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Liu J, Ding C, Liu X, Kang Q. Cytoskeletal Protein 4.1R in Health and Diseases. Biomolecules 2024; 14:214. [PMID: 38397451 PMCID: PMC10887211 DOI: 10.3390/biom14020214] [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: 01/09/2024] [Revised: 02/02/2024] [Accepted: 02/07/2024] [Indexed: 02/25/2024] Open
Abstract
The protein 4.1R is an essential component of the erythrocyte membrane skeleton, serving as a key structural element and contributing to the regulation of the membrane's physical properties, including mechanical stability and deformability, through its interaction with spectrin-actin. Recent research has uncovered additional roles of 4.1R beyond its function as a linker between the plasma membrane and the membrane skeleton. It has been found to play a crucial role in various biological processes, such as cell fate determination, cell cycle regulation, cell proliferation, and cell motility. Additionally, 4.1R has been implicated in cancer, with numerous studies demonstrating its potential as a diagnostic and prognostic biomarker for tumors. In this review, we provide an updated overview of the gene and protein structure of 4.1R, as well as its cellular functions in both physiological and pathological contexts.
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Affiliation(s)
- Jiaojiao Liu
- School of Life Science, Zhengzhou University, Zhengzhou 450001, China
| | - Cong Ding
- Children's Hospital Affiliated of Zhengzhou University, Zhengzhou 450018, China
| | - Xin Liu
- School of Life Science, Zhengzhou University, Zhengzhou 450001, China
| | - Qiaozhen Kang
- School of Life Science, Zhengzhou University, Zhengzhou 450001, China
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Delgadillo LF, Huang YS, Leon S, Palis J, Waugh RE. Development of Mechanical Stability in Late-Stage Embryonic Erythroid Cells: Insights From Fluorescence Imaged Micro-Deformation Studies. Front Physiol 2022; 12:761936. [PMID: 35082687 PMCID: PMC8784407 DOI: 10.3389/fphys.2021.761936] [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: 08/20/2021] [Accepted: 11/02/2021] [Indexed: 11/17/2022] Open
Abstract
The combined use of fluorescence labeling and micro-manipulation of red blood cells has proven to be a powerful tool for understanding and characterizing fundamental mechanisms underlying the mechanical behavior of cells. Here we used this approach to study the development of the membrane-associated cytoskeleton (MAS) in primary embryonic erythroid cells. Erythropoiesis comes in two forms in the mammalian embryo, primitive and definitive, characterized by intra- and extra-vascular maturation, respectively. Primitive erythroid precursors in the murine embryo first begin to circulate at embryonic day (E) 8.25 and mature as a semi-synchronous cohort before enucleating between E12.5 and E16.5. Previously, we determined that the major components of the MAS become localized to the membrane between E10.5 and E12.5, and that this localization is associated with an increase in membrane mechanical stability over this same period. The change in mechanical stability was reflected in the creation of MAS-free regions of the membrane at the tips of the projections formed when cells were aspirated into micropipettes. The tendency to form MAS-free regions decreases as primitive erythroid cells continue to mature through E14.5, at least 2 days after all detectable cytoskeletal components are localized to the membrane, indicating continued strengthening of membrane cohesion after membrane localization of cytoskeletal components. Here we demonstrate that the formation of MAS-free regions is the result of a mechanical failure within the MAS, and not the detachment of membrane bilayer from the MAS. Once a "hole" is formed in the MAS, the skeletal network contracts laterally along the aspirated projection to form the MAS-free region. In protein 4.1-null primitive erythroid cells, the tendency to form MAS-free regions is markedly enhanced. Of note, similar MAS-free regions were observed in maturing erythroid cells from human marrow, indicating that similar processes occur in definitive erythroid cells. We conclude that localization of cytoskeletal components to the cell membrane of mammalian erythroid cells during maturation is insufficient by itself to produce a mature MAS, but that subsequent processes are additionally required to strengthen intraskeletal interactions.
