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Lateral and End-On Kinetochore Attachments Are Coordinated to Achieve Bi-orientation in Drosophila Oocytes.

Radford SJ, Hoang TL, Głuszek AA, Ohkura H, McKim KS - PLoS Genet. (2015)

Bottom Line: We found that the initiation of spindle assembly results from chromosome-microtubule interactions that are kinetochore-independent.Stabilization of the spindle, however, depends on both central spindle and kinetochore components.We propose that the bi-orientation process begins with the kinetochores moving laterally along central spindle microtubules towards their minus ends.

View Article: PubMed Central - PubMed

Affiliation: Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States of America.

ABSTRACT
In oocytes, where centrosomes are absent, the chromosomes direct the assembly of a bipolar spindle. Interactions between chromosomes and microtubules are essential for both spindle formation and chromosome segregation, but the nature and function of these interactions is not clear. We have examined oocytes lacking two kinetochore proteins, NDC80 and SPC105R, and a centromere-associated motor protein, CENP-E, to characterize the impact of kinetochore-microtubule attachments on spindle assembly and chromosome segregation in Drosophila oocytes. We found that the initiation of spindle assembly results from chromosome-microtubule interactions that are kinetochore-independent. Stabilization of the spindle, however, depends on both central spindle and kinetochore components. This stabilization coincides with changes in kinetochore-microtubule attachments and bi-orientation of homologs. We propose that the bi-orientation process begins with the kinetochores moving laterally along central spindle microtubules towards their minus ends. This movement depends on SPC105R, can occur in the absence of NDC80, and is antagonized by plus-end directed forces from the CENP-E motor. End-on kinetochore-microtubule attachments that depend on NDC80 are required to stabilize bi-orientation of homologs. A surprising finding was that SPC105R but not NDC80 is required for co-orientation of sister centromeres at meiosis I. Together, these results demonstrate that, in oocytes, kinetochore-dependent and -independent chromosome-microtubule attachments work together to promote the accurate segregation of chromosomes.

No MeSH data available.


Related in: MedlinePlus

Loss of SPC105R or the CPC disrupts kinetochore assembly in oocytes.Confocal images of localization of (A) NDC80, (B) SPC105R, and (C) NSL1 (Mis12 complex) in wild-type oocytes and after knockdown of Ndc80, Spc105R, or aurB. DNA is shown in blue and tubulin is shown in green in merged images. Kinetochore components are shown in red in merged images and white in single channel images. Scale bars represent 10 μm.
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pgen.1005605.g001: Loss of SPC105R or the CPC disrupts kinetochore assembly in oocytes.Confocal images of localization of (A) NDC80, (B) SPC105R, and (C) NSL1 (Mis12 complex) in wild-type oocytes and after knockdown of Ndc80, Spc105R, or aurB. DNA is shown in blue and tubulin is shown in green in merged images. Kinetochore components are shown in red in merged images and white in single channel images. Scale bars represent 10 μm.

Mentions: We found that localization of NDC80 and SPC105R to kinetochores was absent in Ndc80- or Spc105R-depleted oocytes, respectively (S2 Table and Fig 1A and 1B), showing that the RNAi knockdown was effective. In addition, NDC80 and NSL1 (a member of the Mis12 complex) failed to localize to kinetochores in Spc105R-depleted oocytes (S2 Table and Fig 1A and 1C), while both SPC105R and NSL1 localized to kinetochores in Ndc80-depleted oocytes (S2 Table and Fig 1B and 1C). These results are consistent with results from mitotic cells in Drosophila embryos and cell culture [28, 33]: localization of KMN complex proteins in Drosophila depends on SPC105R but not NDC80.


Lateral and End-On Kinetochore Attachments Are Coordinated to Achieve Bi-orientation in Drosophila Oocytes.

Radford SJ, Hoang TL, Głuszek AA, Ohkura H, McKim KS - PLoS Genet. (2015)

Loss of SPC105R or the CPC disrupts kinetochore assembly in oocytes.Confocal images of localization of (A) NDC80, (B) SPC105R, and (C) NSL1 (Mis12 complex) in wild-type oocytes and after knockdown of Ndc80, Spc105R, or aurB. DNA is shown in blue and tubulin is shown in green in merged images. Kinetochore components are shown in red in merged images and white in single channel images. Scale bars represent 10 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608789&req=5

pgen.1005605.g001: Loss of SPC105R or the CPC disrupts kinetochore assembly in oocytes.Confocal images of localization of (A) NDC80, (B) SPC105R, and (C) NSL1 (Mis12 complex) in wild-type oocytes and after knockdown of Ndc80, Spc105R, or aurB. DNA is shown in blue and tubulin is shown in green in merged images. Kinetochore components are shown in red in merged images and white in single channel images. Scale bars represent 10 μm.
Mentions: We found that localization of NDC80 and SPC105R to kinetochores was absent in Ndc80- or Spc105R-depleted oocytes, respectively (S2 Table and Fig 1A and 1B), showing that the RNAi knockdown was effective. In addition, NDC80 and NSL1 (a member of the Mis12 complex) failed to localize to kinetochores in Spc105R-depleted oocytes (S2 Table and Fig 1A and 1C), while both SPC105R and NSL1 localized to kinetochores in Ndc80-depleted oocytes (S2 Table and Fig 1B and 1C). These results are consistent with results from mitotic cells in Drosophila embryos and cell culture [28, 33]: localization of KMN complex proteins in Drosophila depends on SPC105R but not NDC80.

Bottom Line: We found that the initiation of spindle assembly results from chromosome-microtubule interactions that are kinetochore-independent.Stabilization of the spindle, however, depends on both central spindle and kinetochore components.We propose that the bi-orientation process begins with the kinetochores moving laterally along central spindle microtubules towards their minus ends.

View Article: PubMed Central - PubMed

Affiliation: Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States of America.

ABSTRACT
In oocytes, where centrosomes are absent, the chromosomes direct the assembly of a bipolar spindle. Interactions between chromosomes and microtubules are essential for both spindle formation and chromosome segregation, but the nature and function of these interactions is not clear. We have examined oocytes lacking two kinetochore proteins, NDC80 and SPC105R, and a centromere-associated motor protein, CENP-E, to characterize the impact of kinetochore-microtubule attachments on spindle assembly and chromosome segregation in Drosophila oocytes. We found that the initiation of spindle assembly results from chromosome-microtubule interactions that are kinetochore-independent. Stabilization of the spindle, however, depends on both central spindle and kinetochore components. This stabilization coincides with changes in kinetochore-microtubule attachments and bi-orientation of homologs. We propose that the bi-orientation process begins with the kinetochores moving laterally along central spindle microtubules towards their minus ends. This movement depends on SPC105R, can occur in the absence of NDC80, and is antagonized by plus-end directed forces from the CENP-E motor. End-on kinetochore-microtubule attachments that depend on NDC80 are required to stabilize bi-orientation of homologs. A surprising finding was that SPC105R but not NDC80 is required for co-orientation of sister centromeres at meiosis I. Together, these results demonstrate that, in oocytes, kinetochore-dependent and -independent chromosome-microtubule attachments work together to promote the accurate segregation of chromosomes.

No MeSH data available.


Related in: MedlinePlus