The spindle assembly function of Caenorhabditis elegans katanin does not require microtubule-severing activity

Katanin is a heterodimeric microtubule-severing protein that is conserved among eukaryotes. Loss-of-function mutations in the Caenorhabditis elegans katanin catalytic subunit, MEI-1, cause specific defects in female meiotic spindles. To determine the relationship between katanin's microtubule-severing activity and its role in meiotic spindle formation, we analyzed the MEI-1(A338S) mutant. Unlike wild-type MEI-1, which mediated disassembly of microtubule arrays in Xenopus fibroblasts, MEI-1(A338S) had no effect on fibroblast microtubules, indicating a lack of microtubule-severing activity. In C. elegans, MEI-1(A338S) mediated assembly of extremely long bipolar meiotic spindles. In contrast, a nonsense mutation in MEI-1 caused assembly of meiotic spindles without any poles as assayed by localization of the spindle-pole protein, ASPM-1. These results indicated that katanin protein, but not katanin's microtubule-severing activity, is required for assembly of acentriolar meiotic spindle poles. To understand the nonsevering activities of katanin, we characterized the N-terminal domain of the katanin catalytic subunit. The N-terminal domain was necessary and sufficient for binding to the katanin regulatory subunit. The katanin regulatory subunit in turn caused a dramatic change in the microtubule-binding properties of the N-terminal domain of the catalytic subunit. This unique bipartite microtubule-binding structure may mediate the spindle-pole assembly activity of katanin during female meiosis.     

Muscle-directed mechanosensory feedback activates egg-laying circuit activity and behavior in Caenorhabditis elegans

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Diet-dependent depletion of queuosine in tRNAs in Caenorhabditis elegans does not lead to a developmental block

Queuosine (Q), a hypermodified nucleoside, occurs at the wobble position of transfer RNAs (tRNAs) with GUN anticodons. In eubacteria, absence of Q affects messenger RNA (mRNA) translation and reduces the virulence of certain pathogenic strains. In animal cells, changes in the abundance of Q have been shown to correlate with diverse phenomena including stress tolerance, cell proliferation and tumour growth but the function of Q in animals is poorly understood. Animals are thought to obtain Q (or its analogues) as a micronutrient from dietary sources such as gut microflora. However, the difficulty of maintaining animals under bacteria-free conditions on Q-deficient diets has severely hampered the study of Q metabolism and function in animals. In this study, we show that as in higher animals, tRNAs in the nematode Caenorhabditis elegans are modified by Q and its sugar derivatives. When the worms were fed on Q-deficient Escherichia coli, Q modification was absent from the worm tRNAs suggesting that C. elegans lacks a de novo pathway of Q biosynthesis. The inherent advantages of C. elegans as a model organism, and the simplicity of conferring a Q-deficient phenotype on it make it an ideal system to investigate the function of Q modification in tRNA.     

The epidermal growth factor system in Caenorhabditis elegans

The single known epidermal growth factor-like growth factor and single epidermal growth factor receptor in Caenorhabditis elegans mediate two types of processes, each via a distinct signal transduction pathway. Several instances of cell fate specification during organogenesis require the RAS-MAP kinase pathway, as well as multiple nuclear factors. By contrast, appropriate myoepithelial contractions during ovulation involve IP3-mediated signal transduction. Positive modulators of the RAS pathway include KSR, SUR-8, phosphatase PP2A, and a zinc cation diffusion facilitator. Negative regulators of the RAS pathway include homologs of CBL, GAP-1, ACK, and MAP kinase phosphatase, while negative regulators of the IP3 pathway are enzymes that modify IP3. In addition to its stimulation of RAS activity, the GRB2 homolog SEM-5 acts negatively on both signaling pathways, as does the Ack-related kinase ARK-1.