Morphology and cell type heterogeneities of the inner ear epithelia in adult and juvenile zebrafish (Danio rerio)

Abstract

Although the zebrafish has become an important model for genetic analysis of the vertebrate auditory system, a comprehensive description of the zebrafish ear has been provided for embryonic and larval development only (Haddon and Lewis [1996] J. Comp. Neurol. 365:113). Here we describe the development of sensory maculae in juvenile fish and the morphology of the adult zebrafish ear. This description was obtained via three-dimensional reconstruction of serial sections and confocal microscopy of immunolabeled preparations and includes the Weberian ossicles and fluid spaces. Phalloidin staining, which labels actin filaments of stereocilia, was used to delineate the sensory epithelia, to visualize the distribution of hair cells, to estimate their density in different areas of the maculae, and to perform hair cell counts. Morphology of ciliary bundles in different regions of the lagena, saccule, utricle, macula neglecta, and cristae was characterized with an anti-acetylated tubulin antibody and by phalloidin staining. We have identified two antibodies characterized by region-specific staining patterns in the inner ear epithelia. Zn-1 antibody staining largely correlates with the presence of short-bundle hair cells in the peripheral regions of sensory epithelia. Zn-4 antibody, on the other hand, labels a zone of epithelial cells surrounding the sensory maculae. These analyses extend previous observations of cell-type heterogeneity in both sensory and nonsensory epithelia of the fish ear.

Early Development of Hearing in Zebrafish

“…Based on the size of the zebrafish used by Higgs et al (2003), their ages likely ranged from 1 month old to adult. At 1-month post fertilization, zebrafish have an inner ear whose gross morphology resembles the inner ear of adult zebrafish, including the three otolithic organs and three semicircular canals with associated ampullae (Platt 1993;Bang et al 2001). Second, different independent variables and recording methods were used in the present study compared to the study by Higgs et al (2003).…”

“…The lagena does not appear until 11 days post fertilization (dpf). The inner ear of adult zebrafish has three pairs of otolith organs, each of which is composed of a calcareous otolith and a sensory epithelium covered with hair cells (Platt 1993;Bang et al 2001;Bever and Fekete 2002). The utricle is located in the pars superior whereas the saccule and the lagena are in the pars inferior.…”

Development of the zebrafish inner ear

“…A small evagination of the dorsomedial aspect of each saccule wall at 17 dpf is the first sign of the genesis of the transverse canal, which connects the saccules at the midline by 20 dpf (Bever and Fekete, 2002). This structure is prominent in the adult ear, where its caudal end is enclosed within, but is a distinct compartment from, the perilymph-filled space of the sinus impar (Bang et al, 2001). The lateral saccule wall, conversely, invaginates and thickens to form a saccular ridge, the function of which is unknown (see the Discussion section in Bever and Fekete, 2002).…”

“…These patches may arise from the saccular macula (see the Discussion section in Bever and Fekete, 2002). During larval stages, all three maculae and the cristae continue to grow (Bang et al, 2001). The utricular macula develops a long thin extension, the lacinia, whereas the whole saccular macula becomes very elongated.…”

“…The utricular macula develops a long thin extension, the lacinia, whereas the whole saccular macula becomes very elongated. Hair cell densities and polarity patterns have been mapped for each sensory patch in the adult ear (Platt, 1977;Bang et al, 2001). Hair cells probably continue to be produced into adulthood, as in the goldfish (Lanford et al, 1996).…”