Myosin VI Research Articles

Myosin VI Drives Clathrin-Mediated AMPA Receptor Endocytosis to Facilitate Cerebellar Long-Term Depression

Myosin VI is an actin-based cytoskeletal motor implicated in various steps of membrane trafficking. Here, we investigated whether this myosin is crucial for synaptic function and plasticity in neurons. We find that myosin VI localizes at cerebellar parallel fiber to Purkinje cell synapses and that the myosin is indispensable for long-term depression of AMPA-receptor-mediated synaptic signal transmission at this synapse. Moreover, direct visualization of GluA2-containing AMPA receptors in Purkinje cells reveals that the myosin drives removal of AMPA receptors from the surface of dendritic spines in an activity-dependent manner. Co-immunoprecipitation and super-resolution microscopy indicate that specifically the interaction of myosin VI with the clathrin adaptor component α-adaptin is important during long-term depression. Together, these data suggest that myosin VI directly promotes clathrin-mediated endocytosis of AMPA receptors in Purkinje cells to mediate cerebellar long-term depression. Our results provide insights into myosin VI function and the molecular mechanisms underlying synaptic plasticity.

Generation of new hair cells by DNA methyltransferase (Dnmt) inhibitor 5-azacytidine in a chemically-deafened mouse model

Regeneration of mature mammalian inner ear hair cells remains to be a challenge. This study aims to evaluate the ability of DNA methyltransferase (Dnmt) inhibitor 5-azacytidine (5-aza) to generate outer hair cells (OHCs) in a chemically-deafened adult mouse model. 5-aza was administrated into the mouse inner ear via the round window. Immunofluorescence was used to examine the expression of hair cell specific proteins following 5-aza treatment. The results showed that in the chemically-deafened mouse cochlea, new OHCs were found post 5-aza treatment, whereas OHCs were completely lost in saline-treated mice. New hair cells expressed multiple hair cell markers included Myosin VIIa, Pou4f3 and Myosin VI. Newly-generated hair cells presented in three cochlear turns and were able to survive for at least six weeks. The effects of new hair cells generation by 5-aza were concentration dependent. Quantitative PCR study indicates that 5-aza may function through Dnmt1 inhibition. The results of this report suggest that the Dnmt inhibitor 5-aza may promote hair cell regeneration in a chemically-deafened mouse model.

A humanized mouse model, demonstrating progressive hearing loss caused by MYO6 p.C442Y, is inherited in a semi-dominant pattern

Myosin VI is an actin-associated molecular motor vital for auditory and vestibular function. It is encoded by MYO6 located on chromosome 6q13 in human. Pathogenic variants in MYO6 have been associated with both dominant and recessive forms of hearing loss. However, the molecular mechanisms remain unclear. We established a humanized knock-in mouse model, Myo6-C442Y, to mimic the p.C442Y missense variant identified in human patients with autosomal dominant nonsyndromic hearing loss designated as DFNA22. We characterized hearing and inner ear morphologies of Myo6-C442Y and wild-type control mice. We found that both homozygous and heterozygous Myo6-C442Y mice exhibited hearing loss from three weeks after birth that rapidly progressed to profound deafness by six to nine weeks of age. The hearing loss corresponded to the degeneration of hair cells in the organ of Corti. We also observed disorganized stereocilia with irregular morphological features by immunohistochemistry and scanning electron microscopy. Additionally, hearing loss and inner-ear morphological anomalies were more pronounced and deteriorated more drastically in homozygous than in heterozygous Myo6-C442Y mice, indicating a semi-dominant inheritance pattern. Heterozygous Myo6-C442Y mice recapitulated the progressive postlingual sensorineural deafness in human, thus providing a useful model for elucidating the role myosin VI plays in the mammalian auditory system. Furthermore, the late-onset hearing loss of this mouse model may provide a therapeutic window for the emerging gene therapy, a promising strategy to treat certain forms of genetic deafness.

Distinct roles of two myosins in C. elegans spermatid differentiation.

