FRG1, a gene in the FSH muscular dystrophy region on human chromosome 4q35, is highly conserved in vertebrates and invertebrates

Unveiling FRG1's DNA repair role in breast cancer

The FRG1(FSHD region gene 1) gene has emerged as a pivotal tumor suppressor in both breast and prostate cancer. HPF1 (Histone PARylation Factor 1), a gene crucial in the base excision repair (BER) mechanism for single-stranded DNA (ssDNA) lesions, showcases a robust correlation with FRG1. This implies that FRG1 might have the capacity to influence BER via HPF1, potentially playing a role in tumorigenesis. Using a comprehensive approach that integrates in-silico analyses involving differential gene expression, KEGG (Kyoto Encyclopedia of Genes and Genomes), GO (Gene Ontology), and STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) databases, we unravelled the intricate network of genes and pathways influenced by FRG1, which includes BER. Our linear regression analysis unveiled a positive relationship between FRG1 and key genes crucial for BER. Notably, breast cancer patients with low FRG1 expression exhibited a significantly higher frequency of mutation in TP53. To enhance the accuracy of our analysis, we conducted qRT-PCR assays, which demonstrated that FRG1 affects the transcription of DNA base excision repair genes, showing differential expression in breast cancer cells. Moreover, through the Alkaline Comet Assay, a technique that quantifies DNA damage at the single-cell level, we observed diminished DNA repair capabilities when FRG1 levels are low. Risk scores were calculated using the Cox regression coefficients, and we found notable differences in Overall Survival (OS) and mRNA expression of DEGs in the low and high-risk groups. In summary, our findings shed light on the pivotal role of FRG1 in maintaining DNA repair efficiency within breast cancer cells.

Role of FRG1 in predicting the overall survivability in cancers using multivariate based optimal model

FRG1 has a role in tumorigenesis and angiogenesis. Our preliminary analysis showed that FRG1 mRNA expression is associated with overall survival (OS) in certain cancers, but the effect varies. In cervix and gastric cancers, we found a clear difference in the OS between the low and high FRG1 mRNA expression groups, but the difference was not prominent in breast, lung, and liver cancers. We hypothesized that FRG1 expression level could affect the functionality of the correlated genes or vice versa, which might mask the effect of a single gene on the OS analysis in cancer patients. We used the multivariate Cox regression, risk score, and Kaplan Meier analyses to determine OS in a multigene model. STRING, Cytoscape, HIPPIE, Gene Ontology, and DAVID (KEGG) were used to deduce FRG1 associated pathways. In breast, lung, and liver cancers, we found a distinct difference in the OS between the low and high FRG1 mRNA expression groups in the multigene model, suggesting an independent role of FRG1 in survival. Risk scores were calculated based upon regression coefficients in the multigene model. Low and high-risk score groups showed a significant difference in the FRG1 mRNA expression level and OS. HPF1, RPL34, and EXOSC9 were the most common genes present in FRG1 associated pathways across the cancer types. Validation of the effect of FRG1 mRNA expression level on these genes by qRT-PCR supports that FRG1 might be an upstream regulator of their expression. These genes may have multiple regulators, which also affect their expression, leading to the masking effect in the survival analysis. In conclusion, our study highlights the role of FRG1 in the survivability of cancer patients in tissue-specific manner and the use of multigene models in prognosis.

Analysis of the genomic landscape of yolk sac tumors reveals mechanisms of evolution and chemoresistance

Yolk sac tumors (YSTs) are a major histological subtype of malignant ovarian germ cell tumors with a relatively poor prognosis. The molecular basis of this disease has not been thoroughly characterized at the genomic level. Here we perform whole-exome and RNA sequencing on 41 clinical tumor samples from 30 YST patients, with distinct responses to cisplatin-based chemotherapy. We show that microsatellite instability status and mutational signatures are informative of chemoresistance. We identify somatic driver candidates, including significantly mutated genes KRAS and KIT and copy-number alteration drivers, including deleted ARID1A and PARK2, and amplified ZNF217, CDKN1B, and KRAS. YSTs have very infrequent TP53 mutations, whereas the tumors from patients with abnormal gonadal development contain both KRAS and TP53 mutations. We further reveal a role of OVOL2 overexpression in YST resistance to cisplatin. This study lays a critical foundation for understanding key molecular aberrations in YSTs and developing related therapeutic strategies.

Reduced FRG1 expression promotes prostate cancer progression and affects prostate cancer cell migration and invasion

BACKGROUND

Prostate cancer is the most common form of cancer in males and accounts for high cancer related deaths. Therapeutic advancement in prostate cancer has not been able to reduce the mortality burden of prostate cancer, which warrants further research. FRG1 which affects angiogenesis and cell migration in Xenopus, can be a potential player in tumorigenesis. In this study, we investigated the role of FRG1 in prostate cancer progression.

