Fig. 6

Delayed otolith formation and dysmorphology in otop1 morphant fish. (A–F) Lateral views of 7 dpf otocysts (rostral to left) of a wild-type (A) and 1 ng MO-1-injected fish (B–F). (A) Wild-type fish develop two ovoid otoliths. (B) Delayed otoliths in morphant fish can appear similar to wild type in shape and location. (C) Otoliths that are identical in location, but with an oblong shape and distinct straight edges. (D) Formation of a single otolith that is larger than a wild-type otolith and attached to the saccular macula. The irregular shape and large size may indicate fusion of the early otolith seeding particles. (E) A single cuboidal otolith located in the saccular sensory macula. (F) Multiple otoliths with polyhedral structures. The posterior-most otolith did not appear to be attached to a sensory macula. (G) Four-μm plastic section through a 7 dpf 1 ng MO-1-injected morphant otocyst showing a wild-type-like otolith attached to the saccular macula. Richardson′s stain identifies concentric rings of organic matrix within the otolith structure. (H) Four-μm plastic section through the opposite otocyst showing an angular otolith on the utricular sensory patch with no obvious organic matrix within the crystal. (I) Lateral view of a 4 dpf otocyst (rostral to left) from an 8-ng MO-1-injected fish. At 4 dpf, numerous irregularly shaped otoliths are found throughout the otic cavity and in the semicircular canal (arrow). (J) SEM image of the same 4 dpf morphant otocyst. Note the presence of aggregates of crystals attached to the utricular and saccular otolithic membranes and additional free-floating crystals on the otocyst wall (several otolith particles were lost in preparation). Scale bar for A–F is 250 μm; G–H is 10 μm; I is 250 μm; and J is 25 μm.