1
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Smith CM, Curthoys IS, Laitman JT. A morphometric comparison of the ductus reuniens in humans and guinea pigs, with a note on its evolutionary importance. Anat Rec (Hoboken) 2024. [PMID: 38965777 DOI: 10.1002/ar.25534] [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: 03/14/2024] [Revised: 06/03/2024] [Accepted: 06/03/2024] [Indexed: 07/06/2024]
Abstract
The mammalian inner ear contains the sensory organs responsible for balance (semicircular canals, utricle, and saccule) and hearing (cochlea). While these organs are functionally distinct, there exists a critical structural connection between the two: the ductus reuniens (DR). Despite its functional importance, comparative descriptions of DR morphology are limited, hindering our understanding of the evolutionary diversification of hearing and balance systems among mammals. Using virtual 3D models derived from micro-CT, we examine the morphology of the DR and its relationship to the bony labyrinth in humans compared to that in a commonly used animal model, the guinea pig. Anatomical reconstructions and univariate measurements were carried out in the software 3D Slicer. Data indicate similarities in DR morphology between humans and guinea pigs in terms of overall shape. However, there are considerable differences in relative DR length and width between humans and guinea pigs. Humans possess a relatively shorter and narrower DR but with wider openings to the saccule and cochlear duct. This results in a relatively more constricted DR lumen in humans which may differentially limit fluid transfer between the saccule and cochlea. Our results reveal previously hidden morphological diversity in the communication between the hearing and balance systems of the mammalian inner ear which may indicate alternative strategies for isolating the Organ of Corti from the peripheral vestibular system throughout mammalian evolution.
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Affiliation(s)
- Christopher M Smith
- Division of Anthropology, American Museum of Natural History, New York City, New York, USA
- New York Consortium in Evolutionary Primatology, New York, USA
| | - Ian S Curthoys
- Vestibular Research Laboratory, School of Psychology, University of Sydney, Sydney, New South Wales, Australia
| | - Jeffrey T Laitman
- New York Consortium in Evolutionary Primatology, New York, USA
- Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, New York, USA
- Department of Otolaryngology, Icahn School of Medicine at Mount Sinai, New York, USA
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2
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Lipovsek M. Comparative biology of the amniote vestibular utricle. Hear Res 2024; 448:109035. [PMID: 38763033 DOI: 10.1016/j.heares.2024.109035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2024] [Revised: 05/09/2024] [Accepted: 05/13/2024] [Indexed: 05/21/2024]
Abstract
The sensory epithelia of the auditory and vestibular systems of vertebrates have shared developmental and evolutionary histories. However, while the auditory epithelia show great variation across vertebrates, the vestibular sensory epithelia appear seemingly more conserved. An exploration of the current knowledge of the comparative biology of the amniote utricle, a vestibular sensory epithelium that senses linear acceleration, shows interesting instances of variability between birds and mammals. The distribution of sensory hair cell types, the position of the line of hair bundle polarity reversal and the properties of supporting cells show marked differences, likely impacting vestibular function and hair cell regeneration potential.
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Affiliation(s)
- Marcela Lipovsek
- Ear Institute, Faculty of Brain Sciences, University College London, London, UK.
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3
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Edens BM, Bronner ME. Making developmental sense of the senses, their origin and function. Curr Top Dev Biol 2024; 159:132-167. [PMID: 38729675 DOI: 10.1016/bs.ctdb.2024.01.015] [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] [Indexed: 05/12/2024]
Abstract
The primary senses-touch, taste, sight, smell, and hearing-connect animals with their environments and with one another. Aside from the eyes, the primary sense organs of vertebrates and the peripheral sensory pathways that relay their inputs arise from two transient stem cell populations: the neural crest and the cranial placodes. In this chapter we consider the senses from historical and cultural perspectives, and discuss the senses as biological faculties. We begin with the embryonic origin of the neural crest and cranial placodes from within the neural plate border of the ectodermal germ layer. Then, we describe the major chemical (i.e. olfactory and gustatory) and mechanical (i.e. vestibulo-auditory and somatosensory) senses, with an emphasis on the developmental interactions between neural crest and cranial placodes that shape their structures and functions.
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Affiliation(s)
- Brittany M Edens
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States.
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4
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Henry KS, Guo AA, Abrams KS. Normal behavioral discrimination of envelope statistics in budgerigars with kainate-induced cochlear synaptopathy. Hear Res 2024; 441:108927. [PMID: 38096707 PMCID: PMC10775186 DOI: 10.1016/j.heares.2023.108927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 11/27/2023] [Accepted: 12/04/2023] [Indexed: 12/27/2023]
Abstract
Cochlear synaptopathy is a common pathology in humans associated with aging and potentially sound overexposure. Synaptopathy is widely expected to cause "hidden hearing loss," including difficulty perceiving speech in noise, but support for this hypothesis is controversial. Here in budgerigars (Melopsittacus undulatus), we evaluated the impact of long-term cochlear synaptopathy on behavioral discrimination of Gaussian noise (GN) and low-noise noise (LNN) signals processed to have a flatter envelope. Stimuli had center frequencies of 1-3kHz, 100-Hz bandwidth, and were presented at sensation levels (SLs) from 10 to 30dB. We reasoned that narrowband, low-SL stimuli of this type should minimize spread of excitation across auditory-nerve fibers, and hence might reveal synaptopathy-related defects if they exist. Cochlear synaptopathy was induced without hair-cell injury using kainic acid (KA). Behavioral threshold tracking experiments characterized the minimum stimulus duration above which animals could reliably discriminate between LNN and GN. Budgerigar thresholds for LNN-GN discrimination ranged from 40 to 60ms at 30dB SL, were similar across frequencies, and increased for lower SLs. Notably, animals with long-term 39-77% estimated synaptopathy performed similarly to controls, requiring on average a ∼7.5% shorter stimulus duration (-0.7±1.0dB; mean difference ±SE) for LNN-GN discrimination. Decision-variable correlation analyses of detailed behavioral response patterns showed that individual animals relied on envelope cues to discriminate LNN and GN, with lesser roles of FM and energy cues; no difference was found between KA-exposed and control groups. These results suggest that long-term cochlear synaptopathy does not impair discrimination of low-level signals with different envelope statistics.
