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Zafarullah M, Li J, Tseng E, Tassone F. Structure and Alternative Splicing of the Antisense FMR1 (ASFMR1) Gene. Mol Neurobiol 2023; 60:2051-2061. [PMID: 36598648 PMCID: PMC10461537 DOI: 10.1007/s12035-022-03176-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 12/10/2022] [Indexed: 01/05/2023]
Abstract
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by an expansion of 55-200 CGG repeats (premutation) in the 5'-UTR of the FMR1 gene. Bidirectional transcription at FMR1 locus has been demonstrated and specific alternative splicing of the Antisense FMR1 (ASFMR1) gene has been proposed to have a contributing role in the pathogenesis of FXTAS. The structure of ASFMR1 gene is still uncharacterized and it is currently unknown how many isoforms of the gene are expressed and at what level in premutation carriers (PM) and if they may contribute to the premutation pathology. In this study, we characterized the ASFMR1 gene structure and the transcriptional landscape by using PacBio SMRT sequencing with target enrichment (IDT customized probe panel). We identified 45 ASFMR1 isoforms ranging in sizes from 523 bp to 6 Kb, spanning approximately 59 kb of genomic DNA. Multiplexing and sequencing of six human brain samples from PM samples and normal control (HC) were carried out on the PacBio Sequel platform. We validated the presence of these isoforms by qRT-PCR and Sanger sequencing and characterized the acceptor and donor splicing site consensus sequences. Consistent with previous studies conducted in other tissue types, we found a high expression of ASFMR1 isoform Iso131bp in brain samples of PM as compared to HC, while no differences in expression levels were observed for the newly identified isoforms IsoAS1 and IsoAS2. We investigated the role of the splicing regulatory protein Sam68 which we did not observe in the alternative splicing of the ASFMR1 gene. Our study provides a useful insight into the structure of ASFMR1 gene and transcriptional landscape along with the expression pattern of various newly identified novel isoforms and on their potential role in premutation pathology.
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Affiliation(s)
- Marwa Zafarullah
- Department of Biochemistry and Molecular Medicine, University of California Davis, School of Medicine, Sacramento, CA, 95817, USA
| | - Jie Li
- Bioinformatics Core, Genome Center, University of California Davis, Davis, CA, 95616, USA
| | | | - Flora Tassone
- Department of Biochemistry and Molecular Medicine, University of California Davis, School of Medicine, Sacramento, CA, 95817, USA.
- MIND Institute, University of California Davis Medical Center, Sacramento, CA, 95817, USA.
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Jiraanont P, Manor E, Tabatadze N, Zafarullah M, Mendoza G, Melikishvili G, Tassone F. De Novo Large Deletion Leading to Fragile X Syndrome. Front Genet 2022; 13:884424. [PMID: 35646065 PMCID: PMC9130735 DOI: 10.3389/fgene.2022.884424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Accepted: 04/13/2022] [Indexed: 11/13/2022] Open
Abstract
Fragile X syndrome (FXS) is the most frequent cause of X-linked inherited intellectual disabilities (ID) and the most frequent monogenic form of autism spectrum disorders. It is caused by an expansion of a CGG trinucleotide repeat located in the 5'UTR of the FMR1 gene, resulting in the absence of the fragile X mental retardation protein, FMRP. Other mechanisms such as deletions or point mutations of the FMR1 gene have been described and account for approximately 1% of individuals with FXS. Here, we report a 7-year-old boy with FXS with a de novo deletion of approximately 1.1 Mb encompassing several genes, including the FMR1 and the ASFMR1 genes, and several miRNAs, whose lack of function could result in the observed proband phenotypes. In addition, we also demonstrate that FMR4 completely overlaps with ASFMR1, and there are no sequencing differences between both transcripts (i.e., ASFMR1/FMR4 throughout the article).
