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Contractile Ring (contractile + ring)
Selected AbstractsIn vivo phosphorylation of regulatory light chain of myosin II in sea urchin eggs and its role in controlling myosin localization and function during cytokinesisCYTOSKELETON, Issue 2 2008Ryota Uehara Abstract Phosphorylation of myosin regulatory light chain (RLC) at Ser19 (mono-phosphorylation) promotes filament assembly and enhances actin-activated ATPase activity of non-muscle myosin, while phosphorylation at both Ser19 and Thr18 (di-phosphorylation) further enhances the ATPase activity. However, it has not well been addressed which type of phosphorylation is important in regulating myosin during cytokinesis. Here, we investigated subcellular localization in sea urchin eggs of mono-phosphorylated and di-phosphorylated RLC by both quantitative biochemical and spatiotemporal cytological approaches. Mono-phosphorylated RLC was dominant in the equatorial cortex throughout the whole process of cytokinesis. Inhibition of myosin light chain kinase (MLCK) decreased mono-phosphorylated RLC both in the cortex and in the cleavage furrow, and blocked both formation and contraction of the contractile ring. Two different types of ROCK inhibitor gave inconsistent results: H1152 blocked both RLC mono-phosphorylation in the cleavage furrow and contraction of the contractile ring, while Y27632 affected neither the mono-phosphorylation nor cell division. These results suggest that there may be other targets of H1152 than ROCK, which is involved in the RLC phosphorylation in the cleavage furrow. Furthermore, it was revealed that localization of myosin heavy chain in the cleavage furrow, but not in the cortex, was perturbed by inhibition of RLC mono-phosphorylation. These results suggested that RLC mono-phosphorylation by more than two RLC kinases play a main role in regulation and localization of myosin in the dividing sea urchin eggs. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] Novel functions of ribosomal protein S6 in growth and differentiation of Dictyostelium cellsDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 6 2009Kazutaka Ishii We have previously shown that in Dictyostelium cells a 32 kDa protein is rapidly and completely dephosphorylated in response to starvation that is essential for the initiation of differentiation (Akiyama & Maeda 1992). In the present work, this phosphoprotein was identified as a homologue (Dd-RPS6) of ribosomal protein S6 (RPS6) that is an essential member for protein synthesis. As expected, Dd-RPS6 seems to be absolutely required for cell survival, because we failed to obtain antisense-RNA mediated cells as well as Dd-rps6 -null cells by homologous recombination in spite of many trials. In many kinds of cell lines, RPS6 is known to be located in the nucleus and cytosol, but Dd-RPS6 is predominantly located in the cell cortex with cytoskeletons, and in the contractile ring of just-dividing cells. In this connection, the overexpression of Dd-RPS6 greatly impairs cytokinesis during axenic shake-cultures in growth medium, resulting in the formation of multinucleate cells. Much severe impairment of cytokinesis was observed when Dd-RPS6-overexpressing cells (Dd-RPS6OE cells) were incubated on a living Escherichia coli lawn. The initiation of differentiation triggered by starvation was also delayed in Dd-RPS6OE cells. In addition, Dd-RPS6OE cells exhibit defective differentiation into prespore cells and spores during late development. Thus, it is likely that the proper expression of Dd-RPS6 may be of importance for the normal progression of late differentiation as well as for the initiation of differentiation. [source] Rho1-GEFs Rgf1 and Rgf2 are involved in formation of cell wall and septum, while Rgf3 is involved in cytokinesis in fission yeastGENES TO CELLS, Issue 12 2005Tadashi Mutoh The Rho GTPase acts as a binary molecular switch by converting between a GDP-bound inactive and a GTP-bound active conformational state. The guanine nucleotide exchange factors (GEFs) are critical activators of Rho. Rho1 has been shown to regulate actin cytoskeleton and cell wall synthesis in the fission yeast Schizosaccharomyces pombe. Here we studied function of fission yeast RhoGEFs, Rgf1, Rgf2, and Rgf3. It was shown that these proteins have similar molecular structures, and function as GEFs for Rho1. Disruption of either rgf1 or rgf2 did not show a serious effect on the cell. On the other hand, disruption of rgf3 caused severe defects in contractile ring formation, F-actin patch localization, and septation during cytokinesis. Rgf1 and Rgf2 were localized to the cell ends during interphase and the septum. Rgf3 formed a ring at the division site, which was located outside the contractile ring and inside the septum where Rho1 was accumulated. In summary, Rgf1 and Rgf2 show functional redundancy, and roles of these RhoGEFs are likely to be different from that of Rgf3. Rho1 is likely to be activated by Rgf3 at the division site, and involved in contractile ring formation and/or maintenance and septation. [source] Reining in cytokinesis with a septin corralBIOESSAYS, Issue 1 2005Fern P. Finger Septins are a family of conserved GTP-binding proteins that function in cytokinesis in fungi and animals. In budding yeast, septins form scaffolds for assembly of the actomyosin contractile ring at the cleavage plane, a role that does not appear to be conserved in other organisms. The septins form an hourglass-shaped collar at the mother-bud neck, which splits into two rings flanking the division plane at cytokinesis. A recent study1 demonstrates that these two septin rings constitute diffusion barriers that create a cytokinetic compartment to retain cortical cytokinetic factors in proximity to the cleavage plane. BioEssays 27:5,8, 2005. © 2004 Wiley Periodicals, Inc. [source] Myosin localization during meiosis I of crane-fly spermatocytes gives indications about its role in divisionCYTOSKELETON, Issue 2 2003Rosalind V. Silverman-Gavrila Abstract We showed previously that in crane-fly spermatocytes myosin is required for tubulin flux [Silverman-Gavrila and Forer, 2000a: J Cell Sci 113:597,609], and for normal anaphase chromosome movement and contractile ring contraction [Silverman-Gavrila and Forer, 2001: Cell Motil Cytoskeleton 50:180,197]. Neither the identity nor the distribution of myosin(s) were known. In the present work, we used immunofluorescence and confocal microscopy to study myosin during meiosis-I of crane-fly spermatocytes compared to tubulin, actin, and skeletor, a spindle matrix protein, in order to further understand how myosin might function during cell division. Antibodies to myosin II regulatory light chain and myosin II heavy chain gave similar staining patterns, both dependent on stage: myosin is associated with nuclei, asters, centrosomes, chromosomes, spindle microtubules, midbody microtubules, and contractile rings. Myosin and actin colocalization along kinetochore fibers from prometaphase to anaphase are consistent with suggestions that acto-myosin forces in these stages propel kinetochore fibres poleward and trigger tubulin flux in kinetochore fibres, contributing in this way to poleward chromosome movement. Myosin and actin colocalization at the cell equator in cytokinesis, similar to studies in other cells [e.g., Fujiwara and Pollard, 1978: J Cell Biol 77:182,195], supports a role of actin-myosin interactions in contractile ring function. Myosin and skeletor colocalization in prometaphase spindles is consistent with a role of these proteins in spindle formation. After microtubules or actin were disrupted, myosin remained in spindles and contractile rings, suggesting that the presence of myosin in these structures does not require the continued presence of microtubules or actin. BDM (2,3 butanedione, 2 monoxime) treatment that inhibits chromosome movement and cytokinesis also altered myosin distributions in anaphase spindles and contractile rings, consistent with the physiological effects, suggesting also that myosin needs to be active in order to be properly distributed. Cell Motil. Cytoskeleton 55:97,113, 2003. © 2003 Wiley-Liss, Inc. [source] | ||||||||||