Figure 2.

MKS-5 is required for the formation of transition zone ultrastructure

1. Transmission electron microscopy (TEM) serial cross-section images of wild-type and mks-5(tm3100) amphid channel cilia. Boxed numbers denote proximal positioning of section relative to left-most (anterior) section of the animal. Wild-type amphid channels contain 10 axonemes, each possessing the following: a distal segment (DS) with singlet microtubules (MTs); a middle segment (MS) with doublet MTs and inner singlet MTs; a transition zone (TZ) with Y-link connectors, and doublet MT-associated apical ring; and a basal body/transition fibre (TF) region. mks-5 worms possess grossly normal DSs (although one axoneme is frequently missing), and MSs that frequently display MT singlets and doublets reduced in number and occasionally displaced (see high-magnification images). TZs are not observed in mks-5 worms, replaced instead by abnormal middle segments (labelled “MS?”). Scale bars: 200 nm (low-magnification images); 100 nm (high-magnification images).
2. The TZ region of mks-5 mutants lacks all distinguishing features, including the apical ring (arrow), Y-links (closed arrowhead), and tight connection to the ciliary membrane. Doublet MTs of mks-5 mutant TZs are often displaced. Open arrowhead: inner singlet MT. Scale bars: 100 nm.
3. Schematics summarising ultrastructures of wild-type and mks-5 mutants. PCMC, periciliary membrane compartment.