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The DAF-3 Smad protein antagonizes TGF-beta-related receptor signaling in the Caenorhabditis elegans dauer pathway.

ABSTRACT: Signals from TGF-beta superfamily receptors are transduced to the nucleus by Smad proteins, which transcriptionally activate target genes. In Caenorhabditis elegans, defects in a TGF-beta-related pathway cause a reversible developmental arrest and metabolic shift at the dauer larval stage. Null mutations in daf-3 suppress mutations in genes encoding this TGF-beta signal, its receptors, and associated Smad signal transduction proteins. daf-3 encodes a Smad protein that is most closely related to mammalian DPC4, and is expressed throughout development in many of the tissues that are remodeled during dauer development. DAF-4, the type II TGF-beta receptor in this pathway, is also expressed in remodeled tissues. These data suggest that the DAF-7 signal from sensory neurons acts as a neuroendocrine signal throughout the body to directly regulate developmental and metabolic shifts in tissues that are remodeled during dauer formation. A full-length functional DAF-3/GFP fusion protein is predominantly cytoplasmic, and this localization is independent of activity of the upstream TGF-beta-related pathway. However, this fusion protein is associated with chromosomes in mitotic cells, suggesting that DAF-3 binds DNA directly or indirectly. DAF-3 transgenes also interfere with dauer formation, perhaps attributable to a dosage effect. A truncated DAF-3/GFP fusion protein that is predominantly nuclear interferes with dauer formation, implying a role for DAF-3 in the nucleus. These data suggest that DAF-7 signal transduction antagonizes or modifies DAF-3 Smad activity in the nucleus to induce reproductive development; when DAF-7 signals are disabled, unmodified DAF-3 Smad activity mediates dauer arrest and its associated metabolic shift. Therefore, daf-3 is unique in that it is antagonized, rather than activated, by a TGF-beta pathway.

SUBMITTER: Patterson GI

PROVIDER: S-EPMC316611 | biostudies-literature | 1997 Oct

REPOSITORIES: biostudies-literature

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The DAF-3 Smad protein antagonizes TGF-beta-related receptor signaling in the Caenorhabditis elegans dauer pathway.

Patterson G I GI Koweek A A Wong A A Liu Y Y Ruvkun G G

Genes & development 19971001 20

Signals from TGF-beta superfamily receptors are transduced to the nucleus by Smad proteins, which transcriptionally activate target genes. In Caenorhabditis elegans, defects in a TGF-beta-related pathway cause a reversible developmental arrest and metabolic shift at the dauer larval stage. Null mutations in daf-3 suppress mutations in genes encoding this TGF-beta signal, its receptors, and associated Smad signal transduction proteins. daf-3 encodes a Smad protein that is most closely related to ...[more]

PMID: 9334330

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Project description:Many tissue-specific stem cells maintain the ability to produce multiple cell types during long periods of non-division, or quiescence. FOXO transcription factors promote quiescence and stem cell maintenance, but the mechanisms by which FOXO proteins promote multipotency during quiescence are still emerging. The single FOXO ortholog in C. elegans, daf-16, promotes entry into a quiescent and stress-resistant larval stage called dauer in response to adverse environmental cues. During dauer, stem and progenitor cells maintain or re-establish multipotency to allow normal development to resume after dauer. We find that during dauer, daf-16/FOXO prevents epidermal stem cells (seam cells) from prematurely adopting differentiated, adult characteristics. In particular, dauer larvae that lack daf-16 misexpress collagens that are normally adult-enriched. Using col-19p::gfp as an adult cell fate marker, we find that all major daf-16 isoforms contribute to opposing col-19p::gfp expression during dauer. By contrast, daf-16(0) larvae that undergo non-dauer development do not misexpress col-19p::gfp. Adult cell fate and the timing of col-19p::gfp expression are regulated by the heterochronic gene network, including lin-41 and lin-29. lin-41 encodes an RNA-binding protein orthologous to LIN41/TRIM71 in mammals, and lin-29 encodes a conserved zinc finger transcription factor. In non-dauer development, lin-41 opposes adult cell fate by inhibiting the translation of lin-29, which directly activates col-19 transcription and promotes adult cell fate. We find that during dauer, lin-41 blocks col-19p::gfp expression, but surprisingly, lin-29 is not required in this context. Additionally, daf-16 promotes the expression of lin-41 in dauer larvae. The col-19p::gfp misexpression phenotype observed in dauer larvae with reduced daf-16 requires the downregulation of lin-41, but does not require lin-29. Taken together, this work demonstrates a novel role for daf-16/FOXO as a heterochronic gene that promotes expression of lin-41/TRIM71 to contribute to multipotent cell fate in a quiescent stem cell model.

Dataset Information

The DAF-3 Smad protein antagonizes TGF-beta-related receptor signaling in the Caenorhabditis elegans dauer pathway.

Publications

The DAF-3 Smad protein antagonizes TGF-beta-related receptor signaling in the Caenorhabditis elegans dauer pathway.

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