Worm Breeder's Gazette 14(3): 33 (June 1, 1996)

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.

daf-14 encodes yet another homolog of Drosophila Mad

Takao Inoue, James H. Thomas

Department of Genetics, University of Washington, Seattle, WA 98195

        Based on similarities in phenotypes and genetic interactions,
five Daf-c (dauer constitutive) genes, daf-1, -4, -7, -8 and -14 are
thought to have related functions. Molecular identities of four of these
genes have been reported previously by Don Riddle's group. daf-7 encodes
a homolog of TGF-beta(1), daf-1 and daf-4 encode homologs of TGF-beta 
receptors(2,3), and daf-8 encodes a homolog of Drosophila gene Mad
(Mothers against dpp)(4). We cloned daf-14 in order to understand its
function in the pathway.
        daf-14 is rescued by the cosmid F01G10, recently sequenced by
the genome sequencing project. From the sequence, we identified a
candidate gene based on homology, which was confirmed to be daf-14 by
sequencing mutant alleles. daf-14 is a member of the recently described
gene family(5) that includes Mad from Drosophila(6) and the C. elegans
genes sma-2, sma-3, sma-4(5) and daf-8(4). All of these genes are
implicated in TGF-beta related signal transduction, suggesting they play
a conserved role.
        Known members of this gene family contain two conserved regions,
DH1 and DH2(5). Genefinder analysis and sequence alignment of the daf-14
genomic DNA predicts a protein with strong similarity to the DH2 region
but without a DH1-like domain. Also, no homology to DH1 was detected in
a search of genomic sequence upstream of daf-14 DH2 region. This
suggests that daf-14 is unique in not having a DH1 region. However,
because the mRNA structure has not been confirmed, we do not rule out
the possibility that the DH1 domain is present. All three mutations in
daf-14 disrupt highly conserved residues in the C terminal half of DH2
        We are continuing to study the role of daf-14 in TGF-beta
signaling. We generated two integrants of daf-14(+)-carrying transgenic
arrays which probably overexpress the daf-14 gene product. These arrays
rescue the Daf-c defect of daf-14 and daf-8, but not daf-1, -4 and -7.
These results are consistent with many models, including epistatic
interactions and functional substitution of daf-14 for daf-8.

1. Lim et al., WM93 abstract p15, Lim, Ph.D. Thesis, University of
Missouri, Columbia, Missouri. 
2. Georgi et al., Cell 61:635-645
3. Estevez et al., Nature 365:644-649
4. Estevez and Riddle, WBG14.2 p37
5. Savage et al., PNAS USA 93 790-794
6. Sekelsky et al., Genetics 139: 1347-1358