Worm Breeder's Gazette 8(3): 20
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.
Two dauer-constitutive mutants, daf-9(e1406)X and daf-15(m81)IV, form dauer-like larvae unconditionally. These mutations affect the switch into the dauer developmental sequence, but dauer morphogenesis is abnormal or incomplete. These larvae never reach reproductive maturity, so the daf mutations are genetically lethal. The daf-9 dauer-like larvae are shrunken radially, but have a more transparent appearance than do other dauer-constitutives. A few individuals resume pumping and undergo some gonadal cell proliferation, but they are sterile. daf-15 dauer-like larvae are dark-bodied, continue feeding, and consequently, increase in size, but they do not reproduce. The daf-9 and daf-15 homozygotes live for about 2-3 weeks (20 C). Ultrastructural observations show that daf-9 dauer-like larvae exhibit many features characteristic of wild-type dauer larvae: flattened nose, occluded buccal cavity, striated cuticle, and lateral alae; daf-15 larvae do not. We have positioned daf-9 and daf-15 in the genetic pathway for dauer larva formation, an order of genes based on the ability of some dauer- defective mutations to suppress constitutive mutations (Riddle et al., 1981, Nature 290:668-671). The results indicate that daf-9 and daf-15 are epistatic to all the tested dauer-defectives and, thus, located at the end of the pathway. Interactions between the temperature-sensitive (ts) constitutive mutations daf-2(e1370) or daf-7(e1372) and the lethal constitutives were studied by constructing strains homozygous for the ts mutation and heterozygous for the lethal mutation. The double-constitutive dauer larvae segregated by these strains were treated to determine differences in SDS sensitivity and checked for the ability to recover from the dauer state and resume normal development. (Dauer larvae formed by daf-2 and daf-7 survive a 50-minute 2% SDS treatment; daf-9 dauer-like larvae do not, although there are survivors after 30 minutes in 1% SDS; daf-15 dauer-like larvae are killed by the latter. Both daf-2 and daf-7 dauer larvae resume development at 15 C.) The double constitutives formed with daf-9 were more resistant to SDS treatment than daf-9 alone, and also more resistant than doubles formed with daf-15. This later difference could result from the more dauer-like qualities of the daf-9 parent. Resistance to SDS treatment exhibited varying degrees of temperature-sensitivity. Double constitutive dauer larvae formed at 25 C generally were more resistant than dauer larvae formed at 15 C, and the latter were generally more resistant than daf-9 or daf-15 alone. daf-2;daf-9 and daf-2;daf-15 dauer larvae do not resume development when shifted to 15 C. In summary, daf-9 and daf-15 represent a distinct class of dauer- constitutive mutant which is not suppressed by any known dauer- defective mutation (and therefore must represent 'late' functions), and which may make better dauer larvae with a little help from a true dauer-constitutive like daf-2 or daf-7. The daf-9 and daf-15 mutants seem to initiate a portion of dauer larva morphogenesis in the absence of an appropriate signal, but fail to achieve the ultimate state of true dauerness, a state that all worms may seek but few attain. Tests of interactions between daf-9 and daf-15 are in progress, as is a more detailed ultrastructural analysis of the individual mutants.