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Cytoplasmic dynein is required for distinct aspects of MTOC positioning, including centrosome separation, in the one cell stage Caenorhabditis elegans embryo.

Gönczy P, Pichler S, Kirkham M, Hyman AA - J. Cell Biol. (1999)

Bottom Line: Moreover, in 15% of dhc-1 (RNAi) embryos, centrosomes failed to remain in proximity of the male pronucleus.Therefore, cytoplasmic dynein is required for multiple aspects of MTOC positioning in the one cell stage C. elegans embryo.In conjunction with our observation of cytoplasmic dynein distribution at the periphery of nuclei, these results lead us to propose a mechanism in which cytoplasmic dynein anchored on the nucleus drives centrosome separation.

View Article: PubMed Central - PubMed

Affiliation: European Molecular Biology Laboratory, Heidelberg, D-69117 Germany. gonczy@embl-heidelberg.de

ABSTRACT
We have investigated the role of cytoplasmic dynein in microtubule organizing center (MTOC) positioning using RNA-mediated interference (RNAi) in Caenorhabditis elegans to deplete the product of the dynein heavy chain gene dhc-1. Analysis with time-lapse differential interference contrast microscopy and indirect immunofluorescence revealed that pronuclear migration and centrosome separation failed in one cell stage dhc-1 (RNAi) embryos. These phenotypes were also observed when the dynactin components p50/dynamitin or p150(Glued) were depleted with RNAi. Moreover, in 15% of dhc-1 (RNAi) embryos, centrosomes failed to remain in proximity of the male pronucleus. When dynein heavy chain function was diminished only partially with RNAi, centrosome separation took place, but orientation of the mitotic spindle was defective. Therefore, cytoplasmic dynein is required for multiple aspects of MTOC positioning in the one cell stage C. elegans embryo. In conjunction with our observation of cytoplasmic dynein distribution at the periphery of nuclei, these results lead us to propose a mechanism in which cytoplasmic dynein anchored on the nucleus drives centrosome separation.

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Possible model of dynein-dependent separation of centrosomes. View is on posterior of one cell stage embryo. Male pronucleus: large light disk. Centrosomes: small black disks. Shown also are astral microtubules (black lines) and two-headed cytoplasmic dynein; cytoplasmic dynein molecules that interact with astral microtubules are shown in dark shading, others in light shading. Cytoplasmic dynein is evenly distributed on the male pronucleus. When astral microtubules encounter such anchored motors, their minus end is pulled towards cytoplasmic dynein, along with the centrosome. Longer astral microtubules encounter more motors and, thus, experience a stronger pulling force than shorter ones. Because astral microtubules growing towards the anterior are longer to start with, dynein-dependent forces displace centrosomes towards the anterior initially. When astral microtubules growing in all directions along the nuclear envelope are of equal size, centrosome movement stops. In this model, cytoplasmic dynein also serves to couple male pronucleus and centrosomes. See text for additional information.
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Figure 10: Possible model of dynein-dependent separation of centrosomes. View is on posterior of one cell stage embryo. Male pronucleus: large light disk. Centrosomes: small black disks. Shown also are astral microtubules (black lines) and two-headed cytoplasmic dynein; cytoplasmic dynein molecules that interact with astral microtubules are shown in dark shading, others in light shading. Cytoplasmic dynein is evenly distributed on the male pronucleus. When astral microtubules encounter such anchored motors, their minus end is pulled towards cytoplasmic dynein, along with the centrosome. Longer astral microtubules encounter more motors and, thus, experience a stronger pulling force than shorter ones. Because astral microtubules growing towards the anterior are longer to start with, dynein-dependent forces displace centrosomes towards the anterior initially. When astral microtubules growing in all directions along the nuclear envelope are of equal size, centrosome movement stops. In this model, cytoplasmic dynein also serves to couple male pronucleus and centrosomes. See text for additional information.

Mentions: In the second type of mechanism, separation results from pulling forces acting on astral microtubules in front of the moving centrosomes. Minus end–directed motors are expected to generate the force driving separation in this case. The requirement for cytoplasmic dynein uncovered in this study is fully compatible with this view. Dynein could generate such pulling forces by being anchored throughout the cytoplasm or at the cell cortex, as has been discussed previously (Vaisberg et al. 1993). Here, we propose an alternative model in which pulling forces result from interactions between cytoplasmic dynein anchored on the nucleus and astral microtubules (Fig. 10). Supporting evidence for such a model comes from the presence of cytoplasmic dynein at the periphery of nuclei, both in MDCK cells and in C. elegans (Busson et al. 1998; this work). This model is attractive because it provides a single mechanism to explain both how centrosome separate and how they remain tightly associated with the nucleus.