METHODS

Immunohistochemistry was performed to determine FRG1 expression in patient samples. FRG1 expression perturbation was done to investigate the effect of FRG1 on cell proliferation, migration and invasion, in DU145, PC3 and LNCaP cells. To understand the mechanism, we checked expression of various cytokines and MMPs by q-RT PCR, signaling molecules by western blot, in FRG1 perturbation sets. Results were validated by use of pharmacological inhibitor and activator and, western blot.

RESULTS

In prostate cancer tissue, FRG1 levels were significantly reduced, compared to the uninvolved counterpart. FRG1 expression showed variable effect on PC3 and DU145 cell proliferation. FRG1 levels consistently affected cell migration and invasion, in both DU145 and PC3 cells. Ectopic expression of FRG1 led to significant reduction in cell migration and invasion in both DU145 and PC3 cells, reverse trends were observed with FRG1 knockdown. In androgen receptor positive cell line LNCaP, FRG1 doesn't affect any of the cell properties. FRG1 knockdown led to significantly enhanced expression of GM-CSF, MMP1, PDGFA and CXCL1, in PC3 cells and, in DU145, it led to higher expression of GM-CSF, MMP1 and PLGF. Interestingly, FRG1 knockdown in both the cell lines led to activation of p38 MAPK. Pharmacological activation of p38 MAPK led to increase in the expression of GM-CSF and PLGF in DU145 whereas in PC3 it led to enhanced expression of GM-CSF, MMP1 and CXCL1. On the other hand, inhibition of p38 MAPK led to reduction in the expression of above mentioned cytokines.

CONCLUSION

FRG1 expression is reduced in prostate adenocarcinoma tissue. FRG1 expression affects migration and invasion in AR negative prostate cancer cells through known MMPs and cytokines, which may be mediated primarily via p38 MAPK activation.

Muscular Dystrophy Model

Muscular dystrophy (MD) is a group of muscle weakness disease involving in inherited genetic conditions. MD is caused by mutations or alteration in the genes responsible for the structure and functioning of muscles. There are many different types of MD which have a wide range from mild symptoms to severe disability. Some types involve the muscles used for breathing which eventually affect life expectancy. This chapter provides an overview of the MD types, its gene mutations, and the Drosophila MD models. Specifically, the Duchenne muscular dystrophy (DMD), the most common form of MD, will be thoroughly discussed including Dystrophin genes, their isoforms, possible mechanisms, and signaling pathways of pathogenesis.

Increased FSHD region gene1 expression reduces in vitro cell migration, invasion, and angiogenesis, ex vivo supported by reduced expression in tumors

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is a candidate gene for FSHD. FRG1 regulates various muscle-related functions, but studies have proposed its role in development and angiogenesis also, where it is involved with tumor-associated molecules. Therefore, we decided to look into its role in tumor progression, tumor angiogenesis, and its impact on cellular properties. Cell proliferation, migration, invasion and in vitro angiogenesis assays were performed to decipher the effect of FRG1 on endothelial and epithelial cell functions. Q-RT PCR was done for human embyonic kidney (HEK293T) cells with altered FRG1 levels to identify associated molecules. Further, immunohistochemistry was done to identify FRG1 expression levels in various cancers and its association with tumor angiogenesis. Subsequently, inference was drawn from Oncomine and Kaplan-Meier plotter analysis, for FRG1 expression in different cancers. Ectopic expression of FRG1 affected cell migration and invasion in both HEK293T and human umbilical vein endothelial cells (HUVECs). In HUVECs, FRG1 overexpression led to reduced angiogenesis in vitro No effect was observed in cell proliferation in both the cell types. Q-RT PCR data revealed reduction in granulocyte-colony stimulating factor (G-CSF) expression with FRG1 overexpression and increased expression of matrix metalloproteinase 10 (MMP10) with FRG1 knockdown. Immunohistochemistry analysis showed reduced FRG1 levels in tumors which were supported by in silico analysis data. These findings suggest that reduction in FRG1 expression in gastric, colon and oral cavity tumor might have a role in tumor progression, by regulating cell migration and invasiveness. To elucidate a better understanding of molecular signaling involving FRG1 in angiogenesis regulation, further study is required.

Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral Muscular Dystrophy is a common form of muscular dystrophy that presents clinically with progressive weakness of the facial, scapular, and humeral muscles, with later involvement of the trunk and lower extremities. While typically inherited as autosomal dominant, facioscapulohumeral muscular dystrophy (FSHD) has a complex genetic and epigenetic etiology that has only recently been well described. The most prevalent form of the disease, FSHD1, is associated with the contraction of the D4Z4 microsatellite repeat array located on a permissive 4qA chromosome. D4Z4 contraction allows epigenetic derepression of the array, and possibly the surrounding 4q35 region, allowing misexpression of the toxic DUX4 transcription factor encoded within the terminal D4Z4 repeat in skeletal muscles. The less common form of the disease, FSHD2, results from haploinsufficiency of the SMCHD1 gene in individuals carrying a permissive 4qA allele, also leading to the derepression of DUX4, further supporting a central role for DUX4. How DUX4 misexpression contributes to FSHD muscle pathology is a major focus of current investigation. Misexpression of other genes at the 4q35 locus, including FRG1 and FAT1, and unlinked genes, such as SMCHD1, has also been implicated as disease modifiers, leading to several competing disease models. In this review, we describe recent advances in understanding the pathophysiology of FSHD, including the application of MRI as a research and diagnostic tool, the genetic and epigenetic disruptions associated with the disease, and the molecular basis of FSHD. We discuss how these advances are leading to the emergence of new approaches to enable development of FSHD therapeutics. © 2017 American Physiological Society. Compr Physiol 7:1229-1279, 2017.

Current status and future prospect of FSHD region gene 1

FSHD region gene 1 (FRG1), as the name suggests, is the primary candidate gene for fascioscapulohumeral muscular dystrophy disease. It seemingly affects muscle physiology in normal individuals but in FSHD, where it is found to be highly upregulated, might be involved in disruption of face, scapula and humeral skeletal muscle. Literature on FRG1, reviewed from 1996 to 2016, reveals that it is primarily associated with muscle development and maintenance. Approximately 75% of FSHD patients also show vascular abnormalities indicating that FRG1 might have some part to play in these abnormalities. Research involving vasculature in X. laevis larvae shows that FRG1 positively affects normal vasculature. Few of the well-established angiogenic regulators seem to get affected by abnormal expression level of FRG1. Its primary localization in sub nuclear structures like Cajal bodies and nuclear speckles indicates regulation of the above-mentioned factors by transcriptional and post-transcriptional machineries, but in-depth studies need to be done to conclude a clear statement. In this review, we have attempted to present all the work done on FRG1, all the lacunas which need to be unraveled, and hypothesized a model for our readers to get an insight into its molecular mechanism.

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) expression and possible function in mouse tooth germ development

Abnormal expression of Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is involved in the pathogenesis of FSHD. FRG1 is also important for the normal muscular and vascular development. Our previous study showed that FRG1 is one of the highly expressed genes in the mandible on embryonic day 10.5 (E10.5) than on E12.0. In this study, we investigated the temporospatial expression pattern of FRG1 mRNA and protein during the development of the mouse lower first molar, and also evaluated the subcellular localization of the FRG1 protein in mouse dental epithelial (mDE6) cells. The FRG1 expression was identified in the dental epithelial and mesenchymal cells at the initiation and bud stages. It was detected in the inner enamel epithelium at the cap and early bell stages. At the late bell and root formation stages, these signals were detected in ameloblasts and odontoblasts during the formation of enamel and dentin matrices, respectively. The FRG1 protein was localized in the cytoplasm in the mouse tooth germ in vivo, while FRG1 was detected predominantly in the nucleus and faintly in the cytoplasm in mDE6 cells in vitro. In mDE6 cells treated with bone morphogenetic protein 4 (BMP4), the protein expression of FRG1 increased in cytoplasm, suggesting that FRG1 may translocate to the cytoplasm. These findings suggest that FRG1 is involved in the morphogenesis of the tooth germ, as well as in the formation of enamel and dentin matrices and that FRG1 may play a role in the odontogenesis in the mouse following BMP4 stimulation.

Transgenic Drosophila for Investigating DUX4 and FRG1, Two Genes Associated with Facioscapulohumeral Muscular Dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is typically an adult onset dominant myopathy. Epigenetic changes in the chromosome 4q35 region linked to both forms of FSHD lead to a relaxation of repression and increased somatic expression of DUX4-fl (DUX4-full length), the pathogenic alternative splicing isoform of the DUX4 gene. DUX4-fl encodes a transcription factor expressed in healthy testis and pluripotent stem cells; however, in FSHD, increased levels of DUX4-fl in myogenic cells lead to aberrant regulation of target genes. DUX4-fl has proven difficult to study in vivo; thus, little is known about its normal and pathogenic roles. The endogenous expression of DUX4-fl in FSHD-derived human muscle and myogenic cells is extremely low, exogenous expression of DUX4-fl in somatic cells rapidly induces cytotoxicity, and, due in part to the lack of conservation beyond primate lineages, viable animal models based on DUX4-fl have been difficult to generate. By contrast, the FRG1 (FSHD region gene 1), which is linked to FSHD, is evolutionarily conserved from invertebrates to humans, and has been studied in several model organisms. FRG1 expression is critical for the development of musculature and vasculature, and overexpression of FRG1 produces a myopathic phenotype, yet the normal and pathological functions of FRG1 are not well understood. Interestingly, DUX4 and FRG1 were recently linked when the latter was identified as a direct transcriptional target of DUX4-FL. To better understand the pathways affected in FSHD by DUX4-fl and FRG1, we generated transgenic lines of Drosophila expressing either gene under control of the UAS/GAL4 binary system. Utilizing these lines, we generated screenable phenotypes recapitulating certain known consequences of DUX4-fl or FRG1 overexpression. These transgenic Drosophila lines provide resources to dissect the pathways affected by DUX4-fl or FRG1 in a genetically tractable organism and may provide insight into both muscle development and pathogenic mechanisms in FSHD.

