant. Surprisingly, DNA methylation analysis revealed a pattern resembling the Cornelia de Lange syndrome (CdLS) episignature, suggesting a potential connection between PUF60 and CdLS-related genes. This case report further delineates the clinical and molecular spectrum of VRJS and supports further research to validate the interaction between VRJS and CdLS.

RNA binding proteins in cardiovascular development and disease

Congenital heart disease (CHD) is the most common birth defect affecting>1.35 million newborn babies worldwide. CHD can lead to prenatal, neonatal, postnatal lethality or life-long cardiac complications. RNA binding protein (RBP) mutations or variants are emerging as contributors to CHDs. RBPs are wizards of gene regulation and are major contributors to mRNA and protein landscape. However, not much is known about RBPs in the developing heart and their contributions to CHD. In this chapter, we will discuss our current knowledge about specific RBPs implicated in CHDs. We are in an exciting era to study RBPs using the currently available and highly successful RNA-based therapies and methodologies. Understanding how RBPs shape the developing heart will unveil their contributions to CHD. Identifying their target RNAs in the embryonic heart will ultimately lead to RNA-based treatments for congenital heart disease.

Identification of a novel de novo PUF60 variant causing Verheij syndrome in a fetus

Verheij syndrome (VRJS) is a craniofacial spliceosomopathy with a wide phenotypic spectrum. Haploinsufficiency of the poly-uridine binding splicing factor 60 gene (PUF60) and its loss-of-function (LOF) variants are involved in VRJS. We evaluated a human fetus with congenital heart defects and preaxial polydactyly. Clinical data were obtained from the medical record. Whole-exome sequencing (WES) was used to explore the potential genetic etiology, and the detected variant verified using Sanger sequencing. Functional studies were performed to validate the pathogenic effects of the variant. Using trio-WES, we identified a novel PUF60 variant (NM_078480.2; c.1678 T > A, p.*560Argext*204) in the pedigree. Bioinformatic analyses revealed that the variant is potentially pathogenic, and functional studies indicated that it leads to degradation of the elongated protein and subsequently PUF60 LOF, producing some VRJS phenotypes. These findings confirmed the pathogenicity of the variant. This study implicates PUF60 LOF in the etiopathogenesis of VRJS. It not only expands the PUF60 variant spectrum, and also provides a basis for genetic counseling and the diagnosis of VRJS. Although trio-WES is a well-established approach for identifying the genetic etiology of rare multisystemic conditions, functional studies could aid in verifying the pathogenicity of novel variants.

Novel Genetic and Phenotypic Expansion in Ameliorated PUF60-Related Disorders

Heterozygous variants in the Poly(U) Binding Splicing Factor 60kDa gene (PUF60) have been associated with Verheij syndrome, which has the key features of coloboma, short stature, skeletal abnormalities, developmental delay, palatal abnormalities, and congenital heart and kidney defects. Here, we report five novel patients from unrelated families with PUF60-related disorders exhibiting novel genetic and clinical findings with three truncating variants, one splice-site variant with likely reduced protein expression, and one missense variant. Protein modeling of the patient's missense variant in the PUF60 AlphaFold structure revealed a loss of polar bonds to the surrounding residues. Neurodevelopmental disorders were present in all patients, with variability in speech, motor, cognitive, social-emotional and behavioral features. Novel phenotypic expansions included movement disorders as well as immunological findings with recurrent respiratory, urinary and ear infections, atopic diseases, and skin abnormalities. We discuss the role of PUF60 in immunity with and without infection based on recent organismic and cellular studies. As our five patients showed less-severe phenotypes than classical Verheij syndrome, particularly with the absence of key features such as coloboma or palatal abnormalities, we propose a reclassification as PUF60-related neurodevelopmental disorders with multi-system involvement. These findings will aid in the genetic counseling of patients and families.

Targeting PUF60 prevents tumor progression by retarding mRNA decay of oxidative phosphorylation in ovarian cancer

PURPOSE

Ovarian cancer (OC) is the leading cause of death from gynecological malignancies, and its etiology and pathogenesis are currently unclear. Recent studies have found that PUF60 overexpressed in various cancers. However, the exact function of PUF60 in global RNA processing and its role in OC has been unclear.

METHODS

The expression of PUF60 and its relationship with clinical characteristics were analyzed by multiple database analysis and immunohistochemistry. Phenotypic effects of PUF60 on ovarian cancer cell proliferation and metastasis were examined by in vitro cell proliferation assay, migration assay, and in vivo xenograft models and lung metastasis models. RNA immunoprecipitation, seahorse analyses, RNA stability assay were used to study the effect of PUF60 on the stability of oxidative phosphorylation (OXPHOS)-related genes in OC.

RESULTS

We report PUF60 is highly expressed in OC with frequent amplification of up to 33.9% and its upregulation predicts a poor prognosis. PUF60 promotes the proliferation and migration of OC cells both in vitro and in vivo. Mechanistically, we demonstrated that silencing of PUF60 enhanced the stability of mRNA transcripts involved in OXPHOS and decreased the formation of processing bodies (P-bodies), ultimately elevating the OXPHOS level.

CONCLUSION

Our study unveils a novel function of PUF60 in OC energy metabolism. Thus, PUF60 may serve as a novel target for the treatment of patients with OC.

The Link of mRNA and rRNA Transcription by PUF60/FIR through TFIIH/P62 as a Novel Therapeutic Target for Cancer

The interaction between mRNA and ribosomal RNA (rRNA) transcription in cancer remains unclear. RNAP I and II possess a common N-terminal tail (NTT), RNA polymerase subunit RPB6, which interacts with P62 of transcription factor (TF) IIH, and is a common target for the link between mRNA and rRNA transcription. The mRNAs and rRNAs affected by FUBP1-interacting repressor (FIR) were assessed via RNA sequencing and qRT-PCR analysis. An FIR, a c-myc transcriptional repressor, and its splicing form FIRΔexon2 were examined to interact with P62. Protein interaction was investigated via isothermal titration calorimetry measurements. FIR was found to contain a highly conserved region homologous to RPB6 that interacts with P62. FIRΔexon2 competed with FIR for P62 binding and coactivated transcription of mRNAs and rRNAs. Low-molecular-weight chemical compounds that bind to FIR and FIRΔexon2 were screened for cancer treatment. A low-molecular-weight chemical, BK697, which interacts with FIRΔexon2, inhibited tumor cell growth with rRNA suppression. In this study, a novel coactivation pathway for cancer-related mRNA and rRNA transcription through TFIIH/P62 by FIRΔexon2 was proposed. Direct evidence in X-ray crystallography is required in further studies to show the conformational difference between FIR and FIRΔexon2 that affects the P62-RBP6 interaction.

