Diaph1 knockout inhibits mouse primordial germ cell proliferation and affects gonadal development

BACKGROUND

Exploring the molecular mechanisms of primordial germ cell (PGC) migration and the involvement of gonadal somatic cells in gonad development is valuable for comprehending the origins and potential treatments of reproductive-related diseases.

METHODS

Diaphanous related formin 1 (Diaph1, also known as mDia1) was screened by analyzing publicly available datasets (ATAC-seq, DNase-seq, and RNA-seq). Subsequently, the CRISPR-Cas9 technology was used to construct Diaph1 knockout mice to investigate the role of Diaph1 in gonad development.

RESULTS

Based on data from public databases, a differentially expressed gene Diaph1, was identified in the migration of mouse PGC. Additionally, the number of PGCs was significantly reduced in Diaph1 knockout mice compared to wild type mice, and the expression levels of genes related to proliferation (Dicer1, Mcm9), adhesion (E-cadherin, Cdh1), and migration (Cxcr4, Hmgcr, Dazl) were significantly decreased. Diaph1 knockout also inhibited Leydig cell proliferation and induced apoptosis in the testis, as well as granulosa cell apoptosis in the ovary. Moreover, the sperm count in the epididymal region and the count of ovarian follicles were significantly reduced in Diaph1 knockout mice, resulting in decreased fertility, concomitant with lowered levels of serum testosterone and estradiol. Further research found that in Diaph1 knockout mice, the key enzymes involved in testosterone synthesis (CYP11A1, 3β-HSD) were decreased in Leydig cells, and the estradiol-associated factor (FSH receptor, AMH) in granulosa cells were also downregulated.

CONCLUSIONS

Overall, our findings indicate that the knockout of Diaph1 can disrupt the expression of factors that regulate sex hormone production, leading to impaired secretion of sex hormones, ultimately resulting in damage to reproductive function. These results provide a new perspective on the molecular mechanisms underlying PGC migration and gonadal development, and offer valuable insights for further research on the causes, diagnosis, and treatment of related diseases.

Immune dysregulation due to bi-allelic mutation of the actin remodeling protein DIAPH1

Children with severe inflammatory diseases are challenging to diagnose and treat, and the etiology of disease often remains unexplained. Here we present DIAPH1 deficiency as an unexpected genetic finding in a child with fatal inflammatory bowel disease who also displayed complex neurological and developmental phenotypes. Bi-allelic mutations of DIAPH1 were first described in patients with a severe neurological phenotype including microcephaly, intellectual disability, seizures, and blindness. Recent findings have expanded the clinical phenotype of DIAPH1 deficiency to include severe susceptibility to infections, placing this monogenic disease amongst the etiologies of inborn errors of immunity. Immune phenotypes in DIAPH1 deficiency are largely driven aberrant lymphocyte activation, particularly the failure to form an effective immune synapse in T cells. We present the case of a child with a novel homozygous deletion in DIAPH1, leading to a premature truncation in the Lasso domain of the protein. Unlike other cases of DIAPH1 deficiency, this patient did not have seizures or lung infections. Her major immune-related clinical symptoms were inflammation and enteropathy, diarrhea and failure to thrive. This patient did not show T or B cell lymphopenia but did have dramatically reduced naïve CD4+ and CD8+ T cells, expanded CD4-CD8- T cells, and elevated IgE. Similar to other cases of DIAPH1 deficiency, this patient had non-hematological phenotypes including microcephaly, developmental delay, and impaired vision. This patient's symptSoms of immune dysregulation were not successfully controlled and were ultimately fatal. This case expands the clinical spectrum of DIAPH1 deficiency and reveals that autoimmune or inflammatory enteropathy may be the most prominent immunological manifestation of disease.

A Novel Variant in the DIAPH1 Gene Causing Macrothrombocytopenia and Non-syndromic Hearing Loss in a Pediatric Saudi Girl

Macrothrompocytopenia (MTP) is a rare group of hereditary disorders that lead to impaired hemostasis. Macrothrompocytopenia mostly results from genetic mutations in genes implicated in megakaryocyte differentiation and function. Diaphanous-related formin 1 (DIAPH1) is a protein-coding gene. Dominant gain-of-function DIAPH1 variants cause macrothrombocytopenia and sensorineural deafness (autosomal dominant non-syndromic hearing loss 1 (DFNA1)), while homozygous loss of DIAPH1 results in seizures, cortical blindness, and microcephaly syndrome (SCBMS). This rare genetic disease is characterized by progressive and severe hearing loss with onset in the first decade of life, is associated with mild thrombocytopenia, and has no significant bleeding tendency. This case report presents the clinical findings of a 14-year-old Saudi pediatric girl. We investigated the potential association of DIAPH1 as a novel candidate gene linked to dominant MTP and autosomal dominant non-syndromic hearing loss (ADNSHL), which was evaluated through audiometry. Notably, a novel variant, c.3633_3636del, was identified in the DIAPH1 gene. To date, only a small number of mutations in this gene have been reported as the cause of MTP and ADNSHL.

Mammalian Diaphanous1 signalling in neurovascular complications of diabetes

Over the past few decades, diabetes gradually has become one of the top non-communicable disorders, affecting 476.0 million in 2017 and is predicted to reach 570.9 million people in 2025. It is estimated that 70 to 100% of all diabetic patients will develop some if not all, diabetic complications over the course of the disease. Despite different symptoms, mechanisms underlying the development of diabetic complications are similar, likely stemming from deficits in both neuronal and vascular components supplying hyperglycaemia-susceptible tissues and organs. Diaph1, protein diaphanous homolog 1, although mainly known for its regulatory role in structural modification of actin and related cytoskeleton proteins, in recent years attracted research attention as a cytoplasmic partner of the receptor of advanced glycation end-products (RAGE) a signal transduction receptor, whose activation triggers an increase in proinflammatory molecules, oxidative stressors and cytokines in diabetes and its related complications. Both Diaph1 and RAGE are also a part of the RhoA signalling cascade, playing a significant role in the development of neurovascular disturbances underlying diabetes-related complications. In this review, based on the existing knowledge as well as compelling findings from our past and present studies, we address the role of Diaph1 signalling in metabolic stress and neurovascular degeneration in diabetic complications. In light of the most recent developments in biochemical, genomic and transcriptomic research, we describe current theories on the aetiology of diabetes complications, highlighting the function of the Diaph1 signalling system and its role in diabetes pathophysiology.

Altered Fhod3 expression involved in progressive high-frequency hearing loss via dysregulation of actin polymerization stoichiometry in the cuticular plate

Age-related hearing loss (ARHL) is a common sensory impairment with complex underlying mechanisms. In our previous study, we performed a meta-analysis of genome-wide association studies (GWAS) in mice and identified a novel locus on chromosome 18 associated with ARHL specifically linked to a 32 kHz tone burst stimulus. Consequently, we investigated the role of Formin Homology 2 Domain Containing 3 (Fhod3), a newly discovered candidate gene for ARHL based on the GWAS results. We observed Fhod3 expression in auditory hair cells (HCs) primarily localized at the cuticular plate (CP). To understand the functional implications of Fhod3 in the cochlea, we generated Fhod3 overexpression mice (Pax2-Cre+/-; Fhod3Tg/+) (TG) and HC-specific conditional knockout mice (Atoh1-Cre+/-; Fhod3fl/fl) (KO). Audiological assessments in TG mice demonstrated progressive high-frequency hearing loss, characterized by predominant loss of outer hair cells, and a decreased phalloidin intensities of CP. Ultrastructural analysis revealed loss of the shortest row of stereocilia in the basal turn of the cochlea, and alterations in the cuticular plate surrounding stereocilia rootlets. Importantly, the hearing and HC phenotype in TG mice phenocopied that of the KO mice. These findings suggest that balanced expression of Fhod3 is critical for proper CP and stereocilia structure and function. Further investigation of Fhod3 related hearing impairment mechanisms may lend new insight towards the myriad mechanisms underlying ARHL, which in turn could facilitate the development of therapeutic strategies for ARHL.

The Inheritance of Hearing Loss and Deafness: A Historical Perspective

If the term "genetics" is a relatively recent proposition, introduced in 1905 by English biologist William Bateson, who rediscovered and spread in the scientific community Mendel's principles of inheritance, since the dawn of human civilization the influence of heredity has been recognized, especially in agricultural crops and animal breeding. And, later, in familial dynasties. In this concise review, we outline the evolution of the idea of hereditary hearing loss, up to the current knowledge of molecular genetics and epigenetics.

