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Kim KS, Koo HY, Bok J. Alternative splicing in shaping the molecular landscape of the cochlea. Front Cell Dev Biol 2023; 11:1143428. [PMID: 36936679 PMCID: PMC10018040 DOI: 10.3389/fcell.2023.1143428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 02/16/2023] [Indexed: 03/06/2023] Open
Abstract
The cochlea is a complex organ comprising diverse cell types with highly specialized morphology and function. Until now, the molecular underpinnings of its specializations have mostly been studied from a transcriptional perspective, but accumulating evidence points to post-transcriptional regulation as a major source of molecular diversity. Alternative splicing is one of the most prevalent and well-characterized post-transcriptional regulatory mechanisms. Many molecules important for hearing, such as cadherin 23 or harmonin, undergo alternative splicing to produce functionally distinct isoforms. Some isoforms are expressed specifically in the cochlea, while some show differential expression across the various cochlear cell types and anatomical regions. Clinical phenotypes that arise from mutations affecting specific splice variants testify to the functional relevance of these isoforms. All these clues point to an essential role for alternative splicing in shaping the unique molecular landscape of the cochlea. Although the regulatory mechanisms controlling alternative splicing in the cochlea are poorly characterized, there are animal models with defective splicing regulators that demonstrate the importance of RNA-binding proteins in maintaining cochlear function and cell survival. Recent technological breakthroughs offer exciting prospects for overcoming some of the long-standing hurdles that have complicated the analysis of alternative splicing in the cochlea. Efforts toward this end will help clarify how the remarkable diversity of the cochlear transcriptome is both established and maintained.
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Affiliation(s)
- Kwan Soo Kim
- Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea
- Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - Hei Yeun Koo
- Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - Jinwoong Bok
- Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea
- Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea
- Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Republic of Korea
- *Correspondence: Jinwoong Bok,
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Nakano Y, Wiechert S, Fritzsch B, Bánfi B. Inhibition of a transcriptional repressor rescues hearing in a splicing factor-deficient mouse. Life Sci Alliance 2020; 3:3/12/e202000841. [PMID: 33087486 PMCID: PMC7652395 DOI: 10.26508/lsa.202000841] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2020] [Revised: 10/09/2020] [Accepted: 10/12/2020] [Indexed: 11/26/2022] Open
Abstract
The vital role of the splicing factor SRRM4 in vestibular and inner hair cells of the ear is inactivation of the gene repressor REST; however, in outer hair cells, SRRM4 is dispensable for REST inactivation, which SRRM3 accomplishes independently. In mechanosensory hair cells (HCs) of the ear, the transcriptional repressor REST is continuously inactivated by alternative splicing of its pre-mRNA. This mechanism of REST inactivation is crucial for hearing in humans and mice. Rest is one of many pre-mRNAs whose alternative splicing is regulated by the splicing factor SRRM4; Srrm4 loss-of-function mutation in mice (Srrm4bv/bv) causes deafness, balance defects, and degeneration of all HC types other than the outer HCs (OHCs). The specific splicing alterations that drive HC degeneration in Srrm4bv/bv mice are unknown, and the mechanism underlying SRRM4-independent survival of OHCs is undefined. Here, we show that transgenic expression of a dominant-negative REST fragment in Srrm4bv/bv mice is sufficient for long-term rescue of hearing, balancing, HCs, alternative splicing of Rest, and expression of REST target genes including the Srrm4 paralog Srrm3. We also show that in HCs, SRRM3 regulates many of the same exons as SRRM4; OHCs are unique among HCs in that they transiently down-regulate Rest transcription as they mature to express Srrm3 independently of SRRM4; and simultaneous SRRM4–SRRM3 deficiency causes complete HC loss by preventing inactivation of REST in all HCs. Thus, our data reveal that REST inactivation is the primary and essential role of SRRM4 in the ear, and that OHCs differ from other HCs in the SRRM4-independent expression of the functionally SRRM4-like splicing factor SRRM3.
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Affiliation(s)
- Yoko Nakano
- Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.,Inflammation Program, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Susan Wiechert
- Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.,Inflammation Program, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Bernd Fritzsch
- Department of Biology, College of Liberal Arts and Sciences, University of Iowa, Iowa City, IA, USA
| | - Botond Bánfi
- Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA .,Inflammation Program, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.,Department of Otolaryngology-Head and Neck Surgery, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.,Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
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Uetsuka S, Ogata G, Nagamori S, Isozumi N, Nin F, Yoshida T, Komune S, Kitahara T, Kikkawa Y, Inohara H, Kanai Y, Hibino H. Molecular architecture of the stria vascularis membrane transport system, which is essential for physiological functions of the mammalian cochlea. Eur J Neurosci 2015; 42:1984-2002. [PMID: 26060893 DOI: 10.1111/ejn.12973] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 06/02/2015] [Accepted: 06/02/2015] [Indexed: 11/29/2022]
Abstract
Stria vascularis of the mammalian cochlea transports K(+) to establish the electrochemical property in the endolymph crucial for hearing. This epithelial tissue also transports various small molecules. To clarify the profile of proteins participating in the transport system in the stria vascularis, membrane components purified from the stria of adult rats were analysed by liquid chromatography tandem mass spectrometry. Of the 3236 proteins detected in the analysis, 1807 were membrane proteins. Ingenuity Knowledge Base and literature data identified 513 proteins as being expressed on the 'plasma membrane', these included 25 ion channels and 79 transporters. Sixteen of the former and 62 of the latter had not yet been identified in the stria. Unexpectedly, many Cl(-) and Ca(2+) transport systems were found, suggesting that the dynamics of these ions play multiple roles. Several transporters for organic substances were also detected. Network analysis demonstrated that a few kinases, including protein kinase A, and Ca(2+) were key regulators for the strial transports. In the library of channels and transporters, 19 new candidates for uncloned deafness-related genes were identified. These resources provide a platform for understanding the molecular mechanisms underlying the epithelial transport essential for cochlear function and the pathophysiological processes involved in hearing disorders.
