Gas7-deficient mouse reveals roles in motor function and muscle fiber composition during aging

NMJ-related diseases beyond the congenital myasthenic syndromes

Neuromuscular junctions (NMJs) are a special type of chemical synapse that transmits electrical stimuli from motor neurons (MNs) to their innervating skeletal muscle to induce a motor response. They are an ideal model for the study of synapses, given their manageable size and easy accessibility. Alterations in their morphology or function lead to neuromuscular disorders, such as the congenital myasthenic syndromes, which are caused by mutations in proteins located in the NMJ. In this review, we highlight novel potential candidate genes that may cause or modify NMJs-related pathologies in humans by exploring the phenotypes of hundreds of mouse models available in the literature. We also underscore the fact that NMJs may differ between species, muscles or even sexes. Hence the importance of choosing a good model organism for the study of NMJ-related diseases: only taking into account the specific features of the mammalian NMJ, experimental results would be efficiently translated to the clinic.

A Functional SNP in the Promoter of LBX1 Is Associated With the Development of Adolescent Idiopathic Scoliosis Through Involvement in the Myogenesis of Paraspinal Muscles

Previous studies have shown that LBX1 is associated with adolescent idiopathic scoliosis (AIS) in multiple populations. For the first time, rs1322330 located in the putative promoter region of LBX1 was found significantly associated with AIS in the Chinese population [p = 6.08 × 10^–14, odds ratio (OR) = 1.42, 95% confidence interval of 1.03–1.55]. Moreover, the luciferase assay and electrophoretic mobility shift assay supported that the allele A of rs1322330 could down-regulate the expression of LBX1 in the paraspinal muscles of AIS. In addition, silencing LBX1 in the myosatellite cells resulted in significantly inhibited cell viability and myotube formation, which supported an essential role of LBX1 in muscle development of AIS. To summarize, rs1322330 may be a novel functional SNP regulating the expression of LBX1, which was involved in the etiology of AIS possibly via regulation of myogenesis in the paraspinal muscles.

Detection and Visualization of Heterozygosity-Rich Regions and Runs of Homozygosity in Worldwide Sheep Populations

In this study, we chose 17 worldwide sheep populations of eight breeds, which were intensively selected for different purposes (meat, milk, or wool), or locally-adapted breeds, in order to identify and characterize factors impacting the detection of runs of homozygosity (ROH) and heterozygosity-rich regions (HRRs) in sheep. We also applied a business intelligence (BI) tool to integrate and visualize outputs from complementary analyses. We observed a prevalence of short ROH, and a clear distinction between the ROH profiles across populations. The visualizations showed a fragmentation of medium and long ROH segments. Furthermore, we tested different scenarios for the detection of HRR and evaluated the impact of the detection parameters used. Our findings suggest that HRRs are small and frequent in the sheep genome; however, further studies with higher density SNP chips and different detection methods are suggested for future research. We also defined ROH and HRR islands and identified common regions across the populations, where genes related to a variety of traits were reported, such as body size, muscle development, and brain functions. These results indicate that such regions are associated with many traits, and thus were under selective pressure in sheep breeds raised for different purposes. Interestingly, many candidate genes detected within the HRR islands were associated with brain integrity. We also observed a strong association of high linkage disequilibrium pattern with ROH compared with HRR, despite the fact that many regions in linkage disequilibrium were not located in ROH regions.

SOX10-regulated promoter use defines isoform-specific gene expression in Schwann cells

Background

Multicellular organisms adopt various strategies to tailor gene expression to cellular contexts including the employment of multiple promoters (and the associated transcription start sites (TSSs)) at a single locus that encodes distinct gene isoforms. Schwann cells—the myelinating cells of the peripheral nervous system (PNS)—exhibit a specialized gene expression profile directed by the transcription factor SOX10, which is essential for PNS myelination. SOX10 regulates promoter elements associated with unique TSSs and gene isoforms at several target loci, implicating SOX10-mediated, isoform-specific gene expression in Schwann cell function. Here, we report on genome-wide efforts to identify SOX10-regulated promoters and TSSs in Schwann cells to prioritize genes and isoforms for further study.

