DOCK4 Research Articles

A novel DOCK7 variant as a rare reason for epileptic encephalopathy, cortical blindness, dysmorphic features: A case report and brief review of the literature

Early infantile epileptic encephalopathy 23 (EIEE23; OMIM #615859) is a rare autosomal recessive disorder. It is characterized by refractory seizures, multifocal epileptic activity on electroencephalography, psychomotor development delay, dysmorphic facial features and cortical blindness/visual impairment. DOCK7 is involved in intracellular signaling networks and plays a role in axon formation and neuronal polarization. Function loss of this gene has previously been described in the molecular etiology of EIEE23. Here, we report a boy with a pathogenic novel variant in the DOCK7 gene presenting with, infantile-onset epileptic encephalopathy, severe neurodevelopmental delay, dysmorphic facial features, cortical blindness as well as previously unreported minor dental and extremity anomalies. Few cases with DOCK7 mutations have been reported in the literature. Due to its high genetic heterogeneity and scarcity, it is extremely important to report a novel and specific mutations and their associated clinical phenotypes. Whole exome sequencing revealed a novel pathogenic homozygous frameshift variant which has not been reported (c.5669dup (p.Cys1891ValfsTer2) mutation in the exon 44 of DOCK7).

Genetic variations in DOCK4 contribute to schizophrenia susceptibility in a Chinese cohort: A genetic neuroimaging study

BackgroundEmerging evidence suggests that the DOCK4 gene increases susceptibility to schizophrenia. However, no study has hitherto repeated this association in Chinese, and further investigated the relationship between DOCK4 and clinical symptoms in schizophrenic patients using clinical scales and functional magnetic resonance imaging (fMRI). MethodsIn this study, we genotyped three single nucleotide polymorphisms (SNPs) (rs2074127, rs2217262, and rs2074130) within the DOCK4 gene using a case-control design (including 1289 healthy controls and 1351 patients with schizophrenia). 55 first-episode schizophrenia (FES) patients and 59 healthy participants were divided by the genotypes of rs2074130 into CC and CT+TT groups. We further investigated the association with clinical symptoms and neural characteristics (brain activation/connectivity and nodal network metrics). ResultsOur results showed significant associations between all selected SNPs and schizophrenia (all P < 0.05). In patients, letter fluency and motor speed scores of T allele carriers were significantly higher than the CC group (all P < 0.05). Interestingly, greater brain activity, functional connectivity, and betweenness centrality (BC) in language processing and motor coordination were also observed in the corresponding brain zones in patients with the T allele based on a two-way ANCOVA model. Moreover, a potential positive correlation was found between brain activity/connectivity of these brain regions and verbal fluency and motor speed. ConclusionOur findings suggest that the DOCK4 gene may contribute to the onset of schizophrenia and lead to language processing and motor coordination dysfunction in this patient population from China.

Downregulation of circular RNA circDOCK7 identified from diabetic rats after sleeve gastrectomy contributes to hepatocyte apoptosis through regulating miR-139–3p and MCM3

Sleeve gastrectomy (SG) is the most widely used bariatric procedures globally, which could improve glucose and lipid metabolism dramatically. Circular RNAs (circRNAs) are being increasingly implicated in numerous pathophysiological processes. However, for diabetes mellitus (DM), the expression and function of circRNAs remain largely undetermined, in particular, whether circRNAs mediate the amelioration of DM observed after SG. Using a diabetic rat model, we subjected liver tissue from SG and sham-operated rats to RNA sequencing. Amongst the 103 differentially regulated circRNAs identified in diabetic rats after SG, we focused on circDOCK7, a highly expressed circRNA derived from the back-splicing of the DOCK7 gene. Silencing of circDOCK7 significantly inhibited cellular proliferation and induction of apoptosis in insulin-resistant rat hepatocytes. Further analysis indicated circDOCK7 harbored binding sites for miR-139–3p and regulated the expression of minichromosome maintenance 3 (MCM3) through sequestration of miR-139–3p. Our findings therefore demonstrate a novel regulatory pathway involving circDOCK7 that regulates cellular proliferation and apoptosis through increasing the expression of MCM3. Overall, our study establishes a list of specific circRNAs expressed in diabetic rat liver after SG including circDOCK7 which serve as potential biomarkers and treatment targets for DM patients.

