Development and evolution of the vestibular apparatuses of the inner ear

Abstract

The vertebrate inner ear is a labyrinthine sensory organ responsible for perceiving sound and body motion. While a great deal of research has been invested in understanding the auditory system, a growing body of work has begun to delineate the complex developmental program behind the apparatuses of the inner ear involved with vestibular function. These animal studies have helped identify genes involved in inner ear development and model syndromes known to include vestibular dysfunction, paving the way for generating treatments for people suffering from these disorders. This review will provide an overview of known inner ear anatomy and function and summarize the exciting discoveries behind inner ear development and the evolution of its vestibular apparatuses.

Vestibular Deficits in Deafness: Clinical Presentation, Animal Modeling, and Treatment Solutions

“…Studies in fish, amphibian, chicken, and mouse animal models, either normal or with defects, have provided considerable insight into the signals and pathways governing the identity, proliferation, and differentiation of inner ear cells, and tissue planar polarity. Specific details about these various aspects of development are provided by many excellent recent reviews ( 27 – 29 ). Remarkable progress has been made in our understanding of how different morphogens and transcription factors cooperate to establish anteroposterior and dorsoventral organ patterning, mediate cell-fate commitment into sensory, non-sensory, and neurogenic components, and orchestrate correct cellular remodeling and assembly during organ morphogenesis.…”

“…Like the cochlea, the vestibule displays a high degree of architectural organization in all its compartments and subregions, with multiple parameters, including dimension, volume, liquid composition, radius of the canal, and vestibular vs. cochlear chambers, constructed to facilitate optimal responses to species-specific directional (gravity and motion displacements) and acoustic (frequency range) features ( 29 , 44 , 59 ). The construction of this diversity involves strict developmental programs that are finely tuned in time and space, and necessary for adaptation to the specific needs of aquatic, terrestrial and aerial species ( 1 – 5 ).…”

“…The capacity of the inner ear to detect various stimuli in different environments has led to studies tracing the precise evolutionary origins of its compartments. Comparative anatomy studies based on fossil records, and cross-species studies, have provided a wealth of information about the role of convergent evolution in creating analogous ears adapted to specific needs in distantly-related taxa ( 26 , 29 , 60 , 61 ). Recent reviews have provided detailed information about the development of the inner ear and changes during its evolution, and about the independent evolution of mechanosensitive cells to accommodate mechanical senses ( 26 , 29 , 60 , 61 ).…”

“…Comparative anatomy studies based on fossil records, and cross-species studies, have provided a wealth of information about the role of convergent evolution in creating analogous ears adapted to specific needs in distantly-related taxa ( 26 , 29 , 60 , 61 ). Recent reviews have provided detailed information about the development of the inner ear and changes during its evolution, and about the independent evolution of mechanosensitive cells to accommodate mechanical senses ( 26 , 29 , 60 , 61 ). Focusing on vertebrates, we highlight here some major changes pertaining to the hearing and balance organs of the inner ear ( Figure 3 ).…”

An Integrated Perspective of Evolution and Development: From Genes to Function to Ear, Lateral Line and Electroreception

“…In addition to directly initiating the formation of neurons by Eya1, Sox2, Pax2 and Neurog1/2, another set of genes are regulated to differentiate into Neurod1 [18,20,21,71,73], followed by Isl1, Foxg1, Pou4f1 and Phox2b [71,[74][75][76], which interact with Shh, BMPs and Wnts to define neurons [77,78]. Regional regulation of the distinct vestibular, lateral line, electroreception and auditory neurons are sorted out by downstream genes regulating the distinct innervation.…”