During spermatogenesis, interconnected haploid spermatids segregate undesired cellular contents into residual bodies (RBs) before detaching from RBs. It is unclear how this differentiation process is controlled to produce individual spermatids or motile spermatozoa. Here, we developed a live imaging system to visualize and investigate this process in C. elegans. We found that non-muscle myosin 2 (NMY-2)/myosin II drives incomplete cytokinesis to generate connected haploid spermatids, which are then polarized to segregate undesired cellular contents into RBs under the control of myosin II and myosin VI. NMY-2/myosin II extends from the pseudo-cleavage furrow formed between two haploid spermatids to the spermatid poles, thus promoting RB expansion. In the meantime, defective spermatogenesis 15 (SPE-15)/myosin VI migrates from spermatids towards the expanding RB to promote spermatid budding. Loss of myosin II or myosin VI causes distinct cytoplasm segregation defects, while loss of both myosins completely blocks RB formation. We found that the final separation of spermatids from RBs is achieved through myosin VI–mediated cytokinesis, while myosin II is dispensable at this step. SPE-15/myosin VI and F-actin form a detergent-resistant actomyosin VI ring that undergoes continuous contraction to promote membrane constriction between spermatid and RB. We further identified that RGS-GAIP-interacting protein C terminus (GIPC)-1 and GIPC-2 cooperate with myosin VI to regulate contractile ring formation and spermatid release. Our study reveals distinct roles of myosin II and myosin VI in spermatid differentiation and uncovers a novel myosin VI–mediated cytokinesis process that controls spermatid release.

Assessing fractional hair cell survival in archival human temporal bones.

Histopathological analysis of hair cell survival in human temporal bone sections has historically been binarized such that each hair cell row is rated as either present or absent, thereby greatly underestimating the amount of hair cell loss. Here, we describe and validate a technique to reliably assess fractional hair cell survival in archival sections stained with hematoxylin and eosin (H&E) using high-resolution light microscopy and optical sectioning. Technique validation. Hair cell counts in archival temporal bone slide sets were performed by several observers using either differential interference contrast (DIC) or confocal microscopy of the endogenous eosin fluorescence in hair cells. As a further cross-check, additional decelloidinized sections were immunostained with hair cell markers myosin VI and VIIa. Cuticular plates and stereocilia bundles are routinely resolvable in DIC imaging of archival H&E-stained human material using standard research-grade microscopes, allowing highly accurate counts of fractional hair cell survival that are reproducible across observer and can be verified by confocal microscopy. Reanalysis of cases from the classic temporal bone literature on presbycusis suggests that, contrary to prior reports, differences in audiometric patterns may be well explained by the patterns of hair cell loss. NA Laryngoscope, 130:487-495, 2020.