A novel truncating mutation of DOCK7 gene with an early-onset non-encephalopathic epilepsy

A novel truncating mutation of DOCK7 gene with an early-onset non-encephalopathic epilepsy

SNPs associated with body weight and backfat thickness in two pig breeds identified by a genome-wide association study

Growth and fat deposition are important economic traits due to the influence on production in pigs. In this study, a dataset of 1200 pigs with 345,570 SNPs genotyped by sequencing (GBS) was used to conduct a GWAS with single-marker regression method to identify SNPs associated with body weight and backfat thickness (BFT) and to search for candidate genes in Landrace and Yorkshire pigs. A total of 27 and 13 significant SNPs were associated with body weight and BFT, respectively. In the region of 149.85–149.89 Mb on SSC6, the SNP (SSC6: 149876737) for body weight and the SNP (SSC6: 149876507) for BFT were in the same locus region (a gap of 230 bp). Two SNPs were located in the DOCK7 gene, which is a protein-coding gene that plays an important role in pigmentation. Two SNPs located on SSC8: 54567459 and SSC11: 33043081 were found to overlap weight and BFT; however, no candidate gene was found in these regions. In addition, based on other significant SNPs, two positional candidate genes, NSRP1 and CADPS, were proposed to influence weight. In conclusion, this is the first study report using GBS data to identify the significant SNPs for weight and BFT. A total of four particularly interesting SNPs and one potential candidate genes (DOCK7) were found for these traits in domestic pigs. This study improves our knowledge to better understand the complex genetic architecture of weight and BFT, but further validation studies of these candidate loci and genes are recommended in pigs

Spontaneous mutation of Dock7 results in lower trabecular bone mass and impaired periosteal expansion in aged female Misty mice

Misty mice (m/m) have a loss of function mutation in Dock7 gene, a guanine nucleotide exchange factor, resulting in low bone mineral density, uncoupled bone remodeling and reduced bone formation. Dock7 has been identified as a modulator of osteoblast number and in vitro osteogenic differentiation in calvarial osteoblast culture. In addition, m/m exhibit reduced preformed brown adipose tissue innervation and temperature as well as compensatory increase in beige adipocyte markers. While the low bone mineral density phenotype is in part due to higher sympathetic nervous system (SNS) drive in young mice, it is unclear what effect aging would have in mice homozygous for the mutation in the Dock7 gene. We hypothesized that age-related trabecular bone loss and periosteal envelope expansion would be altered in m/m. To test this hypothesis, we comprehensively characterized the skeletal phenotype of m/m at 16, 32, 52, and 78wks of age. When compared to age-matched wild-type control mice (+/+), m/m had lower areal bone mineral density (aBMD) and areal bone mineral content (aBMC). Similarly, both femoral and vertebral BV/TV, Tb.N, and Conn.D were decreased in m/m while there was also an increase in Tb.Sp. As low bone mineral density and decreased trabecular bone were already present at 16wks of age in m/m and persisted throughout life, changes in age-related trabecular bone loss were not observed highlighting the role of Dock7 in controlling trabecular bone acquisition or bone loss prior to 16wks of age. Cortical thickness was also lower in the m/m across all ages. Periosteal and endosteal circumferences were higher in m/m compared to +/+ at 16wks. However, endosteal and periosteal expansion were attenuated in m/m, resulting in m/m having lower periosteal and endosteal circumferences by 78wks of age compared to +/+, highlighting the critical role of Dock7 in appositional bone expansion. Histomorphometry revealed that osteoblasts were nearly undetectable in m/m and marrow adipocytes were elevated 3.5 fold over +/+ (p=0.014). Consistent with reduced bone formation, osteoblast gene expression of Alp, Col1a1, Runx-2, Sp7, and Bglap was significantly decreased in m/m whole bone. Furthermore, markers of osteoclasts were either unchanged or suppressed. Bone marrow stromal cell migration and motility were inhibited in culture and changes in senescence markers suggest that osteoblast function may also be inhibited with loss of Dock7 expression in m/m. Finally, increased Oil Red O staining in m/m ear mesenchymal stem cells during adipogenesis highlights a potential shift of cells from the osteogenic to adipogenic lineages. In summary, loss of Dock7 in the aging m/m resulted in an impairment of periosteal and endocortical envelope expansion, but did not alter age-related trabecular bone loss. These studies establish Dock7 as a critical regulator of both cortical and trabecular bone mass, and demonstrate for the first time a novel role of Dock7 in modulating compensatory changes in the periosteum with aging.