The genome of the black-footed cat: Revealing a rich natural history and urgent conservation priorities for small felids

Habitat degradation and loss of genetic diversity are common threats faced by almost all of today's wild cats. Big cats, such as tigers and lions, are of great concern and have received considerable conservation attention through policies and international actions. However, knowledge of and conservation actions for small wild cats are lagging considerably behind. The black-footed cat, Felis nigripes, one of the smallest felid species, is experiencing increasing threats with a rapid reduction in population size. However, there is a lack of genetic information to assist in developing effective conservation actions. A de novo assembly of a high-quality chromosome-level reference genome of the black-footed cat was made, and comparative genomics and population genomics analyses were carried out. These analyses revealed that the most significant genetic changes in the evolution of the black-footed cat are the rapid evolution of sensory and metabolic-related genes, reflecting genetic adaptations to its characteristic nocturnal hunting and a high metabolic rate. Genomes of the black-footed cat exhibit a high level of inbreeding, especially for signals of recent inbreeding events, which suggest that they may have experienced severe genetic isolation caused by habitat fragmentation. More importantly, inbreeding associated with two deleterious mutated genes may exacerbate the risk of amyloidosis, the dominant disease that causes mortality of about 70% of captive individuals. Our research provides comprehensive documentation of the evolutionary history of the black-footed cat and suggests that there is an urgent need to investigate genomic variations of small felids worldwide to support effective conservation actions.

What can insects teach us about hearing loss?

Over the last three decades, insects have been utilized to provide a deep and fundamental understanding of many human diseases and disorders. Here, we present arguments for insects as models to understand general principles underlying hearing loss. Despite ∼600 million years since the last common ancestor of vertebrates and invertebrates, we share an overwhelming degree of genetic homology particularly with respect to auditory organ development and maintenance. Despite the anatomical differences between human and insect auditory organs, both share physiological principles of operation. We explain why these observations are expected and highlight areas in hearing loss research in which insects can provide insight. We start by briefly introducing the evolutionary journey of auditory organs, the reasons for using insect auditory organs for hearing loss research, and the tools and approaches available in insects. Then, the first half of the review focuses on auditory development and auditory disorders with a genetic cause. The second half analyses the physiological and genetic consequences of ageing and short- and long-term changes as a result of noise exposure. We finish with complex age and noise interactions in auditory systems. In this review, we present some of the evidence and arguments to support the use of insects to study mechanisms and potential treatments for hearing loss in humans. Obviously, insects cannot fully substitute for all aspects of human auditory function and loss of function, although there are many important questions that can be addressed in an animal model for which there are important ethical, practical and experimental advantages.

A nonneural miRNA cluster mediates hearing via repression of two neural targets

We show here that mir-279/996 are absolutely essential for development and function of Johnston's organ (JO), the primary proprioceptive and auditory organ in Drosophila Their deletion results in highly aberrant cell fate determination, including loss of scolopale cells and ectopic neurons, and mutants are electrophysiologically deaf. In vivo activity sensors and mosaic analyses indicate that these seed-related miRNAs function autonomously to suppress neural fate in nonneuronal cells. Finally, genetic interactions pinpoint two neural targets (elav and insensible) that underlie miRNA mutant JO phenotypes. This work uncovers how critical post-transcriptional regulation of specific miRNA targets governs cell specification and function of the auditory system.

Description and Characterization of the Odontella aurita OAOSH22, a Marine Diatom Rich in Eicosapentaenoic Acid and Fucoxanthin, Isolated from Osan Harbor, Korea

Third-generation biomass production utilizing microalgae exhibits sustainable and environmentally friendly attributes, along with significant potential as a source of physiologically active compounds. However, the process of screening and localizing strains that are capable of producing high-value-added substances necessitates a significant amount of effort. In the present study, we have successfully isolated the indigenous marine diatom Odontella aurita OAOSH22 from the east coast of Korea. Afterwards, comprehensive analysis was conducted on its morphological, molecular, and biochemical characteristics. In addition, a series of experiments was conducted to analyze the effects of various environmental factors that should be considered during cultivation, such as water temperature, salinity, irradiance, and nutrients (particularly nitrate, silicate, phosphate, and iron). The morphological characteristics of the isolate were observed using optical and electron microscopes, and it exhibited features typical of O. aurita. Additionally, the molecular phylogenetic inference derived from the sequence of the small-subunit 18S rDNA confirmed the classification of the microalgal strain as O. aurita. This isolate has been confirmed to contain 7.1 mg g-1 dry cell weight (DCW) of fucoxanthin, a powerful antioxidant substance. In addition, this isolate contains 11.1 mg g-1 DCW of eicosapentaenoic acid (EPA), which is one of the nutritionally essential polyunsaturated fatty acids. Therefore, this indigenous isolate exhibits significant potential as a valuable source of bioactive substances for various bio-industrial applications.

Recent advances in genetic etiology of non-syndromic deafness in children

Congenital auditory impairment is a prevalent anomaly observed in approximately 2-3 per 1,000 infants. The consequences associated with hearing loss among children encompass the decline of verbal communication, linguistic skills, educational progress, social integration, cognitive aptitude, and overall well-being. Approaches to reversing or preventing genetic hearing loss are limited. Patients with mild and moderate hearing loss can only use hearing aids, while those with severe hearing loss can only acquire speech and language through cochlear implants. Both environmental and genetic factors contribute to the occurrence of congenital hearing loss, and advancements in our understanding of the pathophysiology and molecular mechanisms underlying hearing loss, coupled with recent progress in genetic testing techniques, will facilitate the development of innovative approaches for treatment and screening. In this paper, the latest research progress in genetic etiology of non-syndromic deafness in children with the highest incidence is summarized in order to provide help for personalized diagnosis and treatment of deafness in children.

Altered Fhod3 Expression Involved in Progressive High-Frequency Hearing Loss via Dysregulation of Actin Polymerization Stoichiometry in The Cuticular Plate

Age-related hearing loss (ARHL) is a common sensory impairment with comlex underlying mechanisms. In our previous study, we performed a meta-analysis of genome-wide association studies (GWAS) in mice and identified a novel locus on chromosome 18 associated with ARHL specifically linked to a 32 kHz tone burst stimulus. Consequently, we investigated the role of Formin Homology 2 Domain Containing 3 (Fhod3), a newly discovered candidate gene for ARHL based on the GWAS results. We observed Fhod3 expression in auditory hair cells (HCs) and primarily localized at the cuticular plate (CP). To understand the functional implications of Fhod3 in the cochlea, we generated Fhod3 overexpression mice (Pax2-Cre+/-; Fhod3Tg/+) (TG) and HC-specific conditional knockout mice (Atoh1-Cre+/-; Fhod3fl/fl) (KO). Audiological assessments in TG mice demonstrated progressive high-frequency hearing loss, characterized by predominant loss of outer HCs and decrease phalloidin intensities of CP. Ultrastructural analysis revealed shortened stereocilia in the basal turn cochlea. Importantly, the hearing and HC phenotype in TG mice were replicated in KO mice. These findings indicate that Fhod3 plays a critical role in regulating actin dynamics in CP and stereocilia. Further investigation of Fhod3-related hearing impairment mechanisms may facilitate the development of therapeutic strategies for ARHL in humans.

Autosomal Dominant Non-Syndromic Hearing Loss (DFNA): A Comprehensive Narrative Review

Autosomal dominant non-syndromic hearing loss (HL) typically occurs when only one dominant allele within the disease gene is sufficient to express the phenotype. Therefore, most patients diagnosed with autosomal dominant non-syndromic HL have a hearing-impaired parent, although de novo mutations should be considered in all cases of negative family history. To date, more than 50 genes and 80 loci have been identified for autosomal dominant non-syndromic HL. DFNA22 (MYO6 gene), DFNA8/12 (TECTA gene), DFNA20/26 (ACTG1 gene), DFNA6/14/38 (WFS1 gene), DFNA15 (POU4F3 gene), DFNA2A (KCNQ4 gene), and DFNA10 (EYA4 gene) are some of the most common forms of autosomal dominant non-syndromic HL. The characteristics of autosomal dominant non-syndromic HL are heterogenous. However, in most cases, HL tends to be bilateral, post-lingual in onset (childhood to early adulthood), high-frequency (sloping audiometric configuration), progressive, and variable in severity (mild to profound degree). DFNA1 (DIAPH1 gene) and DFNA6/14/38 (WFS1 gene) are the most common forms of autosomal dominant non-syndromic HL affecting low frequencies, while DFNA16 (unknown gene) is characterized by fluctuating HL. A long audiological follow-up is of paramount importance to identify hearing threshold deteriorations early and ensure prompt treatment with hearing aids or cochlear implants.