FHL1 reduces dystrophy in transgenic mice overexpressing FSHD muscular dystrophy region gene 1 (FRG1)

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal-dominant disease with no effective treatment. The genetic cause of FSHD is complex and the primary pathogenic insult underlying the muscle disease is unknown. Several disease candidate genes have been proposed including DUX4 and FRG1. Expression analysis studies of FSHD report the deregulation of genes which mediate myoblast differentiation and fusion. Transgenic mice overexpressing FRG1 recapitulate the FSHD muscular dystrophy phenotype. Our current study selectively examines how increased expression of FRG1 may contribute to myoblast differentiation defects. We generated stable C2C12 cell lines overexpressing FRG1, which exhibited a myoblast fusion defect upon differentiation. To determine if myoblast fusion defects contribute to the FRG1 mouse dystrophic phenotype, this strain was crossed with skeletal muscle specific FHL1-transgenic mice. We previously reported that FHL1 promotes myoblast fusion in vitro and FHL1-transgenic mice develop skeletal muscle hypertrophy. In the current study, FRG1 mice overexpressing FHL1 showed an improvement in the dystrophic phenotype, including a reduced spinal kyphosis, increased muscle mass and myofiber size, and decreased muscle fibrosis. FHL1 expression in FRG1 mice, did not alter satellite cell number or activation, but enhanced myoblast fusion. Primary myoblasts isolated from FRG1 mice showed a myoblast fusion defect that was rescued by FHL1 expression. Therefore, increased FRG1 expression may contribute to a muscular dystrophy phenotype resembling FSHD by impairing myoblast fusion, a defect that can be rescued by enhanced myoblast fusion via expression of FHL1.

AAV6-mediated systemic shRNA delivery reverses disease in a mouse model of facioscapulohumeral muscular dystrophy

Treatment of dominantly inherited muscle disorders remains a difficult task considering the need to eliminate the pathogenic gene product in a body-wide fashion. We show here that it is possible to reverse dominant muscle disease in a mouse model of facioscapulohumeral muscular dystrophy (FSHD). FSHD is a common form of muscular dystrophy associated with a complex cascade of epigenetic events following reduction in copy number of D4Z4 macrosatellite repeats located on chromosome 4q35. Several 4q35 genes have been examined for their role in disease, including FRG1. Overexpression of FRG1 causes features related to FSHD in transgenic mice and the FRG1 mouse is currently the only available mouse model of FSHD. Here we show that systemic delivery of RNA interference expression cassettes in the FRG1 mouse, after the onset of disease, led to a dose-dependent long-term FRG1 knockdown without signs of toxicity. Histological features including centrally nucleated fibers, fiber size reduction, fibrosis, adipocyte accumulation, and inflammation were all significantly improved. FRG1 mRNA knockdown resulted in a dramatic restoration of muscle function. Through RNA interference (RNAi) expression cassette redesign, our method is amenable to targeting any pathogenic gene offering a viable option for long-term, body-wide treatment of dominant muscle disease in humans.

Facioscapulohumeral muscular dystrophy region gene 1 is a dynamic RNA-associated and actin-bundling protein

FSHD region gene 1 (FRG1) is a dynamic nuclear and cytoplasmic protein that, in skeletal muscle, shows additional localization to the sarcomere. Maintaining appropriate levels of FRG1 protein is critical for muscular and vascular development in vertebrates; however, its precise molecular function is unknown. This study investigates the molecular functions of human FRG1, along with mouse FRG1 and Xenopus frg1, using molecular, biochemical, and cellular-biological approaches, to provide further insight into its roles in vertebrate development. The nuclear fraction of the endogenous FRG1 is localized in nucleoli, Cajal bodies, and actively transcribed chromatin; however, contrary to overexpressed FRG1, the endogenous FRG1 is not associated with nuclear speckles. We characterize the nuclear and nucleolar import of FRG1, the potential effect of phosphorylation, and its interaction with the importin karyopherin α2. Consistent with a role in RNA biogenesis, human FRG1 is associated with mRNA in vivo and invitro, interacts directly with TAP (Tip-associated protein; the major mRNA export receptor), and is a dynamic nuclear-cytoplasmic shuttling protein supporting a function for FRG1 in mRNA transport. Biochemically, we characterize FRG1 actin binding activity and show that the cytoplasmic pool of FRG1 is dependent on an intact actin cytoskeleton for its localization. These data provide the first biochemical activities (actin binding and RNA binding) for human FRG1 and the characterization of the endogenous human FRG1, together indicating that FRG1 is involved in multiple aspects of RNA biogenesis, including mRNA transport and, potentially, cytoplasmic mRNA localization.

