Dauer larva formation is a developmentally-controlled response to harsh environmental conditions. In wild-type worms, dauer formation occurs following the L2 molt. Liu and Ambros (Genes and Devel. 3:2039, 1989) showed that a loss-of-function mutation in the heterochronic gene
lin-14 leads to the formation of dauers one stage early; worms form dauers following the Ll molt. These dauers are smaller than wild- type dauers and their developmental stage can be determined by scoring the size of the gonad since
lin-14 does not affect development of the gonad. We have determined the temperature-sensitive period for the effect of
lin-14 on dauer formation. Our results indicate that the tsp is mid to late Ll. In order to identify genes which might be interacting with
lin-14 in the control of dauer formation, we have attempted to isolate new mutations which cause a disruption of the normal timing of dauer formation. Worms containing a temperature-sensitive dauer constitutive mutation such as
daf2(el370) or
daf-7(
el372) which have been synchronized as Lls overnight in the absence of food will begin to produce SDS-resistant dauer larvae ~38 hours after release from starvation at 25 . Therefore, to identify mutations leading to early dauer formation, we mutagenized dauer constitutive worms and selected SDS-resistant dauers 32 hours after feeding in the F2 and F3 generations. As expected, we recovered alleles of
lin-14. In addition, we have isolated other mutations and are in the process of mapping and further characterizing them. One mutant, mgl l, in a
daf-2(el 370) background, forms SDSresistant dauers ~4 hours earlier than wild-type worms and maps to chromosome I, either very close on the left side of or to the right of
unc-29. Surprisingly, after precocious entry into the dauer stage these mutants then exit dauer. That is, mgl l mutant worms are not defective for entry into the dauer pathway but rather are defective in maintenance of the dauer state. Complementation tests between mgl l and two known dauer-defectives,
daf-16(
m26) and
daf-17(
m27), which map to the same genetic region, as well as between
daf-16(
m26) and
daf-17(
m27) themselves, suggest that all three are recessive mutations of the same gene. This gene's effect on the timing of dauer formation is unlike that of
lin-14:
lin-14(1f) mutants form 'little' dauers with small gonads, as described above, while mgl I dauers are wild-type in size. Thus, this gene has a function in both maintaining the dauer state as well as in the control of the timing of entry into dauer. In addition to the selection described above, we are attempting to identify other mutations which affect the timing of dauer formation by selecting for suppression of the dauer-defective phenotypes of
lin-4(
e912) and the
lin-14 gain-of-function mutation
n355.