Fig. 1

Early development of otoliths in wild-type and mnl embryos. Live embryos were viewed with a 100x objective using DIC optics. (A–C) Wild-type ear at 18.5 h (19 somites). (A) Lateral view of otic vesicle showing positions of anterior otolith and naked posterior tether. The anterior end of the vesicle has expanded more than the posterior end. (B) Close-up of the anterior end of the ear shown in A. The otolith, which appears as a composite of smaller particles, is attached to two distinct tethers. (C) Close-up of the posterior end of the ear shown in A. A single tether is visible, but no otolith is yet detectable. 20 min later (20 somites), the first signs of posterior otolith formation are evident (D). (E) Wild-type ear at 21.5 h (25 somites). Otoliths have increased in size and tethers have lengthened by several micrometers. Inset shows close-up of the anterior otolith and two tethers. (F) Wild-type ear at 24 h (30 somites). Otoliths have continued to grow. Inset shows close-up of anterior otolith and two tethers. No additional hair cell cilia are yet visible. (G) Close-up of mutant ear at 19 h (20 somites). Two tethers are visible but no signs of otolith formation are evident. (H) Mutant ear at 21.5 h (25 somites). Otoliths have not yet formed. Inset shows close-up of two anterior tethers lacking an otolith. (I) Mutant ear at 24 h (30 somites). A large posterior otolith is evident, but no anterior otolith has formed. Inset shows close-up of two anterior tethers lacking an otolith. All images are oriented with anterior to the left and dorsal upward. o, otoliths; arrows, tethers without otoliths. Scale bar, 5 (B, C, D, and G) or 25 μm (A, E, F, H, and I). Insets in E, F, H, and I show 2.6x enlargements of indicated features.