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The small GTP-binding protein rho regulates cortical activities in cultured cells during division.

O'Connell CB, Wheatley SP, Ahmed S, Wang YL - J. Cell Biol. (1999)

Bottom Line: All treated, well-adherent cells underwent cleavage-like activities and most of them divided successfully.The effects of C3 appeared to be dependent on cell adhesion; less adherent 3T3 fibroblasts exhibited irregular cortical ingression only when cells started to increase attachment during respreading, but managed to complete cytokinesis.Our results indicate that Rho does not simply activate actin-myosin II interactions during cytokinesis, but regulates the spatial pattern of cortical activities and completion of cytokinesis possibly through modulating the mechanical strength of the cortex.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.

ABSTRACT
We have investigated the role of the small GTP-binding protein Rho in cytokinesis by microinjecting an inhibitor, C3 ribosyltransferase, into cultured cells. Microinjection of C3 into prometaphase or metaphase normal rat kidney epithelial cells induced immediate and global cortical movement of actin toward the metaphase plate, without an apparent effect on the mitotic spindle. During anaphase, concentrated cortical actin filaments migrated with separating chromosomes, leaving no apparent concentration of actin filaments along the equator. Myosin II in injected epithelial cells showed a diffuse distribution throughout cell division. All treated, well-adherent cells underwent cleavage-like activities and most of them divided successfully. However, cytokinesis became abnormal, generating irregular ingressions and ectopic cleavage sites even when mitosis was blocked with nocodazole. The effects of C3 appeared to be dependent on cell adhesion; less adherent 3T3 fibroblasts exhibited irregular cortical ingression only when cells started to increase attachment during respreading, but managed to complete cytokinesis. Poorly adherent HeLa cells showed neither ectopic cleavage nor completion of cytokinesis. Our results indicate that Rho does not simply activate actin-myosin II interactions during cytokinesis, but regulates the spatial pattern of cortical activities and completion of cytokinesis possibly through modulating the mechanical strength of the cortex.

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Organization of  microtubules in control and  C3-injected mitotic NRK cells.  In a control cell microinjected  with rhodamine-labeled tubulin (a–e), kinetochore microtubules shortened, while midzone microtubules elongated.  The spindle poles separated  as the cell progressed from  metaphase through anaphase  (a–c). Prominent microtubule  bundles were associated with  the midbody during telophase  (e). Microtubules in a C3- injected cell (f–j) underwent  similar changes, except that  midzone microtubules became  distorted (compare c and d,  with h and i). A long bundle of  microtubules formed in the  extended cleavage furrow (j).  Bar, 10 μm.
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Figure 8: Organization of microtubules in control and C3-injected mitotic NRK cells. In a control cell microinjected with rhodamine-labeled tubulin (a–e), kinetochore microtubules shortened, while midzone microtubules elongated. The spindle poles separated as the cell progressed from metaphase through anaphase (a–c). Prominent microtubule bundles were associated with the midbody during telophase (e). Microtubules in a C3- injected cell (f–j) underwent similar changes, except that midzone microtubules became distorted (compare c and d, with h and i). A long bundle of microtubules formed in the extended cleavage furrow (j). Bar, 10 μm.

Mentions: Contrary to the dramatic effects on the cortex and actin organization, no apparent effect was observed in C3-injected cells with regard to chromosomal separation or nuclear envelope reformation, confirming that the effects on cortex were not caused by the disruption of mitosis or cell cy-cle. Moreover, imaging of microinjected fluorescent tubulin showed no change in microtubule organization during metaphase or anaphase (Fig. 8, f and g), nor was there apparent effect on the elongation of astral microtubules. During telophase, wavy interzonal microtubules formed along the equator, most likely due to irregular cortical ingressions (Fig. 8, h and i). In addition, the elongated furrows were probably responsible for the formation of an extended bundle of microtubules flanking the midbody (Fig. 8 j). However, no prominent microtubule bundle was detected near ectopic furrows.