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Affiliation(s)
- Kenneth S Henry
- Department of Otolaryngology, University of Rochester, NY 14642, USA; Department of Biomedical Engineering, University of Rochester, Rochester, NY 14642, USA; Department of Neuroscience, University of Rochester, Rochester, NY 14642, USA.
| | - Anna A Guo
- Department of Biomedical Engineering, University of Rochester, Rochester, NY 14642, USA
| | - Kristina S Abrams
- Department of Neuroscience, University of Rochester, Rochester, NY 14642, USA
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5
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Wu Z, Jiang J, Lischka FW, McGrane SJ, Porat-Mesenco Y, Zhao K. Domestic cat nose functions as a highly efficient coiled parallel gas chromatograph. PLoS Comput Biol 2023; 19:e1011119. [PMID: 37384594 PMCID: PMC10309622 DOI: 10.1371/journal.pcbi.1011119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Accepted: 04/20/2023] [Indexed: 07/01/2023] Open
Abstract
The peripheral structures of mammalian sensory organs often serve to support their functionality, such as alignment of hair cells to the mechanical properties of the inner ear. Here, we examined the structure-function relationship for mammalian olfaction by creating an anatomically accurate computational nasal model for the domestic cat (Felis catus) based on high resolution microCT and sequential histological sections. Our results showed a distinct separation of respiratory and olfactory flow regimes, featuring a high-speed dorsal medial stream that increases odor delivery speed and efficiency to the ethmoid olfactory region without compromising the filtration and conditioning purpose of the nose. These results corroborated previous findings in other mammalian species, which implicates a common theme to deal with the physical size limitation of the head that confines the nasal airway from increasing in length infinitely as a straight tube. We thus hypothesized that these ethmoid olfactory channels function as parallel coiled chromatograph channels, and further showed that the theoretical plate number, a widely-used indicator of gas chromatograph efficiency, is more than 100 times higher in the cat nose than an "amphibian-like" straight channel fitting the similar skull space, at restful breathing state. The parallel feature also reduces airflow speed within each coil, which is critical to achieve the high plate number, while feeding collectively from the high-speed dorsal medial stream so that total odor sampling speed is not sacrificed. The occurrence of ethmoid turbinates is an important step in the evolution of mammalian species that correlates to their expansive olfactory function and brain development. Our findings reveal novel mechanisms on how such structure may facilitate better olfactory performance, furthering our understanding of the successful adaptation of mammalian species, including F. catus, a popular pet, to diverse environments.
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Affiliation(s)
- Zhenxing Wu
- Department of Otolaryngology—Head & Neck Surgery, The Ohio State University, Columbus, Ohio, United States of America
| | - Jianbo Jiang
- Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America
| | - Fritz W. Lischka
- Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America
| | - Scott J. McGrane
- Waltham Petcare Science Institute, Freeby Lane, Waltham-on-the-Wolds, Melton Mowbray, Leicestershire, United Kingdom
| | - Yael Porat-Mesenco
- MJ Ryan Veterinary Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Kai Zhao
- Department of Otolaryngology—Head & Neck Surgery, The Ohio State University, Columbus, Ohio, United States of America
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6
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Variations in cochlea shape reveal different evolutionary adaptations in primates and rodents. Sci Rep 2023; 13:2235. [PMID: 36754991 PMCID: PMC9908918 DOI: 10.1038/s41598-023-29478-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Accepted: 02/06/2023] [Indexed: 02/10/2023] Open
Abstract
The presence of a coiled cochlea is a unique feature of the therian inner ear. While some aspects of the cochlea are already known to affect hearing capacities, the full extent of the relationships between the morphology and function of this organ are not yet understood-especially when the effect of body size differences between species is minimized. Here, focusing on Euarchontoglires, we explore cochlear morphology of 33 species of therian mammals with a restricted body size range. Using μCT scans, 3D models and 3D geometric morphometrics, we obtained shape information of the cochlea and used it to build phylogenetically corrected least square models with 12 hearing variables obtained from the literature. Our results reveal that different taxonomic groups differ significantly in cochlea shape. We further show that these shape differences are related to differences in hearing capacities between these groups, despite of similar cochlear lengths. Most strikingly, rodents with good low-frequency hearing display "tower-shaped" cochleae, achieved by increasing the degree of coiling of their cochlea. In contrast, primates present relatively wider cochleae and relative better high frequency hearing. These results suggest that primates and rodents increased their cochlea lengths through different morpho-evolutionary trajectories.
