F-BAR domain protein Rga7 collaborates with Cdc15 and Imp2 to ensure proper cytokinesis in fission yeast

Abstract

F-BAR domain proteins act as linkers between the cell cortex and cytoskeleton, and are involved in membrane binding and bending. Rga7 is one of the seven F-BAR proteins present in the fission yeast Schizosaccharomyces pombe. In addition to the F-BAR domain in the N-terminal region, Rga7 possesses a Rho GTPaseactivating protein (GAP) domain at its C-terminus. We show here that Rga7 is necessary to prevent fragmentation of the contracting ring and incorrect septum synthesis. Accordingly, cultures of cells lacking Rga7 contain a higher percentage of dividing cells and more frequent asymmetric or aberrant septa, which ultimately might cause cell death. The Rga7 F-BAR domain is necessary for the protein localization to the division site and to the cell tips, and also for the Rga7 roles in cytokinesis. In contrast, Rga7 GAP catalytic activity seems to be dispensable. Moreover, we demonstrate that Rga7 cooperates with the two F-BAR proteins Cdc15 and Imp2 to ensure proper cytokinesis. We have also detected association of Rga7 with Imp2, and its binding partners Fic1 and Pxl1. Taken together, our findings suggest that Rga7 forms part of a protein complex that coordinates the late stages of cytokinesis.

A role for F-BAR protein Rga7p during cytokinesis in S. pombe

“…We confirmed the following observations of Martin-Garcia et al (2014). Cells that lack Rga7p have unstable contractile rings, and some lyse when the daughter cells separate.…”

“…Consistent with this interpretation, Δrga7 cells and bgs4 + mutants cwg1-1 and cwg1-2 have similar septal defects and a similar tendency to lyse (Cortes et al, 2012;Martin-Garcia et al, 2014;Munoz et al, 2013).…”

“…5A-C). Septa in Δrga7 cells formed perpendicular to the long axis but accumulated defects, such as bends and bulges, late during septum closure formation (Martin-Garcia et al, 2014), indicating a lack of the rigidity needed to maintain a straight septum (Fig. 5A,D) (Munoz et al, 2013).…”

“…The Rga7p F-BAR domain binds to phospholipids (Martin-Garcia et al, 2014) in vitro and localizes Rga7p to late Golgi compartments containing Bgs4p, but the middle and RhoGAP domains also contribute. Like other F-BAR domains (Frost et al, 2008), Rga7p can sense or induce the membrane curvature that is necessary to form vesicles or tubules.…”

“…Deletion mutations show that Imp2p and Rga7p appear to perform different functions during cytokinesis -Δimp2 cells are multi-septated (Demeter and Sazer, 1998), whereas Δrga7 cells appear to lyse near the end of cytokinesis (Martin et al, 2003;Soto et al, 2010). Martin-Garcia and colleagues have recently investigated the role of Rga7p in the stability of the contractile ring, cell separation and septation, but interesting questions remain about its roles in cytokinesis (Martin-Garcia et al 2014).…”