Characterizing a Novel RGS14:MyosinV/VI Interaction in Brain

RGS14 is a complex multifunctional signaling protein that integrates G protein, Ras/ERK and Ca++/CaM/CaMKII signaling pathways. The protein is composed of an RGS domain that binds active Gαi/o, two tandem Ras/Rap binding domains (R1, R2) which bind active H‐Ras‐GTP and Rap2A‐GTP to regulate MAP kinase signaling, a G protein regulatory (GPR) motif that binds inactive Gαi1/3, and a Ca++/CaM binding site. RGS14 is highly expressed in the hippocampus, the brain center for learning and memory, which is composed of areas CA3, CA2, and CA1. Schaffer collateral (SC) projections from CA3 to CA1 display long term potentiation (LTP), a stable potentiation in post‐synaptic strength in response to brief periods of synaptic stimulation such as during learning in animals. Within the hippocampus RGS14 is highly expressed in postsynaptic dendrites and spines of area CA2, where SC inputs from CA3 to CA2 neurons show a surprising resistance to LTP. CA2 has been shown to be important for social learning and memory, and we have shown that RGS14 is a natural suppressor of LTP and synaptic plasticity in this area. That is, loss of RGS14 in CA2 (RGS14‐KO) restores synaptic plasticity (LTP) in CA2 and markedly enhances hippocampal learning. However, it remains unknown how RGS14 interacts with other signaling proteins to regulate synaptic plasticity. In proteomic studies, RGS14 recovered from mouse brain by immunoprecipitation was subjected to mass spectrometry and proteomic analysis, showing its association with a high molecular‐weight protein complex including actin‐based myosin motor proteins (Myosin V, Myosin VI and Myosin II) and their regulatory proteins, among others. MyoV is involved in activity‐dependent insertion of AMPA glutamate receptor subunits (GluR1, GluR2) and NMDA receptors, regulation of calcium and proper positioning of calcium intracellular stores. MyoVI is enriched at the postsynaptic density where it regulates AMPA receptor recycling. These myosin classes have crucial roles in regulating synaptic plasticity and LTP. Follow up studies have shown RGS14 in complex with MyoV and MyoVI in whole brain lysates. However, it remains unclear how RGS14 interacts with MyoV/VI to regulate synaptic plasticity. Ongoing studies will determine if RGS14 binds directly or indirectly to MyoV/VI and how that is regulated, as well as elucidate the physiological function of this interaction, thereby providing insight into the functions of both RGS14 and MyoV/VI in their roles in modulating synaptic plasticity and hippocampal‐dependent learning and memory.Support or Funding InformationThis research was supported by grants NIH/NINDS to JRH (5R01NS37112 and 1R21NS074975), and in part by the Emory Neuroscience NINDS Core Facilities and NIH/NINDS under award number P30NS055077.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The potential role of myosin motor proteins in mediating the subcellular distribution of NHE3 in the renal proximal tubule.

Isoform 3 of the Na+/H+ exchanger (NHE3) is responsible for the majority of the reabsorption of NaCl, NaHCO3, and, consequently, water in the renal proximal tubule. As such, this transporter plays an essential role in acid-base balance and extracellular fluid volume homeostasis and determining systemic arterial blood pressure levels. NHE3 activity is modulated by a number of mechanisms, including the redistribution of the transporter between the body of the microvilli (where NHE3 is active) and the base of the microvilli (where NHE3 is less active). Although the physiological, pathophysiological, and pharmacological importance of the subcellular distribution of NHE3 has been well established, the exact mechanism whereby NHE3 is translocated along microvilli microdomains of the proximal tubule apical membrane is unknown. Nonmuscle myosin IIA and unconventional myosin VI move cargoes in anterograde and retrograde directions, respectively, and are known to redistribute along with NHE3 in the proximal tubule in response to a variety of natriuretic and antinatriuretic stimuli, including stimulation or inhibition of the renin-angiotensin system, high dietary Na+ intake, and high blood pressure. Therefore, this review aims to discuss the current evidence that suggests a potential role of myosin IIA and myosin VI in mediating the subcellular distribution of NHE3 along the kidney proximal tubule microvilli and their possible contribution in modifying NHE3-mediated Na+ reabsorption under both physiological and pathophysiological conditions.

Protective effect of [Pyr1]-apelin-13 on oxidative stress-induced apoptosis in hair cell-like cells derived from bone marrow mesenchymal stem cells