Dock3-NMDA receptor interaction as a target for glaucoma therapy.

Glaucoma is a neurodegenerative disease of the eye and it is one of the major causes of blindness. Glaucoma is usually associated with elevated intraocular pressure (IOP) and the current therapy focuses on reduction of IOP. However, neuroprotective strategies could also be beneficial for treatment of glaucoma because the pathology of the disease involves retinal ganglion cell (RGC) death and damage to the optic nerve. Dedicator of cytokinesis 3 (Dock3) is an atypical guanine exchange factor (GEF) that belongs to a family of Dock proteins, Dock1-11. Dock3 exerts neuroprotective effects on the retina and optic nerve, and studies revealed that some of the Dock3-mediated effects are GEF-independent. One of these mechanisms is that Dock3 directly binds to the GluN2B subunit of the N-methyl-D-aspartate (NMDA) receptor. Upon stimulation by NMDA or optic nerve crush, overexpression of Dock3 promotes internalization and degradation of the NMDA receptor in the retina in vivo. It is suggested that this process is mediated by inhibition of Fyn, a Src family tyrosine kinase. Reduction in NMDA receptor expression results in decreased excitotoxic damage and oxidative stress, thereby promoting RGC survival. In this review, we discuss the therapeutic potential of neuroprotection for glaucoma and the effects of Dock3 on NMDA receptors. We also discuss apoptosis signal-regulating kinase 1 (ASK1), a member of mitogen-activated protein kinase kinase kinase that is a key regulator of cellular responses to oxidative stress, as an innovative therapeutic target for glaucoma.

GW26-e2222 Polymorphisms in the DOCK7 gene and the risks of coronary artery disease and ischemic stroke

GW26-e2222 Polymorphisms in the DOCK7 gene and the risks of coronary artery disease and ischemic stroke

Family-based association study of ZNF533, DOCK4 and IMMP2L gene polymorphisms linked to autism in a northeastern Chinese Han population

A study in a Caucasian population has identified two single-nucleotide polymorphisms (SNPs) in ZNF533, one in DOCK4, and two in IMMP2L, which were all significantly associated with autism. They are located in AUTS1 and AUTS5, which have been identified as autism susceptibility loci in several genome-wide screens. The present study aimed to investigate whether ZNF533, DOCK4, and IMMP2L genes are also associated with autism in a northeastern Chinese Han population. We performed a similar association study using families with three individuals (one autistic child and two unaffected parents). A family-based transmission disequilibrium test (TDT) was used to analyze the results. There were significant associations between autism and the two SNPs of ZNF533 gene (rs11885327: χ(2)=4.5200, P=0.0335; rs1964081: χ(2)=4.2610, P=0.0390) and the SNP of DOCK4 gene (rs2217262: χ(2)=5.3430, P=0.0208). Our data suggest that ZNF533 and DOCK4 genes are linked to a predisposition to autism in the northeastern Chinese Han population.