PUF60-related developmental disorder: A case series and phenotypic analysis of 10 additional patients with monoallelic PUF60 variants

PUF60-related developmental disorder (also referred to as Verheij syndrome), resulting from haploinsufficiency of PUF60, is associated with multiple congenital anomalies affecting a wide range of body systems. These anomalies include ophthalmic coloboma, and congenital anomalies of the heart, kidney, and musculoskeletal system. Behavioral and intellectual difficulties are also observed. While less common than other features associated with PUF60-related developmental disorder, for instance hearing impairment and short stature, identification of specific anomalies such as ophthalmic coloboma can aid with diagnostic identification given the limited spectrum of genes linked with this feature. We describe 10 patients with PUF60 gene variants, bringing the total number reported in the literature, to varying levels of details, to 56 patients. Patients were recruited both via locally based exome sequencing from international sites and from the DDD study in the United Kingdom. Eight of the variants reported were novel PUF60 variants. The addition of a further patient with a reported c449-457del variant to the existing literature highlights this as a recurrent variant. One variant was inherited from an affected parent. This is the first example in the literature of an inherited variant resulting in PUF60-related developmental disorder. Two patients (20%) were reported to have a renal anomaly consistent with 22% of cases in previously reported literature. Two patients received specialist endocrine treatment. More commonly observed were clinical features such as: cardiac anomalies (40%), ocular abnormalities (70%), intellectual disability (60%), and skeletal abnormalities (80%). Facial features did not demonstrate a recognizable gestalt. Of note, but remaining of unclear causality, we describe a single pediatric patient with pineoblastoma. We recommend that stature and pubertal progress should be monitored in PUF60-related developmental disorder with a low threshold for endocrine investigations as hormone therapy may be indicated. Our study reports an inherited case with PUF60-related developmental disorder which has important genetic counseling implications for families.

De novo PHF5A variants are associated with craniofacial abnormalities, developmental delay, and hypospadias

PURPOSE

The SF3B splicing complex is composed of SF3B1-6 and PHF5A. We report a developmental disorder caused by de novo variants in PHF5A.

METHODS

Clinical, genomic, and functional studies using subject-derived fibroblasts and a heterologous cellular system were performed.

RESULTS

We studied 9 subjects with congenital malformations, including preauricular tags and hypospadias, growth abnormalities, and developmental delay who had de novo heterozygous PHF5A variants, including 4 loss-of-function (LOF), 3 missense, 1 splice, and 1 start-loss variant. In subject-derived fibroblasts with PHF5A LOF variants, wild-type and variant PHF5A mRNAs had a 1:1 ratio, and PHF5A mRNA levels were normal. Transcriptome sequencing revealed alternative promoter use and downregulated genes involved in cell-cycle regulation. Subject and control fibroblasts had similar amounts of PHF5A with the predicted wild-type molecular weight and of SF3B1-3 and SF3B6. SF3B complex formation was unaffected in 2 subject cell lines.

CONCLUSION

Our data suggest the existence of feedback mechanisms in fibroblasts with PHF5A LOF variants to maintain normal levels of SF3B components. These compensatory mechanisms in subject fibroblasts with PHF5A or SF3B4 LOF variants suggest disturbed autoregulation of mutated splicing factor genes in specific cell types, that is, neural crest cells, during embryonic development rather than haploinsufficiency as pathomechanism.

PUF60 promotes cell cycle and lung cancer progression by regulating alternative splicing of CDC25C

Alternative splicing (AS) has been implicated in cell cycle regulation and cancer, but the underlying mechanisms are poorly understood. The poly(U)-binding splicing factor 60 (PUF60) is essential for embryonic development and is overexpressed in multiple types of cancer. Here, we report that PUF60 promotes mitotic cell cycle and lung cancer progression by controlling AS of the cell division cycle 25C (CDC25C). Systematic analysis of splicing factors deregulated in lung adenocarcinoma (LUAD) identifies that elevated copy number and expression of PUF60 correlate with poor prognosis. PUF60 depletion inhibits LUAD cell-cycle G2/M transition, cell proliferation, and tumor development. Mechanistically, PUF60 knockdown leads to exon skipping enriched in mitotic cell cycle genes, including CDC25C. Exon 3 skipping in the full-length CDC25C results in nonsense-mediated mRNA decay and a decrease of CDC25C protein, thereby inhibiting cell proliferation. This study establishes PUF60 as a cell cycle regulator and an oncogenic splicing factor in lung cancer.

Identification of de novo variants in nonsyndromic cleft lip with/without cleft palate patients with low polygenic risk scores

BACKGROUND

Nonsyndromic cleft lip with/without cleft palate (nsCL/P) is a congenital malformation of multifactorial etiology. Research has identified >40 genome-wide significant risk loci, which explain less than 40% of nsCL/P heritability. Studies show that some of the hidden heritability is explained by rare penetrant variants.

METHODS

To identify new candidate genes, we searched for highly penetrant de novo variants (DNVs) in 50 nsCL/P patient/parent-trios with a low polygenic risk for the phenotype (discovery). We prioritized DNV-carrying candidate genes from the discovery for resequencing in independent cohorts of 1010 nsCL/P patients of diverse ethnicities and 1574 population-matched controls (replication). Segregation analyses and rare variant association in the replication cohort, in combination with additional data (genome-wide association data, expression, protein-protein-interactions), were used for final prioritization.

CONCLUSION

In the discovery step, 60 DNVs were identified in 60 genes, including a variant in the established nsCL/P risk gene CDH1. Re-sequencing of 32 prioritized genes led to the identification of 373 rare, likely pathogenic variants. Finally, MDN1 and PAXIP1 were prioritized as top candidates. Our findings demonstrate that DNV detection, including polygenic risk score analysis, is a powerful tool for identifying nsCL/P candidate genes, which can also be applied to other multifactorial congenital malformations.

The diverse pleiotropic effects of spliceosomal protein PUF60: A case series of Verheij syndrome

Verheij syndrome (VRJS) is a rare craniofacial spliceosomopathy presenting with craniofacial dysmorphism, multiple congenital anomalies and variable neurodevelopmental delay. It is caused by single nucleotide variants (SNVs) in PUF60 or interstitial deletions of the 8q24.3 region. PUF60 encodes a splicing factor which forms part of the spliceosome. To date, 36 patients with a sole diagnosis of VRJS due to disease-causing PUF60 SNVs have been reported in peer-reviewed publications. Although the depth of their phenotyping has varied greatly, they exhibit marked phenotypic heterogeneity. We report 10 additional unrelated patients, including the first described patients of Khmer, Indian, and Vietnamese ethnicities, and the eldest patient to date, with 10 heterozygous PUF60 variants identified through exome sequencing, 8 previously unreported. All patients underwent deep phenotyping identifying variable dysmorphism, growth delay, neurodevelopmental delay, and multiple congenital anomalies, including several unique features. The eldest patient is the only reported individual with a germline variant and neither neurodevelopmental delay nor intellectual disability. In combining these detailed phenotypic data with that of previously reported patients (n = 46), we further refine the known frequencies of features associated with VRJS. These include neurodevelopmental delay/intellectual disability (98%), axial skeletal anomalies (74%), appendicular skeletal anomalies (73%), oral anomalies (68%), short stature (66%), cardiac anomalies (63%), brain malformations (48%), hearing loss (46%), microcephaly (41%), colobomata (38%), and other ocular anomalies (65%). This case series, incorporating three patients from previously unreported ethnic backgrounds, further delineates the broad pleiotropy and mutational spectrum of PUF60 pathogenic variants.