Oxidative stress plays an important role in auditory dysfunction. Exogenous cell therapy has brought new hopes for repairing mammalian inner ear hair cells. However, poor cell viability of transplanted cells under oxidative stress conditions has limited their therapeutic potential. The adipocytokine apelin-13 was isolated from a bovine stomach. Apelin-13 might protect oxidative stress-induced hair cell damage was raised considering other oxidative stress-induced injury, including brain ischemia-induced cell death. Therefore, we evaluated the protective effects of apelin- 13 on the damage induced by hydrogen peroxide (H2O2) to the hair cells-derived from bone marrow mesenchymal stem cells (BMSCs) in vitro. Stem cells were differentiated into hair cell- like cells with B27, FGF, EGF and IGF-1. Expression of neuron specific markers including β tubulin III, Nestin, MAP2, Neurofilament 68 and GFAP was tested by flow cytometry. As well, inner ear hair cell markers such as Myosin VIIA, Sox2 and TrkB expression were assayed by immunocytochemistry (ICC) method. We designed an in vitro model of oxidative stress by exposing hair cell- like cells to H2O2. Protein expression levels of caspase-3, Bax and Bcl-2 were detected by western blot. Apoptotic cells were also detected by acridin-orange staining and TUNEL assay. Protein expression of caspase-3 and Bax/Bcl-2 ratio was significantly lower in the apelin-13-pretreated group than only H2O2 treated group. In addition, apoptotic cells were significantly decreased in the apelin-13+H2O2 co-treated cells compared to the H2O2-treated group. Treating hair cells-like cells with apelin13 increases their survival against oxidative stress damage by inhibition of apoptosis signaling pathway.

Myosin VI and its Role in the DNA Damage Response

Myosins are actin-based molecular motor that are involved in various cellular processes including cell migration and endocytosis. More recently, Myosin VI has been characterised in the nucleus where it has a direct interaction with DNA that is critical for RNA polymerase II transcription. Along with this interaction it has also been shown that myosin VI stabilises p53 allowing DNA repair to occur before the cell cycle continues. However, very little is known about how Myosin VI may function in the DNA damage response. We have found cisplatin-induced DNA damage causes a large increase in the nuclear localisation of myosin VI and we wish to understand the reason for this recruitment. We have begun to understand that myosin VI is required for a normal response to DNA damage by analysing the global changes of chromosome arrangement and histone modifications. These chromatin markers are directly or indirectly linked with the DNA damage response, and the work presented here describes how myosin VI may be involved in not only signalling but also repair factories themselves. By using techniques such as high content screening, co-localisation studies and clustering analysis we are beginning to characterise a new role for myosin VI within the nucleus.

Nuclear Myosin VI Stabilizes RNA Polymerase II in Transcription Factories

While it is widely accepted there is temporal regulation of gene expression, more recently there has been increase studies of spatial regulation. Indeed, transcription is known to occur within discrete foci throughout the nucleus with RNA Polymerase II arranged in hubs or factories. The factories bring together several genes and arrange the chromatin to enable simultaneous gene expression. The hubs are estimated to contain 4-30 RNAPII molecules in a region of 40-200 nm. Despite this quantitative knowledge, the mechanism of hub assembly, organisation and stability remains unknown. To this end, we have used advanced single molecule techniques to visualise RNAPII hubs and track their dynamics in live cells. Following our previous work on nuclear myosin VI, we know myosin-actin interactions are critical for RNAPII transcription. Using STORM imaging, we found a decrease in RNAPII hubs when myosin VI or actin was perturbed. Moreover, using 3D single molecule tracking we found an increase in RNAPII mobility when myosin VI was knocked-down or inhibited. We conclude that myosin VI is critical for the RNAPII hubs to enable gene expression whereby the loss of myosin VI activity leads to a disruption of RNAPII organisation. Lastly, we show how myosin VI uses a load-induced anchoring ability to stabilise RNAPII within the hubs as transcription occurs. In this manner, myosin VI uses its force-sensing properties to regulate gene expression. For the first time, we reveal how the properties of myosin are specifically required for transcription.

