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Kinesin-1 mediates translocation of the meiotic spindle to the oocyte cortex through KCA-1, a novel cargo adapter.

Yang HY, Mains PE, McNally FJ - J. Cell Biol. (2005)

Bottom Line: Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell cortex during the time when wild-type spindles translocated to the cortex.After this prolonged stationary period, unc-116(RNAi) spindles moved to the cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex.This study thus reveals two sequential mechanisms for translocating anastral spindles to the oocyte cortex.

View Article: PubMed Central - PubMed

Affiliation: Section of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA.

ABSTRACT
In animals, female meiotic spindles are attached to the egg cortex in a perpendicular orientation at anaphase to allow the selective disposal of three haploid chromosome sets into polar bodies. We have identified a complex of interacting Caenorhabditis elegans proteins that are involved in the earliest step in asymmetric positioning of anastral meiotic spindles, translocation to the cortex. This complex is composed of the kinesin-1 heavy chain orthologue, UNC-116, the kinesin light chain orthologues, KLC-1 and -2, and a novel cargo adaptor, KCA-1. Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell cortex during the time when wild-type spindles translocated to the cortex. After this prolonged stationary period, unc-116(RNAi) spindles moved to the cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex. This study thus reveals two sequential mechanisms for translocating anastral spindles to the oocyte cortex.

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Polar body formation in an unc-116(RNAi) embryo. Images of GFP-histone H2b fluorescence within a meiotic embryo are shown from a representative time-lapse sequence of an unc-116(RNAi) worm. The cortex has been highlighted in each image and drawings corresponding to the top row of images are included for clarity. Note that anaphase of meiosis I is successful (18 min) but the chromosomes that should have been sequestered in a polar body snap back to produce a meiosis II spindle with 12 rather than 6 chromosomes (22.0–24.3 min). Anaphase of meiosis II was also successful (30.3 min), and the chromosomes segregated into the cortex were successfully sequestered in a polar body (36.3 min). Asterisk indicates exit of the zygote from the spermatheca into the uterus. Bar, 10 μm.
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fig2: Polar body formation in an unc-116(RNAi) embryo. Images of GFP-histone H2b fluorescence within a meiotic embryo are shown from a representative time-lapse sequence of an unc-116(RNAi) worm. The cortex has been highlighted in each image and drawings corresponding to the top row of images are included for clarity. Note that anaphase of meiosis I is successful (18 min) but the chromosomes that should have been sequestered in a polar body snap back to produce a meiosis II spindle with 12 rather than 6 chromosomes (22.0–24.3 min). Anaphase of meiosis II was also successful (30.3 min), and the chromosomes segregated into the cortex were successfully sequestered in a polar body (36.3 min). Asterisk indicates exit of the zygote from the spermatheca into the uterus. Bar, 10 μm.

Mentions: We previously demonstrated that both tubulin and the katanin orthologue MEI-1 are required for meiotic spindle translocation (Yang et al., 2003). In both of these cases, however, spindle structure was severely perturbed, making it impossible to discern if MEI-1 is directly involved in spindle translocation or if normal spindle architecture is required for translocation. In contrast, unc-116(RNAi) meiotic spindles observed by GFP-tubulin fluorescence had a wild-type structure (Fig. 1, B and H). These spindles had wild-type length and width (Table I), exhibited normal anaphase chromosome segregation (Fig. 2 and Table I), and shortened with normal kinetics (Table I and Fig. 1 D). These results indicate that UNC-116 is primarily (if not exclusively) required in the early embryo for meiotic spindle translocation.


Kinesin-1 mediates translocation of the meiotic spindle to the oocyte cortex through KCA-1, a novel cargo adapter.

Yang HY, Mains PE, McNally FJ - J. Cell Biol. (2005)

Polar body formation in an unc-116(RNAi) embryo. Images of GFP-histone H2b fluorescence within a meiotic embryo are shown from a representative time-lapse sequence of an unc-116(RNAi) worm. The cortex has been highlighted in each image and drawings corresponding to the top row of images are included for clarity. Note that anaphase of meiosis I is successful (18 min) but the chromosomes that should have been sequestered in a polar body snap back to produce a meiosis II spindle with 12 rather than 6 chromosomes (22.0–24.3 min). Anaphase of meiosis II was also successful (30.3 min), and the chromosomes segregated into the cortex were successfully sequestered in a polar body (36.3 min). Asterisk indicates exit of the zygote from the spermatheca into the uterus. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171918&req=5

fig2: Polar body formation in an unc-116(RNAi) embryo. Images of GFP-histone H2b fluorescence within a meiotic embryo are shown from a representative time-lapse sequence of an unc-116(RNAi) worm. The cortex has been highlighted in each image and drawings corresponding to the top row of images are included for clarity. Note that anaphase of meiosis I is successful (18 min) but the chromosomes that should have been sequestered in a polar body snap back to produce a meiosis II spindle with 12 rather than 6 chromosomes (22.0–24.3 min). Anaphase of meiosis II was also successful (30.3 min), and the chromosomes segregated into the cortex were successfully sequestered in a polar body (36.3 min). Asterisk indicates exit of the zygote from the spermatheca into the uterus. Bar, 10 μm.
Mentions: We previously demonstrated that both tubulin and the katanin orthologue MEI-1 are required for meiotic spindle translocation (Yang et al., 2003). In both of these cases, however, spindle structure was severely perturbed, making it impossible to discern if MEI-1 is directly involved in spindle translocation or if normal spindle architecture is required for translocation. In contrast, unc-116(RNAi) meiotic spindles observed by GFP-tubulin fluorescence had a wild-type structure (Fig. 1, B and H). These spindles had wild-type length and width (Table I), exhibited normal anaphase chromosome segregation (Fig. 2 and Table I), and shortened with normal kinetics (Table I and Fig. 1 D). These results indicate that UNC-116 is primarily (if not exclusively) required in the early embryo for meiotic spindle translocation.

Bottom Line: Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell cortex during the time when wild-type spindles translocated to the cortex.After this prolonged stationary period, unc-116(RNAi) spindles moved to the cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex.This study thus reveals two sequential mechanisms for translocating anastral spindles to the oocyte cortex.

View Article: PubMed Central - PubMed

Affiliation: Section of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA.

ABSTRACT
In animals, female meiotic spindles are attached to the egg cortex in a perpendicular orientation at anaphase to allow the selective disposal of three haploid chromosome sets into polar bodies. We have identified a complex of interacting Caenorhabditis elegans proteins that are involved in the earliest step in asymmetric positioning of anastral meiotic spindles, translocation to the cortex. This complex is composed of the kinesin-1 heavy chain orthologue, UNC-116, the kinesin light chain orthologues, KLC-1 and -2, and a novel cargo adaptor, KCA-1. Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell cortex during the time when wild-type spindles translocated to the cortex. After this prolonged stationary period, unc-116(RNAi) spindles moved to the cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex. This study thus reveals two sequential mechanisms for translocating anastral spindles to the oocyte cortex.

Show MeSH