Atlas of the developing inner ear in zebrafish

Abstract

This report provides a description of the normal developing inner ear of the zebrafish, Danio rerio, with special focus on the pars inferior. Zebrafish specimens, ranging in age from 3 to 30 days postfertilization (dpf), were processed for standard histologic sections or with a paint-fill method to show three-dimensional morphogenesis of the membranous labyrinth. Adult zebrafish (age 2 years) were also processed for inner ear paint-fills. Although development of the semicircular canals occurs rapidly (by 3 dpf), the pars inferior develops more gradually during days 5-20 postfertilization. A rudimentary endolymphatic duct emerges by 8 dpf. Differentiated hair cells of the lagenar macula are evident by 15 dpf, in a chamber located lateral and posterior to the saccule. By 20 dpf, the saccule itself is separated from the utricle, but remains connected by means of the utriculosaccular foramen. The maculae neglectae, each with differentiated hair cells, lie on the floor of the utricle near this foramen. A medial connection between the sacculi of right and left ears, the transverse canal, is also complete by 20 dpf. A ridge of mesenchyme, previously undescribed, bisects the saccule in zebrafish fry at 20 -30 dpf. The images in the paint-fill atlas should provide a baseline for future studies of mutant zebrafish ears.

Early Development of Hearing in Zebrafish

“…Compared with mammals (see a review by Rübsamen and Lippe 1998), the zebrafish is a unique model for the study of early development of hearing and balance in vertebrates because the inner ear of zebrafish embryos is easily accessible for live imaging, physiological recording, and genetic manipulation (Waterman and Bell 1984;Haddon and Lewis 1996;Nicolson et al 1998;Bever and Fekete 2002;Whitfield 2002;Nicolson 2005;Zeddies and Fay 2005;Tanimoto et al 2011). Previous studies have reported on the development of auditory sensitivity in a few juvenile and adult teleosts using various physiological methods (Corwin 1983;Kenyon 1996;Higgs et al 2003;Sisneros and Bass 2005;Vasconcelos and Ladich 2008;Alderks and Sisneros 2011;Lechner et al 2012).…”

“…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

“…Although an endolymphatic duct has not been described in the embryonic or adult zebrafish ear, it is identifiable in larval ears in sectioned material, and occasionally in paint-filled specimens, as a narrow tube, running along the medial surface of the common crus (Bever and Fekete, 2002). In the embryo, dorsal domains of both bmp4 and dachA expression appear to mark the primordium of the duct as it begins to extend, between 2 and 3 dpf (Whitfield, 2000;Mowbray et al, 2001;Hammond et al, in press; C. Mowbray, K. Hammond, and TTW, unpublished data).…”

“…This boundary is not well-defined in zebrafish; even by 5 dpf, the saccular macula remains dorsal to the utricular macula, and there is no evidence of a narrowing of the connection between the presumptive utricular and saccular chambers. A narrow utriculosaccular canal is evident by 17 dpf, however (Bever and Fekete, 2002), but a focus of apoptosis associated with its formation has not been found, although it is possible that it has been missed (Bever and Fekete, 1999).…”

“…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).…”