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is a dynamic nuclear and sarcomeric protein

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is a candidate gene for mediating FSHD pathophysiology, however, very little is known about the endogenous FRG1 protein. This study uses immunocytochemistry (ICC) and histology to provide insight into FRG1's role in vertebrate muscle development and address its potential involvement in FSHD pathophysiology. In cell culture, primary myoblast/myotube cultures, and mouse and human muscle sections, FRG1 showed distinct nuclear and cytoplasmic localizations and nuclear shuttling assays indicated the subcellular pools of FRG1 are linked. During myoblast differentiation, FRG1's subcellular distribution changed dramatically with FRG1 eventually associating with the matured Z-discs. This Z-disc localization was confirmed using isolated mouse myofibers and found to be maintained in adult human skeletal muscle biopsies. Thus, FRG1 is not likely involved in the initial assembly and alignment of the Z-disc but may be involved in sarcomere maintenance or signaling. Further analysis of human tissue showed FRG1 is strongly expressed in arteries, veins, and capillaries, the other prominently affected tissue in FSHD. Overall, we show that in mammalian cells, FRG1 is a dynamic nuclear and cytoplasmic protein, however in muscle, FRG1 is also a developmentally regulated sarcomeric protein suggesting FRG1 may perform a muscle-specific function. Thus, FRG1 is the only FSHD candidate protein linked to the muscle contractile machinery and may address why the musculature and vasculature are specifically susceptible in FSHD.

Facioscapulohumeral dystrophy and scapuloperoneal syndromes

Facioscapulohumeral dystrophy (FSHD) is the third most common muscular dystrophy. It is named for its characteristic involvement of the muscles of the face and upper arm. It is present worldwide, with a prevalence of around 4 per 100000 and an incidence of about 1 in 20000. Overall lifespan is not affected significantly. The scapuloperoneal syndrome is a rarer presentation that may cause some confusion. FSHD is an autosomal dominant condition. The molecular genetics of FSHD are complex, with current understanding focusing on epigenetic effects related to contraction-dependent (FSHD1) and contraction-independent (FSHD2) effects of a hypomethylated repeat sequence (D4Z4), in the presence of a specific 4qA161 phenotype. Molecular genetic diagnosis is available based on these findings, but with some complexities which may lead to false-negative results on routine laboratory investigation. No medication has been demonstrated to alter the clinical course of the disease significantly. A range of supportive measures may be applied. This chapter reviews the epidemiology, pathogenesis, genetics, clinical features, investigation, prognosis, and management of patients with FSHD and the scapuloperoneal syndrome.

The cell biology of disease: FSHD: copy number variations on the theme of muscular dystrophy

In humans, copy number variations (CNVs) are a common source of phenotypic diversity and disease susceptibility. Facioscapulohumeral muscular dystrophy (FSHD) is an important genetic disease caused by CNVs. It is an autosomal-dominant myopathy caused by a reduction in the copy number of the D4Z4 macrosatellite repeat located at chromosome 4q35. Interestingly, the reduction of D4Z4 copy number is not sufficient by itself to cause FSHD. A number of epigenetic events appear to affect the severity of the disease, its rate of progression, and the distribution of muscle weakness. Indeed, recent findings suggest that virtually all levels of epigenetic regulation, from DNA methylation to higher order chromosomal architecture, are altered at the disease locus, causing the de-regulation of 4q35 gene expression and ultimately FSHD.

Facioscapulohumeral muscular dystrophy region gene-1 (FRG-1) is an actin-bundling protein associated with muscle-attachment sites

In vertebrates, overexpression of facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) recapitulates the pathophysiology exhibited by FSHD patients, although the role of FRG1 in FSHD remains controversial and no precise function for FRG1 has been described in any organism. To gain insight into the function and potential role of FRG1 in FSHD, we analyzed the highly conserved Caenorhabditis elegans ortholog, frg-1. C. elegans body-wall muscles contain two distinct subcellular pools of FRG-1: nuclear FRG-1, concentrated in the nucleoli; and cytoplasmic FRG-1, associated with the Z-disk and costamere-like structures known as dense bodies. Functionally, we demonstrate that FRG-1 is an F-actin-bundling protein, consistent with its localization to dense bodies; this activity is conserved in human FRG1. This is particularly intriguing because it places FRG-1 along side the list of dense-body components whose vertebrate orthologs are involved in the myriad myopathies associated with disrupted costameres and Z-disks. Interestingly, overexpressed FRG-1 preferentially accumulates in the nucleus and, when overexpressed specifically from the frg-1 promoter, disrupts the adult ventral muscle structure and organization. Together, these data further support a role for FRG1 overexpression in FSHD pathophysiology and reveal the previously unsuspected direct involvement of FRG-1 in muscle structure and integrity.

