Talk abstracts

Talk on Wednesday 03:15-03:30pm submitted by I-Ju Lee

Characterization of Mid1 domains for targeting and scaffolding in fission yeast cytokinesis

I-Ju Lee (Graduate Program of Molecular, Cellular, and Developmental Biology), Jian-Qiu Wu (Department of Molecular Genetics, Department of Molecular & Cellular Biochemistry)

Abstract:
Cytokinesis partitions a mother cell into two daughter cells. Failure in cytokinesis has been proposed to contribute to tumorigenesis. Division-site selection and contractile-ring assembly are two crucial steps in cytokinesis conserved from yeast to humans. In animal cells, the assembly of contractile ring is scaffolded by anillin, a protein often found overexpressed in tumors. In fission yeast, the anillin-like Mid1 specifies the division site at the cell equator by assembling cortical nodes, the precursors of the contractile ring. Despite its importance, how domains of Mid1 cooperate to regulate cytokinesis is poorly understood. Here we unravel the functions of different Mid1 domains/motifs by a series of truncations. We found that Mid1 physically interacts with at least three cytokinesis node proteins through its N-terminal half. The most N-terminal domain of Mid1 is not able to localize by itself, but is sufficient to assemble cytokinesis nodes and the contractile ring with the help of a localization signal, suggesting that like other anillins, the N-terminus of Mid1 exerts the scaffolding function while the C-terminus regulates its localization. Indeed we found that the C-terminal Pleckstrin Homology domain stabilizes the cortical localization of Mid1 by binding to lipids. In addition, a previous uncharacterized internal region of Mid1 modulates its cortical and nuclear concentrations. Mid1 lacking the internal region suppresses the division-site positioning defects in cells with a deletion of the DYRK kinase Pom1, indicating a change of balance between different regulating systems. Taken together, our study advances our understanding of cytokinesis by recognizing domains regulating Mid1 cortical localization and revealing domains sufficient for contractile-ring assembly.

Keywords: cytokinesis, yeast, anillin