First report of tethered cord syndrome in a patient with Verheij syndrome

BACKGROUND

Verheij syndrome (VRJS) is a rare microdeletion syndrome of chromosome 8q24.3 that is characterized by severe growth retardation, microcephaly, vertebral anomalies, joint laxity/dislocation, psychomotor retardation, cardiac and renal defects, and dysmorphic facial features. Pathogenic variants of PUF60 (Poly-U Binding Splicing Factor 60 kDa) have been found to cause VRJS. Here we present a Turkish patient with Verheij syndrome who has typical facial dysmorphic features and renal and cardiac abnormalities, scoliosis, tethered cord, and mild intellectual disability.

METHODS

This is a case report of a 11-year-old female child who presented with Verheij syndrome. Blood samples were collected from the patient and the family. We performed whole exome sequencing was used to identify potential genetic mutations. We also used 3-dimensional protein structure analysis to identify the effect of the mutation.

RESULTS

A de-novo in-frame variant (c.449_457delCAAAGGGGG; p.Ala150_Phe152del) of the PUF60 gene was identified by whole exome sequencing. According to ACMG guidelines in 2015, the mutation is classified as pathogenic and it has been reported in the clinvar database. Results of in-silico prediction software tools predicted the mutation was pathogenic. Protein structure analysis showed that the three residues affected by the in-frame deletion form could lead to impaired stability and function of the PUF60 protein.

CONCLUSIONS

To date, 25 patients have been reported with PUF60 mutations in the medical literature. In this article, we report a patient with VRJS who had the unusual findings of tethered cord syndrome and renal abnormalities. As far as we know, this is the first patient from Turkey who has been diagnosed with Verheij syndrome.

Decreased spliceosome fidelity and egl-8 intron retention inhibit mTORC1 signaling to promote longevity

Changes in splicing fidelity are associated with loss of homeostasis and aging, yet only a handful of splicing factors have been shown to be causally required to promote longevity, and the underlying mechanisms and downstream targets in these paradigms remain elusive. Surprisingly, we found a hypomorphic mutation within ribonucleoprotein RNP-6/poly(U)-binding factor 60 kDa (PUF60), a spliceosome component promoting weak 3′-splice site recognition, which causes aberrant splicing, elevates stress responses and enhances longevity in Caenorhabditis elegans. Through genetic suppressor screens, we identify a gain-of-function mutation within rbm-39, an RNP-6-interacting splicing factor, which increases nuclear speckle formation, alleviates splicing defects and curtails longevity caused by rnp-6 mutation. By leveraging the splicing changes induced by RNP-6/RBM-39 activities, we uncover intron retention in egl-8/phospholipase C β4 (PLCB4) as a key splicing target prolonging life. Genetic and biochemical evidence show that neuronal RNP-6/EGL-8 downregulates mammalian target of rapamycin complex 1 (mTORC1) signaling to control organismal lifespan. In mammalian cells, PUF60 downregulation also potently and specifically inhibits mTORC1 signaling. Altogether, our results reveal that splicing fidelity modulates lifespan through mTOR signaling.

Systematic exploration of dynamic splicing networks reveals conserved multistage regulators of neurogenesis

Alternative splicing (AS) is a critical regulatory layer; yet, factors controlling functionally coordinated splicing programs during developmental transitions are poorly understood. Here, we employ a screening strategy to identify factors controlling dynamic splicing events important for mammalian neurogenesis. Among previously unknown regulators, Rbm38 acts widely to negatively control neural AS, in part through interactions mediated by the established repressor of splicing, Ptbp1. Puf60, a ubiquitous factor, is surprisingly found to promote neural splicing patterns. This activity requires a conserved, neural-differential exon that remodels Puf60 co-factor interactions. Ablation of this exon rewires distinct AS networks in embryonic stem cells and at different stages of mouse neurogenesis. Single-cell transcriptome analyses further reveal distinct roles for Rbm38 and Puf60 isoforms in establishing neuronal identity. Our results describe important roles for previously unknown regulators of neurogenesis and establish how an alternative exon in a widely expressed splicing factor orchestrates temporal control over cell differentiation.

CNest: A novel copy number association discovery method uncovers 862 new associations from 200,629 whole-exome sequence datasets in the UK Biobank

Copy number variation (CNV) is known to influence human traits, having a rich history of research into common and rare genetic disease, and although CNV is accepted as an important class of genomic variation, progress on copy-number-based genome-wide association studies (GWASs) from next-generation sequencing (NGS) data has been limited. Here we present a novel method for large-scale copy number analysis from NGS data generating robust copy number estimates and allowing copy number GWASs (CN-GWASs) to be performed genome-wide in discovery mode. We provide a detailed analysis in the UK Biobank resource and a specifically designed software package. We use these methods to perform CN-GWAS analysis across 78 human traits, discovering over 800 genetic associations that are likely to contribute strongly to trait distributions. Finally, we compare CNV and SNP association signals across the same traits and samples, defining specific CNV association classes.

Neuron-Specific Deletion of Scrib in Mice Leads to Neuroanatomical and Locomotor Deficits

Scribble (Scrib) is a conserved polarity protein acting as a scaffold involved in multiple cellular and developmental processes. Recent evidence from our group indicates that Scrib is also essential for brain development as early global deletion of Scrib in the dorsal telencephalon induced cortical thickness reduction and alteration of interhemispheric connectivity. In addition, Scrib conditional knockout (cKO) mice have behavioral deficits such as locomotor activity impairment and memory alterations. Given Scrib broad expression in multiple cell types in the brain, we decided to determine the neuronal contribution of Scrib for these phenotypes. In the present study, we further investigate the function of Scrib specifically in excitatory neurons on the forebrain formation and the control of locomotor behavior. To do so, we generated a novel neuronal glutamatergic specific Scrib cKO mouse line called Nex-Scrib^−/− cKO. Remarkably, cortical layering and commissures were impaired in these mice and reproduced to some extent the previously described phenotype in global Scrib cKO. In addition and in contrast to our previous results using Emx1-Scrib^−/− cKO, the Nex-Scrib^−/− cKO mutant mice exhibited significantly reduced locomotion. Altogether, the novel cKO model described in this study further highlights an essential role for Scrib in forebrain development and locomotor behavior.