Results

We performed global TSS analyses and mined previously reported ChIP-seq datasets to assess the activity of SOX10-bound promoters in three models: (i) an adult mammalian nerve; (ii) differentiating primary Schwann cells, and (iii) cultured Schwann cells with ablated SOX10 function. We explored specific characteristics of SOX10-dependent TSSs, which provides confidence in defining them as SOX10 targets. Finally, we performed functional studies to validate our findings at four previously unreported SOX10 target loci: ARPC1A, CHN2, DDR1, and GAS7. These findings suggest roles for the associated SOX10-regulated gene products in PNS myelination.

Conclusions

In sum, we provide comprehensive computational and functional assessments of SOX10-regulated TSS use in Schwann cells. The data presented in this study will stimulate functional studies on the specific mRNA and protein isoforms that SOX10 regulates, which will improve our understanding of myelination in the peripheral nerve.

Gas7 knockout affects PINK1 expression and mitochondrial dynamics in mouse cortical neurons

Dynamic fission and fusion events regulate mitochondrial shape, distribution, and rejuvenation, and proper control of these processes is essential for neuronal homeostasis. Here, we report that Gas7, a known cytoskeleton regulator, controls mitochondrial dynamics within neurons of the central nervous system. In this study, we generated an improved Gas7-knockout mouse and evaluated its mitochondrial phenotype. We first identified Gas7 in mitochondrial fractions from wild-type brain tissue, and observed Gas7 colocalization with mitochondria in primary cortical neurons. In Gas7-deficient brain tissue and neuronal cultures mitochondria were elongated with perinuclear clustering. These morphological abnormalities were associated with increased levels mitochondrial fusion proteins and increased PKA-dependent phosphorylation of Drp-1 in brain tissues, suggesting an imbalance of mitochondrial fusion and fission. Moreover, expression of mitochondrial quality control kinase, PINK1, and PINK1-specific phosphorylation of Mfn-2 (S442), Parkin (S65), and ubiquitin (S65) were all reduced in the knockout cells. Ectopic expression of Gas7 restored mitochondrial morphology and distribution, as well as PINK1 expression in Gas7-null cortical neurons. Collectively, our results introduce a novel role of mouse Gas7 in determining the dynamics, morphology, and intracellular distribution of neuronal mitochondria, which are expected to be required for normal neuronal function.

Growth arrest specific gene 7 is associated with schizophrenia and regulates neuronal migration and morphogenesis

BACKGROUND

Schizophrenia is a highly heritable chronic mental disorder with significant abnormalities in brain function. The neurodevelopmental hypothesis proposes that schizophrenia originates in the prenatal period due to impairments in neuronal developmental processes such as migration and arborization, leading to abnormal brain maturation. Previous studies have identified multiple promising candidate genes that drive functions in neurodevelopment and are associated with schizophrenia. However, the molecular mechanisms of how they exert effects on the pathophysiology of schizophrenia remain largely unknown.

RESULTS

In our research, we identified growth arrest specific gene 7 (GAS7) as a schizophrenia risk gene in two independent Han Chinese populations using a two-stage association study. Functional experiments were done to further explore the underlying mechanisms of the role of Gas7 in cortical development. In vitro, we discovered that Gas7 contributed to neurite outgrowth through the F-BAR domain. In vivo, overexpression of Gas7 arrested neuronal migration by increasing leading process branching, while suppression of Gas7 could inhibit neuronal migration by lengthening leading processes. Through a series of behavioral tests, we also found that Gas7-deficient mice showed sensorimotor gating deficits.

CONCLUSIONS

Our results demonstrate GAS7 as a susceptibility gene for schizophrenia. Gas7 might participate in the pathogenesis of schizophrenia by regulating neurite outgrowth and neuronal migration through its C-terminal F-BAR domain. The impaired pre-pulse inhibition (PPI) of Gas7-deficient mice might mirror the disease-related behavior in schizophrenia.