DOCK4 deletion at 7q31.1 in a de novo acute myeloid leukemia with a normal karyotype

Acute myeloid leukemia with a normal karyotype (NK-AML) has been assigned to an intermediate prognostic risk group. However, there is a marked variability in outcome within this group of AML, suggesting a significant biological and molecular heterogeneity. Chromosomal abnormalities may be cryptic by metaphase cytogenetics, but still have an impact on the process of leukemogenesis and/or the clinical outcome of NK-AML. Therefore, we analyzed the genomic complement of NK-AML cases to search for the presence of submicroscopic genomic imbalances. We applied high-resolution oligo-based aCGH analysis to a cohort of AML patients with a normal karyotype, and FISH to validate the aCGH findings. Relative gene expression levels were examined by qPCR. High-resolution aCGH analysis of 21 NK-AML patients revealed one patient with a rare submicroscopic deletion at 7q31.1. This female patient exhibited a rapid disease progression and a dismal outcome. The deletion was mono-allelic, approximately 189,1 kb in size, and encompassed the major 3' part of the DOCK4 gene. The expression level of the DOCK4 gene in her leukemic cells was decreased when compared to CD34+ cells from healthy controls. When compared to AML patients with -7/del(7q) as the sole chromosomal anomaly, the DOCK4 expression level was found to be similarly low. This is the first report of an acquired partial deletion of the DOCK4 gene in a patient with de novo NK-AML. DOCK4 is a strong tumor suppressor candidate, required for GTPase activation in signal transduction pathways controlling cellular proliferation, adhesion, migration and phagocytosis. Our findings may be relevant for understanding of the process of leukemogenesis and the response to therapy in a subset of NK-AML patients.

Aberrant Expression of DOCK4 Leads to Disruption of the F-Actin Skeleton and Altered Membrane Stability in MDS Erythroblasts and Mature Erythrocytes

AbstractAbstract 924Myelodysplastic syndromes (MDS) are a group of clonal hematopoietic disorders that are commonly characterized by anemia due to ineffective hematopoiesis. Even though a third of patients with MDS may transform to acute leukemias, cytopenias drive morbidity for most patients. Anemia remains a major cause of morbidity from fatigue. Most of the morbidity experienced by such patients is due to low red blood counts and therefore studies on the molecular pathogenesis of dysplastic erythropoiesis leading to anemia are critically needed. We have identified DOCK4, an important cofactor for various GTPases located on the chromosome 7q segment as a novel silenced gene in MDS and show that it's down regulation leads to disruption of normal erythropoiesis.In an attempt to uncover genes aberrantly expressed in MDS, we initially performed an integrative genomic analysis of primary hematopoietic cells from MDS patients. These studies revealed that DOCK4 is significantly under-expressed and hypermethylated in MDS stem and progenitor cells. Immunohistochemcial analysis revealed significantly reduced levels of DOCK4 in MDS erythroblasts. We then evaluated DOCK4 expression in a large published cohort of MDS gene expression datasets (N=183) and found that DOCK4 expression was strikingly reduced in the subset of 55 MDS patients with refractory anemia (RA; P value = 0.006). The RA subset of patients only has isolated anemia as the clinical presentation and has no apparent abnormalities in white cells or platelets. This association strongly alludes to a role of DOCK4 down-regulation in the erythroid dysplasia and anemia seen in this disease. Inorder to elucidate the functional implications of aberrant DOCK4 expression during erythropoiesis we used a dynamic model of human erythropoiesis to determine normal expression pattern during terminal differentiation and the impact of silencing DOCK4 expression on healthy primary erythroblasts. These studies revealed that DOCK4 is highly expressed during late stages of normal erythropoiesis and knockdown of DOCK4 in primary erythroblasts disrupted the F-actin skeleton. We then examined F-actin skeletal disruption in CD34+ derived erythroblasts from MDS patients. In order to quantify the extent of actin filament disruption directly in patient derived erythroblasts we first developed an assay based on multispectral flow cytometry (ImageStream™). This assay not only allowed us to visualize individually F-actin-stained cells but also allowed us to determine the percentages of cells in a given sample that contained shorter fragmented F-actin. These experiments revealed that approximately 85% of the cells in MDS patients with -7q deletion and/or hypermethylated promoter region in the DOCK4 gene contained shorter disrupted actin compared to the healthy controls that showed only 10% of the cells with disrupted F-actin. The level of F-actin disruption in healthy samples treated with cytochalasin D, an inhibitor of actin polymerization was 90%. We then examined the membrane stability of -7q MDS erythrocytes by performing osmotic fragility assays and found that these patients possessed erythrocytes that were more fragile compared to healthy erythrocytes. Based on these results we conclude that DOCK4 is an important signaling intermediate that is instrumental in maintaining erythroblast membrane homeostasis and silencing of DOCK4 in MDS contributes to anemia. Disclosures:No relevant conflicts of interest to declare.