Scribble Controls Social Motivation Behavior through the Regulation of the ERK/Mnk1 Pathway

Social behavior is a basic domain affected by several neurodevelopmental disorders, including ASD and a heterogeneous set of neuropsychiatric disorders. The SCRIB gene that codes for the polarity protein SCRIBBLE has been identified as a risk gene for spina bifida, the most common type of neural tube defect, found at high frequencies in autistic patients, as well as other congenital anomalies. The deletions and mutations of the 8q24.3 region encompassing SCRIB are also associated with multisyndromic and rare disorders. Nonetheless, the potential link between SCRIB and relevant social phenotypes has not been fully investigated. Hence, we show that Scribcrc/+ mice, carrying a mutated version of Scrib, displayed reduced social motivation behavior and social habituation, while other behavioral domains were unaltered. Social deficits were associated with the upregulation of ERK phosphorylation, together with increased c-Fos activity. Importantly, the social alterations were rescued by both direct and indirect pERK inhibition. These results support a link between polarity genes, social behaviors and hippocampal functionality and suggest a role for SCRIB in the etiopathology of neurodevelopmental disorders. Furthermore, our data demonstrate the crucial role of the MAPK/ERK signaling pathway in underlying social motivation behavior, thus supporting its relevance as a therapeutic target.

Copy number variation analysis in Chinese children with complete atrioventricular canal and single ventricle

BACKGROUND

Congenital heart disease (CHD) is one of the most common birth defects. Copy number variations (CNVs) have been proved to be important genetic factors that contribute to CHD. Here we screened genome-wide CNVs in Chinese children with complete atrioventricular canal (CAVC) and single ventricle (SV), since there were scarce researches dedicated to these two types of CHD.

METHODS

We screened CNVs in 262 sporadic CAVC cases and 259 sporadic SV cases respectively, using a customized SNP array. The detected CNVs were annotated and filtered using available databases.

RESULTS

Among 262 CAVC patients, we identified 6 potentially-causative CNVs in 43 individuals (16.41%, 43/262), including 2 syndrome-related CNVs (7q11.23 and 8q24.3 deletion). Surprisingly, 90.70% CAVC patients with detected CNVs (39/43) were found to carry duplications of 21q11.2-21q22.3, which were recognized as trisomy 21 (Down syndrome, DS). In CAVC with DS patients, the female to male ratio was 1.6:1.0 (24:15), and the rate of pulmonary hypertension (PH) was 41.03% (16/39). Additionally, 6 potentially-causative CNVs were identified in the SV patients (2.32%, 6/259), and none of them was trisomy 21. Most CNVs identified in our cohort were classified as rare (< 1%), occurring just once among CAVC or SV individuals except the 21q11.2-21q22.3 duplication (14.89%) in CAVC cohort.

CONCLUSIONS

Our study identified 12 potentially-causative CNVs in 262 CAVC and 259 SV patients, representing the largest cohort of these two CHD types in Chinese population. The results provided strong correlation between CAVC and DS, which also showed sex difference and high incidence of PH. The presence of potentially-causative CNVs suggests the etiology of complex CHD is incredibly diverse, and CHD candidate genes remain to be discovered.

Identification of a New Variant of PUF60 Gene: Case Presentation and Literature Review

BACKGROUND/AIM

The aim of the study was to report the case of a 5-month-old boy with a complex prenatal and neonatal symptomatology diagnosed with a "de novo" pathogenic variant of PUF60 gene.

CASE REPORT

Our hospital, undertook the antenatal and postnatal care of a 27-year-old pregnant lady. This was her second baby with a previously healthy boy. During her routine first-trimester anomaly scan, increased nuchal translucency was noticed. Multiple anomalies were seen throughout her subsequent antenatal visits. This triggered a sequence of tests, examinations and differential diagnosis. The final diagnosis was made at 5 months postpartum following the result of the whole exome sequence, which described a variant of unknown clinical significance (VUS, class 3 variant) in the PUF60 gene. We are mindful that changing the classification of a variant of unknown significance is challenging and requires supporting and robust criteria. Considering clinical symptomatology produced by the pathogenic mutation in the PUF gene, the identified c.1640A>G variant may be categorized as likely pathogenic.

CONCLUSION

Our case adds new insights on the pathology and the underlying process involved in the PUF60 variant spectrum disorders. It also highlights the limits of current prenatal tests.

Emerging roles of spliceosome in cancer and immunity

Precursor messenger RNA (pre-mRNA) splicing is catalyzed by an intricate ribonucleoprotein complex called the spliceosome. Although the spliceosome is considered to be general cell “housekeeping” machinery, mutations in core components of the spliceosome frequently correlate with cell- or tissue-specific phenotypes and diseases. In this review, we expound the links between spliceosome mutations, aberrant splicing, and human cancers. Remarkably, spliceosome-targeted therapies (STTs) have become efficient anti-cancer strategies for cancer patients with splicing defects. We also highlight the links between spliceosome and immune signaling. Recent studies have shown that some spliceosome gene mutations can result in immune dysregulation and notable phenotypes due to mis-splicing of immune-related genes. Furthermore, several core spliceosome components harbor splicing-independent immune functions within the cell, expanding the functional repertoire of these diverse proteins.

Early loss of Scribble affects cortical development, interhemispheric connectivity and psychomotor activity

Neurodevelopmental disorders arise from combined defects in processes including cell proliferation, differentiation, migration and commissure formation. The evolutionarily conserved tumor-suppressor protein Scribble (Scrib) serves as a nexus to transduce signals for the establishment of apicobasal and planar cell polarity during these processes. Human SCRIB gene mutations are associated with neural tube defects and this gene is located in the minimal critical region deleted in the rare Verheij syndrome. In this study, we generated brain-specific conditional cKO mouse mutants and assessed the impact of the Scrib deletion on brain morphogenesis and behavior. We showed that embryonic deletion of Scrib in the telencephalon leads to cortical thickness reduction (microcephaly) and partial corpus callosum and hippocampal commissure agenesis. We correlated these phenotypes with a disruption in various developmental mechanisms of corticogenesis including neurogenesis, neuronal migration and axonal connectivity. Finally, we show that Scrib cKO mice have psychomotor deficits such as locomotor activity impairment and memory alterations. Altogether, our results show that Scrib is essential for early brain development due to its role in several developmental cellular mechanisms that could underlie some of the deficits observed in complex neurodevelopmental pathologies.

Whole Exome Sequencing in Coloboma/Microphthalmia: Identification of Novel and Recurrent Variants in Seven Genes

Coloboma and microphthalmia (C/M) are related congenital eye malformations, which can cause significant visual impairment. Molecular diagnosis is challenging as the genes associated to date with C/M account for only a small percentage of cases. Overall, the genetic cause remains unknown in up to 80% of patients. High throughput DNA sequencing technologies, including whole-exome sequencing (WES), are therefore a useful and efficient tool for genetic screening and identification of new mutations and novel genes in C/M. In this study, we analyzed the DNA of 19 patients with C/M from 15 unrelated families using singleton WES and data analysis for 307 genes of interest. We identified seven novel and one recurrent potentially disease-causing variants in CRIM1, CHD7, FAT1, PTCH1, PUF60, BRPF1, and TGFB2 in 47% of our families, three of which occurred de novo. The detection rate in patients with ocular and extraocular manifestations (67%) was higher than in patients with an isolated ocular phenotype (46%). Our study highlights the significant genetic heterogeneity in C/M cohorts and emphasizes the diagnostic power of WES for the screening of patients and families with C/M.