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7
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Human cochlear microstructures at risk of electrode insertion trauma, elucidated in 3D with contrast-enhanced microCT. Sci Rep 2023; 13:2191. [PMID: 36750646 PMCID: PMC9905077 DOI: 10.1038/s41598-023-29401-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 02/03/2023] [Indexed: 02/09/2023] Open
Abstract
Cochlear implant restores hearing loss through electrical stimulation of the hearing nerve from within the cochlea. Unfortunately, surgical implantation of this neuroprosthesis often traumatizes delicate intracochlear structures, resulting in loss of residual hearing and compromising hearing in noisy environments and appreciation of music. To avoid cochlear trauma, insertion techniques and devices have to be adjusted to the cochlear microanatomy. However, existing techniques were unable to achieve a representative visualization of the human cochlea: classical histology damages the tissues and lacks 3D perspective; standard microCT fails to resolve the cochlear soft tissues; and previously used X-ray contrast-enhancing staining agents are destructive. In this study, we overcame these limitations by performing contrast-enhanced microCT imaging (CECT) with a novel polyoxometalate staining agent Hf-WD POM. With Hf-WD POM-based CECT, we achieved nondestructive, high-resolution, simultaneous, 3D visualization of the mineralized and soft microstructures in fresh-frozen human cochleae. This enabled quantitative analysis of the true intracochlear dimensions and led to anatomical discoveries, concerning surgically-relevant microstructures: the round window membrane, the Rosenthal's canal and the secondary spiral lamina. Furthermore, we demonstrated that Hf-WD POM-based CECT enables quantitative assessment of these structures as well as their trauma.
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8
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Lipovsek M, Elgoyhen AB. The evolutionary tuning of hearing. Trends Neurosci 2023; 46:110-123. [PMID: 36621369 DOI: 10.1016/j.tins.2022.12.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 11/29/2022] [Accepted: 12/06/2022] [Indexed: 01/08/2023]
Abstract
After the transition to life on land, tympanic middle ears emerged separately in different groups of tetrapods, facilitating the efficient detection of airborne sounds and paving the way for high frequency sensitivity. The processes that brought about high-frequency hearing in mammals are tightly linked to the accumulation of coding sequence changes in inner ear genes; many of which were selected during evolution. These include proteins involved in hair bundle morphology, mechanotransduction and high endolymphatic potential, somatic electromotility for sound amplification, ribbon synapses for high-fidelity transmission of sound stimuli, and efferent synapses for the modulation of sound amplification. Here, we review the molecular evolutionary processes behind auditory functional innovation. Overall, the evidence to date supports the hypothesis that changes in inner ear proteins were central to the fine tuning of mammalian hearing.
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Affiliation(s)
- Marcela Lipovsek
- Ear Institute, Faculty of Brain Sciences, University College London, London, UK.
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
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9
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Chen X, Wan H, Bai Y, Zhang Y, Hua Q. Advances in Understanding the Notch Signaling Pathway in the Cochlea. Curr Pharm Des 2023; 29:3266-3273. [PMID: 37990430 DOI: 10.2174/0113816128273532231103110910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 10/17/2023] [Indexed: 11/23/2023]
Abstract
The cochlear structure is highly complex and specific, and its development is regulated by multiple signaling pathways. Abnormalities in cochlear development can lead to different degrees of loss of function. Hair cells (HCs), which are difficult to regenerate in the mature mammalian cochlea, are susceptible to damage from noise and ototoxic drugs, and damage to HCs can cause hearing loss to varying degrees. Notch, a classical developmental signaling molecule, has been shown to be closely associated with embryonic cochlear development and plays an important role in HC regeneration in mammals, suggesting that the Notch signaling pathway may be a potential therapeutic target for cochlear development and hearing impairment due to HC damage. In recent years, the important role of the Notch signaling pathway in the cochlea has received increasing attention. In this paper, we review the role of Notch signaling in cochlear development and HC regeneration, with the aim of providing new research ideas for the prevention and treatment of related diseases.
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Affiliation(s)
- Xiaoying Chen
- Department of Otolaryngology-Head and Neck Surgery, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Huanzhi Wan
- Department of Otolaryngology-Head and Neck Surgery, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Yutong Bai
- Department of Otolaryngology-Head and Neck Surgery, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Yuanyuan Zhang
- Department of Otolaryngology-Head and Neck Surgery, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Qingquan Hua
- Department of Otolaryngology-Head and Neck Surgery, Renmin Hospital of Wuhan University, Wuhan 430060, China
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10
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Li H, Staxäng K, Hodik M, Melkersson KG, Rask-Andersen H. The ultrastructure of a stria vascularis in the auditory organ of the cuban crocodile ( Crocodylus rhombifer). Front Cell Dev Biol 2023; 11:1129074. [PMID: 36891513 PMCID: PMC9986273 DOI: 10.3389/fcell.2023.1129074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 02/06/2023] [Indexed: 02/22/2023] Open
Abstract
Background: An endocochlear potential (EP) exists in the mammalian cochlea generated by the stria vascularis and an associated fibrocyte network. It plays an essential role for sensory cell function and hearing sensitivity. In non-mammalian ectothermic animals the endocochlear potential is low and its origin somewhat unclear. In this study, we explored the crocodilian auditory organ and describe the fine structure of a stria vascularis epithelium that has not been verified in birds. Material and Methods: Three Cuban crocodiles (Crocodylus rhombifer) were analyzed with light and transmission electron microscopy. The ears were fixed in glutaraldehyde The temporal bones were drilled out and decalcified. The ears were dehydrated, and embedded and was followed by semi-thin and thin sectioning. Results: The fine structure of the crocodile auditory organ including the papilla basilaris and endolymph system was outlined. The upper roof of the endolymph compartment was specialized into a Reissner membrane and tegmentum vasculosum. At the lateral limbus an organized, multilayered, vascularized epithelium or stria vascularis was identified. Discussion: Electron microscopy demonstrates that the auditory organ in Crocodylus rhombifer, unlike in birds, contains a stria vascularis epithelium separate from the tegmentum vasculosum. It is believed to secrete endolymph and to generate a low grade endocochlear potential. It may regulate endolymph composition and optimize hearing sensitivity alongside the tegmentum vasculosum. It could represent a parallel evolution essential for the adaptation of crocodiles to their diverse habitats.
