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.

Characterization of Two Dauer-Constitutive Mutants That Form Dauer--like Larvae

P.S. Albert, D.L. Riddle

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.