Unraveling the mechanism of recognition of the 3' splice site of the adenovirus major late promoter intron by the alternative splicing factor PUF60

Pre-mRNA splicing is critical for achieving required amounts of a transcript at a given time and for regulating production of encoded protein. A given pre-mRNA may be spliced in many ways, or not at all, giving rise to multiple gene products. Numerous splicing factors are recruited to pre-mRNA splice sites to ensure proper splicing. One such factor, the 60 kDa poly(U)-binding splicing factor (PUF60), is recruited to sites that are not always spliced, but rather function as alternative splice sites. In this study, we characterized the interaction of PUF60 with a splice site from the adenovirus major late promoter (the AdML 3' splice site, AdML3'). We found that the PUF60-AdML3' dissociation constants are in the micromolar range, with the binding affinity predominantly provided by PUF60's two central RNA recognition motifs (RRMs). A 1.95 Å crystal structure of the two PUF60 RRMs in complex with AdML3' revealed a dimeric organization placing two stretches of nucleic acid tracts in opposing directionalities, which can cause looping of nucleic acid and explain how PUF60 affects pre-mRNA geometry to effect splicing. Solution characterization of this complex by light-scattering and UV/Vis spectroscopy suggested a potential 2:1 (PUF602:AdML3') stoichiometry, consistent with the crystal structure. This work defines the sequence specificity of the alternative splicing factor PUF60 at the pre-mRNA 3' splice site. Our observations suggest that control of pre-mRNA directionality is important in the early stage of spliceosome assembly, and advance our understanding of the molecular mechanism by which alternative and constitutive splicing factors differentiate among 3' splice sites.

Protein elongation variant of PUF60: Milder phenotypic end of the Verheij syndrome

The PUF60 gene encodes a ubiquitously expressed essential splicing factor that is recruited to the U2snRNA complex. The complex binds to the 3' splice site of exons in specific target genes and regulates the inclusion or exclusion of such exons. Recently, pathogenic variants of PUF60 have been shown to cause a relatively specific and potentially recognizable pattern of malformation referred to as Verheij syndrome. Here, we report a 12-year-old female patient with a de novo mutation in PUF60 whose phenotype was representative of the milder end of the phenotypic spectrum of Verheij syndrome; the de novo mutation was a frameshift mutation p.(Ser558Cysfs*21) that resulted in the addition of 21 extra amino acids at the carboxy end of the protein. Among the frequent features of Verheij syndrome, the patient exhibited coloboma, cervical spinal segmentation defects, and borderline intellectual functioning, but lacked cardiac abnormalities, deafness, and urogenital abnormalities. The results of RNA analysis using peripheral blood showed the escape of the mutant allele from nonsense-mediated mRNA decay, possibly accounting for the mild phenotype in the presently reported patient. Based on our clinical observations, we inferred that two embryologic processes, closure of the ocular plate and cervical spinal segmentation, are particularly susceptible to deficient PUF60-mediated splicing regulation, compared with other embryogenetic processes leading to the central nervous system, heart, ear, and kidney.

Cancer-Associated Substitutions in RNA Recognition Motifs of PUF60 and U2AF65 Reveal Residues Required for Correct Folding and 3' Splice-Site Selection

U2AF65 (U2AF2) and PUF60 (PUF60) are splicing factors important for recruitment of the U2 small nuclear ribonucleoprotein to lariat branch points and selection of 3′ splice sites (3′ss). Both proteins preferentially bind uridine-rich sequences upstream of 3′ss via their RNA recognition motifs (RRMs). Here, we examined 36 RRM substitutions reported in cancer patients to identify variants that alter 3′ss selection, RNA binding and protein properties. Employing PUF60- and U2AF65-dependent 3′ss previously identified by RNA-seq of depleted cells, we found that 43% (10/23) and 15% (2/13) of independent RRM mutations in U2AF65 and PUF60, respectively, conferred splicing defects. At least three RRM mutations increased skipping of internal U2AF2 (~9%, 2/23) or PUF60 (~8%, 1/13) exons, indicating that cancer-associated RRM mutations can have both cis- and trans-acting effects on splicing. We also report residues required for correct folding/stability of each protein and map functional RRM substitutions on to existing high-resolution structures of U2AF65 and PUF60. These results identify new RRM residues critical for 3′ss selection and provide relatively simple tools to detect clonal RRM mutations that enhance the mRNA isoform diversity.

Spliceosomopathies and neurocristopathies: Two sides of the same coin?

Mutations in core components of the spliceosome are responsible for a group of syndromes collectively known as spliceosomopathies. Patients exhibit microcephaly, micrognathia, malar hypoplasia, external ear anomalies, eye anomalies, psychomotor delay, intellectual disability, limb, and heart defects. Craniofacial malformations in these patients are predominantly found in neural crest cells-derived structures of the face and head. Mutations in eight genes SNRPB, RNU4ATAC, SF3B4, PUF60, EFTUD2, TXNL4, EIF4A3, and CWC27 are associated with craniofacial spliceosomopathies. In this review, we provide a brief description of the normal development of the head and the face and an overview of mutations identified in genes associated with craniofacial spliceosomopathies. We also describe a model to explain how and when these mutations are most likely to impact neural crest cells. We speculate that mutations in a subset of core splicing factors lead to disrupted splicing in neural crest cells because these cells have increased sensitivity to inefficient splicing. Hence, disruption in splicing likely activates a cellular stress response that includes increased skipping of regulatory exons in genes such as MDM2 and MDM4, key regulators of P53. This would result in P53-associated death of neural crest cells and consequently craniofacial malformations associated with spliceosomopathies.

