Cilia in the developing zebrafish ear

Abstract

The inner ear, which mediates the senses of hearing and balance, derives from a simple ectodermal vesicle in the vertebrate embryo. In the zebrafish, the otic placode and vesicle express a whole suite of genes required for ciliogenesis and ciliary motility. Every cell of the otic epithelium is ciliated at early stages; at least three different ciliary subtypes can be distinguished on the basis of length, motility, genetic requirements and function. In the early otic vesicle, most cilia are short and immotile. Long, immotile kinocilia on the first sensory hair cells tether the otoliths, biomineralized aggregates of calcium carbonate and protein. Small numbers of motile cilia at the poles of the otic vesicle contribute to the accuracy of otolith tethering, but neither the presence of cilia nor ciliary motility is absolutely required for this process. Instead, otolith tethering is dependent on the presence of hair cells and the function of the glycoprotein Otogelin. Otic cilia or ciliary proteins also mediate sensitivity to ototoxins and coordinate responses to extracellular signals. Other studies are beginning to unravel the role of ciliary proteins in cellular compartments other than the kinocilium, where they are important for the integrity and survival of the sensory hair cell. This article is part of the Theo Murphy meeting issue ‘Unity and diversity of cilia in locomotion and transport’.

On the unity and diversity of cilia

“…The fish otic vesicle represents a particularly elegant ciliated system where an inertial, biomineral mass termed the otolith, mediates mechanosensation in the inner ear. Whitfield [66] unravels the fascinating process by which otolith assembly begins at the tips of immotile kinocilia, but correct otolith placement and subsequent development requires both tether hair cells and motile cilia. Similarities between the canonical vertebrate hair cell and the mechanosensory cells of diverse marine invertebrates suggest a common evolutionary origin.…”

Rbm24a Is Necessary for Hair Cell Development Through Regulating mRNA Stability in Zebrafish

“…Otoliths are biomineralized aggregates of calcium carbonate and proteins sitting over hair cells in the maculae, embedded in the otolithic membrane (Schulz-Mirbach et al, 2019). Otolith formation in the zebrafish requires kinocilia and motile cilia, and defects in otolith formation is a characteristic phenotype of ciliary mutants (Stooke-Vaughan et al, 2012;Whitfield, 2020). For example, otolith formation is delayed in zebrafish deficient for lrrc23 gene that encodes a radial spoke protein of the cilia (Han et al, 2018).…”

Aquatic models of human ciliary diseases

“…This leftward flow activated primary cilia (red) on the left half of the cleft resulting in the opening of polycystin calcium channels. Calcium influx inhibits a protein Coco leading to activation of Nodal signaling ear, we know that the zebrafish otic cilia have a similar structure and function as mouse cilia (Kindt, Finch, & Nicolson, 2012;Whitfield, 2020).…”

“…Depolarization of the membrane leads to neurotransmitter release. Though few studies have focused on cilia in the Xenopus or zebrafish ear, we know that the zebrafish otic cilia have a similar structure and function as mouse cilia (Kindt, Finch, & Nicolson, 2012; Whitfield, 2020). However, unlike the adult human ear, regeneration of the ciliated sensory cells occurs in zebrafish (Monroe, Rajadinakaran, & Smith, 2015).…”