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Affiliation(s)
- Luis F. Delgadillo
- Department of Biomedical Engineering, University of Rochester, Rochester, NY, United States
| | - Yu Shan Huang
- Department of Pediatrics, School of Medicine and Dentistry, University of Rochester, Rochester, NY, United States
| | - Sami Leon
- Department of Biostatistics and Computational Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY, United States
| | - James Palis
- Department of Pediatrics, School of Medicine and Dentistry, University of Rochester, Rochester, NY, United States
| | - Richard E. Waugh
- Department of Biomedical Engineering, University of Rochester, Rochester, NY, United States,*Correspondence: Richard E. Waugh,
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Comparative genomics provides insights into the aquatic adaptations of mammals. Proc Natl Acad Sci U S A 2021; 118:2106080118. [PMID: 34503999 PMCID: PMC8449357 DOI: 10.1073/pnas.2106080118] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2021] [Indexed: 12/30/2022] Open
Abstract
Divergent lineages can respond to common environmental factors through convergent processes involving shared genomic components or pathways, but the molecular mechanisms are poorly understood. Here, we provide genomic resources and insights into the evolution of mammalian lineages adapting to aquatic life. Our data suggest convergent evolution, for example, in association with thermoregulation through genes associated with a surface heat barrier (NFIA) and internal heat exchange (SEMA3E). Combined with the support of previous reports showing that the UCP1 locus has been lost in many marine mammals independently, our results suggest that the thermostatic strategy of marine mammals shifted from enhancing heat production to limiting heat loss. The ancestors of marine mammals once roamed the land and independently committed to an aquatic lifestyle. These macroevolutionary transitions have intrigued scientists for centuries. Here, we generated high-quality genome assemblies of 17 marine mammals (11 cetaceans and six pinnipeds), including eight assemblies at the chromosome level. Incorporating previously published data, we reconstructed the marine mammal phylogeny and population histories and identified numerous idiosyncratic and convergent genomic variations that possibly contributed to the transition from land to water in marine mammal lineages. Genes associated with the formation of blubber (NFIA), vascular development (SEMA3E), and heat production by brown adipose tissue (UCP1) had unique changes that may contribute to marine mammal thermoregulation. We also observed many lineage-specific changes in the marine mammals, including genes associated with deep diving and navigation. Our study advances understanding of the timing, pattern, and molecular changes associated with the evolution of mammalian lineages adapting to aquatic life.
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Cao M, Huang Z, Zhou H, Lin J, Zhang D. Clinical and molecular genetic analysis of a Chinese family with hereditary elliptocytosis caused by a novel mutation in the EPB41 gene. J Clin Lab Anal 2021; 35:e23781. [PMID: 33942936 PMCID: PMC8183902 DOI: 10.1002/jcla.23781] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 01/27/2021] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Hereditary elliptocytosis (HE) is a heterogeneous red blood cell membrane disorder characterized by the presence of elliptocytes on a peripheral blood smear. Clinical manifestations of HE vary widely from asymptomatic carriers to patients with severe transfusion-dependent anemia. Most patients are asymptomatic or have mild anemia, which hinders diagnosis. The proband in this case had mild anemia and jaundice over a period of 4 years, the etiology of which was unclear. Hence, he was admitted to our hospital for further diagnosis. METHODS Peripheral blood smears and routine blood tests were performed and biochemical parameters of the proband, and his family members were determined. To confirm the diagnosis, gene mutations were screened in the proband using next-generation sequencing (NGS) and verified by Sanger sequencing in other family members. RESULTS A novel mutation (c.1294delA, p.Ser432 fs) in exon 15 of the EPB41 gene was detected in the proband and his family members. This mutation results in a frameshift and a premature stop codon at position 455, encoding a truncated protein. The variant was likely pathogenic according to the criteria of the American College of Medical Genetics and Genomics. SWISS-MODEL protein structure prediction indicated partial loss of the spectrin and actin binding and C-terminal domains. CONCLUSION A heterozygous mutation 1294delA in exon 15 of the EPB41 gene was identified using NGS and Sanger sequencing in members of a Chinese family. This identification expands the spectrum of EPB41 mutations and contributes to the genetic diagnosis of families with HE.
