Mutations affecting development of the zebrafish inner ear and lateral line

Abstract

Mutations giving rise to anatomical defects in the inner ear have been isolated in a large scale screen for mutations causing visible abnormalities in the zebrafish embryo (Haffter, P., Granato, M., Brand, M. et al. (1996) Development 123, 1–36). 58 mutants have been classified as having a primary ear phenotype; these fall into several phenotypic classes, affecting presence or size of the otoliths, size and shape of the otic vesicle and formation of the semicircular canals, and define at least 20 complementation groups. Mutations in seven genes cause loss of one or both otoliths, but do not appear to affect development of other structures within the ear. Mutations in seven genes affect morphology and patterning of the inner ear epithelium, including formation of the semicircular canals and, in some, development of sensory patches (maculae and cristae). Within this class, dog-eared mutants show abnormal development of semicircular canals and lack cristae within the ear, while in van gogh, semicircular canals fail to form altogether, resulting in a tiny otic vesicle containing a single sensory patch. Both these mutants show defects in the expression of homeobox genes within the otic vesicle. In a further class of mutants, ear size is affected while patterning appears to be relatively normal; mutations in three genes cause expansion of the otic vesicle, while in little ears and microtic, the ear is abnormally small, but still contains all five sensory patches, as in the wild type. Many of the ear and otolith mutants show an expected behavioural phenotype: embryos fail to balance correctly, and may swim on their sides, upside down, or in circles. Several mutants with similar balance defects have also been isolated that have no obvious structural ear defect, but that may include mutants with vestibular dysfunction of the inner ear (Granato, M., van Eeden, F. J. M., Schach, U. et al. (1996) Development, 123, 399–413,). Mutations in 19 genes causing primary defects in other structures also show an ear defect. In particular, ear phenotypes are often found in conjunction with defects of neural crest derivatives (pigment cells and/or cartilaginous elements of the jaw). At least one mutant, dog-eared, shows defects in both the ear and another placodally derived sensory system, the lateral line, while hypersensitive mutants have additional trunk lateral line organs.

From Causal Networks to Adverse Outcome Pathways: A Developmental Neurotoxicity Case Study

“…Biological plausibility—high. There is a number of consistent studies that support the relationship of increased cell death during the development and defect in the development of the inner ear ( Whitfield et al, 1996 ; Kozlowski et al, 2005 ; Schlosser, 2014 ).…”

“…Although the zebrafish ear does not contain a specialized hearing organ—there is no equivalent of the mammalian cochlea—many features are conserved with other vertebrate species ( Whitfield et al, 2002 ). The mature inner ear, found in all jawed vertebrates, has two functions: It serves as an auditory system, which detects sound waves, and as a vestibular system, which detects linear and angular accelerations, enabling the organism to maintain balance ( Whitfield et al, 1996 ).…”

“…The inner ear is the vertebrate organ of hearing and balance ( Whitfield, 2002 ). Several zebrafish mutants for studying development of inner ear like dog-eared or van gogh show defects in inner ear development and irregular swimming patterns ( Whitfield et al, 1996 ).…”

“…Dog-eared mutants show abnormal development of semicircular canals and lack cristae within the ear (Kozlowski et al, 2005). Zebrafish mutant embryos with defects of the inner ear fail to balance correctly, and may swim on their sides, upside down, or in circles (Whitfield et al, 1996). Biological plausibility-high.…”

Knockout of mafba Causes Inner-Ear Developmental Defects in Zebrafish via the Impairment of Proliferation and Differentiation of Ionocyte Progenitor Cells

“…The zebrafish otic vesicles consist of sensory hair cells and other non-sensory epithelial cells [10]. The barrier functions of the inner ear epithelial cells are essential to maintain homoeostasis in the otic lumen and the endolymph, which guides the development of hair cells, semicircular canals, and otoliths [11,12]. Ions and other components are secreted into the otic lumen and endolymph through ion channels of otic epithelial cells' membranes to maintain the steady state of endolymph homeostasis [13], which is also crucial for otolith formation [8,9,14,15].…”