Fig. 1

Architecture of the lateral line in larval zebrafish.

(A–B) Apical aspect of a horizontal neuromast labeled with fluorescent phalloidin (panel A) and its schematic representation (panel B). These images highlight epithelial planar polarization. Hair cell orientation is indicated by an eccentric black dot. In panel B, blue hair cells are rcHCs and green are crHCs. Grey indicates a pair of newborn hair cells whose polarity is not yet evident. (C) Drawing of a larval zebrafish in which double-point arrows indicate the global orientation of horizontal and vertical neuromasts of the posterior lateral line. (D) Simplified scheme of the selective innervation of rcHCs (light blue) by rcLANs (blue) and crHCs (green) by crLANs (red). Polarity-selective synaptogenesis renders LANs tuned to the direction of mechanical stimulation of HCs, and form labeled lines of mechanosensory flow from the periphery to the brain. Each cell is meant to represent the entire population of identically oriented HCs in the neuromast and identically tuned LANs. (E) Confocal image of a lateral view of the trunk of a double-transgenic Tg[pou4f3:GAP-GFP; hsp70l:mCherry-2.0cntnap2a] larval zebrafish, showing LANs (red) and HCs (green). (F) Magnified frontal view of a neuromast of the transgenic line Tg[myo6b:actb1-EGFP] showing HCs (green). Inset at the bottom left shows the planar polarization of the hair cells. A single LAN (red) was marked by mosaic expression of mCherry. (G) Shows a higher magnification of the inset in panel F, in which the HCs that were innervated by the single mCherry-expressing LAN in panel F are marked with a red asterisk. In this example, 7 out of the 8 constituent crHCs were innervated by this identified LAN, and none of the rcHCs were synapsed by the same neuron. Scale bars are 10 μm. In all the panels and figures, dorsal is up and anterior is left. crHC, caudorostral HC; crLAN, caudorostral LAN; HC, hair cell; LAN, lateralis afferent neuron; rcHC, rostrocaudal HC; rcLAN, rostrocaudal LAN.