Muscular dystrophy candidate gene FRG1 is critical for muscle development

The leading candidate gene responsible for facioscapulohumeral muscular dystrophy (FSHD) is FRG1 (FSHD region gene 1). However, the correlation of altered FRG1 expression levels with disease pathology has remained controversial and the precise function of FRG1 is unknown. Here, we carried out a detailed analysis of the normal expression patterns and effects of FRG1 misexpression during vertebrate embryonic development using Xenopus laevis. We show that frg1 is expressed in and essential for the development of the tadpole musculature. FRG1 morpholino injection disrupted myotome organization and led to inhibited myotome growth, while elevated FRG1 led to abnormal epaxial and hypaxial muscle formation. Thus, maintenance of normal FRG1 levels is critical for proper muscle development, supportive of FSHD disease models whereby misregulation of FRG1 plays a causal role underlying the pathology exhibited in FSHD patients. Developmental Dynamics 238:1502-1512, 2009. (c) 2008 Wiley-Liss, Inc.

FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy

The genetic lesion that is diagnostic for facioscapulohumeral muscular dystrophy (FSHD) results in an epigenetic misregulation of gene expression, which ultimately leads to the disease pathology. FRG1 (FSHD region gene 1) is a leading candidate for a gene whose misexpression might lead to FSHD. Because FSHD pathology is most prominent in the musculature, most research and therapy efforts focus on muscle cells. Previously, using Xenopus development as a model, we showed that altering frg1 expression levels systemically leads to aberrant muscle development, illustrating the potential for aberrant FRG1 levels to disrupt the musculature. However, 50-75% of FSHD patients also exhibit retinal vasculopathy and FSHD muscles have increased levels of vascular- and endothelial-related FRG1 transcripts, illustrating an underlying vascular component to the disease. To date, no FSHD candidate gene has been proposed to affect the vasculature. Here, we focus on a role for FRG1 expression in the vasculature. We found that endogenous frg1 is expressed in both the developing and adult vasculature in Xenopus. Furthermore, expression of FRG1 was found to be essential for the development of the vasculature, as a knockdown of FRG1 resulted in decreased angiogenesis and reduced expression of the angiogenic regulator DAB2. Conversely, tadpoles subjected to frg1 overexpression displayed the pro-angiogenic phenotypes of increased blood vessel branching and dilation of blood vessels, and developed edemas, suggesting that their circulation was disrupted. Thus, the systemic upregulation of the FRG1 protein shows the potential for acquiring a disrupted vascular phenotype, providing the first link between a FSHD candidate gene and the vascular component of FSHD pathology. Overall, in conjunction with our previous analysis, we show that FRG1 overexpression is capable of disrupting both the musculature and vasculature, recapitulating the two most prominent features of FSHD.

Epigenetic mechanisms of facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) seems to be caused by a complex epigenetic disease mechanism as a result of contraction of the polymorphic macrosatellite repeat D4Z4 on chromosome 4qter. Currently, the exact mechanism causing the FSHD phenotype is still not elucidated. In this review, we discuss the genetic and epigenetic changes observed in patients with FSHD and the possible disease mechanisms that may be associated with FSHD pathogenesis.

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), a dominantly inherited disorder, is the third most common dystrophy after Duchenne and myotonic muscular dystrophy. No known effective treatments exist for FSHD. The lack of an understanding of the underlying pathophysiology remains an obstacle in the development of targeted therapeutic interventions. The genetic defect is a loss of a critical number of a repetitive element (D4Z4) in the 4q subtelomeric region. The loss of the repeats results in specific changes in chromatin structure, although neither the molecular nor the cellular consequences of this change are known. Nevertheless, these epigenetic changes in chromatin structure offer a potential therapeutic target. This review discusses current management strategies in FSHD as well as potential therapeutic interventions to slow down or reverse the progressive muscle atrophy and weakness.