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Affiliation(s)
- Hao Li
- Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital, Uppsala, Sweden
| | - Karin Staxäng
- The Rudbeck TEM laboratory, Uppsala University, Uppsala, Sweden
| | - Monika Hodik
- The Rudbeck TEM laboratory, Uppsala University, Uppsala, Sweden
| | | | - Helge Rask-Andersen
- Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital, Uppsala, Sweden
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11
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Smith CM, Curthoys IS, Plontke SK, Menzel M, Mukherjee P, Wong C, Laitman JT. Insights into Inner Ear Function and Disease Through Novel Visualization of the Ductus Reuniens, a Seminal Communication Between Hearing and Balance Mechanisms. J Assoc Res Otolaryngol 2022; 23:633-645. [PMID: 35804276 PMCID: PMC9613819 DOI: 10.1007/s10162-022-00858-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 06/29/2022] [Indexed: 11/27/2022] Open
Abstract
The sensory end-organs responsible for hearing and balance in the mammalian inner ear are connected via a small membranous duct known as the ductus reuniens (also known as the reuniting duct (DR)). The DR serves as a vital nexus linking the hearing and balance systems by providing the only endolymphatic connection between the cochlea and vestibular labyrinth. Recent studies have hypothesized new roles of the DR in inner ear function and disease, but a lack of knowledge regarding its 3D morphology and spatial configuration precludes testing of such hypotheses. We reconstructed the 3D morphology of the DR and surrounding anatomy using osmium tetroxide micro-computed tomography and digital visualizations of three human inner ear specimens. This provides a detailed, quantitative description of the DR's morphology, spatial relationships to surrounding structures, and an estimation of its orientation relative to head position. Univariate measurements of the DR, inner ear, and cranial planes were taken using the software packages 3D Slicer and Zbrush. The DR forms a narrow, curved, flattened tube varying in lumen size, shape, and wall thickness, with its middle third being the narrowest. The DR runs in a shallow bony sulcus superior to the osseus spiral lamina and adjacent to a ridge of bone that we term the "crista reuniens" oriented posteromedially within the cranium. The DR's morphology and structural configuration relative to surrounding anatomy has important implications for understanding aspects of inner ear function and disease, particularly after surgical alteration of the labyrinth and potential causative factors for Ménière's disease.
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Affiliation(s)
- Christopher M Smith
- Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, Annenberg Building Room 12-90, 1468 Madison Ave, New York, NY, 10029, USA.
- Department of Anthropology, The Graduate Center, City University of New York, New York, NY, USA.
- New York Consortium in Evolutionary Primatology, New York, NY, USA.
| | - Ian S Curthoys
- Vestibular Research Laboratory, School of Psychology, University of Sydney, Sydney, NSW, Australia
| | - Stefan K Plontke
- Department of Otorhinolaryngology, Head and Neck Surgery, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Matthias Menzel
- Fraunhofer Institute for Microstructure of Materials and Systems, Halle (Saale), Germany
| | - Payal Mukherjee
- RPA Institute of Academic Surgery, Royal Prince Alfred Hospital, Sydney, NSW, Australia
| | - Christopher Wong
- Vestibular Research Laboratory, School of Psychology, University of Sydney, Sydney, NSW, Australia
| | - Jeffrey T Laitman
- Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, Annenberg Building Room 12-90, 1468 Madison Ave, New York, NY, 10029, USA
- Department of Anthropology, The Graduate Center, City University of New York, New York, NY, USA
- New York Consortium in Evolutionary Primatology, New York, NY, USA
- Department of Otolaryngology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
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12
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Kelley MW. Cochlear Development; New Tools and Approaches. Front Cell Dev Biol 2022; 10:884240. [PMID: 35813214 PMCID: PMC9260282 DOI: 10.3389/fcell.2022.884240] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 05/19/2022] [Indexed: 12/21/2022] Open
Abstract
The sensory epithelium of the mammalian cochlea, the organ of Corti, is comprised of at least seven unique cell types including two functionally distinct types of mechanosensory hair cells. All of the cell types within the organ of Corti are believed to develop from a population of precursor cells referred to as prosensory cells. Results from previous studies have begun to identify the developmental processes, lineage restrictions and signaling networks that mediate the specification of many of these cell types, however, the small size of the organ and the limited number of each cell type has hampered progress. Recent technical advances, in particular relating to the ability to capture and characterize gene expression at the single cell level, have opened new avenues for understanding cellular specification in the organ of Corti. This review will cover our current understanding of cellular specification in the cochlea, discuss the most commonly used methods for single cell RNA sequencing and describe how results from a recent study using single cell sequencing provided new insights regarding cellular specification.
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13
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Maudoux A, Vitry S, El-Amraoui A. Vestibular Deficits in Deafness: Clinical Presentation, Animal Modeling, and Treatment Solutions. Front Neurol 2022; 13:816534. [PMID: 35444606 PMCID: PMC9013928 DOI: 10.3389/fneur.2022.816534] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 02/23/2022] [Indexed: 11/13/2022] Open
Abstract
The inner ear is responsible for both hearing and balance. These functions are dependent on the correct functioning of mechanosensitive hair cells, which convert sound- and motion-induced stimuli into electrical signals conveyed to the brain. During evolution of the inner ear, the major changes occurred in the hearing organ, whereas the structure of the vestibular organs remained constant in all vertebrates over the same period. Vestibular deficits are highly prevalent in humans, due to multiple intersecting causes: genetics, environmental factors, ototoxic drugs, infections and aging. Studies of deafness genes associated with balance deficits and their corresponding animal models have shed light on the development and function of these two sensory systems. Bilateral vestibular deficits often impair individual postural control, gaze stabilization, locomotion and spatial orientation. The resulting dizziness, vertigo, and/or falls (frequent in elderly populations) greatly affect patient quality of life. In the absence of treatment, prosthetic devices, such as vestibular implants, providing information about the direction, amplitude and velocity of body movements, are being developed and have given promising results in animal models and humans. Novel methods and techniques have led to major progress in gene therapies targeting the inner ear (gene supplementation and gene editing), 3D inner ear organoids and reprograming protocols for generating hair cell-like cells. These rapid advances in multiscale approaches covering basic research, clinical diagnostics and therapies are fostering interdisciplinary research to develop personalized treatments for vestibular disorders.
