Asymmetric mechanotransduction by hair cells of the zebrafish lateral line (Part 1/2)

In the lateral line system, water motion is detected by neuromast organs, fundamental units that are arrayed on a fish’s surface. Each neuromast contains hair cells, specialized mechanoreceptors that convert mechanical stimuli, in the form of water movement, into electrical signals. The orientation of hair cells’ mechanosensitive structures ensures that the opening of mechanically-gated channels is maximal when deflected in a single direction. In each neuromast organ, hair cells have two opposing orientations, enabling bi-directional detection of water movement. Interestingly, Tmc2b and Tmc2a proteins, which constitute the mechanotransduction channels in neuromasts, distribute asymmetrically so that Tmc2a is expressed in hair cells of only one orientation. Here, using both in vivo recording of extracellular potentials and calcium imaging of neuromasts, we demonstrate that hair cells of one orientation have larger mechanosensitive responses. The associated afferent neuron processes that ..., Calcium imaging
Acquisition:
GCaMP6s-based calcium imaging of zebrafish hair bundles and of the afferent processes (day 4-6). A fluid jet was used to mechanically stimulate the apical bundles of hair cells of the A-P (L1-L4) neuromasts. To stimulate the two orientations of hair cells (A-to-P sensitive and P-to-A sensitive) a 500-ms ‘push’ was delivered. Larvae were rotated 180° to deliver a comparable ‘push’ stimulus to both the A-to-P sensitive and P-to-A sensitive cells. To image calcium-dependent mechanosensation in apical hair bundles or calcium-dependent activity in the afferent process, a Bruker swept-field confocal system was used. The system was equipped with a Rolera EM-C2 CCD camera (QImaging) and a Nikon CFI Fluor 60✕ 1.0 NA water immersion objective. Images were acquired in 5 planes along the Z-axis at 0.5 mm intervals (hair bundles) or 1 mm intervals (afferent processes), at a 50 Hz frame rate yielding a 10 Hz volume rate.
Processing:
The 5 plane Z-stacks were projected int...,
FIJI (to open calcium imaging and immunostain data)
Prism 8 (to open spreadsheets)