Growth-Arrest-Specific 7 Gene Regulates Neural Crest Formation and Craniofacial Development in Zebrafish

Growth-arrest-specific 7 (Gas7) is preferentially expressed in the nervous system and plays an important role during neuritogenesis in vertebrates. We recently demonstrated that gas7 is highly expressed in zebrafish neurons, where it regulates neural development. The possibility that gas7 may also regulate the development of other tissues remains to be examined. In this study, we investigate the role of Gas7 in the development of craniofacial tissues. Knockdown of gas7 using morpholino oligomers produced abnormal phenotypes in neural crest (NC) cells and their derivatives. NC-derived cartilage maturation was altered in Gas7 morphants as revealed by aberrant sox9b and dlx2 expression, a phenotype that could be rescued by coinjection of gas7 mRNA. While rhombomere morphology remained normal in Gas7 morphants, we observed reduced expression of the prechondrogenic genes sox9b and dlx2 in cells populating the posterior pharyngeal arches, but the fundamental structure of pharyngeal arches was preserved. In addition, NC cell sublineages that migrate to form neurons, glial cells, and melanocytes were altered in Gas7 morphants as revealed by aberrant expression of neurod, foxd3, and mitfa, respectively. Development of NC progenitors was also examined in Gas7 morphants at 12 hpf, and we observed that the reduction of cell precursors in Gas7 morphants was due to increased apoptosis level. These results indicate that the formation of NC progenitors and derivatives depends on Gas7 expression. Our observations also suggest that Gas7 regulates the formation of NC derivatives constituting the internal tissues of pharyngeal arches, without affecting the fundamental structure of mesodermal-derived pharyngeal arches.

Complex network-driven view of genomic mechanisms underlying Parkinson's disease: analyses in dorsal motor vagal nucleus, locus coeruleus, and substantia nigra

Parkinson's disease (PD)—classically characterized by severe loss of dopaminergic neurons in the substantia nigra pars compacta—has a caudal-rostral progression, beginning in the dorsal motor vagal nucleus and, in a less extent, in the olfactory system, progressing to the midbrain and eventually to the basal forebrain and the neocortex. About 90% of the cases are idiopathic. To study the molecular mechanisms involved in idiopathic PD we conducted a comparative study of transcriptional interaction networks in the dorsal motor vagal nucleus (VA), locus coeruleus (LC), and substantia nigra (SN) of idiopathic PD in Braak stages 4-5 (PD) and disease-free controls (CT) using postmortem samples. Gene coexpression networks (GCNs) for each brain region (patients and controls) were obtained to identify highly connected relevant genes (hubs) and densely interconnected gene sets (modules). GCN analyses showed differences in topology and module composition between CT and PD networks for each anatomic region. In CT networks, VA, LC, and SN hub modules are predominantly associated with neuroprotection and homeostasis in the ageing brain, whereas in the patient's group, for the three brain regions, hub modules are mostly related to stress response and neuron survival/degeneration mechanisms.

DNA copy number variants of known glaucoma genes in relation to primary open-angle glaucoma

PURPOSE

We examined the role of DNA copy number variants (CNVs) of known glaucoma genes in relation to primary open angle glaucoma (POAG).

METHODS

Our study included DNA samples from two studies (NEIGHBOR and GLAUGEN). All the samples were genotyped with the Illumina Human660W_Quad_v1 BeadChip. After removing non-blood-derived and amplified DNA samples, we applied quality control steps based on the mean Log R Ratio and the mean B allele frequency. Subsequently, data from 3057 DNA samples (1599 cases and 1458 controls) were analyzed with PennCNV software. We defined CNVs as those ≥5 kilobases (kb) in size and interrogated by ≥5 consecutive probes. We further limited our investigation to CNVs in known POAG-related genes, including CDKN2B-AS1, TMCO1, SIX1/SIX6, CAV1/CAV2, the LRP12-ZFPM2 region, GAS7, ATOH7, FNDC3B, CYP1B1, MYOC, OPTN, WDR36, SRBD1, TBK1, and GALC.