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Affiliation(s)
- Audrey Maudoux
- Unit Progressive Sensory Disorders, Pathophysiology and Therapy, Institut Pasteur, Institut de l'Audition, Université de Paris, INSERM-UMRS1120, Paris, France.,Center for Balance Evaluation in Children (EFEE), Otolaryngology Department, Assistance Publique des Hôpitaux de Paris, Robert-Debré University Hospital, Paris, France
| | - Sandrine Vitry
- Unit Progressive Sensory Disorders, Pathophysiology and Therapy, Institut Pasteur, Institut de l'Audition, Université de Paris, INSERM-UMRS1120, Paris, France
| | - Aziz El-Amraoui
- Unit Progressive Sensory Disorders, Pathophysiology and Therapy, Institut Pasteur, Institut de l'Audition, Université de Paris, INSERM-UMRS1120, Paris, France
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14
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Botto C, Dalkara D, El-Amraoui A. Progress in Gene Editing Tools and Their Potential for Correcting Mutations Underlying Hearing and Vision Loss. Front Genome Ed 2021; 3:737632. [PMID: 34778871 PMCID: PMC8581640 DOI: 10.3389/fgeed.2021.737632] [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: 07/07/2021] [Accepted: 10/14/2021] [Indexed: 12/12/2022] Open
Abstract
Blindness and deafness are the most frequent sensory disorders in humans. Whatever their cause - genetic, environmental, or due to toxic agents, or aging - the deterioration of these senses is often linked to irreversible damage to the light-sensing photoreceptor cells (blindness) and/or the mechanosensitive hair cells (deafness). Efforts are increasingly focused on preventing disease progression by correcting or replacing the blindness and deafness-causal pathogenic alleles. In recent years, gene replacement therapies for rare monogenic disorders of the retina have given positive results, leading to the marketing of the first gene therapy product for a form of childhood hereditary blindness. Promising results, with a partial restoration of auditory function, have also been reported in preclinical models of human deafness. Silencing approaches, including antisense oligonucleotides, adeno-associated virus (AAV)-mediated microRNA delivery, and genome-editing approaches have also been applied to various genetic forms of blindness and deafness The discovery of new DNA- and RNA-based CRISPR/Cas nucleases, and the new generations of base, prime, and RNA editors offers new possibilities for directly repairing point mutations and therapeutically restoring gene function. Thanks to easy access and immune-privilege status of self-contained compartments, the eye and the ear continue to be at the forefront of developing therapies for genetic diseases. Here, we review the ongoing applications and achievements of this new class of emerging therapeutics in the sensory organs of vision and hearing, highlighting the challenges ahead and the solutions to be overcome for their successful therapeutic application in vivo.
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Affiliation(s)
- Catherine Botto
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Deniz Dalkara
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Aziz El-Amraoui
- Unit Progressive Sensory Disorders, Pathophysiology and Therapy, Institut Pasteur, Institut de l'Audition, Université de Paris, INSERM-UMRS1120, Paris, France
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15
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Moreira A, Croze M, Delehelle F, Cussat-Blanc S, Luga H, Mollereau C, Balaresque P. Hearing Sensitivity of Primates: Recurrent and Episodic Positive Selection in Hair Cells and Stereocilia Protein-Coding Genes. Genome Biol Evol 2021; 13:6302699. [PMID: 34137817 PMCID: PMC8358225 DOI: 10.1093/gbe/evab133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/06/2021] [Indexed: 12/29/2022] Open
Abstract
The large spectrum of hearing sensitivity observed in primates results from the impact of environmental and behavioral pressures to optimize sound perception and localization. Although evidence of positive selection in auditory genes has been detected in mammals including in Hominoids, selection has never been investigated in other primates. We analyzed 123 genes highly expressed in the inner ear of 27 primate species and tested to what extent positive selection may have shaped these genes in the order Primates tree. We combined both site and branch-site tests to obtain a comprehensive picture of the positively selected genes (PSGs) involved in hearing sensitivity, and drew a detailed description of the most affected branches in the tree. We chose a conservative approach, and thus focused on confounding factors potentially affecting PSG signals (alignment, GC-biased gene conversion, duplications, heterogeneous sequencing qualities). Using site tests, we showed that around 12% of these genes are PSGs, an α selection value consistent with average human genome estimates (10-15%). Using branch-site tests, we showed that the primate tree is heterogeneously affected by positive selection, with the black snub-nosed monkey, the bushbaby, and the orangutan, being the most impacted branches. A large proportion of these genes is inclined to shape hair cells and stereocilia, which are involved in the mechanotransduction process, known to influence frequency perception. Adaptive selection, and more specifically recurrent adaptive evolution, could have acted in parallel on a set of genes (ADGRV1, USH2A, PCDH15, PTPRQ, and ATP8A2) involved in stereocilia growth and the whole complex of bundle links connecting them, in species across different habitats, including high altitude and nocturnal environments.