Monogenic Causes of Low-Frequency Non-Syndromic Hearing Loss

BACKGROUND

Low-frequency non-syndromic hearing loss (LFNSHL) is a rare form of hearing loss (HL). It is defined as HL at low frequencies (≤2,000 Hz) resulting in a characteristic ascending audiogram. LFNSHL is usually diagnosed postlingually and is progressive, leading to HL affecting other frequencies as well. Sometimes it occurs with tinnitus. Around half of the diagnosed prelingual HL cases have a genetic cause and it is usually inherited in an autosomal recessive mode. Postlingual HL caused by genetic changes generally has an autosomal dominant pattern of inheritance and its incidence remains unknown.

SUMMARY

To date, only a handful of genes have been found as causing LFNSHL: well-established WFS1 and, reported in some cases, DIAPH1, MYO7A, TNC, and CCDC50 (respectively, responsible for DFNA6/14/38, DFNA1, DFNA11, DFNA56, and DFNA44). In this review, we set out audiological phenotypes, causative genetic changes, and molecular mechanisms leading to the development of LFNSHL.

KEY MESSAGES

LFNSHL is most commonly caused by pathogenic variants in the WFS1 gene, but it is also important to consider changes in other HL genes, which may result in similar audiological phenotype.

In-depth genetic and molecular characterization of diaphanous related formin 2 (DIAPH2) and its role in the inner ear

Diaphanous related formins are regulatory cytoskeletal protein involved in actin elongation and microtubule stabilization. In humans, defects in two of the three diaphanous genes (DIAPH1 and DIAPH3) have been associated with different types of hearing loss. Here, we investigate the role of the third member of the family, DIAPH2, in nonsyndromic hearing loss, prompted by the identification, by exome sequencing, of a predicted pathogenic missense variant in DIAPH2. This variant occurs at a conserved site and segregated with nonsyndromic X-linked hearing loss in an Italian family. Our immunohistochemical studies indicated that the mouse ortholog protein Diaph2 is expressed during development in the cochlea, specifically in the actin-rich stereocilia of the sensory outer hair cells. In-vitro studies showed a functional impairment of the mutant DIAPH2 protein upon RhoA-dependent activation. Finally, Diaph2 knock-out and knock-in mice were generated by CRISPR/Cas9 technology and auditory brainstem response measurements performed at 4, 8 and 14 weeks. However, no hearing impairment was detected. Our findings indicate that DIAPH2 may play a role in the inner ear; further studies are however needed to clarify the contribution of DIAPH2 to deafness.

Mutation analysis of the WFS1 gene in a Chinese family with autosomal-dominant non-syndrome deafness

To analyse the pathogenic genes and mutations of a family with hereditary deafness. We recruited a three-generation family with NSHL. A detailed medical history inquiry and related examinations were performed. Next-generation sequencing (NGS) was used to confirm the gene mutation in the proband, and Sanger sequencing was used for verification. The effect of the WFS1 mutation on the function and structure of the wolframin protein was predicted by multiple computational software. From the Gene Expression Omnibus (GEO) database, we obtained GSE40585 dataset and performed enrichment analyses. The family clinically manifested as autosomal dominant NSHL. A novel WFS1 c.2421C>G (p.Ser807Arg) mutation was identified in four affected individuals in the pedigree . The p.Ser807Arg mutation is a highly conserved residue and causes an increase in protein stability. It had an important influence on not only amino acid size, charge and hydrophobicity but also protein intermolecular hydrogen bonding and spatial structure. There were differentially expressed genes (DEGs) in GSE40585 dataset. Enrichment analysis revealed that DEGs mainly functioned in amino acid metabolism, signal transduction and dephosphorylation. We reported a novel mutation c.2421C>G (p.Ser807Arg in WFS1. This study expands the mutation spectrum of WFS1.

Diaphanous-related formin subfamily: Novel prognostic biomarkers and tumor microenvironment regulators for pancreatic adenocarcinoma

The diaphanous-related formin subfamily includes diaphanous homolog 1 (DIAPH1), DIAPH2, and DIAPH3. DIAPHs play a role in the regulation of actin nucleation and polymerization and in microtubule stability. DIAPH3 also regulates the assembly and bipolarity of mitotic spindles. Accumulating evidence has shown that DIAPHs are anomalously regulated during malignancy. In this study, we reviewed The Cancer Genome Atlas database and found that DIAPHs are abundantly expressed in pancreatic adenocarcinoma (PAAD). Furthermore, we analyzed the gene alteration profiles, protein expression, prognosis, and immune reactivity of DIAPHs in PAAD using data from several well-established databases. In addition, we conducted gene set enrichment analysis to investigate the potential mechanisms underlying the roles of DIAPHs in the carcinogenesis of PAAD. Finally, we performed the experimental validation of DIAPHs expression in several pancreatic cancer cell lines and tissues of patients. This study demonstrated significant correlations between DIAPHs expression and clinical prognosis, oncogenic signature gene sets, T helper 2 cell infiltration, plasmacytoid dendritic cell infiltration, myeloid-derived suppressor cell infiltration, ImmunoScore, and immune checkpoints in PAAD. These data may provide important information regarding the role and mechanisms of DIAPHs in tumorigenesis and PAAD immunotherapy.

Deletion of the Notch ligand Jagged1 during cochlear maturation leads to inner hair cell defects and hearing loss

The mammalian cochlea is an exceptionally well-organized epithelium composed of hair cells, supporting cells, and innervating neurons. Loss or defects in any of these cell types, particularly the specialized sensory hair cells, leads to deafness. The Notch pathway is known to play a critical role in the decision to become either a hair cell or a supporting cell during embryogenesis; however, little is known about how Notch functions later during cochlear maturation. Uniquely amongst Notch ligands, Jagged1 (JAG1) is localized to supporting cells during cell fate acquisition and continues to be expressed into adulthood. Here, we demonstrate that JAG1 in maturing cochlear supporting cells is essential for normal cochlear function. Specifically, we show that deletion of JAG1 during cochlear maturation disrupts the inner hair cell pathway and leads to a type of deafness clinically similar to auditory neuropathy. Common pathologies associated with disruptions in inner hair cell function, including loss of hair cells, synapses, or auditory neurons, were not observed in JAG1 mutant cochleae. Instead, RNA-seq analysis of JAG1-deficient cochleae identified dysregulation of the Rho GTPase pathway, known to be involved in stereocilia development and maintenance. Interestingly, the overexpression of one of the altered genes, Diaph3, is responsible for autosomal dominant auditory neuropathy-1 (AUNA1) in humans and mice, and is associated with defects in the inner hair cell stereocilia. Strikingly, ultrastructural analyses of JAG1-deleted cochleae revealed stereocilia defects in inner hair cells, including fused and elongated bundles, that were similar to those stereocilia defects reported in AUNA1 mice. Taken together, these data indicate a novel role for Notch signaling in normal hearing development through maintaining stereocilia integrity of the inner hair cells during cochlear maturation.

Homozygous Autosomal Recessive DIAPH1 Mutation Associated with Central Nervous System Involvement and Aspergillosis: A Rare Case

The DIAPH1 gene fulfills critical immune and neurodevelopmental roles. It encodes the mammalian Diaphanous-related formin (mDia1) protein, which acts downstream of Rho GTPases to promote F-actin polymerization and stabilize microtubules. During mitosis, this protein is expressed in human neuronal precursor cells and considerably affects spindle formation and cell division. In humans, dominant gain-of-function DIAPH1 variants cause sensorineural deafness and macrothrombocytopenia (DFNA1), while homozygous DIAPH1 loss leads to seizures, cortical blindness, and microcephaly syndrome (SCBMS). To date, only 16 patients with SCBMS have been reported, none of whom were from Iran. Furthermore, aspergillosis is yet to be reported in patients with homozygous DIAPH1 loss, and the link between SCBMS and immunodeficiency remains elusive. In this study, we shed further light on this matter by reporting the clinical, genetic, and phenotypic characteristics of an Iranian boy with a long history of recurrent infections, diagnosed with SCBMS and immunodeficiency (NM_005219.5 c.3145C > T; p.R1049X variant) following aspergillosis and SARS-CoV-2 coinfection.

