| Summary: | As in many organisms, Caenorhabditis elegans oocytes assemble bipolar meiotic spindles in the absence of centrosomes. While the assembly of the mitotic spindle in C. elegans has been studied in some detail, how the poles assemble in the absence of centrosomes remains poorly understood. In an ongoing screen for temperature-sensitive (TS), embryonic-lethal mutants, we have identified TS mutations in multiple genes required for oocyte meiotic spindle pole assembly. We have so far identified mutations in four genes: or1178ts in mei-1, which encodes the catalytic domain of the microtubule severing complex katanin; or447ts in klp-18, which encodes a kinesin 12 family member; or645ts in aspm-1, which encodes a microtubule scaffolding protein; and or1092ts and or1292ts in klp-7, which encode a kinesin 13/MCAK family member. By using live cell imaging of oocytes from transgenic strains expressing GFP and mCherry fusion to proteins associated with the spindle, we have found and confirmed other findings that klp-18 promotes spindle bipolarity and that MEI-1 promotes pole assembly both by severing microtubules and by recruiting ASPM-1. More recently, we have found that klp-7 is required for maintaining bipolarity in the meiotic spindle by preventing the number of poles that can form. In klp-7(-) mutants, we observed in addition to extraneous poles an excess accumulation of microtubules during Meiosis I. Futhermore, reducing klp-7 function can restore bipolarity in a klp-18(-) monopolar spindle mutant background. We also observed that disruption of the kinetochore factor KNL-1 in klp-7(-) mutants exacerbates the extra spindle pole phenotype. We suggest that in oocyte meiosis, klp-7 is required to limit microtubule accumulation and pole assembly and that it may carry out these functions in a kinetochore-dependent manner.
This dissertation includes previously published co-authored material.
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