Mutations in
daf-7 result in constitutive dauer formation (Daf-c) even with abundant food. At 25 degrees C,
daf-7 mutants form 100% dauers and they fail to recover.
daf-7 encodes a novel member of the transforming growth factor beta (TGF-b) superfamily. We have found that a
daf-7 promoter::gfp construct is expressed in one pair of chemosensory neurons, ASI. Pheromone inhibits
daf-7 expression and results in dauer formation, whereas food reactivates
daf-7 expression during recovery from the dauer state. Therefore,
daf-7 is a signalling molecule required for transducing environmental cues that control dauer formation. To study whether other daf genes affect
daf-7 expression, we have analyzed
daf-7p::gfp expression in several Daf-d (dauer-defective) mutants (e.g.
daf-10,
daf-12,
daf-22) and Daf-c mutants (e.g.
daf-1,
daf-4,
daf-7,
daf-11,
daf-21). GFP was expressed in the
daf-22 mutant, which is defective in pheromone production. In the presence of exogenous pheromone, GFP expression was suppressed and the animals formed dauer larvae. Mutations in
daf-10 result in abnormal amphid cilia. In the
daf-10 background, GFP expression was observed either in the presence or absence of exogenous pheromone. This supports the notion that the
daf-7 signal is produced constitutively to promote non-dauer development if chemosensory neurons are isolated from the environment. In the
daf-12 background, GFP expression was observed in the presence of plentiful food, but not in the presence of pheromone.
daf-12 encodes a nuclear hormone receptor. These results suggest that wild-type
daf-12 does not inhibit
daf-7 expression by a feedback loop in response to pheromone stimuli. In
daf-1,
daf-4 and
daf-7 backgrounds, GFP expression was detected in well-fed animals and in dauer larvae formed constitutively at 25 degrees C. Both
daf-1 and
daf-4 encode receptor kinases in the TGF-b receptor family and are candidate receptors for DAF-7. These data indicate that DAF-1, DAF-4 and DAF-7 are not required for maintaining
daf-7 expression. However, in
daf-11 and
daf-21, GFP expression was suppressed, indicating
daf-11 and
daf-21 are required for
daf-7 expression in ASI to control dauer larvae development. In a control cross, when
daf-11 mutants carrying
daf-7p::gfp were crossed with wild-type, the progeny expressed GFP.