Post-transcriptional regulation of BRG1 by FIRΔexon2 in gastric cancer

Brahma-related gene 1 (BRG1), an ATPase subunit of the SWItch/sucrose non-fermentable (SWI/SNF) chromatin remodeling complex controls multipotent neural crest formation by regulating epithelial-mesenchymal transition (EMT)-related genes with adenosine triphosphate-dependent chromodomain-helicase DNA-binding protein 7 (CHD7). The expression of BRG1 engages in pre-mRNA splicing through interacting RNPs in cancers; however, the detailed molecular pathology of how BRG1and CHD7 relate to cancer development remains largely unveiled. This study demonstrated novel post-transcriptional regulation of BRG1 in EMT and relationship with FIRΔexon2, which is a splicing variant of the far-upstream element-binding protein (FUBP) 1-interacting repressor (FIR) lacking exon 2, which fails to repress c-myc transcription in cancers. Previously, we have reported that FIR complete knockout mice (FIR-/-) was embryonic lethal before E9.5, suggesting FIR is crucial for development. FIRΔexon2 acetylated H3K27 on promoter of BRG1 by CHIP-sequence and suppressed BRG1 expression post-transcriptionally; herein BRG1 suppressed Snai1 that is a transcriptional suppressor of E-cadherin that prevents cancer invasion and metastasis. Ribosomal proteins, hnRNPs, splicing-related factors, poly (A) binding proteins, mRNA-binding proteins, tRNA, DEAD box, and WD-repeat proteins were identified as co-immunoprecipitated proteins with FIR and FIRΔexon2 by redoing exhaustive mass spectrometry analysis. Furthermore, the effect of FIRΔexon2 on FGF8 mRNA splicing was examined as an indicator of neural development due to impaired CHD7 revealed in CHARGE syndrome. Expectedly, siRNA of FIRΔexon2 altered FGF8 pre-mRNA splicing, indicated close molecular interaction among FIRΔexon2, BRG1 and CHD7. FIRΔexon2 mRNA was elevated in human gastric cancers but not in non-invasive gastric tumors in FIR+/ mice (K19-Wnt1/C2mE x FIR+/-). The levels of FIR family (FIR, FIRΔexon2 and PUF60), BRG1, Snai1, FBW7, E-cadherin, c-Myc, cyclin-E, and SAP155 increased in the gastric tumors in FIR+/- mice compared to those expressed in wild-type mice. FIR family, Snai1, cyclin-E, BRG1, and c-Myc showed trends toward higher expression in larger tumors than in smaller tumors in Gan-mice (K19-Wnt1/C2mE). The expressions of BRG1 and Snai1 were positively correlated in the gastric tumors of the Gan-mice. Finally, BRG1 is a candidate substrate of F-box and WD-repeat domain-containing 7 (FBW7) revealed by three-dimensional crystal structure analysis that the U2AF-homology motif (UHM) of FIRΔexon2 interacted with tryptophan-425 and asparate-399 (WD)-like motif in the degron pocket of FBW7 as a UHM-ligand motif. Together, FIRΔexon2 engages in multi-step post-transcriptional regulation of BRG1, affecting EMT through the BRG1/Snai1/E-cadherin pathway and promoting tumor proliferation and invasion of gastric cancers.

PUF60-activated exons uncover altered 3' splice-site selection by germline missense mutations in a single RRM

PUF60 is a splicing factor that binds uridine (U)-rich tracts and facilitates association of the U2 small nuclear ribonucleoprotein with primary transcripts. PUF60 deficiency (PD) causes a developmental delay coupled with intellectual disability and spinal, cardiac, ocular and renal defects, but PD pathogenesis is not understood. Using RNA-Seq, we identify human PUF60-regulated exons and show that PUF60 preferentially acts as their activator. PUF60-activated internal exons are enriched for Us upstream of their 3′ splice sites (3′ss), are preceded by longer AG dinucleotide exclusion zones and more distant branch sites, with a higher probability of unpaired interactions across a typical branch site location as compared to control exons. In contrast, PUF60-repressed exons show U-depletion with lower estimates of RNA single-strandedness. We also describe PUF60-regulated, alternatively spliced isoforms encoding other U-bound splicing factors, including PUF60 partners, suggesting that they are co-regulated in the cell, and identify PUF60-regulated exons derived from transposed elements. PD-associated amino-acid substitutions, even within a single RNA recognition motif (RRM), altered selection of competing 3′ss and branch points of a PUF60-dependent exon and the 3′ss choice was also influenced by alternative splicing of PUF60. Finally, we propose that differential distribution of RNA processing steps detected in cells lacking PUF60 and the PUF60-paralog RBM39 is due to the RBM39 RS domain interactions. Together, these results provide new insights into regulation of exon usage by the 3′ss organization and reveal that germline mutation heterogeneity in RRMs can enhance phenotypic variability at the level of splice-site and branch-site selection.

Targeted next‑generation sequencing for research and diagnostics in congenital heart disease, and cleft lip and/or palate

Congenital heart disease (CHD), and cleft lip and palate (CLP) are currently the most common types of structural malformation in infants. Various methods have been used to identify the disease‑associated genes. However, targeted next‑generation sequencing (NGS) is not yet considered an option for routine use. Thus, the present study aimed to assess the safety and feasibility of using targeted NGS in patients with CHD concomitant with CLP. Between November 2015 and May 2017, a total of 17 patients with CHD concomitant with CLP, who were excluded from a diagnosis of trisomy syndrome, were selected at The Second Xiangya Hospital of Central South University (Changsha, China). Genomic DNA was extracted from peripheral blood samples of the patients. The copy number variants (CNVs) were determined by conducting a single nucleotide polymorphism (SNP) array with Illumina HumanOmni1‑Quad Beadchip, while information on other gene mutations was obtained from targeted sequencing. The functions of gene mutations were then predicted using the PolyPhen‑2, SIFT and Mutation Taster tools. Finally, Sanger sequencing was used to verify the mutations. The results identified no pathogenic mutations in CNVs analyzed by high‑throughput SNP sequencing. Targeted NGS results demonstrated that 10 patients (58.8%) carried gene mutations, including 4 (23.5%) genetically diagnosed cases and 6 (35.3%) cases with unknown etiology. The 4 known diseases were Opitz G/BBB syndrome caused by MID1 gene mutation, Loeys‑Dietz syndrome caused by TGFBR1 gene mutation, Ritscher‑Schinzel/3C syndrome caused by KIAA0196 gene mutation and CHARGE syndrome caused by CHD7 gene mutation. The remaining 6 cases were not genetically diagnosed, although they carried candidate genes. In conclusion, the present study demonstrated that targeted NGS was an effective and accurate candidate gene detection method in patients with CHD concomitant with CLP.

Homozygous frameshift mutations in FAT1 cause a syndrome characterized by colobomatous-microphthalmia, ptosis, nephropathy and syndactyly

A failure in optic fissure fusion during development can lead to blinding malformations of the eye. Here, we report a syndrome characterized by facial dysmorphism, colobomatous microphthalmia, ptosis and syndactyly with or without nephropathy, associated with homozygous frameshift mutations in FAT1. We show that Fat1 knockout mice and zebrafish embryos homozygous for truncating fat1a mutations exhibit completely penetrant coloboma, recapitulating the most consistent developmental defect observed in affected individuals. In human retinal pigment epithelium (RPE) cells, the primary site for the fusion of optic fissure margins, FAT1 is localized at earliest cell-cell junctions, consistent with a role in facilitating optic fissure fusion during vertebrate eye development. Our findings establish FAT1 as a gene with pleiotropic effects in human, in that frameshift mutations cause a severe multi-system disorder whereas recessive missense mutations had been previously associated with isolated glomerulotubular nephropathy.

Loss of the cadherin FAT1 has been associated with nephropathy and epithelial cell adhesion defects. Here, the authors report five families with a syndromic form of coloboma associated with homozygous frameshift variants in FAT1 and recapitulate the phenotype in mutant mice and zebrafish.

PUF60-SCRIB fusion transcript in a patient with 8q24.3 microdeletion and atypical Verheij syndrome

Expression of the fusion genes is considered to be an important mechanism of tumorigenesis. However it is hardly ever discussed in relation to the neurodevelopmental disorders. Here we report on an 18-years-old female patient with 13.1 kb deletion of 8q24.3 fusing the 5'-portion of SCRIB with the 3'-portion of PUF60 and presenting with borderline intellectual disability, eye coloboma, short stature, scoliosis, heart defects and interestingly postnatal megalencephaly, in contrast to microcephaly, which is usually associated with 8q24.3 deletion (Verheij syndrome). Using next generation sequencing we mapped the breakpoints at nucleotide resolution and showed that the deletion preserved the reading frame. In contrast to the laborious techniques previously used for the precise mapping of deletion breakpoints, our approach identified an accurate interval very rapidly. We demonstrated the expression of the PUF60-SCRIB fusion gene in patient's cells and suggest that the fusion transcript might be a cause of the atypical clinical presentation.

