FIGURE 4

FIGURE 4

Spontaneous calcium activity occurs in the mechanosensory bundle and at the presynapse. (A) Cartoon of a neuromast organ illustrating hair cells (green) expressing memGCaMP6s, surrounded by supporting cells (gray). (B1) Image of a representative neuromast showing the hair cell presynaptic region indicated by the dashed box in (A) taken from immature hair cells at day 2. Hair cells at three different developmental stages are labeled: early (no detectable hair bundle), intermediate (3, 4), and late (1, 2). (B2) An image of the hair bundles from the same cells as (B1) through the plane indicated by the dash line in (A). (B3) Paired temporal curves of spontaneous calcium activity in hair bundles (B2 black) and the presynaptic regions (B1 blue) taken from the same hair cells. (C) Pearson’s R values of spontaneous calcium activity between hair bundles and the presynaptic regions of the same sets of immature hair cells, n = 32 hair cells (n = 6 neuromasts), day 2 and n = 56 hair cells (n = 6 neuromasts), day 3. (D,E) The average magnitude of spontaneous calcium activity in hair bundles (D) and presynaptic region (E) in the same set of hair cells during the progressive stages of development: early, intermediate, late and mature. No activity can be measured in early hair bundles (N/A) as the bundles are not yet detectable. The spontaneous calcium activity in hair bundles peaks at the intermediate stage (D) and decreases upon maturation, while spontaneous calcium activity in the presynaptic regions peaks at the late stage (D′) and decreases upon maturation. Scale bar = 5 μm.