FRG1P-mediated aggregation of proteins involved in pre-mRNA processing

FRG1 is considered a candidate gene for facioscapulohumeral muscular dystrophy (FSHD) based on its location at chromosome 4qter and its upregulation in FSHD muscle. The FRG1 protein (FRG1P) localizes to nucleoli, Cajal bodies (and speckles), and has been suggested to be a component of the human spliceosome but its exact function is unknown. Recently, transgenic mice overexpressing high levels of FRG1P in skeletal muscle were described to present with muscular dystrophy. Moreover, upregulation of FRG1P was demonstrated to correlate with missplicing of specific pre-mRNAs. In this study, we have combined colocalization studies with yeast two-hybrid screens to identify proteins that associate with FRG1P. We demonstrate that artificially induced nucleolar aggregates of VSV-FRG1P specifically sequester proteins involved in pre-mRNA processing. In addition, we have identified SMN, PABPN1, and FAM71B, a novel speckle and Cajal body protein, as binding partners of FRG1P. All these proteins are, or seem to be, involved in RNA biogenesis. Our data confirm the presence of FRG1P in protein complexes containing human spliceosomes and support a potential role of FRG1P in either splicing or another step in nuclear RNA biogenesis. Intriguingly, among FRG1P-associated proteins are SMN and PABPN1, both being involved in neuromuscular disorders, possibly through RNA biogenesis-related processes.

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is caused by a cascade of epigenetic events following contraction of the polymorphic macrosatellite repeat D4Z4 in the subtelomere of chromosome 4q. Currently, the central issue is whether immediate downstream effects are local (i.e., at chromosome 4q) or global (genome-wide) and there is evidence for both scenarios. Currently, there is no therapy for FSHD, mostly because of our lack of understanding of the primary pathogenic process in FSHD muscle. Clinical trials based on suppression of inflammatory reactions or increasing muscle mass by drugs or training have been disappointing. A recent, probably the first evidence-based pilot trial to revert epigenetic changes did also not provide grounds for a larger clinical study. Clearly, better disease models need to be developed to identify and test novel intervention strategies to eventually improve the quality of life for patients with FSHD.

Facioscapulohumeral muscular dystrophy can be a cause of isolated childhood cognitive dysfunction

Facioscapulohumeral muscular dystrophy is one of the most prevalent muscular dystrophies in the world, resulting from the deletion of tandem repeats on chromosome 4q35. Extramuscular associations include sensorineural hearing loss, mental retardation, and epilepsy. These manifestations are commonly found in those with large deletions and early onset of weakness. A 26-year-old patient with a long-standing history of hearing loss, learning disabilities, and epilepsy presented with new-onset weakness and an elevated serum creatinine kinase level. Genetic testing confirmed sporadic facioscapulohumeral muscular dystrophy with a fragment length of 12 kilobases (normal > 35 kilobases). This unique presentation suggests that facioscapulohumeral muscular dystrophy should be considered in the differential diagnosis of children with cognitive impairment, seizures, and hearing loss.

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a dominantly inherited disorder with an initially restricted pattern of weakness. Early involvement of the facial and scapular stabilizer muscles results in a distinctive clinical presentation. Progression is descending, with subsequent involvement of either the distal anterior leg or hip-girdle muscles. There is wide variability in age at onset, disease severity, and side-to-side symmetry, which is evident even within affected members of the same family. Although FSHD is considered a relatively benign dystrophy by some, as many as 20% of patients eventually become wheelchair-bound. Associated nonskeletal muscle manifestations include high-frequency hearing loss as well as retinal telangiectasias, both of which are rarely symptomatic. The causal genetic lesion in FSHD was described over a decade ago, raising hope that knowledge about its molecular and cellular pathophysiology was soon to follow. In the vast majority of cases, FSHD results from a heterozygous partial deletion of a critical number of repetitive elements (D4Z4) on chromosome 4q35; yet, to date, no causal gene has been identified. The accumulating evidence points to a complex, perhaps unique, molecular genetic mechanism. The absence of detectable expressed sequences from D4Z4, the association of FSHD-causing 4q35 deletions with a specific distal genomic sequence (4qA allele), altered DNA methylation patterns on 4q35, as well as other direct and indirect evidence point to epigenetic mechanisms. As a consequence, partial deletion of D4Z4 results in a (local) chromatin change and ultimately results in the loss of appropriate control of gene expression. There is at present no effective treatment for FSHD. A better understanding of the underlying pathophysiology is needed to design targeted interventions. Despite these limitations, however, two randomized controlled clinical trials have been conducted on FSHD. These trials, along with a previous natural history study, have helped to better define outcome measures for future trials in FSHD as well as other dystrophies.

FRG2, an FSHD candidate gene, is transcriptionally upregulated in differentiating primary myoblast cultures of FSHD patients

BACKGROUND

Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is associated with partial deletion of the subtelomeric D4Z4 repeat array on chromosome 4qter. This chromosomal rearrangement may result in regional chromatin relaxation and transcriptional deregulation of genes nearby.