DOCK4 and CEACAM21 as novel schizophrenia candidate genes in the Jewish population

It is well accepted that schizophrenia has a strong genetic component. Several genome-wide association studies (GWASs) of schizophrenia have been published in recent years; most of them population based with a case-control design. Nevertheless, identifying the specific genetic variants which contribute to susceptibility to the disorder remains a challenging task. A family-based GWAS strategy may be helpful in the identification of schizophrenia susceptibility genes since it is protected against population stratification, enables better accounting for genotyping errors and is more sensitive for identification of rare variants which have a very low frequency in the general population. In this project we implemented a family-based GWAS of schizophrenia in a sample of 107 Jewish-Israeli families. We found one genome-wide significant association in the intron of the DOCK4 gene (rs2074127, p value=1.134×10⁻⁷) and six additional nominally significant association signals with p<1×10⁻⁵. One of the top single nucleotide polymorphisms (p<1×10⁻⁵) which is located in the predicted intron of the CEACAM21 gene was significantly replicated in independent family-based sample of Arab-Israeli origin (rs4803480: p value=0.002; combined p value=9.61×10⁻⁸), surviving correction for multiple testing. Both DOCK4 and CEACAM21 are biologically reasonable candidate genes for schizophrenia although generalizability of the association of DOCK4 with schizophrenia should be investigated in further studies. In addition, gene-wide significant associations were found within three schizophrenia candidate genes: PGBD1, RELN and PRODH, replicating previously reported associations. By application of a family-based strategy to GWAS, our study revealed new schizophrenia susceptibility loci in the Jewish-Israeli population.

Knockdown of Dock7 &amp;lt;i&amp;gt;in vivo&amp;lt;/i&amp;gt; specifically affects myelination by Schwann cells and increases myelin thickness in sciatic nerves without affecting axon thickness

During development of the peripheral nervous system (PNS), Schwann cells (SCs) wrap individual axons to form myelin sheaths, which act as surrounding insulators and markedly enhance the propagation of the action potential. In peripheral neuropathies such as Guillain-Barré syndrome (GBS) and inherited demyelinating Charcot-Marie-Tooth (CMT) disease and diabetic neuropathies, chronic demyelination and defective remyelination are repeated, causing more severe neuropathies. It is thus thought that development of a drug that promotes proper myelination with minimal side effects could provide an effective therapy for these diseases. As yet, however, little is known about therapeutic target molecules and genetically-modified mice for testing such approaches. We previously cloned the dock7 gene and characterized Dock7 as the regulator controlling SC myelination; however, an important issue, whether knockdown of Dock7 specifically affects myelination by SCs but not leaves neurons unaffected, has remained unclear. Here, we generate newly-produced transgenic mice harboring short-hairpin RNA (shRNA) targeting Dock7. We also describe that Dock7 shRNA transgenic mice exhibit enhanced myelin thickness without affecting axon thickness in sciatic nerves of the PNS, as reduced thickness of the axon diameter is the primary indicator of denatured neurons. Similarly, purified in vitro SC-neuronal cocultures established from transgenic mice exhibit enhanced formation of myelin segments, suggesting that knockdown of Dock7 promotes myelination by SCs. Collectively, Dock7 knockdown specifically affects SC myelination in sciatic nerves, providing evidence that Dock7 may be a promising drug-target-specific molecules for developing a therapy for peripheral neuropathies that aims to enhance myeliantion.