Full etiologic spectrum of pediatric severe to profound hearing loss of consecutive 119 cases

Determining the etiology of severe-to-profound sensorineural hearing loss (SP-SNHL) in pediatric subjects is particularly important in aiding the decision for auditory rehabilitation. We aimed to update the etiologic spectrum of pediatric SP-SNHL by combining internal auditory canal (IAC)-MRI with comprehensive and state-of-the-art genetic testings. From May 2013 to September 2020, 119 cochlear implantees under the age of 15 years with SP-SNHL were all prospectively recruited. They were subjected to genetic tests, including exome sequencing, and IAC-MRI for etiologic diagnosis. Strict interpretation of results were made based on ACMG/AMP guidelines and by an experienced neuroradiologist. The etiology was determined in of 65.5% (78/119) of our cohort. If only one of the two tests was done, the etiologic diagnostic rate would be reduced by at least 21.8%. Notably, cochlear nerve deficiency (n = 20) detected by IAC-MRI topped the etiology list of our cohort, followed by DFNB4 (n = 18), DFNB1 (n = 10), DFNB9 (n = 10) and periventricular leukomalacia associated with congenital CMV infection (n = 8). Simultaneous application of state-of-the-art genetic tests and IAC-MRI is essential for etiologic diagnosis, and if lesions of the auditory nerve or central nerve system are carefully examined on an MRI, we can identify the cause of deafness in more than 65% of pediatric SP-SNHL cases.

Role of Cytoskeletal Diaphanous-Related Formins in Hearing Loss

Hearing relies on the proper functioning of auditory hair cells and on actin-based cytoskeletal structures. Diaphanous-related formins (DRFs) are evolutionarily conserved cytoskeletal proteins that regulate the nucleation of linear unbranched actin filaments. They play key roles during metazoan development, and they seem particularly pivotal for the correct physiology of the reproductive and auditory systems. Indeed, in Drosophila melanogaster, a single diaphanous (dia) gene is present, and mutants show sterility and impaired response to sound. Vertebrates, instead, have three orthologs of the diaphanous gene: DIAPH1, DIAPH2, and DIAPH3. In humans, defects in DIAPH1 and DIAPH3 have been associated with different types of hearing loss. In particular, heterozygous mutations in DIAPH1 are responsible for autosomal dominant deafness with or without thrombocytopenia (DFNA1, MIM #124900), whereas regulatory mutations inducing the overexpression of DIAPH3 cause autosomal dominant auditory neuropathy 1 (AUNA1, MIM #609129). Here, we provide an overview of the expression and function of DRFs in normal hearing and deafness.

AudioGene: refining the natural history of KCNQ4, GSDME, WFS1, and COCH-associated hearing loss

Autosomal dominant non-syndromic hearing loss (ADNSHL) displays gene-specific progression of hearing loss, which is amenable to sequential audioprofiling. We sought to refine the natural history of ADNSHL by examining audiometric data in 5-year increments. 2175 audiograms were included from four genetic causes of ADNSHL-KCNQ4 (DFNA2), GSDME (DFNA5), WFS1 (DFNA6/14/38), and COCH (DFNA9). Annual threshold deterioration (ATD) was calculated for each gene: for the speech-frequency pure tone average, the ATD, respectively, was 0.72 dB/year, 0.94 dB/year, 0.53 dB/year, and 1.41 dB/year, with the largest drops occurring from ages 45-50 (0.89 dB/year; KCNQ4), 5-10 (1.42 dB/year; GSDME), 40-45 (0.83 dB/year; WFS1), and 50-55 (2.09 dB/year; COCH). 5-year interval analysis of audiograms reveals the gene specific natural history of KCNQ4, GSDME, WFS1 and COCH-related progressive hearing loss. Identifying ages at which hearing loss is most rapid informs clinical care and patient expectations. Natural history data are also essential to define outcomes of clinical trials that test novel therapies designed to correct or ameliorate these genetic forms of hearing loss.

Human deafness-associated variants alter the dynamics of key molecules in hair cell stereocilia F-actin cores

Stereocilia protrude up to 100 µm from the apical surface of vertebrate inner ear hair cells and are packed with cross-linked filamentous actin (F-actin). They function as mechanical switches to convert sound vibration into electrochemical neuronal signals transmitted to the brain. Several genes encode molecular components of stereocilia including actin monomers, actin regulatory and bundling proteins, motor proteins and the proteins of the mechanotransduction complex. A stereocilium F-actin core is a dynamic system, which is continuously being remodeled while maintaining an outwardly stable architecture under the regulation of F-actin barbed-end cappers, severing proteins and crosslinkers. The F-actin cores of stereocilia also provide a pathway for motor proteins to transport cargos including components of tip-link densities, scaffolding proteins and actin regulatory proteins. Deficiencies and mutations of stereocilia components that disturb this "dynamic equilibrium" in stereocilia can induce morphological changes and disrupt mechanotransduction causing sensorineural hearing loss, best studied in mouse and zebrafish models. Currently, at least 23 genes, associated with human syndromic and nonsyndromic hearing loss, encode proteins involved in the development and maintenance of stereocilia F-actin cores. However, it is challenging to predict how variants associated with sensorineural hearing loss segregating in families affect protein function. Here, we review the functions of several molecular components of stereocilia F-actin cores and provide new data from our experimental approach to directly evaluate the pathogenicity and functional impact of reported and novel variants of DIAPH1 in autosomal-dominant DFNA1 hearing loss using single-molecule fluorescence microscopy.

Late‐onset hearing loss case associated with a heterozygous truncating variant of DIAPH1

Diaphanous-related formin 1 (DIAPH1) is a formin homology F-actin elongating protein encoded by DIAPH1. Homozygous recessive variants resulting in the loss of DIAPH1 function cause seizures, cortical blindness, and microcephaly syndrome (SCBMS), but hearing loss has not been reported. In contrast, dominant variants of human DIAPH1 are associated with DFNA1 non-syndromic sensorineural hearing loss. The deafness phenotype is due partly to abnormal F-actin elongation activity caused by disruption of the DIAPH1 autoinhibitory mechanism. We report an elderly female heterozygous for the c.3145C>T: p.R1049X variant who showed late-onset sensorineural hearing loss in her fifth decade. p.R1049X lacks F-actin elongation activity because this variant truncates one-third of the FH2 domain, which is vital for DIAPH1 dimerization and processive F-actin elongation activity. Concordantly, no increase of F-actin or processive F-actin elongation activity was observed after overexpression of p.R1049X DIAPH1 in HeLa cells or by single-molecule microscopy using Xenopus XTC cells. However, overexpression of the p.R1049X variant impairs formation of cell-cell junctions and mitosis. We speculate that late-onset hearing loss is a long-term consequence of heterozygosity for the recessive p.R1049X variant, a phenotype that may have been overlooked among carriers of other recessive alleles of DIAPH1.

Genetic etiology of non-syndromic hearing loss in Europe

Hearing impairment not etiologically associated with clinical signs in other organs (non-syndromic) is genetically heterogeneous, so that over 120 genes are currently known to be involved. The frequency of mutations in each gene and the most frequent mutations vary throughout populations. Here we review the genetic etiology of non-syndromic hearing impairment (NSHI) in Europe. Over the years, epidemiological data were scarce because of the large number of involved genes, whose screening was not cost-effective until implementation of massively parallel DNA sequencing. In Europe, the most common form of autosomal recessive NSHI is DFNB1, which accounts for 11-57% of the cases. Mutations in STRC account for 16% of the recessive cases, and only a few more (MYO15A, MYO7A, LOXHD1, USH2A, TMPRSS3, CDH23, TMC1, OTOF, OTOA, SLC26A4, ADGRV1 and TECTA) have contributions higher than 2%. As regards autosomal-dominant NSHI, DFNA22 (MYO6) and DFNA8/12 (TECTA) represent the most common forms, accounting for 21% and 18% of elucidated cases, respectively. The contribution of ACTG1 and WFS1 drops to 9% in both cases, followed by POU4F3 (6.5%), MYO7A (5%), MYH14 and COL11A2 (4% each). Four additional genes contribute 2.5% each one (MITF, KCNQ4, EYA4, SOX10) and the remaining are residually represented. X-linked hearing loss and maternally-inherited NSHI have minor contributions in most countries. Further knowledge on the genetic epidemiology of NSHI in Europe needs a standardization of the experimental approaches and a stratification of the results according to clinical features, familial history and patterns of inheritance, to facilitate comparison between studies.