Cytoplasmic dynein is required for distinct aspects of MTOC positioning, including centrosome separation, in the one cell stage Caenorhabditis elegans embryo.

Gönczy P, Pichler S, Kirkham M, Hyman AA - J. Cell Biol. (1999)

Possible model of dynein-dependent separation of centrosomes. View is on posterior of one cell stage embryo. Male pronucleus: large light disk. Centrosomes: small black disks. Shown also are astral microtubules (black lines) and two-headed cytoplasmic dynein; cytoplasmic dynein molecules that interact with astral microtubules are shown in dark shading, others in light shading. Cytoplasmic dynein is evenly distributed on the male pronucleus. When astral microtubules encounter such anchored motors, their minus end is pulled towards cytoplasmic dynein, along with the centrosome. Longer astral microtubules encounter more motors and, thus, experience a stronger pulling force than shorter ones. Because astral microtubules growing towards the anterior are longer to start with, dynein-dependent forces displace centrosomes towards the anterior initially. When astral microtubules growing in all directions along the nuclear envelope are of equal size, centrosome movement stops. In this model, cytoplasmic dynein also serves to couple male pronucleus and centrosomes. See text for additional information.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2164971&req=5

Figure 10: Possible model of dynein-dependent separation of centrosomes. View is on posterior of one cell stage embryo. Male pronucleus: large light disk. Centrosomes: small black disks. Shown also are astral microtubules (black lines) and two-headed cytoplasmic dynein; cytoplasmic dynein molecules that interact with astral microtubules are shown in dark shading, others in light shading. Cytoplasmic dynein is evenly distributed on the male pronucleus. When astral microtubules encounter such anchored motors, their minus end is pulled towards cytoplasmic dynein, along with the centrosome. Longer astral microtubules encounter more motors and, thus, experience a stronger pulling force than shorter ones. Because astral microtubules growing towards the anterior are longer to start with, dynein-dependent forces displace centrosomes towards the anterior initially. When astral microtubules growing in all directions along the nuclear envelope are of equal size, centrosome movement stops. In this model, cytoplasmic dynein also serves to couple male pronucleus and centrosomes. See text for additional information.
Mentions: In the second type of mechanism, separation results from pulling forces acting on astral microtubules in front of the moving centrosomes. Minus end–directed motors are expected to generate the force driving separation in this case. The requirement for cytoplasmic dynein uncovered in this study is fully compatible with this view. Dynein could generate such pulling forces by being anchored throughout the cytoplasm or at the cell cortex, as has been discussed previously (Vaisberg et al. 1993). Here, we propose an alternative model in which pulling forces result from interactions between cytoplasmic dynein anchored on the nucleus and astral microtubules (Fig. 10). Supporting evidence for such a model comes from the presence of cytoplasmic dynein at the periphery of nuclei, both in MDCK cells and in C. elegans (Busson et al. 1998; this work). This model is attractive because it provides a single mechanism to explain both how centrosome separate and how they remain tightly associated with the nucleus.

Bottom Line: Moreover, in 15% of dhc-1 (RNAi) embryos, centrosomes failed to remain in proximity of the male pronucleus.Therefore, cytoplasmic dynein is required for multiple aspects of MTOC positioning in the one cell stage C. elegans embryo.In conjunction with our observation of cytoplasmic dynein distribution at the periphery of nuclei, these results lead us to propose a mechanism in which cytoplasmic dynein anchored on the nucleus drives centrosome separation.

View Article: PubMed Central - PubMed

Affiliation: European Molecular Biology Laboratory, Heidelberg, D-69117 Germany. gonczy@embl-heidelberg.de

ABSTRACT
We have investigated the role of cytoplasmic dynein in microtubule organizing center (MTOC) positioning using RNA-mediated interference (RNAi) in Caenorhabditis elegans to deplete the product of the dynein heavy chain gene dhc-1. Analysis with time-lapse differential interference contrast microscopy and indirect immunofluorescence revealed that pronuclear migration and centrosome separation failed in one cell stage dhc-1 (RNAi) embryos. These phenotypes were also observed when the dynactin components p50/dynamitin or p150(Glued) were depleted with RNAi. Moreover, in 15% of dhc-1 (RNAi) embryos, centrosomes failed to remain in proximity of the male pronucleus. When dynein heavy chain function was diminished only partially with RNAi, centrosome separation took place, but orientation of the mitotic spindle was defective. Therefore, cytoplasmic dynein is required for multiple aspects of MTOC positioning in the one cell stage C. elegans embryo. In conjunction with our observation of cytoplasmic dynein distribution at the periphery of nuclei, these results lead us to propose a mechanism in which cytoplasmic dynein anchored on the nucleus drives centrosome separation.

Show MeSH
Related in: MedlinePlus