Deciphering Load-Induced Anchoring by Myosin VI

Deciphering Load-Induced Anchoring by Myosin VI

Nuclear Ndp52 - a Putative Transcription Regulator

NDP52/CALCOCO2 has been well characterised as an autophagy receptor, however a population of the protein exists in the nucleus. Moreover, NDP52 shares significant homology to a transcription co-activator CoCoA. We have recently described the activation of Myosin VI by NDP52 in RNA Polymerase II (RNAPII)-dependent transcription. Although depletion of NDP52 is known to reduce the steady-state levels of mRNA in cells, the molecular role of NDP52 in the nucleus is not clear. We are using cell biology combined with biophysical techniques to understand the functions of NDP52 in nucleus. Using SEC-MALS, Microscale Thermophoresis and Electron Microscopy, we can show that NDP52 is an elongated dimer of approximately 110 kDa that is capable of binding double-stranded DNA in vitro with high affinity. This interaction can also be observed in cells through Chromatin Immunoprecipitation (ChIP). We observed NDP52 bound to promoter regions of several oestrogen-responsive genes. When we knock-down NDP52 in these cells, we see dysregulation of known gene-targets of the oestrogen receptor, as well as of those relating to apoptosis, DNA repair and recruitment of RNAPII. Our proteomics data now suggest that this regulation might not only be sustained through direct interactions with DNA, but also through protein-protein interactions with binding partners of NDP52 in the nucleus. Overall, we propose that NDP52 may be functioning as a transcription regulator in human cells. To test this idea, we have started using super-resolution imaging - PALM-STORM, combined with Cluster analysis software, to image NDP52 at single-molecule level in combination with RNAPII and other candidate binding partners.

Kinetic Model for Myosin Gating and Backward Stepping Mechanisms

Members of the myosin superfamily form “processive” dimers, meaning they take many consecutive mechanical steps per diffusional encounter with an actin filament. Processivity requires synchronization between the two heads, or gating, to ensure that the trailing head steps first and binds forward, which is necessary for unidirectional motility. Synchronization, which is thought to occur through “biochemical gating” due to inter-head tension created by the strain in the two-headed attachment, modifies the rates for nucleotide binding, hydrolysis and/or release to favor detachment of the trailing head. Alternatively, the myosin power stroke may bias reattachment of the free head to bind to a forward actin subunit - a process we refer to as “mechanical gating”. Evidence exists to support both the mechanisms, but the dominant one is both highly debated and could be myosin isoform specific. Myosin motors also take occasional backward steps that may or may not be initiated by ATP binding. To utilize existing experimental data and infer the mechanisms governing gating, we present a general kinetic model for the processivity of myosin dimers. By including multiple pathways for forward and backward stepping, and both spontaneous and ATP-induced detachment from actin, the model predicts the consequences of different types of gating on processivity. Further, by fitting recently published data for myosin VI, we are able to predict which gating mechanisms are compatible with the data. Thus, the kinetic model serves as a generalized tool for researchers to use experimentally derived metrics of motility (processivity, backwards stepping, velocity, run length, and their nucleotide dependencies) to infer the molecular gating mechanisms of each myosin motor.

Myosin VIIa Supports Spermatid/Organelle Transport and Cell Adhesion During Spermatogenesis in the Rat Testis.

The biology of transport of spermatids and spermatid adhesion across the seminiferous epithelium during the epithelial cycle remains largely unexplored. Nonetheless, studies have implicated the role of motor proteins in these cellular events. In this article, we report findings to unravel the role of myosin VIIa, an F-actin-based barbed (+)-end-directed motor protein, to support cellular transport and adhesion in the testis. Using RNA interference to knock down myosin VIIa in Sertoli cells cultured in vitro as a study model was shown to perturb the Sertoli cell tight junction permeability barrier, mediated through disorganization of actin- or microtubule (MT)-based cytoskeletons owing to disruptive changes on the spatiotemporal expression of F-actin or MT-regulatory proteins. Consistent with these in vitro findings, knockdown of myosin VIIa in the testis in vivo also induced disorganization of the actin- and MT-based cytoskeletons across the seminiferous epithelium, mediated by disruptive changes in the spatiotemporal expression of actin- and MT-based regulatory proteins. More important, the transport of spermatids and organelles across the epithelium, as well as cell adhesion, was grossly disrupted. For instance, step 19 spermatids failed to be transported to the adluminal compartment near the tubule lumen to undergo spermiation; in this manner, step 19 spermatids were persistently detected in stage IX and XII tubules, intermingling with step 9 and 12 spermatids, respectively. Also, phagosomes were detected near the tubule lumen in stage I to III tubules when they should have been degraded near the base of the seminiferous epithelium via the lysosomal pathway. In summary, myosin VIIa motor protein was crucial to support cellular transport and adhesion during spermatogenesis.

