Project Summary For 30 years now, our laboratory has used live cell imaging with fluorescently marked proteins, and classical and molecular genetic approaches with the early embryo of the nematode Caenorhabditis elegans to investigate cytoskeletal function and regulation. In addition to having isolated temperature-sensitive mutations in many essential genes that control cytoskeletal function, bypassing earlier requirements, we have more recently incorporated extensive use of CRISPR/Cas9 to rapidly generate fluorescent protein fusions to endogenous loci, and to degron-tag genes required for cytoskeletal function such that we can bypass earlier requirements with auxin treatment. The advent of CRISPR/Cas9 and degron-tagging, along with gene replacement strategies that benefit from CRISPR/Cas9 technology, now enable still more powerful investigation of gene function in vivo using this model system. Our research program over the next five years will focus on oocyte meiotic cell division in C. elegans, which provides a powerful platform for investigating acentrosomal spindle assembly and the regulation and function of an animal cell cortex, with relevance to cancer, human fertility, and tissue engineering. The power of C. elegans genetics, and its amenability to live cell imaging, together with ongoing advances in high resolution light microscopy and our proposed novel and exciting application of Atomic Force Microscopy, make C. elegans an exceptional model system for investigation of these essential processes.