Comprehensive molecular-genetic analysis of mid-frequency sensorineural hearing loss

The genetic heterogeneity of sensorineural hearing loss (SNHL) is a major hurdle to the detection of disease-causing variants. We aimed to identify underlying causal genes associated with mid-frequency hearing loss (HL), which contributes to less than about 1% of SNHL cases, by whole exome sequencing (WES). Thirty families segregating mid-frequency SNHL, in whom biallelic GJB2 mutations had been previously excluded, were selected from among 851 families in our DNA repository of SNHL. DNA samples from the probands were subjected to WES analysis and searched for candidate variants associated with SNHL. We were able to identify the genetic aetiology in six probands (20%). In total, we found three pathogenic and three likely pathogenic variants in four genes (COL4A5, OTOGL, TECTA, TMPRSS3). One more proband was a compound heterozygote for a pathogenic variant and a variant of uncertain significance (VUS) in MYO15A gene. To date, MYO15A and TMPRSS3 have not yet been described in association with mid-frequency SNHL. In eight additional probands, eight candidate VUS variants were detected in five genes (DIAPH1, MYO7A, TECTA, TMC1, TSPEAR). Seven of these 16 variants have not yet been published or mentioned in the available databases. The most prevalent gene was TECTA, identified in 23% of all tested families. Furthermore, we confirmed the hypothesis that a substantive portion of cases with this conspicuous audiogram shape is a consequence of a genetic disorder.

Genetics & Epigenetics of Hereditary Deafness: An Historical Overview

Hearing loss (HL) is one of the most common sensory impairments worldwide and represents a critical medical and public health issue. Since the mid-1900s, great efforts have been aimed at understanding the etiology of both syndromic and non-syndromic HL and identifying correlations with specific audiological phenotypes. The extraordinary discoveries in the field of molecular genetics during the last three decades have contributed substantially to the current knowledge. Next-generation sequencing technologies have dramatically increased the diagnostic rate for genetic HL, enabling the detection of novel variants in known deafness-related genes and the discovery of new genes implicated in hearing disease. Overall, genetic factors account for at least 40% of the cases with HL, but a portion of affected patients still lack a definite molecular diagnosis. Important steps forward have been made, but many aspects still have to be clarified. In particular, the role of epigenetics in the development, function and pathology of hearing is a research field that still needs to be explored. This research is extremely challenging due to the time- and tissue-dependent variability of the epigenetic changes. Multisystem diseases are expected to be investigated at first: specific epi-signatures have been identified for several syndromic disorders and represent potential markers for molecular diagnostics.

The Rho GTPase Cell Division Cycle 42 Regulates Stereocilia Development in Cochlear Hair Cells

Stereocilia are actin-based cell protrusions on the apical surface of inner ear hair cells, playing a pivotal role in hearing and balancing sensation. The development and maintenance of stereocilia is tightly regulated and deficits in this process usually lead to hearing or balancing disorders. The Rho GTPase cell division cycle 42 (CDC42) is a key regulator of the actin cytoskeleton. It has been reported to localize in the hair cell stereocilia and play important roles in stereocilia maintenance. In the present work, we utilized hair cell-specific Cdc42 knockout mice and CDC42 inhibitor ML141 to explore the role of CDC42 in stereocilia development. Our data show that stereocilia height and width as well as stereocilia resorption are affected in Cdc42-deficient cochlear hair cells when examined at postnatal day 8 (P8). Moreover, ML141 treatment leads to planar cell polarity (PCP) deficits in neonatal hair cells. We also show that overexpression of a constitutively active mutant CDC42 in cochlear hair cells leads to enhanced stereocilia developmental deficits. In conclusion, the present data suggest that CDC42 plays a pivotal role in regulating hair cell stereocilia development.

Genetic etiology of non-syndromic hearing loss in Latin America

Latin America comprises all countries from South and Central America, in addition to Mexico. It is characterized by a complex mosaic of regions with heterogeneous genetic profiles regarding the geographical origin of the ancestors and proportions of admixture between the Native American, European and African components. In the first years following the findings of the role of the GJB2/GJB6 genes in the etiology of hearing loss, most scientific investigations about the genetics of hearing loss in Latin America focused on assessing the frequencies of pathogenic variants in these genes. More recently, modern techniques allowed researchers in Latin America to make exciting contributions to the finding of new candidate genes, novel mechanisms of inheritance in previously known genes, and characterize a wide diversity of variants, many of them unique to Latin America. This review aimed to provide a general landscape of the genetic studies about non-syndromic hearing loss in Latin America and their main scientific contributions. It allows the conclusion that, although there are similar contributions of some genes, such as GJB2/GJB6, when compared to European and North American countries, Latin American populations revealed some peculiarities that indicate the need for tailored strategies of screening and diagnosis to specific geographic regions.

Inner hair cell dysfunction in Klhl18 mutant mice leads to low frequency progressive hearing loss

Age-related hearing loss in humans (presbycusis) typically involves impairment of high frequency sensitivity before becoming progressively more severe at lower frequencies. Pathologies initially affecting lower frequency regions of hearing are less common. Here we describe a progressive, predominantly low-frequency recessive hearing impairment in two mutant mouse lines carrying different mutant alleles of the Klhl18 gene: a spontaneous missense mutation (Klhl18lowf) and a targeted mutation (Klhl18tm1a(KOMP)Wtsi). Both males and females were studied, and the two mutant lines showed similar phenotypes. Threshold for auditory brainstem responses (ABR; a measure of auditory nerve and brainstem neural activity) were normal at 3 weeks old but showed progressive increases from 4 weeks onwards. In contrast, distortion product otoacoustic emission (DPOAE) sensitivity and amplitudes (a reflection of cochlear outer hair cell function) remained normal in mutants. Electrophysiological recordings from the round window of Klhl18lowf mutants at 6 weeks old revealed 1) raised compound action potential thresholds that were similar to ABR thresholds, 2) cochlear microphonic potentials that were normal compared with wildtype and heterozygous control mice and 3) summating potentials that were reduced in amplitude compared to control mice. Scanning electron microscopy showed that Klhl18lowf mutant mice had abnormally tapering of the tips of inner hair cell stereocilia in the apical half of the cochlea while their synapses appeared normal. These results suggest that Klhl18 is necessary to maintain inner hair cell stereocilia and normal inner hair cell function at low frequencies.

Formins in Human Disease

Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insufficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging-related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.

DIAPH1 Variants in Non-East Asian Patients With Sporadic Moyamoya Disease

Importance

Moyamoya disease (MMD), a progressive vasculopathy leading to narrowing and ultimate occlusion of the intracranial internal carotid arteries, is a cause of childhood stroke. The cause of MMD is poorly understood, but genetic factors play a role. Several familial forms of MMD have been identified, but the cause of most cases remains elusive, especially among non-East Asian individuals.

Objective

To assess whether ultrarare de novo and rare, damaging transmitted variants with large effect sizes are associated with MMD risk.

Design, Setting, and Participants

A genetic association study was conducted using whole-exome sequencing case-parent MMD trios in a small discovery cohort collected over 3.5 years (2016-2019); data were analyzed in 2020. Medical records from US hospitals spanning a range of 1 month to 1.5 years were reviewed for phenotyping. Exomes from a larger validation cohort were analyzed to identify additional rare, large-effect variants in the top candidate gene. Participants included patients with MMD and, when available, their parents. All participants who met criteria and were presented with the option to join the study agreed to do so; none were excluded. Twenty-four probands (22 trios and 2 singletons) composed the discovery cohort, and 84 probands (29 trios and 55 singletons) composed the validation cohort.

