Fig. 3.

Ribbons in neurog1 mutants are cytoplasmic and show an increased pool of synaptic vesicles. (A) TEM transverse section of a posterior lateral line neuromast showing four mature hair cells (HC) surrounded by clearer cytoplasm (arrowheads) of support cells (SC). Even at this low magnification, two ribbons (arrows) are clearly seen. The ribbon in the inset is enlarged in A′ showing more clearly its ectopic position (not anchored at membrane) and a greater amount of surrounding synaptic vesicles (SV) not tethered to the ribbon (R). At the basal pole of the hair cell only the clear cytoplasm of the support cell can be seen. (B) A hair cell from another neuromast shows a double-ribbon, also ectopic, with a profusion of untethered SVs. (C) A ribbon in a wild-type 7 dpf hair cell is shown for comparison. A monolayer of SVs surrounds the ribbon. AN, afferent neuron.