Figure 3. FHOD-1 localizes close to Z lines in BWM cells. (A) Model of BWM sarcomere organization. Side view of one sarcomere shows that Z-line dense bodies (blue) anchor actin filaments (yellow), and M lines (black) anchor myosin filaments (gray). M lines and dense bodies attach to the plasma membrane, placing the contractile lattice between the membrane and the cell body. In top views, sarcomeres can be seen to combine to form oblique striations, in which rows of dense bodies (blue spots) within the F-actin-rich striations form discontinuous Z lines that alternate with M lines. Striations in turn form the spindle-shaped contractile lattice of BWM cells. At boundaries between BWM cells, attachment plaques (larger dark spots) replace dense bodies (smaller dark spots) as Z-line structures. Myosin filaments have been omitted from striation and BWM models for clarity. (B) Ventral view (anterior to the left) of an FHOD-1::GFP-expressing larva stained with fluorescent phalloidin shows FHOD-1-containing puncta along the edges of F-actin-rich BWM cell contractile lattices (large arrows) and in faint striations across the lattices (small arrows). (C) Ventral view of a wild-type larva stained with anti-FHOD-1 reveals endogenous FHOD-1 in similar puncta (large arrows) and striations (small arrows). (D) Animals double-stained for FHOD-1 and either Z-line marker ATN-1 or DEB-1 show that the formin is closely associated with Z lines. In ventral views or in side views of the discontinuous Z line (xz projection), anti-FHOD-1-stained striations are seen in the contractile lattice (cl) of wild-type but not fhod-1
) animals, and anti-FHOD-1-stained puncta intermingle with DEB-1-stained attachment plaques (arrows) at the cell edge. Staining of the cell body (cb in xz view) or of an elongated structure that parallels BWMs (bottom, arrowheads) is nonspecific. (E) FHOD-1 striations alternate with MYO-3 striations. (F) Anti-GFP-stained striations in FHOD-1::GFP-expressing animals partially overlap with UNC-60B. (G) Proximal to the plasma membrane, LIM-8 occupies two sets of striations, one near Z lines and a fainter one near M lines (arrows), whereas distal to the membrane, LIM-8 detectable near Z lines strongly comingles with FHOD-1::GFP. (H) Worms stained with anti-FHOD-1 and two secondary antibodies with different fluorophores show extensive, but imperfect, comingling of signal along FHOD-1 striations. Bars: (B) 10 um; (C) 25 um; (D-H) 5 um.