An extracellular matrix protein prevents cytokinesis failure and aneuploidy in the C. elegans germline.

Interactions between extracellular matrix (ECM) proteins and their transmembrane receptors mediate cytoskeletal reorganization and corresponding changes in cell shape during cell migration, adhesion, differentiation and polarization. Cytokinesis is the final step in cell division as cells employ a contractile ring composed of actin and myosin to partition one cell into two. Cells undergo dramatic changes in cell shape during the division process, creating new membrane and forming an extracellular invagination called the cleavage furrow. However, existing models of cytokinesis include no role for the ECM. In a recent paper, we demonstrate that depletion of a large secreted protein, hemicentin, results in membrane destabilization, cleavage furrow retraction and cytokinesis failure in C. elegans germ cells and in pre-implantation mouse embryos. Here, we demonstrate that cytokinesis failure produces tetraploid intermediate cells with multipolar spindles, providing a potential explanation for the large number of aneuploid progeny observed among C. elegans hemicentin mutant hermaphrodites.

Dynamic localization of yeast Fus2p to an expanding ring at the cell fusion junction during mating.

Fus2p is a pheromone-induced protein associated with the amphiphysin homologue Rvs161p, which is required for cell fusion during mating in Saccharomyces cerevisiae. We constructed a functional Fus2p-green fluorescent protein (GFP), which exhibits highly dynamic localization patterns in pheromone-responding cells (shmoos): diffuse nuclear, mobile cytoplasmic dots and stable cortical patches concentrated at the shmoo tip. In mitotic cells, Fus2p-GFP is nuclear but becomes cytoplasmic as cells form shmoos, dependent on the Fus3p protein kinase and high levels of pheromone signaling. The rapid cytoplasmic movement of Fus2p-GFP dots requires Rvs161p and polymerized actin and is aberrant in mutants with compromised actin organization, which suggests that the Fus2p dots are transported along actin cables, possibly in association with vesicles. Maintenance of Fus2p-GFP patches at the shmoo tip cortex is jointly dependent on actin and a membrane protein, Fus1p, which suggests that Fus1p is an anchor for Fus2p. In zygotes, Fus2p-GFP forms a dilating ring at the cell junction, returning to the nucleus at the completion of cell fusion.