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Affiliation(s)
- Andreia Moreira
- Anthropologie Moléculaire et Imagerie de Synthèse (AMIS), Faculté de Médecine Purpan, CNRS UMR5288, Université de Toulouse, Université Toulouse III Paul Sabatier, France.,Institut de Recherche en Informatique de Toulouse (IRIT), CNRS UMR5505, Université Toulouse III Paul Sabatier, France
| | - Myriam Croze
- Anthropologie Moléculaire et Imagerie de Synthèse (AMIS), Faculté de Médecine Purpan, CNRS UMR5288, Université de Toulouse, Université Toulouse III Paul Sabatier, France
| | - Franklin Delehelle
- Anthropologie Moléculaire et Imagerie de Synthèse (AMIS), Faculté de Médecine Purpan, CNRS UMR5288, Université de Toulouse, Université Toulouse III Paul Sabatier, France.,Institut de Recherche en Informatique de Toulouse (IRIT), CNRS UMR5505, Université Toulouse III Paul Sabatier, France
| | - Sylvain Cussat-Blanc
- Institut de Recherche en Informatique de Toulouse (IRIT), CNRS UMR5505, Université Toulouse III Paul Sabatier, France
| | - Hervé Luga
- Institut de Recherche en Informatique de Toulouse (IRIT), CNRS UMR5505, Université Toulouse III Paul Sabatier, France
| | - Catherine Mollereau
- Anthropologie Moléculaire et Imagerie de Synthèse (AMIS), Faculté de Médecine Purpan, CNRS UMR5288, Université de Toulouse, Université Toulouse III Paul Sabatier, France
| | - Patricia Balaresque
- Anthropologie Moléculaire et Imagerie de Synthèse (AMIS), Faculté de Médecine Purpan, CNRS UMR5288, Université de Toulouse, Université Toulouse III Paul Sabatier, France
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16
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Rutherford MA, von Gersdorff H, Goutman JD. Encoding sound in the cochlea: from receptor potential to afferent discharge. J Physiol 2021; 599:2527-2557. [PMID: 33644871 PMCID: PMC8127127 DOI: 10.1113/jp279189] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Accepted: 02/22/2021] [Indexed: 12/17/2022] Open
Abstract
Ribbon-class synapses in the ear achieve analog to digital transformation of a continuously graded membrane potential to all-or-none spikes. In mammals, several auditory nerve fibres (ANFs) carry information from each inner hair cell (IHC) to the brain in parallel. Heterogeneity of transmission among synapses contributes to the diversity of ANF sound-response properties. In addition to the place code for sound frequency and the rate code for sound level, there is also a temporal code. In series with cochlear amplification and frequency tuning, neural representation of temporal cues over a broad range of sound levels enables auditory comprehension in noisy multi-speaker settings. The IHC membrane time constant introduces a low-pass filter that attenuates fluctuations of the receptor potential above 1-2 kHz. The ANF spike generator adds a high-pass filter via its depolarization-rate threshold that rejects slow changes in the postsynaptic potential and its phasic response property that ensures one spike per depolarization. Synaptic transmission involves several stochastic subcellular processes between IHC depolarization and ANF spike generation, introducing delay and jitter that limits the speed and precision of spike timing. ANFs spike at a preferred phase of periodic sounds in a process called phase-locking that is limited to frequencies below a few kilohertz by both the IHC receptor potential and the jitter in synaptic transmission. During phase-locking to periodic sounds of increasing intensity, faster and facilitated activation of synaptic transmission and spike generation may be offset by presynaptic depletion of synaptic vesicles, resulting in relatively small changes in response phase. Here we review encoding of spike-timing at cochlear ribbon synapses.
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Affiliation(s)
- Mark A. Rutherford
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Henrique von Gersdorff
- Vollum Institute, Oregon Hearing Research Center, Oregon Health and Sciences University, Portland, Oregon 97239
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17
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Mao F, Liu C, Chase MH, Smith AK, Meng J. Exploring ancestral phenotypes and evolutionary development of the mammalian middle ear based on Early Cretaceous Jehol mammals. Natl Sci Rev 2021; 8:nwaa188. [PMID: 34691634 PMCID: PMC8288399 DOI: 10.1093/nsr/nwaa188] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 08/20/2020] [Accepted: 08/21/2020] [Indexed: 01/25/2023] Open
Abstract
We report a new Cretaceous multituberculate mammal with 3D auditory bones preserved. Along with other fossil and extant mammals, the unequivocal auditory bones display features potentially representing ancestral phenotypes of the mammalian middle ear. These phenotypes show that the ectotympanic and the malleus-incus complex changed notably during their retreating from the dentary at various evolutionary stages and suggest convergent evolution of some features to extant mammals. In contrast, the incudomalleolar joint was conservative in having a braced hinge configuration, which narrows the morphological gap between the quadroarticular jaw joint of non-mammalian cynodonts and the incudomalleolar articulations of extant mammals. The saddle-shaped and abutting malleus-incus complexes in therians and monotremes, respectively, could have evolved from the braced hinge joint independently. The evolutionary changes recorded in the Mesozoic mammals are largely consistent with the middle ear morphogenesis during the ontogeny of extant mammals, supporting the relation between evolution and development.
