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The inhibition of polo kinase by matrimony maintains G2 arrest in the meiotic cell cycle.

Xiang Y, Takeo S, Florens L, Hughes SE, Huo LJ, Gilliland WD, Swanson SK, Teeter K, Schwartz JW, Washburn MP, Jaspersen SL, Hawley RS - PLoS Biol. (2007)

Bottom Line: Loss-of-function mtrm mutants result in precocious NEB.The meiotic defects observed in mtrm/+ heterozygotes are fully suppressed by reducing the dose of polo+, demonstrating that Mtrm acts as an inhibitor of Polo.Our data suggest a model in which the eventual activation of Cdc25 by an excess of Polo at stage 13 triggers NEB and entry into prometaphase.

View Article: PubMed Central - PubMed

Affiliation: Stowers Institute for Medical Research, Kansas City, Missouri, United States of America.

ABSTRACT
Many meiotic systems in female animals include a lengthy arrest in G2 that separates the end of pachytene from nuclear envelope breakdown (NEB). However, the mechanisms by which a meiotic cell can arrest for long periods of time (decades in human females) have remained a mystery. The Drosophila Matrimony (Mtrm) protein is expressed from the end of pachytene until the completion of meiosis I. Loss-of-function mtrm mutants result in precocious NEB. Coimmunoprecipitation experiments reveal that Mtrm physically interacts with Polo kinase (Polo) in vivo, and multidimensional protein identification technology mass spectrometry analysis reveals that Mtrm binds to Polo with an approximate stoichiometry of 1:1. Mutation of a Polo-Box Domain (PBD) binding site in Mtrm ablates the function of Mtrm and the physical interaction of Mtrm with Polo. The meiotic defects observed in mtrm/+ heterozygotes are fully suppressed by reducing the dose of polo+, demonstrating that Mtrm acts as an inhibitor of Polo. Mtrm acts as a negative regulator of Polo during the later stages of G2 arrest. Indeed, both the repression of Polo expression until stage 11 and the inactivation of newly synthesized Polo by Mtrm until stage 13 play critical roles in maintaining and properly terminating G2 arrest. Our data suggest a model in which the eventual activation of Cdc25 by an excess of Polo at stage 13 triggers NEB and entry into prometaphase.

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mtrm Is Defective in Karyosome Maturation before NEBThe karyosomes in stage 11–12 oocytes, which have a nuclear envelope, were imaged after the injection of Oli-green and Rhodamine-tubulin until NEB. NEB was defined as the time when the nuclear envelope seems ruffled and the Rhodamine-tubulin enters the nucleus.(A) Representative examples of karyosomes 12–16 min before and at NEB are shown for wild type, mtrm126/mtrm+, and mtrm126 polo+/mtrm+ polo16–1 with achiasmate X chromosomes (FM7/X). Wild type displays a circular karyosome with a smooth outline for 12–16 min before NEB, whereas mtrm126/mtrm+ oocytes bear scabrous or bi-lobed karyosomes. The disordered morphology of karyosomes in mtrm126/mtrm+ oocytes was suppressed by simultaneously reducing the dose of polo. Scale, 5 μm.(B) Summary of karyosome morphology during the 20 min before NEB.
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pbio-0050323-g006: mtrm Is Defective in Karyosome Maturation before NEBThe karyosomes in stage 11–12 oocytes, which have a nuclear envelope, were imaged after the injection of Oli-green and Rhodamine-tubulin until NEB. NEB was defined as the time when the nuclear envelope seems ruffled and the Rhodamine-tubulin enters the nucleus.(A) Representative examples of karyosomes 12–16 min before and at NEB are shown for wild type, mtrm126/mtrm+, and mtrm126 polo+/mtrm+ polo16–1 with achiasmate X chromosomes (FM7/X). Wild type displays a circular karyosome with a smooth outline for 12–16 min before NEB, whereas mtrm126/mtrm+ oocytes bear scabrous or bi-lobed karyosomes. The disordered morphology of karyosomes in mtrm126/mtrm+ oocytes was suppressed by simultaneously reducing the dose of polo. Scale, 5 μm.(B) Summary of karyosome morphology during the 20 min before NEB.

Mentions: The precocious breakdown of the nuclear envelope at stages 11 to 12 is important because the karyosome undergoes dramatic changes in structure during this period [2]. As noted above, in stages 9–10, the karyosome expands to the point that individual chromosomes can be detected [22–24]. These chromosomes recondense into a compact karyosome during stages 11–12, the exact time at which a reduction in the level of Mtrm causes precocious NEB. Thus, the early NEB events promoted by heterozygosity for mtrm might be expected to result in the release of incompletely condensed or disordered karyosomes. To test this hypothesis, we examined karyosome morphology during the 20 min that preceded NEB in wild-type, mtrm126/mtrm+, and mtrm126 polo+/mtrm+ polo16–1 oocytes. As shown in Figure 6, only two out of 28 (7%) wild-type oocytes with incompletely compacted or disordered karyosomes were observed. However, 7 out of 27 (26%) mtrm126/mtrm+ oocytes displayed a disordered karyosome, an effect that was largely suppressed (to 8%) by simultaneous heterozygosity for polo16–1 (Figure 6). These data support the view that the precocious NEB that is induced by lowering the level of Mtrm results in the release of improperly formed karyosomes into the cytoplasm and are again consistent with the possibility that Mtrm inhibits meiotic progression through its effects on Polo.


