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]