Main Outcomes and Measures

Gene variants were identified and filtered using stringent criteria. Enrichment and case-control tests assessed gene-level variant burden. In silico modeling estimated the probability of variant association with protein structure. Integrative genomics assessed expression patterns of MMD risk genes derived from single-cell RNA sequencing data of human and mouse brain tissue.

Results

Of the 24 patients in the discovery cohort, 14 (58.3%) were men and 18 (75.0%) were of European ancestry. Three of 24 discovery cohort probands contained 2 do novo (1-tailed Poisson P = 1.1 × 10-6) and 1 rare, transmitted damaging variant (12.5% of cases) in DIAPH1 (mammalian diaphanous-1), a key regulator of actin remodeling in vascular cells and platelets. Four additional ultrarare damaging heterozygous DIAPH1 variants (3 unphased) were identified in 3 other patients in an 84-proband validation cohort (73.8% female, 77.4% European). All 6 patients were non-East Asian. Compound heterozygous variants were identified in ena/vasodilator-stimulated phosphoproteinlike protein EVL, a mammalian diaphanous-1 interactor that regulates actin polymerization. DIAPH1 and EVL mutant probands had severe, bilateral MMD associated with transfusion-dependent thrombocytopenia. DIAPH1 and other MMD risk genes are enriched in mural cells of midgestational human brain. The DIAPH1 coexpression network converges in vascular cell actin cytoskeleton regulatory pathways.

Conclusions and Relevance

These findings provide the largest collection to date of non-East Asian individuals with sporadic MMD harboring pathogenic variants in the same gene. The results suggest that DIAPH1 is a novel MMD risk gene and impaired vascular cell actin remodeling in MMD pathogenesis, with diagnostic and therapeutic ramifications.

Variable Autoinhibition among Deafness-Associated Variants of Diaphanous 1 (DIAPH1)

One of the earliest mapped human deafness genes, DIAPH1, encodes the formin DIAPH1. To date, at least three distinct mutations in the C-terminal domains and two additional mutations in the N-terminal region are associated with autosomal dominant hearing loss. The underlying molecular mechanisms are not known, and the role of formins in the inner ear is not well understood. In this study, we use biochemical assays to test the hypotheses that autoinhibition and/or actin assembly activities are disrupted by DFNA1 mutations. Our results indicate that C-terminal mutant forms of DIAPH1 are functional in vitro and promote actin filament assembly. Similarly, N-terminal mutants are well-folded and have quaternary structures and thermal stabilities similar to those of the wild-type (WT) protein. The strength of the autoinhibitory interactions varies widely among mutants, with the ttaa, A265S, and I530S mutations having an affinity similar to that of WT and the 1213x and Δag mutations completely abolishing autoinhibition. These data indicate that, in some cases, hearing loss may be linked to weakened inhibition of actin assembly.

Building platelet phenotypes: diaphanous-related formin 1 (DIAPH1)-related disorder

Variants of the Diaphanous-Related Formin 1 (DIAPH-1) gene have recently been reported causing inherited macrothrombocytopenia. The essential/"diagnostic" characteristics associated with the disorder are emerging; however, robust and complete criteria are not established. Here, we report the first cases of DIAPH1-related disorder in Australia caused by the autosomal dominant gain-of-function DIAPH1 R1213X variant formed by truncation of the protein within the diaphanous auto-regulatory domain (DAD) with loss of regulatory motifs responsible for autoinhibitory interactions within the DIAPH1 protein. We affirm phenotypic changes induced by the DIAPH1 R1213X variant to include macrothrombocytopenia, early-onset progressive sensorineural hearing loss, and mild asymptomatic neutropenia. High-resolution microscopy confirms perturbations of cytoskeletal dynamics caused by the DIAPH1 variant and we extend the repertoire of changes generated by this variant to include alteration of procoagulant platelet formation and possible dental anomalies.

Navigating Hereditary Hearing Loss: Pathology of the Inner Ear

Inherited forms of deafness account for a sizable portion of hearing loss among children and adult populations. Many patients with sensorineural deficits have pathological manifestations in the peripheral auditory system, the inner ear. Within the hearing organ, the cochlea, most of the genetic forms of hearing loss involve defects in sensory detection and to some extent, signaling to the brain via the auditory cranial nerve. This review focuses on peripheral forms of hereditary hearing loss and how these impairments can be studied in diverse animal models or patient-derived cells with the ultimate goal of using the knowledge gained to understand the underlying biology and treat hearing loss.

Deficiency of Klc2 Induces Low-Frequency Sensorineural Hearing Loss in C57BL/6 J Mice and Human

The transport system in cochlear hair cells (HCs) is important for their function, and the kinesin family of proteins transports numerous cellular cargos via the microtubule network in the cytoplasm. Here, we found that Klc2 (kinesin light chain 2), the light chain of kinesin-1 that mediates cargo binding and regulates kinesin-1 motility, is essential for cochlear function. We generated mice lacking Klc2, and they suffered from low-frequency hearing loss as early as 1 month of age. We demonstrated that deficiency of Klc2 resulted in abnormal transport of mitochondria and the down-regulation of the GABAA receptor family. In addition, whole-genome sequencing (WGS) of patient showed that KLC2 was related to low-frequency hearing in human. Hence, to explore therapeutic approaches, we developed adeno-associated virus containing the Klc2 wide-type cDNA sequence, and Klc2-null mice delivered virus showed apparent recovery, including decreased ABR threshold and reduced out hair cell (OHC) loss. In summary, we show that the kinesin transport system plays an indispensable and special role in cochlear HC function in mice and human and that mitochondrial localization is essential for HC survival.

Disruption of actin dynamics regulated by Rho effector mDia1 attenuates pressure overload-induced cardiac hypertrophic responses and exacerbates dysfunction

AIMS

Cardiac hypertrophy is a compensatory response to pressure overload, leading to heart failure. Recent studies have demonstrated that Rho is immediately activated in left ventricles after pressure overload and that Rho signalling plays crucial regulatory roles in actin cytoskeleton rearrangement during cardiac hypertrophic responses. However, the mechanisms by which Rho and its downstream proteins control actin dynamics during hypertrophic responses remain not fully understood. In this study, we identified the pivotal roles of mammalian homologue of Drosophila diaphanous (mDia) 1, a Rho-effector molecule, in pressure overload-induced ventricular hypertrophy.

METHODS AND RESULTS

Male wild-type (WT) and mDia1-knockout (mDia1KO) mice (10-12 weeks old) were subjected to a transverse aortic constriction (TAC) or sham operation. The heart weight/tibia length ratio, cardiomyocyte cross-sectional area, left ventricular wall thickness, and expression of hypertrophy-specific genes were significantly decreased in mDia1KO mice 3 weeks after TAC, and the mortality rate was higher at 12 weeks. Echocardiography indicated that mDia1 deletion increased the severity of heart failure 8 weeks after TAC. Importantly, we could not observe apparent defects in cardiac hypertrophic responses in mDia3-knockout mice. Microarray analysis revealed that mDia1 was involved in the induction of hypertrophy-related genes, including immediate early genes, in pressure overloaded hearts. Loss of mDia1 attenuated activation of the mechanotransduction pathway in TAC-operated mice hearts. We also found that mDia1 was involved in stretch-induced activation of the mechanotransduction pathway and gene expression of c-fos in neonatal rat ventricular cardiomyocytes (NRVMs). mDia1 regulated the filamentous/globular (F/G)-actin ratio in response to pressure overload in mice. Additionally, increases in nuclear myocardin-related transcription factors and serum response factor were perturbed in response to pressure overload in mDia1KO mice and to mechanical stretch in mDia1 depleted NRVMs.

CONCLUSION

mDia1, through actin dynamics, is involved in compensatory cardiac hypertrophy in response to pressure overload.

Loss of DIAPH1 causes SCBMS, combined immunodeficiency, and mitochondrial dysfunction

BACKGROUND

Homozygous loss of DIAPH1 results in seizures, cortical blindness, and microcephaly syndrome (SCBMS). We studied 5 Finnish and 2 Omani patients with loss of DIAPH1 presenting with SCBMS, mitochondrial dysfunction, and immunodeficiency.

OBJECTIVE

We sought to further characterize phenotypes and disease mechanisms associated with loss of DIAPH1.

