Worm Breeder's Gazette 11(5): 99
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 hypodermal cells of C. elegans are responsible for transforming the round embryo into a long thin worm, apparently by constricting circumferentially-oriented bundles of microfilaments at their apical surface (Priess and Hirsh, 1986). These microfilament bundles appear to be responsible for both generating and maintaining the shape of the worm until the embryonic cuticle has been formed. We have been interested in whether these microfilament bundles are also involved in post-embryonic molting periods, when the animal must produce a new cuticle and detach from the old. Since we have found that the position of the microfilament bundles across the embryonic surface are precisely correlated with where the annuli are seen in the first larval cuticle, we predicted that annuli of post embryonic cuticles would similarly correspond to microfilament bundles in the hypodermis of molting worms. Synchronized populations of N2 worms were fixed at various stages between L3 and adults and stained with Rhodamine-Phalloidin. We find that during each molt, actin microfilament bundles are present and are regularly spaced and circumferentially-oriented, very similar to what is seen during embryonic morphogenesis (pictured below is L3 molt). These bundles largely disappear after molting and do not reappear until the following molt. They are not present in adult worms. Visualization of microtubules during the molts reveals that they too are regularly spaced and circumferentially-oriented, again similar to embryonic morphogenesis. But unlike the microfilament bundles, circumferential microtubules persist during the inter-molt periods and are seen in adult worms. Although the shape of the worm is initially generated by a mechanism involving the hypodermal cytoskeleton, larval and adult shape is dependent on an intact cuticle and a high internal hydrostatic pressure. This property produces obvious problems for a molting worm: how can a worm maintain its shape and internal pressure and at the same time reduce its volume in order to shed its old cuticle? We propose that nematodes employ the same cytoskeletal machinery used during embryonic morphogenesis. Actin microfilament bundles in the hypodermal cells constrict the worm and microtubules distribute this pressure evenly along the length of the worm. The deformation of the hypodermal membrane caused by this constriction is once again responsible for patterning the cuticle being deposited at this time, which accounts for the annuli of larval and adult cuticles. [See Figure 1]