A Caenorhabditis elegans type I TGF beta receptor can function in the absence of type II kinase to promote larval development.
The daf-4 gene encodes a type II bone morphogenetic protein receptor in Caenorhabditis elegans that regulates dauer larva formation, body size and male tail patterning. The putative type I receptor partner for DAF-4 in regulating dauer larva formation is DAF-1. Genetic tests of the mechanism of activation of these receptors show that DAF-1 can signal in the absence of DAF-4 kinase activity. A daf-1 mutation enhances dauer formation in a daf-4 null background, whereas overexpression of daf-1 partially rescues a daf-4 mutant. DAF-1 alone cannot fully compensate for the loss of DAF-4 activity, indicating that nondauer development normally results from the activities of both receptors. DAF-1 signaling in the absence of a type II kinase is unique in the type I receptor family. The activity may be an evolutionary remnant, owing to daf-1's origin near the type I/type II divergence, or it may be an innovation that evolved in nematodes. daf-1 and daf-4 promoters both mediated expression of green fluorescent protein in the nervous system, indicating that a DAF-1/DAF-4 receptor complex may activate a neuronal signaling pathway. Signaling from a strong DAF-1/DAF-4 receptor complex or a weaker DAF-1 receptor alone may provide larvae with more precise control of the dauer/nondauer decision in a range of environmental conditions.
Gunther
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Molecular Biology Program and Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA.
Georgi
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Riddle
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D030201:Activin Receptors, Type I; D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins; D015870:Gene Expression; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007814:Larva; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology*; D000077293:Receptor, Transforming Growth Factor-beta Type I; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D019076:Transgenes
D029742:Caenorhabditis elegans Proteins; C064359:DAF-1 protein, C elegans; D015801:Helminth Proteins; D011956:Receptors, Cell Surface; D018125:Receptors, Transforming Growth Factor beta; C083704:daf-4 protein, C elegans; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I