|
Fig. 3 Hair-bundle misorientation in trilobite mutants.
(A) A time-lapse series of a neuromast from a cldnB:lynGFP;tri larva demonstrates that nascent hair cells have an impaired capacity to complete rearrangements. Two precursor divisions, each marked by a pair of dots, occur simultaneously at the lateral edges of the neuromast. The divisions occur perpendicularly to the neuromast′s axis of polarity and parallel with its plane of mirror symmetry (dashed line). Although the daughter cells initiate rearrangements, they do not reverse positions. The scale bar represents 10μm. (B) Micrographs of the cellular apices taken at the end of the same recording document the final orientations of the four newly formed hair cells (arrowheads). The scale bar represents 5μm. (C) Phalloidin staining of a more mature neuromast shows the randomized orientation of mature hair cells in a trilobite mutant, which is schematized in the insert. The scale bar represents 5μm. Panels D–F provide quantification of hair-cell rearrangements under different experimental conditions and with various genetic backgrounds. All larvae, including those in control experiments, were exposed to 1% dimethyl sulfoxide, the solubilization vehicle for DAPT. (D) The percentage of position reversals between pairs of nascent hair cells differs strongly between 22 wild-type neuromasts (green) and 15 trilobite organs (red). The other experimental conditions are described in the text. (E) The average time devoted to rearrangements is significantly greater for 15 trilobite larvae than for 22 wild-type animals (p<0.01). The duration of rearrangements in animals treated with 100µM DAPT could not be accurately determined. (F) The orientation of divisions of hair-cell precursors relative to the neuromast′s polarity axis shows the profound effect of the trilobite mutation.