C. elegans serine-threonine kinase KIN-29 modulates TGFβ signaling and regulates body size formation

BACKGROUND: In C. elegans there are two well-defined TGFβ-like signaling pathways. The Sma/Mab pathway affects body size morphogenesis, male tail development and spicule formation while the Daf pathway regulates entry into and exit out of the dauer state. To identify additional factors that modulate TGFβ signaling in the Sma/Mab pathway, we have undertaken a genetic screen for small animals and have identified kin-29. RESULTS: kin-29 encodes a protein with a cytoplasmic serine-threonine kinase and a novel C-terminal domain. The kinase domain is a distantly related member of the EMK (ELKL motif kinase) family, which interacts with microtubules. We show that the serine-threonine kinase domain has in vitro activity. kin-29 mutations result in small animals, but do not affect male tail morphology as do several of the Sma/Mab signal transducers. Adult worms are smaller than the wild-type, but also develop more slowly. Rescue by kin-29 is achieved by expression in neurons or in the hypodermis. Interaction with the dauer pathway is observed in double mutant combinations, which have been seen with Sma/Mab pathway mutants. We show that kin-29 is epistatic to the ligand dbl-1, and lies upstream of the Sma/Mab pathway target gene, lon-1. CONCLUSION: kin-29 is a new modulator of the Sma/Mab pathway. It functions in neurons and in the hypodermis to regulate body size, but does not affect all TGFβ outputs, such as tail morphogenesis

The Role of eIF1 in Translation Initiation Codon Selection in Caenorhabditis elegans

The selection of a proper AUG start codon requires the base-pairing interactions between the codon on the mRNA and the anticodon of the initiator tRNA. This selection process occurs in a pre-initiation complex that includes multiple translation initiation factors and the small ribosomal subunit. To study how these initiation factors are involved in start codon recognition in multicellular organisms, we isolated mutants that allow the expression of a GFP reporter containing a non-AUG start codon. Here we describe the characterization of mutations in eif-1, which encodes the Caenorhabditis elegans translation initiation factor 1 (eIF1). Two mutations were identified, both of which are substitutions of amino acid residues that are identical in all eukaryotic eIF1 proteins. These residues are located in a structural region where the amino acid residues affected by the Saccharomyces cerevisiae eIF1 mutations are also localized. Both C. elegans mutations are dominant in conferring a non-AUG translation initiation phenotype and lead to growth arrest defects in homozygous animals. By assaying reporter constructs that have base changes at the AUG start codon, these mutants are found to allow expression from most reporters that carry single base changes within the AUG codon. This trend of non-AUG mediated initiation was also observed previously for C. elegans eIF2β mutants, indicating that these two factors play a similar role. These results support that eIF1 functions in ensuring the fidelity of AUG start codon recognition in a multicellular organism

Caenorhabditis elegans Galectins LEC-6 and LEC-10 Interact with Similar Glycoconjugates in the Intestine

Galectins are a family of metazoan proteins that show binding to various β-galactoside-containing glycans. Because of a lack of proper tools, the interaction of galectins with their specific glycan ligands in the cells and tissues are largely unknown. We have investigated the localization of galectin ligands in Caenorhabditis elegans using a novel technology that relies on the high binding specificity between galectins and their endogenous ligands. Fluorescently labeled recombinant galectin fusions are found to bind to ligands located in diverse tissues including the intestine, pharynx, and the rectal valve. Consistent with their role as galactoside-binding proteins, the interaction with their ligands is inhibited by galactose or lactose. Two of the galectins, LEC-6 and LEC-10, recognize ligands that co-localize along the intestinal lumen. The ligands for LEC-6 and LEC-10 are absent in three glycosylation mutants bre-1, fut-8, and galt-1, which have been shown to be required to synthesize the Gal-β1,4-Fuc modifications of the core N-glycans unique to C. elegans and several other invertebrates. Both galectins pull down the same set of glycoproteins in a manner dependent on the presence of these carbohydrate modifications. Endogenous LEC-6 and LEC-10 are expressed in the intestinal cells, but they are localized to different subcellular compartments that do not appear to overlap with each other or with the location of their glycan targets. An altered subcellular distribution of these ligands is found in mutants lacking both galectins. These results suggest a model where LEC-6 and LEC-10 interact with glycoproteins through specific glycans to regulate their cellular fate