Root localizes to the ciliary rootlet in adult Ch and Es neurons. (A) Illustration of ChOs and EsOs in the antenna and leg. The JO in the antennal a2 segment is a specialized ChO composed of arrays of scolopidia, each containing two or three neurons. In the leg, scolopidia, each containing two neurons, are present in bundles in the fChO and tChO. EsOs, consisting of Es neurons and supporting cells, usually associate with external bristles. Bb, basal body; Cd, ciliary dilation; Ci, cilium; Cr, ciliary rootlet; Sr, scolopale rod; Tz, transition zone. (B) In Ch neurons of the JO, endogenous Root (upper panel) or GFP-Root (bottom panel) localizes to the ciliary rootlet, typically 15–25 µm long. The rootlet stretches from the base of the cilium to the neuron cell body (arrows). Upper panel shows immunostaining of antenna cryosections. Actin marks scolopale rods; mCD8-RFP localizes to plasma membranes and outlines the neurons. (C) Endogenous Root localizes to the approximately 20-µm rootlet in Ch neurons of the fChO. Each scolopidium has two Ch neurons and hence two rootlets (arrows). Actin marks scolopale rods, 21A6 marks the cilium base and the region right below the ciliary dilation. (D) Endogenous Root resides at the ∼2- to 10-µm rootlet in Es neurons (olfactory neurons) in the antennal a3 segment. Each set of olfactory organs has one to four neurons, as indicated by different numbers of rootlets. 21A6 marks the cilium base. (E) In leg Es neurons, endogenous Root (left) or GFP-Root driven by elav-GAL4 (right) localizes at the ∼2- to 8-µm rootlet. 21A6 marks the cilium base, mCD8-RFP outlines the neurons. Bars, 10 µm.