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Affiliation(s)
- Satoru Uetsuka
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Niigata, 951-8510, Japan.,Center for Transdisciplinary Research, Niigata University, Niigata, Japan.,Department of Otorhinolaryngology - Head and Neck Surgery, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Genki Ogata
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Niigata, 951-8510, Japan.,Center for Transdisciplinary Research, Niigata University, Niigata, Japan
| | - Shushi Nagamori
- Division of Bio-system Pharmacology, Department of Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Noriyoshi Isozumi
- Division of Bio-system Pharmacology, Department of Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Fumiaki Nin
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Niigata, 951-8510, Japan.,Center for Transdisciplinary Research, Niigata University, Niigata, Japan
| | - Takamasa Yoshida
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Niigata, 951-8510, Japan.,Center for Transdisciplinary Research, Niigata University, Niigata, Japan.,Department of Otorhinolaryngology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Shizuo Komune
- Department of Otorhinolaryngology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Tadashi Kitahara
- Department of Otorhinolaryngology - Head and Neck Surgery, Graduate School of Medicine, Osaka University, Osaka, Japan.,Department of Otorhinolaryngology - Head and Neck Surgery, Nara Medical University, Nara, Japan
| | - Yoshiaki Kikkawa
- Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Hidenori Inohara
- Department of Otorhinolaryngology - Head and Neck Surgery, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Yoshikatsu Kanai
- Division of Bio-system Pharmacology, Department of Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Hiroshi Hibino
- Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Niigata, 951-8510, Japan.,Center for Transdisciplinary Research, Niigata University, Niigata, Japan
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The candidate splicing factor Sfswap regulates growth and patterning of inner ear sensory organs. PLoS Genet 2014; 10:e1004055. [PMID: 24391519 PMCID: PMC3879212 DOI: 10.1371/journal.pgen.1004055] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 11/08/2013] [Indexed: 12/15/2022] Open
Abstract
The Notch signaling pathway is thought to regulate multiple stages of inner ear development. Mutations in the Notch signaling pathway cause disruptions in the number and arrangement of hair cells and supporting cells in sensory regions of the ear. In this study we identify an insertional mutation in the mouse Sfswap gene, a putative splicing factor, that results in mice with vestibular and cochlear defects that are consistent with disrupted Notch signaling. Homozygous Sfswap mutants display hyperactivity and circling behavior consistent with vestibular defects, and significantly impaired hearing. The cochlea of newborn Sfswap mutant mice shows a significant reduction in outer hair cells and supporting cells and ectopic inner hair cells. This phenotype most closely resembles that seen in hypomorphic alleles of the Notch ligand Jagged1 (Jag1). We show that Jag1; Sfswap compound mutants have inner ear defects that are more severe than expected from simple additive effects of the single mutants, indicating a genetic interaction between Sfswap and Jag1. In addition, expression of genes involved in Notch signaling in the inner ear are reduced in Sfswap mutants. There is increased interest in how splicing affects inner ear development and function. Our work is one of the first studies to suggest that a putative splicing factor has specific effects on Notch signaling pathway members and inner ear development.
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Chen Q, Mahendrasingam S, Tickle JA, Hackney CM, Furness DN, Fettiplace R. The development, distribution and density of the plasma membrane calcium ATPase 2 calcium pump in rat cochlear hair cells. Eur J Neurosci 2012; 36:2302-10. [PMID: 22672315 DOI: 10.1111/j.1460-9568.2012.08159.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Calcium is tightly regulated in cochlear outer hair cells (OHCs). It enters mainly via mechanotransducer (MT) channels and is extruded by the plasma membrane calcium ATPase (PMCA)2 isoform of the PMCA, mutations in which cause hearing loss. To assess how pump expression matches the demands of Ca(2+) homeostasis, the distribution of PMCA2 at different cochlear locations during development was quantified using immunofluorescence and post-embedding immunogold labeling. The PMCA2 isoform was confined to stereociliary bundles, first appearing at the base of the cochlea around post-natal day (P)0 followed by the middle and then the apex by P3, and was unchanged after P8. The developmental appearance matched the maturation of the MT channels in rat OHCs. High-resolution immunogold labeling in adult rats showed that PMCA2 was distributed along the membranes of all three rows of OHC stereocilia at similar densities and at about a quarter of the density in inner hair cell stereocilia. The difference between OHCs and inner hair cells was similar to the ratio of their MT channel resting open probabilities. Gold particle counts revealed no difference in PMCA2 density between low- and high-frequency OHC bundles despite larger MT currents in high-frequency OHCs. The PMCA2 density in OHC stereocilia was determined in low- and high-frequency regions from calibration of immunogold particle counts as 2200/μm(2) from which an extrusion rate of ∼200 ions/s per pump was inferred. The limited ability of PMCA2 to extrude the Ca(2+) load through MT channels may constitute a major cause of OHC vulnerability and high-frequency hearing loss.
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Affiliation(s)
- Qingguo Chen
- Department of Otolaryngology - Head and Neck Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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