RESULTS

Genomic duplications of CDKN2B-AS1 and TMCO1 were each found in a single case. Two cases carried duplications in the GAS7 region. Genomic deletions of SIX6 and ATOH7 were each identified in one case. One case carried a TBK1 deletion and another case carried a TBK1 duplication. No controls had duplications or deletions in these six genes. A single control had a duplication in the MYOC region. Deletions of GALC were observed in five cases and two controls.

CONCLUSIONS

The CNV analysis of a large set of cases and controls revealed the presence of rare CNVs in known POAG susceptibility genes. Our data suggest that these rare CNVs may contribute to POAG pathogenesis and merit functional evaluation.

Gas7 is required for mesenchymal stem cell-derived bone development

Mesenchymal stem cells (MSCs) can differentiate into osteoblasts and lead to bone formation in the body. Osteoblast differentiation and bone development are regulated by a network of molecular signals and transcription factors induced by several proteins, including BMP2, osterix, and Runx2. We recently observed that the growth-arrest-specific 7 gene (Gas7) is upregulated during differentiation of human MSCs into osteoblasts. Downregulation of Gas7 using short-hairpin RNA decreased the expression of Runx2, a master regulator of osteogenesis, and its target genes (alkaline phosphatase, type I collagen, osteocalcin, and osteopontin). In addition, knockdown of Gas7 decreased the mineralization of dexamethasone-treated MSCs in culture. Conversely, ectopic expression of Gas7 induced Runx2-dependent transcriptional activity and gene expression leading to osteoblast differentiation and matrix mineralization. Genetic mutations of the Gas7 gene increased body fat levels and decreased bone density in mice. These results showed that Gas7 plays a role in regulating the pathways which are essential for osteoblast differentiation and bone development. In this review, we summarize the involvement of Gas7 in MSC-based osteogenesis and osteoporosis and describe the possible mechanisms responsible for the maintenance of cellular homeostasis in MSCs and osteoblasts.

Genome-wide identification of Sox8-, and Sox9-dependent genes during early post-natal testis development in the mouse

The SOX8 and SOX9 transcription factors are involved in, among others, sex differentiation, male gonad development and adult maintenance of spermatogenesis. Sox8(-/-) mice lacking Sox9 in Sertoli cells fail to form testis cords and cannot establish spermatogenesis. Although genetic and histological data show an important role for these transcription factors in regulating spermatogenesis, it is not clear which genes depend upon them at a genome-wide level. To identify transcripts that respond to the absence of Sox8 in all cells and Sox9 in Sertoli cells we measured mRNA concentrations in testicular samples from mice at 0, 6 and 18 days post-partum. In total, 621 and 629 transcripts were found at decreased or increased levels, respectively, at different time points in the mutant as compared to the control samples. These mRNAs were categorized as preferentially expressed in Sertoli cells or germ cells using data obtained with male and female gonad samples and enriched testicular cell populations. Five candidate genes were validated at the protein level. Furthermore, we identified putative direct SOX8 and SOX9 target genes by integrating predicted SOX-binding sites present in potential regulatory regions upstream of the transcription start site. Finally, we used protein network data to gain insight into the effects on regulatory interactions that occur when Sox8 and Sox9 are absent in developing Sertoli cells. The integration of testicular samples with enriched Sertoli cells, germ cells and female gonads enabled us to broadly distinguish transcripts directly affected in Sertoli cells from others that respond to secondary events in testicular cell types. Thus, combined RNA profiling signals, motif predictions and network data identified putative SOX8/SOX9 target genes in Sertoli cells and yielded insight into regulatory interactions that depend upon these transcription factors. In addition, our results will facilitate the interpretation of genome-wide in vivo SOX8 and SOX9 DNA binding data.