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Affiliation(s)
- Fangyuan Mao
- Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China
- CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China
- Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA
| | - Cunyu Liu
- Beipiao Pterosaur Museum of China, Beipiao 122100, China
| | - Morgan Hill Chase
- Microscopy and Imaging Facility, American Museum of Natural History, New York, NY 10024, USA
| | - Andrew K Smith
- Microscopy and Imaging Facility, American Museum of Natural History, New York, NY 10024, USA
| | - Jin Meng
- Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA
- Earth and Environmental Sciences, Graduate Center, City University of New York, New York, NY 10016, USA
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18
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Pyott SJ, van Tuinen M, Screven LA, Schrode KM, Bai JP, Barone CM, Price SD, Lysakowski A, Sanderford M, Kumar S, Santos-Sacchi J, Lauer AM, Park TJ. Functional, Morphological, and Evolutionary Characterization of Hearing in Subterranean, Eusocial African Mole-Rats. Curr Biol 2020; 30:4329-4341.e4. [PMID: 32888484 DOI: 10.1016/j.cub.2020.08.035] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 06/09/2020] [Accepted: 08/07/2020] [Indexed: 12/26/2022]
Abstract
Naked mole-rats are highly vocal, eusocial, subterranean rodents with, counterintuitively, poor hearing. The causes underlying their altered hearing are unknown. Moreover, whether altered hearing is degenerate or adaptive to their unique lifestyles is controversial. We used various methods to identify the factors contributing to altered hearing in naked and the related Damaraland mole-rats and to examine whether these alterations result from relaxed or adaptive selection. Remarkably, we found that cochlear amplification was absent from both species despite normal prestin function in outer hair cells isolated from naked mole-rats. Instead, loss of cochlear amplification appears to result from abnormal hair bundle morphologies observed in both species. By exploiting a well-curated deafness phenotype-genotype database, we identified amino acid substitutions consistent with abnormal hair bundle morphology and reduced hearing sensitivity. Amino acid substitutions were found in unique groups of six hair bundle link proteins. Molecular evolutionary analyses revealed shifts in selection pressure at both the gene and the codon level for five of these six hair bundle link proteins. Substitutions in three of these proteins are associated exclusively with altered hearing. Altogether, our findings identify the likely mechanism of altered hearing in African mole-rats, making them the only identified mammals naturally lacking cochlear amplification. Moreover, our findings suggest that altered hearing in African mole-rats is adaptive, perhaps tailoring hearing to eusocial and subterranean lifestyles. Finally, our work reveals multiple, unique evolutionary trajectories in African mole-rat hearing and establishes species members as naturally occurring disease models to investigate human hearing loss.
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Affiliation(s)
- Sonja J Pyott
- University Medical Center Groningen and University of Groningen, Department of Otorhinolaryngology and Head/Neck Surgery, 9713GZ Groningen, the Netherlands.
| | - Marcel van Tuinen
- University Medical Center Groningen and University of Groningen, Department of Otorhinolaryngology and Head/Neck Surgery, 9713GZ Groningen, the Netherlands
| | - Laurel A Screven
- Johns Hopkins School of Medicine, Department of Otolaryngology, Baltimore, MD 21205, USA
| | - Katrina M Schrode
- Johns Hopkins School of Medicine, Department of Otolaryngology, Baltimore, MD 21205, USA
| | - Jun-Ping Bai
- Yale University School of Medicine, Department of Neurology, 333 Cedar Street, New Haven, CT 06510, USA
| | - Catherine M Barone
- University of Illinois at Chicago, Department of Biological Sciences, Chicago, IL 60612, USA
| | - Steven D Price
- University of Illinois at Chicago, Department of Anatomy and Cell Biology, Chicago, IL 60612, USA
| | - Anna Lysakowski
- University of Illinois at Chicago, Department of Anatomy and Cell Biology, Chicago, IL 60612, USA
| | - Maxwell Sanderford
- Temple University, Institute for Genomics and Evolutionary Medicine and Department of Biology, Philadelphia, PA 19122, USA
| | - Sudhir Kumar
- Temple University, Institute for Genomics and Evolutionary Medicine and Department of Biology, Philadelphia, PA 19122, USA; King Abdulaziz University, Center for Excellence in Genome Medicine and Research, Jeddah, Saudi Arabia
| | - Joseph Santos-Sacchi
- Yale University School of Medicine, Department of Surgery (Otolaryngology) and Department of Neuroscience and Cellular and Molecular Physiology, 333 Cedar Street, New Haven, CT 06510, USA
| | - Amanda M Lauer
- Johns Hopkins School of Medicine, Department of Otolaryngology, Baltimore, MD 21205, USA
| | - Thomas J Park
- University of Illinois at Chicago, Department of Biological Sciences, Chicago, IL 60612, USA
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19
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Le Maître A, Grunstra NDS, Pfaff C, Mitteroecker P. Evolution of the Mammalian Ear: An Evolvability Hypothesis. Evol Biol 2020; 47:187-192. [PMID: 32801400 PMCID: PMC7399675 DOI: 10.1007/s11692-020-09502-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 05/12/2020] [Indexed: 11/29/2022]
Abstract
Encapsulated within the temporal bone and comprising the smallest elements of the vertebrate skeleton, the ear is key to multiple senses: balance, posture control, gaze stabilization, and hearing. The transformation of the primary jaw joint into the mammalian ear ossicles is one of the most iconic transitions in vertebrate evolution, but the drivers of this complex evolutionary trajectory are not fully understood. We propose a novel hypothesis: The incorporation of the bones of the primary jaw joint into the middle ear has considerably increased the genetic, regulatory, and developmental complexity of the mammalian ear. This increase in the number of genetic and developmental factors may, in turn, have increased the evolutionary degrees of freedom for independent adaptations of the different functional ear units. The simpler ear anatomy in birds and reptiles may be less susceptible to developmental instabilities and disorders than in mammals but also more constrained in its evolution. Despite the tight spatial entanglement of functional ear components, the increased "evolvability" of the mammalian ear may have contributed to the evolutionary success and adaptive diversification of mammals in the vast diversity of ecological and behavioral niches observable today. A brief literature review revealed supporting evidence for this hypothesis.
