RESUMO
A double septin ring accompanies cytokinesis in yeasts and mammalian cells. In budding yeast, reorganisation of the septin collar at the bud neck into a dynamic double ring is essential for actomyosin ring constriction and cytokinesis. Septin reorganisation requires the Mitotic Exit Network (MEN), a kinase cascade essential for cytokinesis. However, the effectors of MEN in this process are unknown. Here we identify the F-BAR protein Hof1 as a critical target of MEN in septin remodelling. Phospho-mimicking HOF1 mutant alleles overcome the inability of MEN mutants to undergo septin reorganisation by decreasing Hof1 binding to septins and facilitating its translocation to the actomyosin ring. Hof1-mediated septin rearrangement requires its F-BAR domain, suggesting that it may involve a local membrane remodelling that leads to septin reorganisation. In vitro Hof1 can induce the formation of intertwined septin bundles, while a phosphomimetic Hof1 protein has impaired septin-bundling activity. Altogether, our data indicate that Hof1 modulates septin architecture in distinct ways depending on its phosphorylation status.
Assuntos
Citocinese , Proteínas Associadas aos Microtúbulos , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Septinas , Proteínas de Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Fosforilação , Septinas/metabolismo , Septinas/genética , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ciclo Celular/genética , Actomiosina/metabolismo , Saccharomycetales/metabolismo , Saccharomycetales/genética , Mutação , Ligação ProteicaRESUMO
During cytokinesis, signals from the anaphase spindle direct the formation and position of a contractile ring at the cell cortex [1]. The chromosomal passenger complex (CPC) participates in cytokinesis initiation by signaling from the spindle midzone and equatorial cortex [2], but the mechanisms underlying the anaphase-specific CPC localization are currently unresolved. Accumulation of the CPC at these sites requires the presence of microtubules and the mitotic kinesin-like protein 2, MKLP2 (KIF20A), a member of the kinesin-6 family [2-7], and this has led to the hypothesis that the CPC is transported along microtubules by MKLP2 [3-5, 7]. However, the structure of the MKLP2 motor domain with its extended neck-linker region suggests that this kinesin might not be able to drive processive transport [8, 9]. Furthermore, experiments in Xenopus egg extracts indicated that the CPC might be transported by kinesin-4, KIF4A [10]. Finally, CPC-MKLP2 complexes might be directly recruited to the equatorial cortex via association with actin and myosin II, independent of kinesin activity [4, 8]. Using microscopy-based assays with purified proteins, we demonstrate that MKLP2 is a processive plus-end directed motor that can transport the CPC along microtubules in vitro. In cells, strong suppression of MKLP2-dependent CPC motility by expression of an MKLP2 P-loop mutant perturbs CPC accumulation at both the spindle midzone and equatorial cortex, whereas a weaker inhibition of MKLP2 motor using Paprotrain mainly affects CPC localization to the equatorial cortex. Our data indicate that control of cytokinesis initiation by the CPC requires its directional MKLP2-dependent transport.
Assuntos
Anáfase/fisiologia , Citocinese , Cinesinas/genética , Família Multigênica , Células HEK293 , Células HeLa , Humanos , Cinesinas/metabolismo , Transporte ProteicoRESUMO
Cytokinesis begins upon anaphase onset. An early step involves local activation of the small GTPase RhoA, which triggers assembly of an actomyosin-based contractile ring at the equatorial cortex. Here, we delineated the contributions of PLK1 and Aurora B to RhoA activation and cytokinesis initiation in human cells. Knock-down of PRC1, which disrupts the spindle midzone, revealed the existence of two pathways that can initiate cleavage furrow ingression. One pathway depends on a well-organized spindle midzone and PLK1, while the other depends on Aurora B activity and centralspindlin at the equatorial cortex and can operate independently of PLK1. We further show that PLK1 inhibition sequesters centralspindlin onto the spindle midzone, making it unavailable for Aurora B at the equatorial cortex. We propose that PLK1 activity promotes the release of centralspindlin from the spindle midzone through inhibition of PRC1, allowing centralspindlin to function as a regulator of spindle midzone formation and as an activator of RhoA at the equatorial cortex.