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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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Study of chromatin and kinetochore–microtubule interactions during the first meiotic M phase by EM. (A) 2 h after GVBD. (B) 6 h after GVBD. (C and D) 8 h after GVBD. Asterisks, kinetochores; arrows, microtubules. Bars, 1 μm.
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Figure 3: Study of chromatin and kinetochore–microtubule interactions during the first meiotic M phase by EM. (A) 2 h after GVBD. (B) 6 h after GVBD. (C and D) 8 h after GVBD. Asterisks, kinetochores; arrows, microtubules. Bars, 1 μm.

Mentions: 2 h after GVBD, no kinetochore–microtubule end interactions were observed (Fig. 3 A). Numerous microtubules interacted with the chromosome surface or penetrated within the chromosome (Fig. 3 A, arrows). A similar situation was observed 4 h after GVBD (not shown). 6 h after GVBD, microtubules interacted with the chromosome surface, but no longer penetrated chromosomes (Fig. 3 B). Some microtubules were present near the kinetochores, but insertion of microtubule ends in the kinetochore plate was not detected (Fig. 3 B, arrows). However, the kinetochores and adjacent chromatin appeared to be pulled out from the main chromatin mass. This likely is due to lateral interactions between some microtubules and the kinetochores, in the absence of stable kinetochore bundles. 8 h after GVBD, end interactions were not detected at some kinetochores (Fig. 3 C, arrows), but they were observed in others (Fig. 3 D, arrows), as in metaphase II-arrested oocytes (not shown). When a systematic analysis of microtubule end interactions with kinetochores was performed at 6 and 7 h after GVBD (Table ), none were observed at 6 h, the spindle areas facing the kinetochores being deprived of microtubules (Fig. 4A and Fig. B). A few microtubule ends were observed interacting with kinetochores at 7 h (Fig. 4 C, arrows), however, they were less numerous than at 8 h (compare Fig. 3 and Fig. 4C). All kinetochore regions observed were stretched towards the poles, suggesting that unstable lateral interactions with microtubules are able to position the kinetochores towards the poles.


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)

Study of chromatin and kinetochore–microtubule interactions during the first meiotic M phase by EM. (A) 2 h after GVBD. (B) 6 h after GVBD. (C and D) 8 h after GVBD. Asterisks, kinetochores; arrows, microtubules. Bars, 1 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199729&req=5

Figure 3: Study of chromatin and kinetochore–microtubule interactions during the first meiotic M phase by EM. (A) 2 h after GVBD. (B) 6 h after GVBD. (C and D) 8 h after GVBD. Asterisks, kinetochores; arrows, microtubules. Bars, 1 μm.
Mentions: 2 h after GVBD, no kinetochore–microtubule end interactions were observed (Fig. 3 A). Numerous microtubules interacted with the chromosome surface or penetrated within the chromosome (Fig. 3 A, arrows). A similar situation was observed 4 h after GVBD (not shown). 6 h after GVBD, microtubules interacted with the chromosome surface, but no longer penetrated chromosomes (Fig. 3 B). Some microtubules were present near the kinetochores, but insertion of microtubule ends in the kinetochore plate was not detected (Fig. 3 B, arrows). However, the kinetochores and adjacent chromatin appeared to be pulled out from the main chromatin mass. This likely is due to lateral interactions between some microtubules and the kinetochores, in the absence of stable kinetochore bundles. 8 h after GVBD, end interactions were not detected at some kinetochores (Fig. 3 C, arrows), but they were observed in others (Fig. 3 D, arrows), as in metaphase II-arrested oocytes (not shown). When a systematic analysis of microtubule end interactions with kinetochores was performed at 6 and 7 h after GVBD (Table ), none were observed at 6 h, the spindle areas facing the kinetochores being deprived of microtubules (Fig. 4A and Fig. B). A few microtubule ends were observed interacting with kinetochores at 7 h (Fig. 4 C, arrows), however, they were less numerous than at 8 h (compare Fig. 3 and Fig. 4C). All kinetochore regions observed were stretched towards the poles, suggesting that unstable lateral interactions with microtubules are able to position the kinetochores towards the poles.

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