Worm Breeder's Gazette 10(3): 106
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
The 95 body muscles are attached to the dorsal and the ventral
hypodermis in two wide, longitudinal bands, each roughly four cells
abreast. In unc-5, we observed
that occasional cells are positioned obliquely on the lateral
hypodermis, bridging dorsal and ventral muscle quadrants (Fig. 1A).
A second, perhaps unrelated, defect is that muscle cells, which are
normally rhomboid (Fig. 2A), often fork where they abut their
neighbors (Fig. 2B). Such split sarcomeres also have been observed
in unc-104 mutants and may reflect an influence of muscle innervation
or contraction on cell shape.
Mispositioned muscle cells can create permanent bends or kinks in
body posture. When many cells are mispositioned, individuals are
locked into rigid postures, usually irregular circles ('cheerios').
We have used this phenotype to make a small collection of muscle
positioning (mup) mutants in which variable numbers of body muscle
cells bridge between dorsal and ventral muscle quadrants (Figs. 1A,
1B).
A second class of mutants, similar in gross phenotype, have
abnormally weak muscle attachments (mua) to the body wall. These
cells tear away from the hypodermis during embryonic, early, or late
larval stages depending on the mutant. In unc-23, for example,
muscles progressively detach from the head on backwards during late
larval stages (Waterston et al., Dev. Biol. 77, 271 (1980)). The
Drosophila mutant, lethal myospheroid, disrupts a -integrin gene.
Conceivably the various mua mutations disrupt nematode genes that
provide mechanical strength to muscle-hypodermis or muscle-muscle
attachments. The force of muscle contraction probably increases as
the myofilament volume (Q3) while the area of muscle-hypodermal
contact increases as Q2. In mua mutants, a 10-fold increase in body
length, causing a proportionate increase in contractile
force/attachment area, may tear weakly attached cells from the body
wall at characteristic forces, and hence, larval sizes.
[See Figures 1 & 2]