METHODS

Exome sequencing, genotyping and haplotype analysis, B- and T-cell phenotyping, in vitro lymphocyte stimulation assays, analyses of mitochondrial function, immunofluorescence staining for cytoskeletal proteins and mitochondria, and CRISPR-Cas9 DIAPH1 knockout in heathy donor PBMCs were used.

RESULTS

Genetic analyses found all Finnish patients homozygous for a rare DIAPH1 splice-variant (NM_005219:c.684+1G>A) enriched in the Finnish population, and Omani patients homozygous for a previously described pathogenic DIAPH1 frameshift-variant (NM_005219:c.2769delT;p.F923fs). In addition to microcephaly, epilepsy, and cortical blindness characteristic to SCBMS, the patients presented with infection susceptibility due to defective lymphocyte maturation and 3 patients developed B-cell lymphoma. Patients' immunophenotype was characterized by poor lymphocyte activation and proliferation, defective B-cell maturation, and lack of naive T cells. CRISPR-Cas9 knockout of DIAPH1 in PBMCs from healthy donors replicated the T-cell activation defect. Patient-derived peripheral blood T cells exhibited impaired adhesion and inefficient microtubule-organizing center repositioning to the immunologic synapse. The clinical symptoms and laboratory tests also suggested mitochondrial dysfunction. Experiments with immortalized, patient-derived fibroblasts indicated that DIAPH1 affects the amount of complex IV of the mitochondrial respiratory chain.

CONCLUSIONS

Our data demonstrate that individuals with SCBMS can have combined immune deficiency and implicate defective cytoskeletal organization and mitochondrial dysfunction in SCBMS pathogenesis.

NCOA3 identified as a new candidate to explain autosomal dominant progressive hearing loss

Hearing loss is a frequent sensory impairment in humans and genetic factors account for an elevated fraction of the cases. We have investigated a large family of five generations, with 15 reported individuals presenting non-syndromic, sensorineural, bilateral and progressive hearing loss, segregating as an autosomal dominant condition. Linkage analysis, using SNP-array and selected microsatellites, identified a region of near 13 cM in chromosome 20 as the best candidate to harbour the causative mutation. After exome sequencing and filtering of variants, only one predicted deleterious variant in the NCOA3 gene (NM_181659, c.2810C > G; p.Ser937Cys) fit in with our linkage data. RT-PCR, immunostaining and in situ hybridization showed expression of ncoa3 in the inner ear of mice and zebrafish. We generated a stable homozygous zebrafish mutant line using the CRISPR/Cas9 system. ncoa3-/- did not display any major morphological abnormalities in the ear, however, anterior macular hair cells showed altered orientation. Surprisingly, chondrocytes forming the ear cartilage showed abnormal behaviour in ncoa3-/-, detaching from their location, invading the ear canal and blocking the cristae. Adult mutants displayed accumulation of denser material wrapping the otoliths of ncoa3-/- and increased bone mineral density. Altered zebrafish swimming behaviour corroborates a potential role of ncoa3 in hearing loss. In conclusion, we identified a potential candidate gene to explain hereditary hearing loss, and our functional analyses suggest subtle and abnormal skeletal behaviour as mechanisms involved in the pathogenesis of progressive sensory function impairment.

The actin polymerization factor Diaphanous and the actin severing protein Flightless I collaborate to regulate sarcomere size

The sarcomere is the basic contractile unit of muscle, composed of repeated sets of actin thin filaments and myosin thick filaments. During muscle development, sarcomeres grow in size to accommodate the growth and function of muscle fibers. Failure in regulating sarcomere size results in muscle dysfunction; yet, it is unclear how the size and uniformity of sarcomeres are controlled. Here we show that the formin Diaphanous is critical for the growth and maintenance of sarcomere size: Dia sets sarcomere length and width through regulation of the number and length of the actin thin filaments in the Drosophila flight muscle. To regulate thin filament length and sarcomere size, Dia interacts with the Gelsolin superfamily member Flightless I (FliI). We suggest that these actin regulators, by controlling actin dynamics and turnover, generate uniformly sized sarcomeres tuned for the muscle contractions required for flight.

Early truncation of the N-terminal variable region of EYA4 gene causes dominant hearing loss without cardiac phenotype

Background

Autosomal dominant hearing loss (ADHL) accounts for about 20% of all hereditary non‐syndromic HL. Truncating mutations of the EYA4 gene can cause either non‐syndromic ADHL or syndromic ADHL with cardiac abnormalities. It has been proposed that truncations of the C‐terminal Eya domain lead to non‐syndromic HL, whereas early truncations of the N‐terminal variable region cause syndromic HL with cardiac phenotype.

Methods

The proband and all the other hearing impaired members of the family underwent a thorough clinical and audiological evaluation. The cardiac phenotype was examined by ECG and echocardiography. Their DNA was subjected to target exome sequencing of 129 known deafness genes. The sequencing data were analyzed and the candidate variants were interpreted following the ACMG guidelines for clinical sequence interpretation. The effect of candidate variant on EYA4 gene expression was assessed by quantitative PCR and western blot of gene production in blood.

Results

We report a Chinese family cosegregating post‐lingual onset, progressive ADHL with a novel nonsense mutation NM_004100.4:c.543C>G (p.Tyr181Ter) of EYA4. Two affected members show no cardiac abnormalities at least until now revealed by electrocardiography and echocardiography. The overall expression level of the EYA4 gene in the proband was lower than that in his unaffected relative.

Conclusion

This report expands the mutational spectrum of the EYA4 gene and highlights the fact that more data are needed to elucidate the complex genotype–phenotype correlation of EYA4 mutations.

The formin INF2 in disease: progress from 10 years of research

Formins are a conserved family of proteins that primarily act to form linear polymers of actin. Despite their importance to the normal functioning of the cytoskeleton, for a long time, the only two formin genes known to be a genetic cause of human disorders were DIAPH1 and DIAPH3, whose mutation causes two distinct forms of hereditary deafness. In the last 10 years, however, the formin INF2 has emerged as an important target of mutations responsible for the appearance of focal segmental glomerulosclerosis, which are histological lesions associated with glomerulus degeneration that often leads to end-stage renal disease. In some rare cases, focal segmental glomerulosclerosis concurs with Charcot-Marie-Tooth disease, which is a degenerative neurological disorder affecting peripheral nerves. All known INF2 gene mutations causing disease map to the exons encoding the amino-terminal domain. In this review, we summarize the structure, biochemical features and functions of INF2, conduct a systematic and comprehensive analysis of the pathogenic INF2 mutations, including a detailed study exon-by-exon of patient cases and mutations, address the impact of the pathogenic mutations on the structure, regulation and known functions of INF2, draw a series of conclusions that could be useful for INF2-related disease diagnosis, and suggest lines of research for future work on the molecular mechanisms by which INF2 causes disease.

Small fish, big prospects: using zebrafish to unravel the mechanisms of hereditary hearing loss

Over the past decade, advancements in high-throughput sequencing have greatly enhanced our knowledge of the mutational signatures responsible for hereditary hearing loss. In its present state, the field has a largely uncensored view of protein coding changes in a growing number of genes that have been associated with hereditary hearing loss, and many more that have been proposed as candidate genes. Sequencing data can now be generated using methods that have become widespread and affordable. The greatest hurdles facing the field concern functional validation of uncharacterized genes and rapid application to human diseases, including hearing and balance disorders. To date, over 30 hearing-related disease models exist in zebrafish. New genome editing technologies, including CRISPR/Cas9 will accelerate the functional validation of hearing loss genes and variants in zebrafish. Here, we discuss current progress in the field and recent advances in genome editing approaches.

DIAPH1 regulates ciliogenesis and trafficking in primary cilia

Primary cilia are critical hubs for several signaling pathways, and defects in ciliogenesis or cilia maintenance produce a range of diseases collectively known as ciliopathies. Ciliogenesis requires vesicle trafficking along a network of microtubules and actin filaments to the basal body. The DIAPH1 (Diaphanous-related formin) family of formins promotes both actin polymerization and EB1-dependent microtubule (MT) stability. EB1 and EB3 have previously been implicated in cilia biogenesis to carry out centrosome-related functions. However, the role of DIAPH1 proteins had not been examined. Here we show that the depletion of DIAPH1 decreased ciliogenesis, cilia length, and reduced trafficking within cilia. Additionally, both actin nucleating and microtubule-stabilizing properties of DIAPH1 are important for their cilia functions. To assess their roles in ciliogenesis in isolation, we targeted DIAPH1 specifically to the basal body, which caused an increase in cilia length and increased trafficking within cilia. Intriguingly, expression of DIAPH1 mutants associated with human deafness and microcephaly impaired ciliation and caused cilia elongation and bulb formation. These results suggest that the actin and microtubule functions of DIAPH1 proteins regulate cilia maintenance in part by regulating vesicular trafficking to the base of the primary cilia.