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Affiliation(s)
- Manxiong Cao
- Department of Hematologythe First Affiliated Hospital of Shantou University Medical CollegeShantouP.R. China
| | - Zhanqin Huang
- Department of PharmacologyShantou University Medical CollegeShantouP.R. China
| | - Huanbing Zhou
- Department of Laboratory Medicinethe First Affiliated Hospital of Shantou University Medical CollegeShantouP.R. China
| | - Jinghua Lin
- Department of Laboratory Medicinethe First Affiliated Hospital of Shantou University Medical CollegeShantouP.R. China
| | - Dongqing Zhang
- Department of Laboratory Medicinethe First Affiliated Hospital of Shantou University Medical CollegeShantouP.R. China
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Conboy JG. Unannotated splicing regulatory elements in deep intron space. WILEY INTERDISCIPLINARY REVIEWS-RNA 2021; 12:e1656. [PMID: 33887804 DOI: 10.1002/wrna.1656] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Revised: 03/14/2021] [Accepted: 03/23/2021] [Indexed: 12/21/2022]
Abstract
Deep intron space harbors a diverse array of splicing regulatory elements that cooperate with better-known exon-proximal elements to enforce proper tissue-specific and development-specific pre-mRNA processing. Many deep intron elements have been highly conserved through vertebrate evolution, yet remain poorly annotated in the human genome. Recursive splicing exons (RS-exons) and intraexons promote noncanonical, multistep resplicing pathways in long introns, involving transient intermediate structures that are greatly underrepresented in RNA-seq datasets. Decoy splice sites and decoy exons act at a distance to inhibit splicing catalysis at annotated splice sites, with functional consequences such as exon skipping and intron retention. RNA:RNA bridges can juxtapose distant sequences within or across introns to activate deep intron splicing enhancers and silencers, to loop out exons to be skipped, or to select one member of a mutually exclusive set of exons. Similarly, protein bridges mediated by interactions among transcript-bound RNA binding proteins (RBPs) can modulate splicing outcomes. Experimental disruption of deep intron elements serving any of these functions can abrogate normal splicing, strongly suggesting that natural mutations of deep intron elements can do likewise to cause human disease. Understanding noncanonical splicing pathways and discovering deep intron regulatory signals, many of which map hundreds to many thousands of nucleotides from annotated splice junctions, is of great academic interest for basic scientists studying alternative splicing mechanisms. Hopefully, this knowledge coupled with increased analysis of deep intron sequences will also have important medical applications, as better interpretation of deep intron mutations may reveal new disease mechanisms and suggest new therapies. This article is categorized under: RNA Processing > Splicing Regulation/Alternative Splicing.
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Affiliation(s)
- John G Conboy
- Lawrence Berkeley National Laboratory, Biological Systems and Engineering Division, Berkeley, California, USA
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Naval-Sánchez M, Porto-Neto LR, Cardoso DF, Hayes BJ, Daetwyler HD, Kijas J, Reverter A. Selection signatures in tropical cattle are enriched for promoter and coding regions and reveal missense mutations in the damage response gene HELB. Genet Sel Evol 2020; 52:27. [PMID: 32460767 PMCID: PMC7251699 DOI: 10.1186/s12711-020-00546-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2019] [Accepted: 05/11/2020] [Indexed: 01/14/2023] Open
Abstract
Background Distinct domestication events, adaptation to different climatic zones, and divergent selection in productive traits have shaped the genomic differences between taurine and indicine cattle. In this study, we assessed the impact of artificial selection and environmental adaptation by comparing whole-genome sequences from European taurine and Asian indicine breeds and from African cattle. Next, we studied the impact of divergent selection by exploiting predicted and experimental functional annotation of the bovine genome. Results We identified selective sweeps in beef cattle taurine and indicine populations, including a 430-kb selective sweep on indicine cattle chromosome 5 that is located between 47,670,001 and 48,100,000 bp and spans five genes, i.e. HELB, IRAK3, ENSBTAG00000026993, GRIP1 and part of HMGA2. Regions under selection in indicine cattle display significant enrichment for promoters and coding genes. At the nucleotide level, sites that show a strong divergence in allele frequency between European taurine and Asian indicine are enriched for the same functional categories. We identified nine single nucleotide polymorphisms (SNPs) in coding regions that are fixed for different alleles between subspecies, eight of which were located within the DNA helicase B (HELB) gene. By mining information from the 1000 Bull Genomes Project, we found that HELB carries mutations that are specific to indicine cattle but also found in taurine cattle, which are known to have been subject to indicine introgression from breeds, such as N’Dama, Anatolian Red, Marchigiana, Chianina, and Piedmontese. Based on in-house genome sequences, we proved that mutations in HELB segregate independently of the copy number variation HMGA2-CNV, which is located in the same region. Conclusions Major genomic sequence differences between Bos taurus and Bos indicus are enriched for promoter and coding regions. We identified a 430-kb selective sweep in Asian indicine cattle located on chromosome 5, which carries SNPs that are fixed in indicine populations and located in the coding sequences of the HELB gene. HELB is involved in the response to DNA damage including exposure to ultra-violet light and is associated with reproductive traits and yearling weight in tropical cattle. Thus, HELB likely contributed to the adaptation of tropical cattle to their harsh environment.