The inhibition of polo kinase by matrimony maintains G2 arrest in the meiotic cell cycle.

Xiang Y, Takeo S, Florens L, Hughes SE, Huo LJ, Gilliland WD, Swanson SK, Teeter K, Schwartz JW, Washburn MP, Jaspersen SL, Hawley RS - PLoS Biol. (2007)

mtrm Is Defective in Karyosome Maturation before NEBThe karyosomes in stage 11–12 oocytes, which have a nuclear envelope, were imaged after the injection of Oli-green and Rhodamine-tubulin until NEB. NEB was defined as the time when the nuclear envelope seems ruffled and the Rhodamine-tubulin enters the nucleus.(A) Representative examples of karyosomes 12–16 min before and at NEB are shown for wild type, mtrm126/mtrm+, and mtrm126 polo+/mtrm+ polo16–1 with achiasmate X chromosomes (FM7/X). Wild type displays a circular karyosome with a smooth outline for 12–16 min before NEB, whereas mtrm126/mtrm+ oocytes bear scabrous or bi-lobed karyosomes. The disordered morphology of karyosomes in mtrm126/mtrm+ oocytes was suppressed by simultaneously reducing the dose of polo. Scale, 5 μm.(B) Summary of karyosome morphology during the 20 min before NEB.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2100146&req=5

pbio-0050323-g006: mtrm Is Defective in Karyosome Maturation before NEBThe karyosomes in stage 11–12 oocytes, which have a nuclear envelope, were imaged after the injection of Oli-green and Rhodamine-tubulin until NEB. NEB was defined as the time when the nuclear envelope seems ruffled and the Rhodamine-tubulin enters the nucleus.(A) Representative examples of karyosomes 12–16 min before and at NEB are shown for wild type, mtrm126/mtrm+, and mtrm126 polo+/mtrm+ polo16–1 with achiasmate X chromosomes (FM7/X). Wild type displays a circular karyosome with a smooth outline for 12–16 min before NEB, whereas mtrm126/mtrm+ oocytes bear scabrous or bi-lobed karyosomes. The disordered morphology of karyosomes in mtrm126/mtrm+ oocytes was suppressed by simultaneously reducing the dose of polo. Scale, 5 μm.(B) Summary of karyosome morphology during the 20 min before NEB.
Mentions: The precocious breakdown of the nuclear envelope at stages 11 to 12 is important because the karyosome undergoes dramatic changes in structure during this period [2]. As noted above, in stages 9–10, the karyosome expands to the point that individual chromosomes can be detected [22–24]. These chromosomes recondense into a compact karyosome during stages 11–12, the exact time at which a reduction in the level of Mtrm causes precocious NEB. Thus, the early NEB events promoted by heterozygosity for mtrm might be expected to result in the release of incompletely condensed or disordered karyosomes. To test this hypothesis, we examined karyosome morphology during the 20 min that preceded NEB in wild-type, mtrm126/mtrm+, and mtrm126 polo+/mtrm+ polo16–1 oocytes. As shown in Figure 6, only two out of 28 (7%) wild-type oocytes with incompletely compacted or disordered karyosomes were observed. However, 7 out of 27 (26%) mtrm126/mtrm+ oocytes displayed a disordered karyosome, an effect that was largely suppressed (to 8%) by simultaneous heterozygosity for polo16–1 (Figure 6). These data support the view that the precocious NEB that is induced by lowering the level of Mtrm results in the release of improperly formed karyosomes into the cytoplasm and are again consistent with the possibility that Mtrm inhibits meiotic progression through its effects on Polo.

Bottom Line: Loss-of-function mtrm mutants result in precocious NEB.The meiotic defects observed in mtrm/+ heterozygotes are fully suppressed by reducing the dose of polo+, demonstrating that Mtrm acts as an inhibitor of Polo.Our data suggest a model in which the eventual activation of Cdc25 by an excess of Polo at stage 13 triggers NEB and entry into prometaphase.

View Article: PubMed Central - PubMed

Affiliation: Stowers Institute for Medical Research, Kansas City, Missouri, United States of America.

ABSTRACT
Many meiotic systems in female animals include a lengthy arrest in G2 that separates the end of pachytene from nuclear envelope breakdown (NEB). However, the mechanisms by which a meiotic cell can arrest for long periods of time (decades in human females) have remained a mystery. The Drosophila Matrimony (Mtrm) protein is expressed from the end of pachytene until the completion of meiosis I. Loss-of-function mtrm mutants result in precocious NEB. Coimmunoprecipitation experiments reveal that Mtrm physically interacts with Polo kinase (Polo) in vivo, and multidimensional protein identification technology mass spectrometry analysis reveals that Mtrm binds to Polo with an approximate stoichiometry of 1:1. Mutation of a Polo-Box Domain (PBD) binding site in Mtrm ablates the function of Mtrm and the physical interaction of Mtrm with Polo. The meiotic defects observed in mtrm/+ heterozygotes are fully suppressed by reducing the dose of polo+, demonstrating that Mtrm acts as an inhibitor of Polo. Mtrm acts as a negative regulator of Polo during the later stages of G2 arrest. Indeed, both the repression of Polo expression until stage 11 and the inactivation of newly synthesized Polo by Mtrm until stage 13 play critical roles in maintaining and properly terminating G2 arrest. Our data suggest a model in which the eventual activation of Cdc25 by an excess of Polo at stage 13 triggers NEB and entry into prometaphase.

Show MeSH
Related in: MedlinePlus