The integrity of cochlear hair cells is established and maintained through the localization of Dia1 at apical junctional complexes and stereocilia

Dia1, which belongs to the diaphanous-related formin family, influences a variety of cellular processes through straight actin elongation activity. Recently, novel DIA1 mutants such as p.R1213X (p.R1204X) and p.A265S, have been reported to cause an autosomal dominant sensorineural hearing loss (DFNA1). Additionally, active DIA1 mutants induce progressive hearing loss in a gain-of-function manner. However, the subcellular localization and pathological function of DIA1(R1213X/R1204X) remains unknown. In the present study, we demonstrated the localization of endogenous Dia1 and the constitutively active DIA1 mutant in the cochlea, using transgenic mice expressing FLAG-tagged DIA1(R1204X) (DIA1-TG). Endogenous Dia1 and the DIA1 mutant were regionally expressed at the organ of Corti and the spiral ganglion from early life; alongside cochlear maturation, they became localized at the apical junctional complexes (AJCs) between hair cells (HCs) and supporting cells (SCs). To investigate HC vulnerability in the DIA1-TG mice, we exposed 4-week-old mice to moderate noise, which induced temporary threshold shifts with cochlear synaptopathy and ultrastructural changes in stereocilia 4 weeks post noise exposure. Furthermore, we established a knock-in (KI) mouse line expressing AcGFP-tagged DIA1(R1213X) (DIA1-KI) and confirmed mutant localization at AJCs and the tips of stereocilia in HCs. In MDCK^{AcGFP-DIA1(R1213X)} cells with stable expression of AcGFP-DIA1(R1213X), AcGFP-DIA1(R1213X) revealed marked localization at microvilli on the apical surface of cells and decreased localization at cell-cell junctions. The DIA1-TG mice demonstrated hazy and ruffled circumferential actin belts at AJCs and abnormal stereocilia accompanied with HC loss at 5 months of age. In conclusion, Dia1 plays a pivotal role in the development and maintenance of AJCs and stereocilia, ensuring cochlear and HC integrity. Subclinical/latent vulnerability of HCs may be the cause of progressive hearing loss in DFNA1 patients, thus suggesting new therapeutic targets for preventing HC degeneration and progressive hearing loss associated with DFNA1.

DCDC2 READ1 regulatory element: how temporal processing differences may shape language

Classic linguistic theory ascribes language change and diversity to population migrations, conquests, and geographical isolation, with the assumption that human populations have equivalent language processing abilities. We hypothesize that spectral and temporal characteristics make some consonant manners vulnerable to differences in temporal precision associated with specific population allele frequencies. To test this hypothesis, we modelled association between RU1-1 alleles of DCDC2 and manner of articulation in 51 populations spanning five continents, and adjusting for geographical proximity, and genetic and linguistic relatedness. RU1-1 alleles, acting through increased expression of DCDC2, appear to increase auditory processing precision that enhances stop-consonant discrimination, favouring retention in some populations and loss by others. These findings enhance classical linguistic theories by adding a genetic dimension, which until recently, has not been considered to be a significant catalyst for language change.

A novel variant in diaphanous homolog 1 (DIAPH1) as the cause of auditory neuropathy in a Chinese family

OBJECTIVES

To determine the genetic cause of non-syndromic autosomal dominant deafness segregating in a Chinese Auditory neuropathy (AN) family.

INTRODUCTION

AN is a genetically related rare disease characterized by sensorineural hearing loss and retention of hair cell function. Diaphanous Homolog 1 (DIAPH1) is the causative gene of DFNA1. To date, no evidence has been detected to reveal the connection between gene DIAPH1 and AN.

MATERIAL AND METHODS

Audiological and imageological examinations, genome-wide linkage analysis, and whole exome sequencing (WES) were carried out on the family members.

RESULTS

In the 13-member branch of the family, 4 patients with preserved otoacoustic emission or cochlear microphonic and abnormal auditory brainstem responses were diagnosed with AN. Linkage analysis detected an interval with a LOD (log odds) score >4 on chr5:138.845-149.509 cM. Using WES we identified a novel frameshift variant c.3551_3552del (p.Glu1184AlafsTer11) in exon 26 of DIAPH1 located in the linkage region. The variant was co-segregated with hearing impairment phenotype in the family except 4 members below the average age of onset. We have found sufficient evidence conforming with the American College of Medical Genetics and Genomics Guideline to consider c.3551_3552del as the genetic cause of the family patients.

CONCLUSION

It is the first report to expand DIAPH1-related phenotypic spectrum to include AN. Our findings could facilitate the clinical diagnosis and genetic counselling for AN, especially for those with DIAPH1 variants.

Genetics of pediatric hearing loss: A functional perspective

OBJECTIVES

This article reviews the current role of genetics in pediatric hearing loss (HL).

METHODS

A review of the current literature regarding the genetic basis of HL in children was performed.

RESULTS

To date, 119 nonsyndromic genes have been associated with HL. There are also hundreds of syndromic causes that have HL as part of the clinical phenotype.

CONCLUSIONS

Identifying HL genes coupled with clinical characteristics ("genotype-phenotype") yields a more accurate diagnosis and prognosis. Although the complexity of the auditory apparatus presents challenges, gene therapy is emerging and may be a viable management option in the future.

Protein diaphanous homolog 1 (Diaph1) promotes myofibroblastic activation of hepatic stellate cells by regulating Rab5a activity and TGFβ receptor endocytosis

TGFβ induces the differentiation of hepatic stellate cells (HSCs) into tumor-promoting myofibroblasts but underlying mechanisms remain incompletely understood. Because endocytosis of TGFβ receptor II (TβRII), in response to TGFβ stimulation, is a prerequisite for TGF signaling, we investigated the role of protein diaphanous homolog 1 (known as Diaph1 or mDia1) for the myofibroblastic activation of HSCs. Using shRNA to knockdown Diaph1 or SMIFH2 to target Diaph1 activity of HSCs, we found that the inactivation of Diaph1 blocked internalization and intracellular trafficking of TβRII and reduced SMAD3 phosphorylation induced by TGFβ1. Mechanistic studies revealed that the N-terminal portion of Diaph1 interacted with both TβRII and Rab5a directly and that Rab5a activity of HSCs was increased by Diaph1 overexpression and decreased by Diaph1 knockdown. Additionally, expression of Rab5aQ79L (active Rab5a mutant) increased whereas the expression of Rab5aS34N (inactive mutant) reduced the endosomal localization of TβRII in HSCs compared to the expression of wild-type Rab5a. Functionally, TGFβ stimulation promoted HSCs to express tumor-promoting factors, and α-smooth muscle actin, fibronection, and CTGF, markers of myofibroblastic activation of HSCs. Targeting Diaph1 or Rab5a suppressed HSC activation and limited tumor growth in a tumor implantation mouse model. Thus, Dipah1 and Rab5a represent targets for inhibiting HSC activation and the hepatic tumor microenvironment.

Genetics of Postlingual Sensorineural Hearing Loss

Literature and clinical practice around adult-onset hearing loss (HL) has traditionally focused on environmental risk factors, including noise exposure, ototoxic drug exposure, and cardiovascular disease. The most common diagnosis in adult-onset HL is presbycusis. However, the age of onset of presbycusis varies, and patients often describe family history of HL as well as individual variation in progression and severity. In recent years, there has been accumulating evidence of gene-environment interactions underlying adult cases of HL. Susceptibility loci for age-related HL have been identified, and genes related to postlingual nonsyndromic HL continue to be discovered through individual reports and genome-wide association studies. This review will outline main concepts in genetics as related to HL, identify implicated genes, and discuss clinical implications. Laryngoscope, 131:401-409, 2021.