Role of PUF60 gene in Verheij syndrome: a case report of the first Chinese Han patient with a de novo pathogenic variant and review of the literature

Background

Verheij syndrome is a rare microdeletion syndrome of chromosome 8q24.3 that harbors PUF60, SCRIB, and NRBP2 genes. Subsequently, loss of function mutations in PUF60 have been found in children with clinical features significantly overlapping with Verheij.

Case presentation

Here we present the first Chinese Han patient with a de novo nonsense variant (c.1357C > T, p.Gln453*) in PUF60 by clinical whole exome sequencing. The 5-year-old boy presents with dysmorphic facial features, intellectual disability, and growth retardation but without apparent cardiac, renal, ocular, and spinal anomalies.

Conclusions

Our finding contributes to the understanding of the genotype and phenotype in PUF60 related disorder.

Survey of Human Chromosome 21 Gene Expression Effects on Early Development in Danio rerio

Trisomy for human chromosome 21 (Hsa21) results in Down syndrome (DS), one of the most genetically complex conditions compatible with human survival. Assessment of the physiological consequences of dosage-driven overexpression of individual Hsa21 genes during early embryogenesis and the resulting contributions to DS pathology in mammals are not tractable in a systematic way. A recent study looked at loss-of-function of a subset of Caenorhabditis elegans orthologs of Hsa21 genes and identified ten candidates with behavioral phenotypes, but the equivalent over-expression experiment has not been done. We turned to zebrafish as a developmental model and, using a number of surrogate phenotypes, we screened Hsa21 genes for effects on early embyrogenesis. We prepared a library of 164 cDNAs of conserved protein coding genes, injected mRNA into early embryos and evaluated up to 5 days post-fertilization (dpf). Twenty-four genes produced a gross morphological phenotype, 11 of which could be reproduced reliably. Seven of these gave a phenotype consistent with down regulation of the sonic hedgehog (Shh) pathway; two showed defects indicative of defective neural crest migration; one resulted consistently in pericardial edema; and one was embryonic lethal. Combinatorial injections of multiple Hsa21 genes revealed both additive and compensatory effects, supporting the notion that complex genetic relationships underlie end phenotypes of trisomy that produce DS. Together, our data suggest that this system is useful in the genetic dissection of dosage-sensitive gene effects on early development and can inform the contribution of both individual loci and their combinatorial effects to phenotypes relevant to the etiopathology of DS.

Clinical and cytogenomic findings in OAV spectrum

The oculoauriculovertebral spectrum (OAVS) is characterized by anomalies involving the development of the first and second pharyngeal arches during the embryonic period. The phenotype is highly heterogeneous, involving ears, eyes, face, neck, and other systems and organs. There is no agreement in the literature for the minimum phenotypic inclusion criteria, but the primary phenotype involves hemifacial microsomia with facial asymmetry and microtia. Most cases are sporadic and the etiology of this syndrome is not well known. Environmental factors, family cases that demonstrate Mendelian inheritance, such as preauricular appendages, microtia, mandibular hypoplasia, and facial asymmetry; chromosomal abnormalities and some candidate genes suggest a multifactorial inheritance model. We evaluated clinical, cytogenomic and molecularly 72 patients with OAVS, and compared our findings with patients from the literature. We found 15 CNVs (copy number variations) considered pathogenic or possibly pathogenic in 13 out of 72 patients. Our results did not indicated a single candidate genomic region, but recurrent chromosomal imbalances were observed in chromosome 4 and 22, in regions containing genes relevant to the OAVS phenotype or related to known OMIM diseases suggesting different pathogenic mechanisms involved in this genetically and phenotypic heterogeneous spectrum.

Exome sequencing reveals NAA15 and PUF60 as candidate genes associated with intellectual disability

Intellectual Disability (ID) is a clinically heterogeneous condition that affects 2-3% of population worldwide. In recent years, exome sequencing has been a successful strategy for studies of genetic causes of ID, providing a growing list of both candidate and validated ID genes. In this study, exome sequencing was performed on 28 ID patients in 27 patient-parent trios with the aim to identify de novo variants (DNVs) in known and novel ID associated genes. We report the identification of 25 DNVs out of which five were classified as pathogenic or likely pathogenic. Among these, a two base pair deletion was identified in the PUF60 gene, which is one of three genes in the critical region of the 8q24.3 microdeletion syndrome (Verheij syndrome). Our result adds to the growing evidence that PUF60 is responsible for the majority of the symptoms reported for carriers of a microdeletion across this region. We also report variants in several genes previously not associated with ID, including a de novo missense variant in NAA15. We highlight NAA15 as a novel candidate ID gene based on the vital role of NAA15 in the generation and differentiation of neurons in neonatal brain, the fact that the gene is highly intolerant to loss of function and coding variation, and previously reported DNVs in neurodevelopmental disorders.

Involvement of PUF60 in Transcriptional and Post-transcriptional Regulation of Hepatitis B Virus Pregenomic RNA Expression

Here we identified PUF60, a splicing factor and a U2 small nuclear ribonucleoprotein auxiliary factor, as a versatile regulator of transcriptional and post-transcriptional steps in expression of hepatitis B virus (HBV) 3.5 kb, precore plus pregenomic RNA. We demonstrate that PUF60 is involved in: 1) up-regulation of core promoter activity through its interaction with transcription factor TCF7L2, 2) promotion of 3.5 kb RNA degradation and 3) suppression of 3.5 kb RNA splicing. When the 1.24-fold HBV genome was introduced into cells with the PUF60-expression plasmid, the 3.5 kb RNA level was higher at days 1–2 post-transfection but declined thereafter in PUF60-expressing cells compared to viral replication control cells. Deletion analyses showed that the second and first RNA recognition motifs (RRMs) within PUF60 are responsible for core promoter activation and RNA degradation, respectively. Expression of PUF60 mutant deleting the first RRM led to higher HBV production. To our knowledge, this is the first to identify a host factor involved in not only positively regulating viral gene expression but also negative regulation of the same viral life cycle. Functional linkage between transcriptional and post-transcriptional controls during viral replication might be involved in mechanisms for intracellular antiviral defense and viral persistence.

