Supplementary Figure 2: Different ciliary bases show both similar and variable elements.

a) Left: Longitudinal tomogram stills of the ciliary base in olfactory neurons showing a proximal BB (pBB-white arrowhead), a distal BB (dBB- red arrowhead) and the transition zone (TZ). Right: Model based on the tomogram data. Model of the BB and ciliary microtubules (light green), cytoplasmic MTs (orange) that nucleate from the BBs, MTs that nucleate from the proximal BB and extend into the cilia (brown), non-MT electron densities around BBs (dark blue), the electron densities of rootlet (cyan), vesicles at the ciliary base (magenta), connections between dBB-cell membrane (golden) and the cell/ciliary membranes (black) (see also Fig. 1 and Supplementary Video V1). Based on features at the ciliary base, olfactory neurons can be divided into two types: Type-1) where singlet MTs are absent in the lumen of both BB and TZ (example 1) and Type-2) where one or more singlet MTs (orange) are present in the lumen of BBs and TZ (example 2). ~70% of olfactory neurons are of Type-1, while ~30% of them are of Type-2 (quantification not shown). b) Longitudinal tomogram stills of the ciliary base in auditory neurons showing pBB (white arrowhead), dBB (red arrowhead) and TZ. Right: Model based on the tomogram data. For auditory neurons, we modelled all objects described in a, electron density around the MTs in TZ (dark blue), and the rootlet striations (magenta). Notably, in the example 2 of olfactory cilia (a) we observed singlet microtubules (white arrows) that are bent in olfactory neurons, and the connections between the dBB and the cell membrane are less obvious in single sections of both types of neurons, justifying the importance of collecting and analysing tomograms to model these ciliary bases. c) Electron micrographs of different types of bases showing cytoplasmic MTs around BB and rootlets. The insets present regions marked with dotted squares. d, e) Representative electron micrographs of longitudinal (i) and sets of serial cross sections of marked regions (ii) of BBs in olfactory (d) and auditory neurons (e). For the cross-section series analysis, 70 nm serial sections were collected. Note that the number of singlets and the relative position of singlets and doublets in the pBB varies between individual auditory neurons. All electron micrographs in c-e represent features observed in 3 samples (the experiments presented in this figure were repeated independently twice with similar results). Scale bars on the longitudinal (a, b, c, di and fi) and cross (dii and fii) section micrographs are 500 nm and 100 nm, respectively.