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Kinetochore fibers are not involved in the formation of the first meiotic spindle in mouse oocytes, but control the exit from the first meiotic M phase.

Brunet S, Maria AS, Guillaud P, Dujardin D, Kubiak JZ, Maro B - J. Cell Biol. (1999)

Bottom Line: The first meiotic division is unique in that homologous chromosomes are segregated while the cohesion between sister chromatids is maintained, resulting in a reductional division.This event allows the final alignment of the chromosomes and exit from metaphase.Finally, the ability of kinetochores to interact with microtubules is acquired at the end of the first meiotic M phase and determines the timing of polar body extrusion.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Biologie Cellulaire du Développement, Université Paris 6, Paris, France.

ABSTRACT
During meiosis, two successive divisions occur without any intermediate S phase to produce haploid gametes. The first meiotic division is unique in that homologous chromosomes are segregated while the cohesion between sister chromatids is maintained, resulting in a reductional division. Moreover, the duration of the first meiotic M phase is usually prolonged when compared with mitotic M phases lasting 8 h in mouse oocytes.We investigated the spindle assembly pathway and its role in the progression of the first meiotic M phase in mouse oocytes. During the first 4 h, a bipolar spindle forms and the chromosomes congress near the equatorial plane of the spindle without stable kinetochore- microtubule end interactions. This late prometaphase spindle is then maintained for 4 h with chromosomes oscillating in the central region of the spindle. The kinetochore-microtubule end interactions are set up at the end of the first meiotic M phase (8 h after entry into M phase). This event allows the final alignment of the chromosomes and exit from metaphase. The continuous presence of the prometaphase spindle is not required for progression of the first meiotic M phase. Finally, the ability of kinetochores to interact with microtubules is acquired at the end of the first meiotic M phase and determines the timing of polar body extrusion.

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Kinetics of first meiotic spindle formation. Microtubules appear in green and chromosomes in red. (A) 1 h after GVBD. (B) 2 h after GVBD. (C) 4 h after GVBD. (D) 6 h after GVBD. (E–H) 8 h after GVBD. Note that some chromosomes are not aligned in E (late prometaphase), while all chromosomes are aligned on the metaphase plate in F. Bar, 10 μm.
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Figure 1: Kinetics of first meiotic spindle formation. Microtubules appear in green and chromosomes in red. (A) 1 h after GVBD. (B) 2 h after GVBD. (C) 4 h after GVBD. (D) 6 h after GVBD. (E–H) 8 h after GVBD. Note that some chromosomes are not aligned in E (late prometaphase), while all chromosomes are aligned on the metaphase plate in F. Bar, 10 μm.

Mentions: 1 h after GVBD, short microtubules are radiating around the chromosomes (Fig. 1 A). 2 h after GVBD, the microtubules have formed a bipolar spindle and the chromosomes are dispersed within the structure (Fig. 1 B). 4 h after GVBD, the spindle has acquired a barrel shape morphology, typical of meiosis (Fig. 1 C), and the chromosomes are located near the equatorial plane of the spindle. From 4 to 8 h after GVBD, the spindle morphology remains unchanged with unaligned chromosomes (Fig. 1D and Fig. E). 8 h after GVBD, metaphase plates could be observed (Fig. 1 F) with the chromosomes perfectly aligned and a symmetrical arrangement of their arms. Anaphase (Fig. 1 G) and telophase (Fig. 1 H) figures were also present. Finally, we observed that the spindle length decreases 2–8 h after GVBD (reaching ∼50% of its initial length) before elongation at anaphase.


Kinetochore fibers are not involved in the formation of the first meiotic spindle in mouse oocytes, but control the exit from the first meiotic M phase.

Brunet S, Maria AS, Guillaud P, Dujardin D, Kubiak JZ, Maro B - J. Cell Biol. (1999)

Kinetics of first meiotic spindle formation. Microtubules appear in green and chromosomes in red. (A) 1 h after GVBD. (B) 2 h after GVBD. (C) 4 h after GVBD. (D) 6 h after GVBD. (E–H) 8 h after GVBD. Note that some chromosomes are not aligned in E (late prometaphase), while all chromosomes are aligned on the metaphase plate in F. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199729&req=5

Figure 1: Kinetics of first meiotic spindle formation. Microtubules appear in green and chromosomes in red. (A) 1 h after GVBD. (B) 2 h after GVBD. (C) 4 h after GVBD. (D) 6 h after GVBD. (E–H) 8 h after GVBD. Note that some chromosomes are not aligned in E (late prometaphase), while all chromosomes are aligned on the metaphase plate in F. Bar, 10 μm.
Mentions: 1 h after GVBD, short microtubules are radiating around the chromosomes (Fig. 1 A). 2 h after GVBD, the microtubules have formed a bipolar spindle and the chromosomes are dispersed within the structure (Fig. 1 B). 4 h after GVBD, the spindle has acquired a barrel shape morphology, typical of meiosis (Fig. 1 C), and the chromosomes are located near the equatorial plane of the spindle. From 4 to 8 h after GVBD, the spindle morphology remains unchanged with unaligned chromosomes (Fig. 1D and Fig. E). 8 h after GVBD, metaphase plates could be observed (Fig. 1 F) with the chromosomes perfectly aligned and a symmetrical arrangement of their arms. Anaphase (Fig. 1 G) and telophase (Fig. 1 H) figures were also present. Finally, we observed that the spindle length decreases 2–8 h after GVBD (reaching ∼50% of its initial length) before elongation at anaphase.

Bottom Line: The first meiotic division is unique in that homologous chromosomes are segregated while the cohesion between sister chromatids is maintained, resulting in a reductional division.This event allows the final alignment of the chromosomes and exit from metaphase.Finally, the ability of kinetochores to interact with microtubules is acquired at the end of the first meiotic M phase and determines the timing of polar body extrusion.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Biologie Cellulaire du Développement, Université Paris 6, Paris, France.

ABSTRACT
During meiosis, two successive divisions occur without any intermediate S phase to produce haploid gametes. The first meiotic division is unique in that homologous chromosomes are segregated while the cohesion between sister chromatids is maintained, resulting in a reductional division. Moreover, the duration of the first meiotic M phase is usually prolonged when compared with mitotic M phases lasting 8 h in mouse oocytes.We investigated the spindle assembly pathway and its role in the progression of the first meiotic M phase in mouse oocytes. During the first 4 h, a bipolar spindle forms and the chromosomes congress near the equatorial plane of the spindle without stable kinetochore- microtubule end interactions. This late prometaphase spindle is then maintained for 4 h with chromosomes oscillating in the central region of the spindle. The kinetochore-microtubule end interactions are set up at the end of the first meiotic M phase (8 h after entry into M phase). This event allows the final alignment of the chromosomes and exit from metaphase. The continuous presence of the prometaphase spindle is not required for progression of the first meiotic M phase. Finally, the ability of kinetochores to interact with microtubules is acquired at the end of the first meiotic M phase and determines the timing of polar body extrusion.

Show MeSH
Related in: MedlinePlus