The Immune Signaling Adaptor LAT Contributes to the Neuroanatomical Phenotype of 16p11.2 BP2-BP3 CNVs

Copy-number changes in 16p11.2 contribute significantly to neuropsychiatric traits. Besides the 600 kb BP4-BP5 CNV found in 0.5%-1% of individuals with autism spectrum disorders and schizophrenia and whose rearrangement causes reciprocal defects in head size and body weight, a second distal 220 kb BP2-BP3 CNV is likewise a potent driver of neuropsychiatric, anatomical, and metabolic pathologies. These two CNVs are engaged in complex reciprocal chromatin looping, intimating a functional relationship between genes in these regions that might be relevant to pathomechanism. We assessed the drivers of the distal 16p11.2 duplication by overexpressing each of the nine encompassed genes in zebrafish. Only overexpression of LAT induced a reduction of brain proliferating cells and concomitant microcephaly. Consistently, suppression of the zebrafish ortholog induced an increase of proliferation and macrocephaly. These phenotypes were not unique to zebrafish; Lat knockout mice show brain volumetric changes. Consistent with the hypothesis that LAT dosage is relevant to the CNV pathology, we observed similar effects upon overexpression of CD247 and ZAP70, encoding members of the LAT signalosome. We also evaluated whether LAT was interacting with KCTD13, MVP, and MAPK3, major driver and modifiers of the proximal 16p11.2 600 kb BP4-BP5 syndromes, respectively. Co-injected embryos exhibited an increased microcephaly, suggesting the presence of genetic interaction. Correspondingly, carriers of 1.7 Mb BP1-BP5 rearrangements that encompass both the BP2-BP3 and BP4-BP5 loci showed more severe phenotypes. Taken together, our results suggest that LAT, besides its well-recognized function in T cell development, is a major contributor of the 16p11.2 220 kb BP2-BP3 CNV-associated neurodevelopmental phenotypes.

Haploinsufficiency of the Chromatin Remodeler BPTF Causes Syndromic Developmental and Speech Delay, Postnatal Microcephaly, and Dysmorphic Features

Bromodomain PHD finger transcription factor (BPTF) is the largest subunit of nucleosome remodeling factor (NURF), a member of the ISWI chromatin-remodeling complex. However, the clinical consequences of disruption of this complex remain largely uncharacterized. BPTF is required for anterior-posterior axis formation of the mouse embryo and was shown to promote posterior neuroectodermal fate by enhancing Smad2-activated wnt8 expression in zebrafish. Here, we report eight loss-of-function and two missense variants (eight de novo and two of unknown origin) in BPTF on 17q24.2. The BPTF variants were found in unrelated individuals aged between 2.1 and 13 years, who manifest variable degrees of developmental delay/intellectual disability (10/10), speech delay (10/10), postnatal microcephaly (7/9), and dysmorphic features (9/10). Using CRISPR-Cas9 genome editing of bptf in zebrafish to induce a loss of gene function, we observed a significant reduction in head size of F0 mutants compared to control larvae. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and phospho-histone H3 (PH3) staining to assess apoptosis and cell proliferation, respectively, showed a significant increase in cell death in F0 mutants compared to controls. Additionally, we observed a substantial increase of the ceratohyal angle of the craniofacial skeleton in bptf F0 mutants, indicating abnormal craniofacial patterning. Taken together, our data demonstrate the pathogenic role of BPTF haploinsufficiency in syndromic neurodevelopmental anomalies and extend the clinical spectrum of human disorders caused by ablation of chromatin remodeling complexes.

Development and dynamics of cell polarity at a glance

Cells exhibit morphological and molecular asymmetries that are broadly categorized as cell polarity. The cell polarity established in early embryos prefigures the macroscopic anatomical asymmetries characteristic of adult animals. For example, eggs and early embryos have polarized distributions of RNAs and proteins that generate global anterior/posterior and dorsal/ventral axes. The molecular programs that polarize embryos are subsequently reused in multiple contexts. Epithelial cells require apical/basal polarity to establish their barrier function. Migrating cells polarize in the direction of movement, creating distinct leading and trailing structures. Asymmetrically dividing stem cells partition different molecules between themselves and their daughter cells. Cell polarity can develop de novo, be maintained through rounds of cell division and be dynamically remodeled. In this Cell Science at a Glance review and poster, we describe molecular asymmetries that underlie cell polarity in several cellular contexts. We highlight multiple developmental systems that first establish cell/developmental polarity, and then maintain it. Our poster showcases repeated use of the Par, Scribble and Crumbs polarity complexes, which drive the development of cell polarity in many cell types and organisms. We then briefly discuss the diverse and dynamic changes in cell polarity that occur during cell migration, asymmetric cell division and in planar polarized tissues.

Genetic causes of optic nerve hypoplasia

Optic nerve hypoplasia (ONH) is the most common congenital optic nerve anomaly and a leading cause of blindness in the USA. Although most cases of ONH occur as isolated cases within their respective families, the advancement in molecular diagnostic technology has made us realise that a substantial fraction of cases has identifiable genetic causes, typically de novo mutations. An increasing number of genes has been reported, mutations of which can cause ONH. Many of the genes involved serve as transcription factors, participating in an intricate multistep process critical to eye development and neurogenesis in the neural retina. This review will discuss the respective genes and mutations, human phenotypes, and animal models that have been created to gain a deeper understanding of the disorders. The identification of the underlying gene and mutation provides an important step in diagnosis, medical care and counselling for the affected individuals and their families. We envision that future research will lead to further disease gene identification, but will also teach us about gene-gene and gene-environment interactions relevant to optic nerve development. How much of the functional impairment of the various forms of ONH is a reflection of altered morphogenesis versus neuronal homeostasis will determine the prospect of therapeutic intervention, with the ultimate goal of improving the quality of life of the individuals affected with ONH.

PUF60 variants cause a syndrome of ID, short stature, microcephaly, coloboma, craniofacial, cardiac, renal and spinal features

PUF60 encodes a nucleic acid-binding protein, a component of multimeric complexes regulating RNA splicing and transcription. In 2013, patients with microdeletions of chromosome 8q24.3 including PUF60 were found to have developmental delay, microcephaly, craniofacial, renal and cardiac defects. Very similar phenotypes have been described in six patients with variants in PUF60, suggesting that it underlies the syndrome. We report 12 additional patients with PUF60 variants who were ascertained using exome sequencing: six through the Deciphering Developmental Disorders Study and six through similar projects. Detailed phenotypic analysis of all patients was undertaken. All 12 patients had de novo heterozygous PUF60 variants on exome analysis, each confirmed by Sanger sequencing: four frameshift variants resulting in premature stop codons, three missense variants that clustered within the RNA recognition motif of PUF60 and five essential splice-site (ESS) variant. Analysis of cDNA from a fibroblast cell line derived from one of the patients with an ESS variants revealed aberrant splicing. The consistent feature was developmental delay and most patients had short stature. The phenotypic variability was striking; however, we observed similarities including spinal segmentation anomalies, congenital heart disease, ocular colobomata, hand anomalies and (in two patients) unilateral renal agenesis/horseshoe kidney. Characteristic facial features included micrognathia, a thin upper lip and long philtrum, narrow almond-shaped palpebral fissures, synophrys, flared eyebrows and facial hypertrichosis. Heterozygote loss-of-function variants in PUF60 cause a phenotype comprising growth/developmental delay and craniofacial, cardiac, renal, ocular and spinal anomalies, adding to disorders of human development resulting from aberrant RNA processing/spliceosomal function.