Figure 4
Anatomical features of the head region and comparison of the hemicentin-rich pharyngeal tendons between wild-type and a mutant with the twisted pharynx phenotype. (A) and (B) show transverse and cross sections of the head region in idealized forms. For clarity, many structures were omitted here, including axons, excretory canals, muscle arms and complex hypodermal cell shapes that sometimes cover the body muscles. Of particular importance is that the pharynx seems to float in pseudocoelomic fluid and to make almost no contact with the worm body along its entire length: except for the tendons, the pharynx is secured only at its anterior and posterior ends, where it is connected to the mouth and intestine, respectively. (C) Transverse thin section of an adult wild type nose, showing a left ventral tendon (red arrows) connecting the basal laminae (red arrowheads) of the pharyngeal epithelium (PH) and of the body-wall muscles (BWM). Major cells bordering the tendon include the amphid sheath cell (AMSh) and several other sheath cells (Sh) for mechanosensors of the lips. Smaller caliber processes include many sensory dendrites and some arcade processes. Hemidesmosomes link the pharyngeal epithelium's intermediate filaments to the basal lamina. Dense bodies (modified adherens junctions) link the muscle sarcomeres to the muscle's basal lamina. Because it is tilted with respect to the body axis, the tendon is better seen close to the pharynx in this image, but goes out of the plane of section as it passes between the muscle cells. Image is rotated about 20 degrees clockwise for convenience. Scale bar is 1 ÎĽm. (D) and (E) show images of a wild-type and mnm-4 mutant that carry the hemicentin::GFP transgene rhIs23 [30], respectively. (F) and (H): geometry of the tendons (brown) and pharynx (blue circle) viewed in cross sections if the pharynx is not twisted (F) or if it were twisted as a whole while held by the tendons (H). (G) and (I) show cross section views of the flattened confocal image stacks from (D) and (E); note the spiral-oriented tendons in (I). Specimens were immersion fixed using buffered aldehydes and then osmium tetroxide as described previously [40]. Three or four animals were aligned within agar blocks then embedded in plastic resin and sectioned together. Thin cross sections were collected on slot grids, post-stained with uranyl acetate and lead citrate, then examined with a JEOL 1200EX electron microscope. Scale bars in D and H are 10 ÎĽm.