Advances in Cytokinesis Research. Cytokinesis in the C. elegans Embryo: Regulating Contractile Forces and a Late Role for the Central Spindle.

Abstract

ABSTRACT. Genetic and molecular studies in the nematode Caenorhabditis elegans have identified multiple essential pathways that regulate and execute cytokinesis in early embryonic cells. These pathways influence both the microfilament cytoskeleton and the microtubule cytoskeleton. Microfilaments are enriched throughout the cell cortex at all times during the cell cycle in embryonic cells. Cortical microfilaments are required for multiple processes in embryonic cells, including polar body extrusion during meiosis, anterior-posterior axis specification by the sperm-donated microtubule-organizing center, and cytokinesis during mitosis. In addition to contractile apparatus proteins that are required positively for cleavage furrow ingression, the Nedd8 ubiquitin-like protein modification pathway negatively regulates contractile forces outside the cleavage furrow during cytokinesis. Another pathway that acts positively during cytokinesis involves the mitotic spindle. The central spindle, where anti-parallel non-kinetochore microtubules overlap and are cross-linked, is required for a late step in cytokinesis, and other pathway(s) involved in membrane addition during cytokinesis may also require the central spindle. The amenability of C. elegans to classical genetics, the ease of reducing gene function with RNA interference, the completion of the genome sequence, and the availability of transgenic GFP fusion proteins that render the cytoskeleton fluorescent, all serve to make the early worm embryo an especially promising system for further advances in the identification of cytokinesis pathways, and in defining their interactions.

Kinesins to the core: The role of microtubule-based motor proteins in building the mitotic spindle midzone

“…Here we have focused on reviewing mechanisms for midzone assembly and function. There are several excellent reviews that deal with the issue of midzone microtubules vs. astral microtubules in signaling for cytokinesis [1, 3, 20, 22, 27, 28]; and we will not address this issue here, except to acknowledge that the debate over the respective roles of the midzone vs. the asters continues.…”