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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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Spindle reformation after nocodazole treatment. Oocytes were cultured in the presence of 10 μg/ml nocodazole from 3 to 5 h (A–D) and from 6 to 8 h (E–H) after GVBD. Microtubules appear in green and chromosomes in red. Oocytes were fixed 20 (A and E), 50 (B and F), 120 (C and G), and 150 min (D and H) after removal of the drug.
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Figure 7: Spindle reformation after nocodazole treatment. Oocytes were cultured in the presence of 10 μg/ml nocodazole from 3 to 5 h (A–D) and from 6 to 8 h (E–H) after GVBD. Microtubules appear in green and chromosomes in red. Oocytes were fixed 20 (A and E), 50 (B and F), 120 (C and G), and 150 min (D and H) after removal of the drug.

Mentions: In both experiments, 20 min after drug removal a bipolar structure formed, although it was larger in the NZ/3h–5h group (Fig. 7A and Fig. E). 50 and 120 min after drug removal, the chromosomes were localized near the equatorial plane (Fig. 7B, Fig. C, Fig. F, and Fig. G). However, the spindle length did not change until metaphase in the NZ/6h–8h group (Fig. 7, E–G), while it decreased progressively until 120 min in the NZ/3h–5h group (Fig. 7 C). This late prometaphase spindle was maintained until 7.5 h after GVBD (Fig. 7 D), just before PBE. In the NZ/6h–8h group, the chromosomes seemed to congress progressively to the equatorial plane of the spindle (Fig. 7, E–G). PBE occurred 2.5 h after removal of the drug (Fig. 7 H). In the NZ/6h–8h group, nocodazole induced chromosome dispersal in some oocytes (∼1/3). After drug removal, a spindle reformed around each group of chromosomes and a polar body was extruded for each spindle. However, the only difference between the two groups was that the prometaphase spindle persisted for 3 h in the NZ/3h–5h group.


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)

Spindle reformation after nocodazole treatment. Oocytes were cultured in the presence of 10 μg/ml nocodazole from 3 to 5 h (A–D) and from 6 to 8 h (E–H) after GVBD. Microtubules appear in green and chromosomes in red. Oocytes were fixed 20 (A and E), 50 (B and F), 120 (C and G), and 150 min (D and H) after removal of the drug.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 7: Spindle reformation after nocodazole treatment. Oocytes were cultured in the presence of 10 μg/ml nocodazole from 3 to 5 h (A–D) and from 6 to 8 h (E–H) after GVBD. Microtubules appear in green and chromosomes in red. Oocytes were fixed 20 (A and E), 50 (B and F), 120 (C and G), and 150 min (D and H) after removal of the drug.
Mentions: In both experiments, 20 min after drug removal a bipolar structure formed, although it was larger in the NZ/3h–5h group (Fig. 7A and Fig. E). 50 and 120 min after drug removal, the chromosomes were localized near the equatorial plane (Fig. 7B, Fig. C, Fig. F, and Fig. G). However, the spindle length did not change until metaphase in the NZ/6h–8h group (Fig. 7, E–G), while it decreased progressively until 120 min in the NZ/3h–5h group (Fig. 7 C). This late prometaphase spindle was maintained until 7.5 h after GVBD (Fig. 7 D), just before PBE. In the NZ/6h–8h group, the chromosomes seemed to congress progressively to the equatorial plane of the spindle (Fig. 7, E–G). PBE occurred 2.5 h after removal of the drug (Fig. 7 H). In the NZ/6h–8h group, nocodazole induced chromosome dispersal in some oocytes (∼1/3). After drug removal, a spindle reformed around each group of chromosomes and a polar body was extruded for each spindle. However, the only difference between the two groups was that the prometaphase spindle persisted for 3 h in the NZ/3h–5h group.

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