A Mechanosensitive RhoA Pathway that Protects Epithelia against Acute Tensile Stress

Adherens junctions are tensile structures that couple epithelial cells together. Junctional tension can arise from cell-intrinsic application of contractility or from the cell-extrinsic forces of tissue movement. Here, we report a mechanosensitive signaling pathway that activates RhoA at adherens junctions to preserve epithelial integrity in response to acute tensile stress. We identify Myosin VI as the force sensor, whose association with E-cadherin is enhanced when junctional tension is increased by mechanical monolayer stress. Myosin VI promotes recruitment of the heterotrimeric Gα12 protein to E-cadherin, where it signals for p114 RhoGEF to activate RhoA. Despite its potential to stimulate junctional actomyosin and further increase contractility, tension-activated RhoA signaling is necessary to preserve epithelial integrity. This is explained by an increase in tensile strength, especially at the multicellular vertices of junctions, that is due to mDia1-mediated actin assembly.

A role for myosin VI in retinal pigment epithelium phagocytosis

The retinal pigment epithelium (RPE) is a monolayer of pigmented cells adjacent to the choroid coat, the vascular layer of the eye. Among other functions, these cells are responsible for the phagocytosis of rod and cone cell waste shed from the photoreceptor outer segments. We describe here studies to understand the involvement of the motor protein myosin VI in the trafficking of internalized microspheres by a human retinal pigment epithelium primary cell line (ARPE-19). We perturbed the myosin VI-actin interaction by overexpressing a dominant negative myosin VI construct in these cells. We used single particle tracking to characterize the trajectories of internalized fluorescent microspheres. Analysis of the speed of the microspheres' motions revealed that the magnitude of the average speed over short time scales is reduced in the presence of the dominant negative motor. Analysis of the mean-squared displacement of these trajectories demonstrated that trafficking of phagosomes involves two modes of motion, a rapid, more randomly directed motion that is myosin VI dependent and a slower, more directed motion that is independent of the motor. From these data, we posit that this trafficking process involves an interplay between myosin VI motors, which are involved in motion through the actin periphery of the cell, and microtubule motors.

Multiple myosin motors interact with sodium/potassium-ATPase alpha 1 subunits

The alpha1 (α1) subunit of the sodium/potassium ATPase (i.e., Na+/K+-ATPase α1), the prototypical sodium pump, is expressed in each eukaryotic cell. They pump out three sodium ions in exchange for two extracellular potassium ions to establish a cellular electrochemical gradient important for firing of neuronal and cardiac action potentials. We hypothesized that myosin (myo or myh) motor proteins might interact with Na+/K+-ATPase α1 subunits in order for them to play an important role in the transport and trafficking of sodium pump. To this end immunoassays were performed to determine whether class II non-muscle myosins (i.e., NMHC-IIA/myh9, NMHC-IIB/myh10 or NMHC-IIC/myh14), myosin Va (myoVa) and myosin VI (myoVI) would interact with Na+/K+-ATPase α1 subunits. Immunoprecipitation of myh9, myh10, myh14, myoVa and myoVI from rat brain tissues led to the co-immunoprecipitation of Na+/K+-ATPase α1 subunits expressed there. Heterologous expression studies using HEK293 cells indicated that recombinant myh9, myh10, myh14 and myoVI interact with Na+/K+-ATPase α1 subunits expressed in HEK293 cells. Additional results indicated that loss of tail regions in recombinant myh9, myh10, myh14 and myoVI did not affect their interaction with Na+/K+-ATPase α1 subunits. However, recombinant myh9, myh10 and myh14 mutants having reduced or no actin binding ability, as a result of loss of their actin binding sites, displayed greatly reduced or null interaction with Na+/K+-ATPase α1 subunits. These results suggested the involvement of the actin binding site, but not tail regions, of NMHC-IIs in their interaction with Na+/K+-ATPase α1 subunits. Overall these results suggest a role for these diverse myosins in the trafficking and transport of sodium pump in neuronal and non-neuronal tissues.