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Affiliation(s)
- Marina Naval-Sánchez
- CSIRO Agriculture & Food, 306 Carmody Rd., St. Lucia, Brisbane, QLD, 4067, Australia. .,Institute of Molecular Biosciences, The University of Queensland, 306 Carmody Road, St. Lucia, Brisbane, QLD, 4067, Australia.
| | - Laercio R Porto-Neto
- CSIRO Agriculture & Food, 306 Carmody Rd., St. Lucia, Brisbane, QLD, 4067, Australia
| | - Diercles F Cardoso
- CSIRO Agriculture & Food, 306 Carmody Rd., St. Lucia, Brisbane, QLD, 4067, Australia.,Department of Animal Science, School of Agricultural and Veterinarian Sciences, Sao Paulo State University (UNESP), Jaboticabal, SP, Brazil.,Centre for Genetic Improvement of Livestock, University of Guelph, 50 Stone Road East, Guelph, ON, N1G2W1, Canada
| | - Ben J Hayes
- Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St. Lucia, QLD, 4067, Australia
| | - Hans D Daetwyler
- Agriculture Victoria, AgriBio, Centre for AgriBioscience, Bundoora, VIC, 3083, Australia.,School of Applied Systems Biology, La Trobe University, Bundoora, VIC, 3083, Australia
| | - James Kijas
- CSIRO Agriculture & Food, 306 Carmody Rd., St. Lucia, Brisbane, QLD, 4067, Australia
| | - Antonio Reverter
- CSIRO Agriculture & Food, 306 Carmody Rd., St. Lucia, Brisbane, QLD, 4067, Australia
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Lacy JN, Ulirsch JC, Grace RF, Towne MC, Hale J, Mohandas N, Lux SE, Agrawal PB, Sankaran VG. Exome sequencing results in successful diagnosis and treatment of a severe congenital anemia. Cold Spring Harb Mol Case Stud 2016; 2:a000885. [PMID: 27551681 PMCID: PMC4990811 DOI: 10.1101/mcs.a000885] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Whole-exome sequencing is increasingly used for diagnosis and identification of appropriate therapies in patients. Here, we present the case of a 3-yr-old male with a lifelong and severe transfusion-dependent anemia of unclear etiology, despite an extensive clinical workup. Given the difficulty of making the diagnosis and the potential side effects from performing interventions in patients with a congenital anemia of unknown etiology, we opted to perform whole-exome sequencing on the patient and his parents. This resulted in the identification of homozygous loss-of-function mutations in the EPB41 gene, encoding erythrocyte protein band 4.1, which therefore causes a rare and severe form of hereditary elliptocytosis in the patient. Based on prior clinical experience in similar patients, a surgical splenectomy was performed that resulted in subsequent transfusion independence in the patient. This case illustrates how whole-exome sequencing can lead to accurate diagnoses (and exclusion of diagnoses where interventions, such as splenectomy, would be contraindicated), thereby resulting in appropriate and successful therapeutic intervention—a major goal of precision medicine.
