In C. elegans , at least three TGF-b superfamily signaling pathways are genetically characterized: the Daf pathway, the Sma/Mab pathway and the
unc-129 pahtway. The Daf pathway regulates dauer formation in response to starvation or overcrowding conditions. In contrast, the Sma/Mab pathway controls body size and male copulatory structure, and
unc-129 pathway regulates axon guidance. TIF encodes a new F-box protein constituting ubiquitin ligase E3 complex, and is induced by TGF-b stimulation in mammailan cell (Higuchi/Akiyama pers. comm.). TIF protein is highly conserved in many animal species, suggesting that the function of this protein is important biologically. Here we have cloned and genetically characterized C. elegans TIF ortholog,
tif-1 . The expression of
tif-1 ::GFP was detected in many head neurons, ventral nerve cord, intestinal cells and tail neurons, consisting with the expression patterns of
daf-1,
daf-3 and
daf-4 , which encode the components of the Daf pathway. To investigate the in vivo function of TIF-1, we have screened a library consisting of 7.5 X 10 5 mutagenized animals and isolated the deletion mutation that lack of N-terminal region of the
tif-1 gene. Homozygote for this deletion mutation was healthy, viable and did not exhibit Daf-c or Daf-d phenotype. However, combination of
daf-7 or
daf-1 mutation with
tif-1 mutation strongly enhanced their constitutive dauer formation phenotype. Moreover,
tif-1(RNAi) in Daf-c mutants (
daf-7,
daf-1,
daf-4 and
daf-14 ) also showed similar phenotype, but not in
daf-2 involved in the insulin-like signaling pathway. These results suggest that TIF-1 is involved in the Daf signaling pathway.