Fig. 1

Afferent neuronal innervation is correlated with Emx2 expression and hair bundle orientation.

(A) Schematic diagram of zebrafish neuromasts in the posterior lateral line showing HCs (magenta and yellow) in A-P (dark green) and D-V (light green) oriented neuromasts, which are innervated by neurons of the posterior lateral line ganglion (red). A side view of the hair bundles (kinocilium plus stereocilia) on the apical surfaces of HCs is shown. Only the posterior- or ventral-oriented HCs (magenta) are Emx2-positive. (B) Sensitivity to the direction of water flow within a neuromast is mediated by the two sets of HCs with opposite bundle orientations and their segregated neuronal innervations. (C–J) An afferent neuron (E) is associated with A > P (asterisks in (C)), Emx2-positive HCs ((F-J), circles; (H,I), yellow arrowhead) in a myo6b:actb1-GFP neuromast (C,D) that is comprised of six A > P (red asterisks), five P > A, and six immature HCs (yellow and white arrows, (C)). (G–J) Selected optical sections of (D–F). (K–R) An afferent neuron (M) contacts six Emx2-negative P > A HCs ((K), asterisks, (N-R), circles) and one immature HC ((N), white arrow; (R), arrowhead) in a myo6b:actb1-GFP neuromast that is comprised of six A > P, six P < A (red asterisks) and two pairs of immature HCs (yellow and white arrows, (K)). Yellow and white arrowheads in (I) and (R) repectively, point to nerve fibers associating with immature HCs. Total sample number for (C–J) and (K–R) = 5. Scale bar = 10 μm.