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Affiliation(s)
- Poonnada Jiraanont
- Faculty of Medicine, King Mongkut's Institute of Technology Ladkrabang, Bangkok, Thailand
| | - Esther Manor
- Faculty of Health Sciences, Ben-Gurion University of the Negev, Beersheba, Israel.,Genetics Institute, Soroka Medical Center, Beersheba, Israel
| | - Nazi Tabatadze
- Department of Pediatrics, MediClub Georgia Medical Center, Tbilisi, Georgia
| | - Marwa Zafarullah
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California, Davis, Sacramento, CA, United States
| | - Guadalupe Mendoza
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California, Davis, Sacramento, CA, United States
| | - Gia Melikishvili
- Department of Pediatrics, MediClub Georgia Medical Center, Tbilisi, Georgia
| | - Flora Tassone
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California, Davis, Sacramento, CA, United States.,UC Davis MIND Institute, UC Davis Health, Sacramento, CA, United States
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Molecular Pathogenesis and Peripheral Monitoring of Adult Fragile X-Associated Syndromes. Int J Mol Sci 2021; 22:ijms22168368. [PMID: 34445074 PMCID: PMC8395059 DOI: 10.3390/ijms22168368] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 07/29/2021] [Accepted: 07/30/2021] [Indexed: 12/16/2022] Open
Abstract
Abnormal trinucleotide expansions cause rare disorders that compromise quality of life and, in some cases, lifespan. In particular, the expansions of the CGG-repeats stretch at the 5’-UTR of the Fragile X Mental Retardation 1 (FMR1) gene have pleiotropic effects that lead to a variety of Fragile X-associated syndromes: the neurodevelopmental Fragile X syndrome (FXS) in children, the late-onset neurodegenerative disorder Fragile X-associated tremor-ataxia syndrome (FXTAS) that mainly affects adult men, the Fragile X-associated primary ovarian insufficiency (FXPOI) in adult women, and a variety of psychiatric and affective disorders that are under the term of Fragile X-associated neuropsychiatric disorders (FXAND). In this review, we will describe the pathological mechanisms of the adult “gain-of-function” syndromes that are mainly caused by the toxic actions of CGG RNA and FMRpolyG peptide. There have been intensive attempts to identify reliable peripheral biomarkers to assess disease progression and onset of specific pathological traits. Mitochondrial dysfunction, altered miRNA expression, endocrine system failure, and impairment of the GABAergic transmission are some of the affectations that are susceptible to be tracked using peripheral blood for monitoring of the motor, cognitive, psychiatric and reproductive impairment of the CGG-expansion carriers. We provided some illustrative examples from our own cohort. Understanding the association between molecular pathogenesis and biomarkers dynamics will improve effective prognosis and clinical management of CGG-expansion carriers.
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Zafarullah M, Tang HT, Durbin-Johnson B, Fourie E, Hessl D, Rivera SM, Tassone F. FMR1 locus isoforms: potential biomarker candidates in fragile X-associated tremor/ataxia syndrome (FXTAS). Sci Rep 2020; 10:11099. [PMID: 32632326 PMCID: PMC7338407 DOI: 10.1038/s41598-020-67946-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2019] [Accepted: 05/18/2020] [Indexed: 12/12/2022] Open
Abstract
Fragile X associated tremor/ataxia syndrome (FXTAS) is a late adult-onset neurodegenerative disorder that affects movement and cognition in male and female carriers of a premutation allele of 55-200 CGG repeats in the Fragile X mental retardation (FMR1) gene. It is currently unknown if and when an individual carrier of a premutation allele will develop FXTAS, as clinical assessment fails to identify carriers at risk before significant neurological symptoms are evident. The primary objective of this study was to investigate the alternative splicing landscape at the FMR1 locus in conjunction with brain measures in male individuals with a premutation allele enrolled in a very first longitudinal study, compared to age-matched healthy male controls, with the purpose of identifying biomarkers for early diagnosis, disease prediction and, a progression of FXTAS. Our findings indicate that increased expression of FMR1 mRNA isoforms, including Iso4/4b, Iso10/10b, as well as of the ASFMR1 mRNAs Iso131bp, are present in premutation carriers as compared to non-carrier healthy controls. More specifically, we observed a higher expression of Iso4/4b and Iso10/10b, which encode for truncated proteins, only in those premutation carriers who developed symptoms of FXTAS over time as compared to non-carrier healthy controls, suggesting a potential role in the development of the disorder. In addition, we found a significant association of these molecular changes with various measurements of brain morphology, including the middle cerebellar peduncle (MCP), superior cerebellar peduncle (SCP), pons, and midbrain, indicating their potential contribution to the pathogenesis of FXTAS. Interestingly, the high expression levels of Iso4/4b observed both at visit 1 and visit 2 and found to be associated with a decrease in mean MCP width only in those individuals who developed FXTAS over time, suggests their role as potential biomarkers for early diagnosis of FXTAS.
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Affiliation(s)
- Marwa Zafarullah
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California Davis, Sacramento, 95817 CA, USA
| | - Hiu-Tung Tang
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California Davis, Sacramento, 95817 CA, USA
| | - Blythe Durbin-Johnson
- Division of Biostatistics, School of Medicine, University of California Davis, Davis, CA, USA
| | - Emily Fourie
- Center for Mind and Brain, University of California Davis, Davis, CA, USA
- Department of Psychology, University of California, Davis, Davis, CA, USA
| | - David Hessl
- MIND Institute, University of California Davis Medical Center, Sacramento, 95817 CA, USA
- Department of Psychiatry and Behavioral Sciences, University of California Davis Medical Center, Sacramento, 95817 CA, USA
| | - Susan M Rivera
- Center for Mind and Brain, University of California Davis, Davis, CA, USA
- Department of Psychology, University of California, Davis, Davis, CA, USA
- MIND Institute, University of California Davis Medical Center, Sacramento, 95817 CA, USA
| | - Flora Tassone
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California Davis, Sacramento, 95817 CA, USA.
- MIND Institute, University of California Davis Medical Center, Sacramento, 95817 CA, USA.
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