The small GTP-binding protein rho regulates cortical activities in cultured cells during division.

O'Connell CB, Wheatley SP, Ahmed S, Wang YL - J. Cell Biol. (1999)

Organization of  microtubules in control and  C3-injected mitotic NRK cells.  In a control cell microinjected  with rhodamine-labeled tubulin (a–e), kinetochore microtubules shortened, while midzone microtubules elongated.  The spindle poles separated  as the cell progressed from  metaphase through anaphase  (a–c). Prominent microtubule  bundles were associated with  the midbody during telophase  (e). Microtubules in a C3- injected cell (f–j) underwent  similar changes, except that  midzone microtubules became  distorted (compare c and d,  with h and i). A long bundle of  microtubules formed in the  extended cleavage furrow (j).  Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132903&req=5

Figure 8: Organization of microtubules in control and C3-injected mitotic NRK cells. In a control cell microinjected with rhodamine-labeled tubulin (a–e), kinetochore microtubules shortened, while midzone microtubules elongated. The spindle poles separated as the cell progressed from metaphase through anaphase (a–c). Prominent microtubule bundles were associated with the midbody during telophase (e). Microtubules in a C3- injected cell (f–j) underwent similar changes, except that midzone microtubules became distorted (compare c and d, with h and i). A long bundle of microtubules formed in the extended cleavage furrow (j). Bar, 10 μm.
Mentions: Contrary to the dramatic effects on the cortex and actin organization, no apparent effect was observed in C3-injected cells with regard to chromosomal separation or nuclear envelope reformation, confirming that the effects on cortex were not caused by the disruption of mitosis or cell cy-cle. Moreover, imaging of microinjected fluorescent tubulin showed no change in microtubule organization during metaphase or anaphase (Fig. 8, f and g), nor was there apparent effect on the elongation of astral microtubules. During telophase, wavy interzonal microtubules formed along the equator, most likely due to irregular cortical ingressions (Fig. 8, h and i). In addition, the elongated furrows were probably responsible for the formation of an extended bundle of microtubules flanking the midbody (Fig. 8 j). However, no prominent microtubule bundle was detected near ectopic furrows.

Bottom Line: All treated, well-adherent cells underwent cleavage-like activities and most of them divided successfully.The effects of C3 appeared to be dependent on cell adhesion; less adherent 3T3 fibroblasts exhibited irregular cortical ingression only when cells started to increase attachment during respreading, but managed to complete cytokinesis.Our results indicate that Rho does not simply activate actin-myosin II interactions during cytokinesis, but regulates the spatial pattern of cortical activities and completion of cytokinesis possibly through modulating the mechanical strength of the cortex.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.

ABSTRACT
We have investigated the role of the small GTP-binding protein Rho in cytokinesis by microinjecting an inhibitor, C3 ribosyltransferase, into cultured cells. Microinjection of C3 into prometaphase or metaphase normal rat kidney epithelial cells induced immediate and global cortical movement of actin toward the metaphase plate, without an apparent effect on the mitotic spindle. During anaphase, concentrated cortical actin filaments migrated with separating chromosomes, leaving no apparent concentration of actin filaments along the equator. Myosin II in injected epithelial cells showed a diffuse distribution throughout cell division. All treated, well-adherent cells underwent cleavage-like activities and most of them divided successfully. However, cytokinesis became abnormal, generating irregular ingressions and ectopic cleavage sites even when mitosis was blocked with nocodazole. The effects of C3 appeared to be dependent on cell adhesion; less adherent 3T3 fibroblasts exhibited irregular cortical ingression only when cells started to increase attachment during respreading, but managed to complete cytokinesis. Poorly adherent HeLa cells showed neither ectopic cleavage nor completion of cytokinesis. Our results indicate that Rho does not simply activate actin-myosin II interactions during cytokinesis, but regulates the spatial pattern of cortical activities and completion of cytokinesis possibly through modulating the mechanical strength of the cortex.

Show MeSH
Related in: MedlinePlus