Our goal is to understand the mechanisms that position female meiotic spindles at the egg cortex and that mediate polar body formation. In the long term, we hope to elucidate the reasons why asymmetric meiotic spindle positioning is so conserved across animal phyla. The specific goals of this proposal are to elucidate the detailed mechanisms of three distinct pathways that mediate meiotic spindle positioning and polar body formation in Caenorhabitis elegans. 1) Kinesin-1 heavy chain, kinesin light chains and a novel protein called KCA-1 are each required to move the meiotic spindle to the egg cortex before the metaphase-anaphase transition. In contrast, movement of the meiotic spindle to the egg cortex after the metaphase-anaphase transition is kinesin-independent. We will use fluorescence microscopy and in vitro biochemistry to test the hypothesis that a kinesin/KCA-1 complex directly transports the spindle along cytoplasmic microtubules and that a distinct mechanism is responsible for both spindle translocation in the absence of kinesin and spindle rotation during wild-type meiosis. 2) Complete loss of the microtubule-severing protein, katanin, results in failure to assemble a meiotic spindle whereas partial loss of katanin function results in abnormally long meiotic spindles and abnormally large polar bodies. We will use fluorescence microscopy and genetics to test the hypothesis that microtubule-severing activity restricts meiotic spindle length and thereby polar body size. 3) SPE-11 is a sperm protein introduced into the egg at fertilization and which is required for polar body formation. We will use a combination of fluorescence microscopy and genetics to test the hypothesis that SPE-11 mediates polar body formation by interacting with conserved cytokinesis regulators in the egg. Meiotic spindles are relevant to public health for two major reasons. First, abnormal meiotic spindle function leads to aneuploidy that causes Down syndrome and miscarriage. Second, the potential for treating numerous human diseases with patient-matched stem cells is currently limited by abnormal meiotic spindle assembly during animal cloning. A detailed molecular understanding of meiotic spindle function could thus lead to treatments that prevent birth defects and that allow stem cell therapy of human diseases.
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