Centrioles are lost early in neuronal differentiation. (A) Stills from time-lapse video of embryo expressing myristoylated GFP (myrGFP) in amphid neurons undergoing retrograde migration. DIC and single-plane GFP images taken at the indicated time intervals corresponding to comma, 1.5-fold, twofold, and threefold stages. Note the position of dendritic tips (arrowheads) remains fixed as cell bodies (asterisks) move. At the threefold stage, the worm begins to move inside the egg because of muscle contraction. See also Video 3. (B) Tomographic slice and 3D reconstruction model of centriole in a myristoylated GFP–positive neuron of a comma-stage embryo. Note the centriole displays doublet microtubules. Electron densities at the center of the centriole may represent elements of the central tube/cartwheel (arrowhead). See also Video 4. (C and D) Immunofluorescence micrographs of comma-, 1.5-fold–, twofold-, and threefold-stage embryos expressing myristoylated GFP in amphid neurons and stained for HYLS-1 and SAS-6 (C) or SAS-4 (D). Insets show magnified view of ciliary base (1) and nonneuronal cells elsewhere in the head of the embryo (2). Centriolar signal is lost from the ciliary base, with loss of SAS-6 preceding that of SAS-4, while HYLS-1 remains. All three proteins are lost in nonneuronal cells coinciding with terminal differentiation. (E and F) Quantitation of centriolar signal in amphid neurons (percentage of HYLS-1 foci positive for SAS-6 or SAS-4; E) and nonneuronal cells (HYLS-1 foci per nucleus; F) from images as in C and D. Error bars are 95% confidence intervals. n = 5–9 animals per condition. Bars: (A, C, and D) 10 µm; (B) 50 nm; (C and D, insets)1 µm.