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Affiliation(s)
- Anne Le Maître
- Department of Evolutionary Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
- Department of Palaeontology, University of Vienna, Vienna, Austria
- PALEVOPRIM - UMR 7262CNRS INEE, Université de Poitiers, Poitiers, France
| | - Nicole D. S. Grunstra
- Department of Evolutionary Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
- KLI Institute for Evolution and Cognition Research, Klosterneuburg, Austria
- Mammal Collection, Natural History Museum Vienna, Vienna, Austria
| | - Cathrin Pfaff
- Department of Palaeontology, University of Vienna, Vienna, Austria
| | - Philipp Mitteroecker
- Department of Evolutionary Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
- KLI Institute for Evolution and Cognition Research, Klosterneuburg, Austria
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20
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Mao F, Hu Y, Li C, Wang Y, Chase MH, Smith AK, Meng J. Integrated hearing and chewing modules decoupled in a Cretaceous stem therian mammal. Science 2019; 367:305-308. [PMID: 31806694 DOI: 10.1126/science.aay9220] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Accepted: 11/21/2019] [Indexed: 12/13/2022]
Abstract
On the basis of multiple skeletal specimens from Liaoning, China, we report a new genus and species of Cretaceous stem therian mammal that displays decoupling of hearing and chewing apparatuses and functions. The auditory bones, including the surangular, have no bone contact with the ossified Meckel's cartilage; the latter is loosely lodged on the medial rear of the dentary. This configuration probably represents the initial morphological stage of the definitive mammalian middle ear. Evidence shows that hearing and chewing apparatuses have evolved in a modular fashion. Starting as an integrated complex in non-mammaliaform cynodonts, the two modules, regulated by similar developmental and genetic mechanisms, eventually decoupled during the evolution of mammals, allowing further improvement for more efficient hearing and mastication.
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Affiliation(s)
- Fangyuan Mao
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China. .,CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China.,Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA
| | - Yaoming Hu
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China
| | - Chuankui Li
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.,CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China
| | - Yuanqing Wang
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.,CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China
| | - Morgan Hill Chase
- Microscopy and Imaging Facility, American Museum of Natural History, New York, NY 10024, USA
| | - Andrew K Smith
- Microscopy and Imaging Facility, American Museum of Natural History, New York, NY 10024, USA
| | - Jin Meng
- Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA. .,Earth and Environmental Sciences, Graduate Center, City University of New York, New York, NY 10016, USA
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21
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Harper T, Rougier GW. Petrosal morphology and cochlear function in Mesozoic stem therians. PLoS One 2019; 14:e0209457. [PMID: 31412094 PMCID: PMC6693738 DOI: 10.1371/journal.pone.0209457] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 06/07/2019] [Indexed: 11/19/2022] Open
Abstract
Here we describe the bony anatomy of the inner ear and surrounding structures seen in three plesiomorphic crown mammalian petrosal specimens. Our study sample includes the triconodont Priacodon fruitaensis from the Upper Jurassic of North America, and two isolated stem therian petrosal specimens colloquially known as the Höövör petrosals, recovered from Aptian-Albian sediments in Mongolia. The second Höövör petrosal is here described at length for the first time. All three of these petrosals and a comparative sample of extant mammalian taxa have been imaged using micro-CT, allowing for detailed anatomical descriptions of the osteological correlates of functionally significant neurovascular features, especially along the abneural wall of the cochlear canal. The high resolution imaging provided here clarifies several hypotheses regarding the mosaic evolution of features of the cochlear endocast in early mammals. In particular, these images demonstrate that the membranous cochlear duct adhered to the bony cochlear canal abneurally to a secondary bony lamina before the appearance of an opposing primary bony lamina or tractus foraminosus. Additionally, while corroborating the general trend of reduction of venous sinuses and plexuses within the pars cochlearis seen in crownward mammaliaforms generally, the Höövör petrosals show the localized enlargement of a portion of the intrapetrosal venous plexus. This new vascular feature is here interpreted as the bony accommodation for the vein of cochlear aqueduct, a structure that is solely, or predominantly, responsible for the venous drainage of the cochlear apparatus in extant therians. Given that our fossil stem therian inner ear specimens appear to have very limited high-frequency capabilities, the development of these modern vascular features of the cochlear endocast suggest that neither the initiation or enlargement of the stria vascularis (a unique mammalian organ) was originally associated with the capacity for high-frequency hearing or precise sound-source localization.
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Affiliation(s)
- Tony Harper
- Center for Functional Anatomy and Evolution, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Guillermo W. Rougier
- Department of Anatomical Sciences and Neurobiology, University of Louisville, Louisville, Kentucky, United States of America
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22
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Abstract
Outer hair cells (OHCs) of the mammalian cochlea behave like actuators: they feed energy into the cochlear partition and determine the overall mechanics of hearing. They do this by generating voltage-dependent axial forces. The resulting change in the cell length, observed by microscopy, has been termed "electromotility." The mechanism of force generation OHCs can be traced to a specific protein, prestin, a member of a superfamily SLC26 of transporters. This short review will identify some of the more recent findings on prestin. Although the tertiary structure of prestin has yet to be determined, results from the presence of its homologs in nonmammalian species suggest a possible conformation in mammalian OHCs, how it can act like a transport protein, and how it may have evolved.
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Affiliation(s)
- Jonathan Ashmore
- University College London Ear Institute, London WC1X8EE, United Kingdom
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