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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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Chromosome movements during the metaphase II arrest (A) and the first meiotic M phase (B). Pictures were taken every 3 min. Because the chromosomes did not move in metaphase II, one picture out of two is shown in A (6 min interval).
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Figure 2: Chromosome movements during the metaphase II arrest (A) and the first meiotic M phase (B). Pictures were taken every 3 min. Because the chromosomes did not move in metaphase II, one picture out of two is shown in A (6 min interval).

Mentions: During the metaphase II arrest, the chromosomes are aligned on the metaphase plate and do not move (Fig. 2 A). In contrast, during the last 4 h of the first meiotic M phase, the chromosomes oscillate with a low amplitude around the equatorial plane of the spindle (Fig. 2 B). For example, the top right chromosome protruding from the main mass in Fig. 2 B, at 27 min (arrow) has moved back into it at 87 min, and out again at 105 min; the center right chromosome at 60 min (arrowhead) is in the main mass, out at 105 min, and in again at 117 min. They became aligned in metaphase for only a short period immediately before their segregation in anaphase (Fig. 2 B, at 195 min). Thus, during virtually all of the second half of the first meiotic M phase, the spindle appears to be maintained in a late prometaphase state.


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)

Chromosome movements during the metaphase II arrest (A) and the first meiotic M phase (B). Pictures were taken every 3 min. Because the chromosomes did not move in metaphase II, one picture out of two is shown in A (6 min interval).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 2: Chromosome movements during the metaphase II arrest (A) and the first meiotic M phase (B). Pictures were taken every 3 min. Because the chromosomes did not move in metaphase II, one picture out of two is shown in A (6 min interval).
Mentions: During the metaphase II arrest, the chromosomes are aligned on the metaphase plate and do not move (Fig. 2 A). In contrast, during the last 4 h of the first meiotic M phase, the chromosomes oscillate with a low amplitude around the equatorial plane of the spindle (Fig. 2 B). For example, the top right chromosome protruding from the main mass in Fig. 2 B, at 27 min (arrow) has moved back into it at 87 min, and out again at 105 min; the center right chromosome at 60 min (arrowhead) is in the main mass, out at 105 min, and in again at 117 min. They became aligned in metaphase for only a short period immediately before their segregation in anaphase (Fig. 2 B, at 195 min). Thus, during virtually all of the second half of the first meiotic M phase, the spindle appears to be maintained in a late prometaphase state.

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