METHODS AND RESULTS

Here we describe the isolation and characterisation of FRG2, a member of a chromosomally dispersed gene family, mapping only 37 kb proximal to the D4Z4 repeat array. Homology and motif searches yielded no clues to the function of the predicted protein. FRG2 expression is undetectable in all tissues tested except for differentiating myoblasts of FSHD patients, which display low, yet distinct levels of FRG2 expression, partly from chromosome 4 but predominantly originating from its homologue on chromosome 10. However, in non-FSHD myopathy patients only distantly related FRG2 homologues are transcribed, while differentiating myoblasts from healthy controls fail to express any member of this gene family. Moreover, fibroblasts of FSHD patients and control individuals undergoing forced Ad5-MyoD mediated myogenesis show expression of FRG2 mainly originating from chromosome 10. Luciferase reporter assays show that the FRG2 promoter region can direct high levels of expression but is inhibited by increasing numbers of D4Z4 repeat units. Transient transfection experiments with FRG2 fusion-protein constructs reveal nuclear localisation and apparently FRG2 overexpression causes a wide range of morphological changes.

CONCLUSION

The localisation of FRG2 genes close to the D4Z4 repeats on chromosome 4 and 10, their transcriptional upregulation specifically in FSHD myoblast cultures, potential involvement in myogenesis, and promoter properties qualify FRG2 as an attractive candidate for FSHD pathogenesis.

Intron loss in the SART1 genes of Fugu rubripes and Tetraodon nigroviridis

The human SART1 gene was initially identified in a screen for proteins recognised by IgE, which may be implicated in atopic disease. We have examined the genomic structure and cDNA sequence of the SART1 gene in the compact genomes of the pufferfish Fugu rubripes and Tetraodon nigroviridis. The entire coding regions of both the Fugu and Tetraodon SART1 genes are contained within single exons. The Fugu gene contains only one intron located in the 5' untranslated region. Southern blot hybridisation of Fugu genomic DNA confirmed the SART1 gene to be single copy. Partial genomic structures were also determined for the human, mouse, Drosophila and C. elegans SART1 homologues. The human and mouse genes both contain many introns in the coding region, the human gene possessing at least 20 exons. The Drosophila and C. elegans homologues contain 6 and 12 exons, respectively. This is only the second time such a difference in the organization of homologous Fugu and human genes has been reported. The Fugu and Tetraodon SART1 genes encode putative proteins of 772 and 774 aa, respectively, each having 65% amino acid identity to human SART1. Leucine zipper and basic motifs are conserved in the predicted Fugu and Tetraodon proteins.

Mutant glycosyltransferase and altered glycosylation of alpha-dystroglycan in the myodystrophy mouse

Spontaneous and engineered mouse mutants have facilitated our understanding of the pathogenesis of muscular dystrophy and they provide models for the development of therapeutic approaches. The mouse myodystrophy (myd) mutation produces an autosomal recessive, neuromuscular phenotype. Homozygotes have an abnormal gait, show abnormal posturing when suspended by the tail and are smaller than littermate controls. Serum creatine kinase is elevated and muscle histology is typical of a progressive myopathy with focal areas of acute necrosis and clusters of regenerating fibers. Additional aspects of the phenotype include sensorineural deafness, reduced lifespan and decreased reproductive fitness. The myd mutation maps to mouse chromosome 8 at approximately 33 centimorgans (cM) (refs. 2, 4-7). Here we show that the gene mutated in myd encodes a glycosyltransferase, Large. The human homolog of this gene (LARGE) maps to chromosome 22q. In myd, an intragenic deletion of exons 4-7 causes a frameshift in the resultant mRNA and a premature termination codon before the first of the two catalytic domains. On immunoblots, a monoclonal antibody to alpha-dystroglycan (a component of the dystrophin-associated glycoprotein complex) shows reduced binding in myd, which we attribute to altered glycosylation of this protein. We speculate that abnormal post-translational modification of alpha-dystroglycan may contribute to the myd phenotype.

Recent amplification of the human FRG1 gene during primate evolution

There is evidence of multiple copies of the FSHD Region Candidate Gene 1 (FRG1) in humans. Analysis of human FRG1 ESTs showed many of them to be non-processed pseudogenes dispersed throughout the genome. To determine when the amplification of FRG1 occurred, we used a PCR-based approach to identify FRG1 sequences from great apes, chimpanzee, gorilla and orang-utan, and an Old World monkey, Macaca mulatta. In common with humans, multiple copies of FRG1 were detected in the great apes. However, in Macaca mulatta, only two FRG1 loci were identified, one presumed to be the homologue of the human chromosome 4q gene. This is strikingly similar to the distribution of a dispersed 3.3-kb repeat family in primates. A member of this family, D4Z4, maps to the subtelomeric region of 4q, in close proximity to FRG1. We propose that an ancestral duplication of distal 4q included FRG1. This duplication is present in Macaca mulatta whose divergence from hominoids is thought to have occurred at least 33 million years ago. We propose that this telomeric region then underwent further amplification and dispersion events in the great ape lineage, with copies of FRG1 and the 3.3-kb repeats being localized in heterochromatic regions.