MusFIG 21: Vulval and uterine muscles.

There are two sets of vulval (vm1 and vm2) and uterine (um1 and um2) muscles with four cells in each set.
A. Vulval muscles are single sarcomeric. Each vulval muscle attaches to the vulval toroid epithelium on one end and body wall on the opposite end via hemiadherens junctions. A single sarcomere traverses the length of each muscle cell between the body wall and the vulval epithelium. Half I bands end in hemiadherens junctions, whereas the thick filaments occupy the middle region. (Asterisk) Remaining thick and thin filaments of the single sarcomere on the right side are out of plane of section. TEM, horizontal section. Bar, 1 μm. (Image source: MIT [E. Hartwieg and R.H. Horvitz] EH5358-5370.)
B. Same image as in A, magnified. (Arrowheads) Hemiadherens junctions that anchor the thin (actin) filaments of the vulval muscle to the vulval epithelium. (Arrows) Hemidesmosomes within the vulval epithelium that may function to link the muscle attachments to the vulval cuticle.
C. vm1, vm2, and um1 muscles in the adult hermaphrodite, ventral view. (Dotted lines) Level of the seam cells and ventral midline on this epifluorescent image taken from a transgenic animal expressing the reporter gene unc-27::GFP. (Strain source: L. Jia and S.W. Emmons.)

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