Architectural dynamics and gene replacement of coronin suggest its role in cytokinesis

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Abstract
Coronin is a ubiquitous actin‐binding protein representing a member of proteins portraying a WD‐repeat sequence, including the β‐subunits of trimeric G‐proteins. Coronin has been suggested to participate in multiple, actin‐based physiological activities such as cell movement and cell division. Although the slow growth of coronin deletion mutants has been attributed to a defect in the fluid‐phase uptake of nutrients, the exact role of coronin in cytoskeletal organization has not been elucidated. In this study, we examined a role of coronin in cytokinesis by analyzing the effect of coronin deletion on the actin cytoskeleton and its dynamic distribution using a green fluorescent protein (GFP)‐coronin fusion protein. We show that GFP‐coronin works similarly to natural coronin in vivo and in vitro. In live cells, GFP‐coronin was found to accumulate into the cleavage furrow during cytokinesis. The fluorescence pattern suggests its association to the contractile ring throughout cytokinesis. Interestingly, a substantial amount of coronin was also bound to F‐actin at the prospective posterior cortex of the daughter cells. We also show that the coronin null cells reveal irregularities in organization of actin and myosin II and divide by a process identical to the traction‐mediated cytofission reported in myosin II mutants. Overall, this study suggests that coronin is essential for organizing the normal actin cytoskeleton and plays a significant role in cell division. Cell Motil. Cytoskeleton 42:204–217, 1999.