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Affiliation(s)
- Jessica N Lacy
- Division of Hematology/Oncology, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA;; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA;; Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, USA
| | - Jacob C Ulirsch
- Division of Hematology/Oncology, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA;; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA;; Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, USA
| | - Rachael F Grace
- Division of Hematology/Oncology, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA;; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Meghan C Towne
- Division of Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - John Hale
- New York Blood Center, New York, New York 10065, USA
| | | | - Samuel E Lux
- Division of Hematology/Oncology, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA;; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Pankaj B Agrawal
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, USA;; Division of Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA;; Division of Newborn Medicine, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Vijay G Sankaran
- Division of Hematology/Oncology, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA;; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA;; Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, USA
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King MJ, Garçon L, Hoyer JD, Iolascon A, Picard V, Stewart G, Bianchi P, Lee SH, Zanella A. ICSH guidelines for the laboratory diagnosis of nonimmune hereditary red cell membrane disorders. Int J Lab Hematol 2015; 37:304-25. [PMID: 25790109 DOI: 10.1111/ijlh.12335] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 01/22/2015] [Indexed: 01/19/2023]
Abstract
INTRODUCTION Hereditary spherocytosis (HS), hereditary elliptocytosis (HE), and hereditary stomatocytosis (HSt) are inherited red cell disorders caused by defects in various membrane proteins. The heterogeneous clinical presentation, biochemical and genetic abnormalities in HS and HE have been well documented. The need to raise the awareness of HSt, albeit its much lower prevalence than HS, is due to the undesirable outcome of splenectomy in these patients. METHODS The scope of this guideline is to identify the characteristic clinical features, the red cell parameters (including red cell morphology) for these red cell disorders associated, respectively, with defective cytoskeleton (HS and HE) and abnormal cation permeability in the lipid bilayer (HSt) of the red cell. The current screening tests for HS are described, and their limitations are highlighted. RESULTS An appropriate diagnosis can often be made when the screening test result(s) is reviewed together with the patient's clinical/family history, blood count results, reticulocyte count, red cell morphology, and chemistry results. SDS-polyacrylamide gel electrophoresis of erythrocyte membrane proteins, monovalent cation flux measurement, and molecular analysis of membrane protein genes are specialist tests for further investigation. CONCLUSION Specialist tests provide additional evidence in supporting the diagnosis and that will facilitate the management of the patient. In the case of a patient's clinical phenotype being more severe than the affected members within the immediate family, molecular testing of all family members is useful for confirming the diagnosis and allows an insight into the molecular basis of the abnormality such as a recessive mode of inheritance or a de novo mutation.
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Affiliation(s)
- M-J King
- Membrane Biochemistry, NHS Blood and Transplant, Bristol, UK
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Nauroy P, Delhommeau F, Baklouti F. JAK2V617F mRNA metabolism in myeloproliferative neoplasm cell lines. Blood Cancer J 2014; 4:e222. [PMID: 24972151 PMCID: PMC4080214 DOI: 10.1038/bcj.2014.43] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Affiliation(s)
- P Nauroy
- mRNA Metabolism in Normal and Pathological Cells, CNRS UMR 5534, Université Lyon 1, Villeurbanne, France
| | - F Delhommeau
- 1] Sorbonne Universités, UPMC Univ Paris 06, GRC no. 07, Groupe de Recherche Clinique sur les Myéloproliférations Aiguës et Chroniques MyPAC, Paris, France [2] AP-HP, Hôpital Saint-Antoine, Laboratoire d'Hématologie, Paris, France [3] Sorbonne Universités, UPMC Univ Paris 06, UMR_S 938, CDR Saint-Antoine, Paris, France [4] INSERM, UMR_S 938, CDR Saint-Antoine, Paris, France
| | - F Baklouti
- mRNA Metabolism in Normal and Pathological Cells, CNRS UMR 5534, Université Lyon 1, Villeurbanne, France
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Deep intron elements mediate nested splicing events at consecutive AG dinucleotides to regulate alternative 3' splice site choice in vertebrate 4.1 genes. Mol Cell Biol 2012; 32:2044-53. [PMID: 22473990 DOI: 10.1128/mcb.05716-11] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Distal intraexon (iE) regulatory elements in 4.1R pre-mRNA govern 3' splice site choice at exon 2 (E2) via nested splicing events, ultimately modulating expression of N-terminal isoforms of cytoskeletal 4.1R protein. Here we explored intrasplicing in other normal and disease gene contexts and found conservation of intrasplicing through vertebrate evolution. In the paralogous 4.1B gene, we identified ∼120 kb upstream of E2 an ultradistal intraexon, iE(B), that mediates intrasplicing by promoting two intricately coupled splicing events that ensure selection of a weak distal acceptor at E2 (E2dis) by prior excision of the competing proximal acceptor (E2prox). Mutating iE(B) in minigene splicing reporters abrogated intrasplicing, as did blocking endogenous iE(B) function with antisense morpholinos in live mouse and zebrafish animal models. In a human elliptocytosis patient with a mutant 4.1R gene lacking E2 through E4, we showed that aberrant splicing is consistent with iE(R)-mediated intrasplicing at the first available exons downstream of iE(R), namely, alternative E5 and constitutive E6. Finally, analysis of heterologous acceptor contexts revealed a strong preference for nested 3' splice events at consecutive pairs of AG dinucleotides. Distal regulatory elements may control intrasplicing at a subset of alternative 3' splice sites in vertebrate pre-mRNAs to generate proteins with functional diversity.
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