Regenerating hair cells in vestibular sensory epithelia from humans.

Human vestibular sensory epithelia in explant culture were incubated in gentamicin to ablate hair cells. Subsequent transduction of supporting cells with ATOH1 using an Ad-2 viral vector resulted in generation of highly significant numbers of cells expressing the hair cell marker protein myosin VIIa. Cells expressing myosin VIIa were also generated after blocking the Notch signalling pathway with TAPI-1 but less efficiently. Transcriptomic analysis following ATOH1 transduction confirmed up-regulation of 335 putative hair cell marker genes, including several downstream targets of ATOH1. Morphological analysis revealed numerous cells bearing dense clusters of microvilli at the apical surfaces which showed some hair cell-like characteristics confirming a degree of conversion of supporting cells. However, no cells bore organised hair bundles and several expected hair cell markers genes were not expressed suggesting incomplete differentiation. Nevertheless, the results show a potential to induce conversion of supporting cells in the vestibular sensory tissues of humans.

Engaging myosin VI tunes motility, morphology and identity in endocytosis.

While unconventional myosins interact with different stages of the endocytic pathway, they are ascribed a transport function that is secondary to the protein complexes that control organelle identity. Endosomes are subject to a dynamic, continuous flux of proteins that control their characteristic properties, including their motility within the cell. Efforts to describe the changes in identity of this compartment have largely focused on the adaptors present on the compartment and not on the motile properties of the compartment itself. In this study, we use a combination of optogenetic and chemical-dimerization strategies to target exogenous myosin VI to early endosomes, and probe its influence on organelle motility, morphology and identity. Our analysis across timescales suggests a model wherein the artificial engagement of myosin VI motility on early endosomes restricts microtubule-based motion, followed by morphological changes characterized by the rapid condensation and disintegration of organelles, ultimately leading to the enhanced overlap of markers that demarcate endosomal compartments. Together, our findings show that synthetic engagement of myosin VI motility is sufficient to alter organelle homeostasis in the endocytic pathway.

Whole-exome sequencing identifies R1279X of MYH6 gene to be associated with congenital heart disease

BackgroundMyosin VI, encoded by MYH6, is expressed dominantly in human cardiac atria and plays consequential roles in cardiac muscle contraction and comprising the cardiac muscle thick filament. It has been reported that the mutations in the MYH6 gene associated with sinus venosus atrial septal defect (ASD type III), hypertrophic (HCM) and dilated (DCM) cardiomyopathies.MethodsTwo patients in an Iranian family have been identified who affected to Congenital Heart Disease (CHD). The male patient, besides CHD, shows that the thyroglossal sinus, refractive errors of the eye and mitral stenosis. The first symptoms emerged at the birth and diagnosis based on clinical features was made at about 5 years. The family had a history of ASD. For recognizing mutated gene (s), whole exome sequencing (WES) was performed for the male patient and variants were analyzed by autosomal dominant inheritance mode.ResultsEventually, by several filtering processes, a mutation in MYH6 gene (NM_002471.3), c.3835C > T; R1279X, was identified as the most likely disease-susceptibility variant and then confirmed by Sanger sequencing in the family. The mutation frequency was checked out in the local databases. This mutation results in the elimination of the 660 amino acids in the C-terminal of Myosin VI protein, including the vital parts of the coiled-coil structure of the tail domain.ConclusionsOur study represents the first case of Sinus venosus defect caused directly by MYH6 stop codon mutation. Our data indicate that by increase haploinsufficiency of myosin VI, c.3835C > T mutation with reduced penetrance could be associated with CHD.