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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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CLIP-170 staining during the first meiotic M phase. CLIP-170 appears in green and chromosomes in red. CLIP-170 on kinetochores appears yellow because of the merged green and red images. 10–15 optical sections were merged for the final images. (A) 2 h after GVBD, side view. (B) 5 h after GVBD, side view. (C) 7 h after GVBD, polar view. (D and E) 8 h after GVBD, side view. Bar, 10 μm.
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Figure 6: CLIP-170 staining during the first meiotic M phase. CLIP-170 appears in green and chromosomes in red. CLIP-170 on kinetochores appears yellow because of the merged green and red images. 10–15 optical sections were merged for the final images. (A) 2 h after GVBD, side view. (B) 5 h after GVBD, side view. (C) 7 h after GVBD, polar view. (D and E) 8 h after GVBD, side view. Bar, 10 μm.

Mentions: During the first meiotic M phase, CLIP-170 stains kinetochores already at GVBD and persists until 7 h after GVBD (Fig. 6, A–C). At this time, some kinetochores are no longer stained (Fig. 6 C). By 8 h after GVBD, the staining has disappeared from most kinetochores when chromosomes were still not aligned (Fig. 6 D), and completely absent at metaphase (Fig. 6 E). Thus, we can conclude that CLIP-170 remains on kinetochores until ∼7–8 h after GVBD and disappears just before the final alignment of the chromosomes. It is noteworthy that bivalents are correctly oriented (kinetochores of homologous chromosomes facing opposite poles) 5 h after GVBD, which suggests that lateral interactions between some microtubules and the kinetochores take place in the absence of stable kinetochore bundles. These data confirm our EM observations and show that the long late prometaphase state is correlated with the lack of kinetochore fibers.


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)

CLIP-170 staining during the first meiotic M phase. CLIP-170 appears in green and chromosomes in red. CLIP-170 on kinetochores appears yellow because of the merged green and red images. 10–15 optical sections were merged for the final images. (A) 2 h after GVBD, side view. (B) 5 h after GVBD, side view. (C) 7 h after GVBD, polar view. (D and E) 8 h after GVBD, side view. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: CLIP-170 staining during the first meiotic M phase. CLIP-170 appears in green and chromosomes in red. CLIP-170 on kinetochores appears yellow because of the merged green and red images. 10–15 optical sections were merged for the final images. (A) 2 h after GVBD, side view. (B) 5 h after GVBD, side view. (C) 7 h after GVBD, polar view. (D and E) 8 h after GVBD, side view. Bar, 10 μm.
Mentions: During the first meiotic M phase, CLIP-170 stains kinetochores already at GVBD and persists until 7 h after GVBD (Fig. 6, A–C). At this time, some kinetochores are no longer stained (Fig. 6 C). By 8 h after GVBD, the staining has disappeared from most kinetochores when chromosomes were still not aligned (Fig. 6 D), and completely absent at metaphase (Fig. 6 E). Thus, we can conclude that CLIP-170 remains on kinetochores until ∼7–8 h after GVBD and disappears just before the final alignment of the chromosomes. It is noteworthy that bivalents are correctly oriented (kinetochores of homologous chromosomes facing opposite poles) 5 h after GVBD, which suggests that lateral interactions between some microtubules and the kinetochores take place in the absence of stable kinetochore bundles. These data confirm our EM observations and show that the long late prometaphase state is correlated with the lack of kinetochore fibers.

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