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Microdomains bounded by endoplasmic reticulum segregate cell cycle calcium transients in syncytial Drosophila embryos.

Parry H, McDougall A, Whitaker M - J. Cell Biol. (2005)

Bottom Line: Cell. 92:193-204).Constructs that chelate InsP3 also prevent nuclear division.An analysis of nuclear calcium concentrations demonstrates that they are differentially regulated.

View Article: PubMed Central - PubMed

Affiliation: Institute for Cell and Molecular Biosciences, University of Newcastle upon Tyne Medical School, Newcastle upon Tyne NE2 4HH, England, UK.

ABSTRACT
Cell cycle calcium signals are generated by the inositol trisphosphate (InsP3)-mediated release of calcium from internal stores (Ciapa, B., D. Pesando, M. Wilding, and M. Whitaker. 1994. Nature. 368:875-878; Groigno, L., and M. Whitaker. 1998. Cell. 92:193-204). The major internal calcium store is the endoplasmic reticulum (ER); thus, the spatial organization of the ER during mitosis may be important in shaping and defining calcium signals. In early Drosophila melanogaster embryos, ER surrounds the nucleus and mitotic spindle during mitosis, offering an opportunity to determine whether perinuclear localization of ER conditions calcium signaling during mitosis. We establish that the nuclear divisions in syncytial Drosophila embryos are accompanied by both cortical and nuclear localized calcium transients. Constructs that chelate InsP3 also prevent nuclear division. An analysis of nuclear calcium concentrations demonstrates that they are differentially regulated. These observations demonstrate that mitotic calcium signals in Drosophila embryos are confined to mitotic microdomains and offer an explanation for the apparent absence of detectable global calcium signals during mitosis in some cell types.

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The [Cai] increases are slow, periodic calcium waves that originate at both poles of the embryo and annihilate upon collision. (A) The images display the CaGr/TMR confocal ratio of a section through an embryo in cycle 9. Slow calcium waves are seen moving toward the equator of the embryo from the poles and annihilating upon collision. The calcium wave speed in this cycle is ∼0.4 μm/s (Table II). (B) Topographical representation of another slow calcium wave during cycle 10. The polar origin of the calcium wave is evident. The waves propagate cortically toward the equator of the embryo. (C) The slow calcium waves precede the wave of cortical contraction, which is seen as retraction of the plasma membrane away from the vitelline membrane. The images display CaGr/TMR confocal ratio images in a cycle 8 embryo. The slow cortical calcium wave moves vertically downwards away from the anterior pole, as indicated by the movement of arrowheads. The displacement of both the calcium wave and the cortical contraction are progressive. The arrowheads mark the region of highest calcium increase in each successive image, and the white arrow marks the starting position of the calcium increase at time = 0. The leading edge of the cortical contraction is marked by a yellow dot. Note that in this image, the embryo equator is beyond the bottom of the images and that the widest part of the image at the top is a property of the confocal section; it is not the embryo equator, which lies beyond the bottom of the images. Temperature is 18°C.
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fig2: The [Cai] increases are slow, periodic calcium waves that originate at both poles of the embryo and annihilate upon collision. (A) The images display the CaGr/TMR confocal ratio of a section through an embryo in cycle 9. Slow calcium waves are seen moving toward the equator of the embryo from the poles and annihilating upon collision. The calcium wave speed in this cycle is ∼0.4 μm/s (Table II). (B) Topographical representation of another slow calcium wave during cycle 10. The polar origin of the calcium wave is evident. The waves propagate cortically toward the equator of the embryo. (C) The slow calcium waves precede the wave of cortical contraction, which is seen as retraction of the plasma membrane away from the vitelline membrane. The images display CaGr/TMR confocal ratio images in a cycle 8 embryo. The slow cortical calcium wave moves vertically downwards away from the anterior pole, as indicated by the movement of arrowheads. The displacement of both the calcium wave and the cortical contraction are progressive. The arrowheads mark the region of highest calcium increase in each successive image, and the white arrow marks the starting position of the calcium increase at time = 0. The leading edge of the cortical contraction is marked by a yellow dot. Note that in this image, the embryo equator is beyond the bottom of the images and that the widest part of the image at the top is a property of the confocal section; it is not the embryo equator, which lies beyond the bottom of the images. Temperature is 18°C.

Mentions: When displayed at higher temporal resolution, the [Cai] changes have a spatial substructure. Fig. 2 A shows two examples of the spatial pattern of [Cai] increase. In the top panel, two [Cai] waves are arriving from poles at the equator of the embryo and are annihilating there. In Fig. 2 B, the initiation of a calcium wave at the anterior pole is followed by progression of the wave toward the equator and out of the frame. Thus, the calcium signal shows the same behavior as mitotic waves, originating at both embryonic poles and moving toward the equator. Table II gives the mean wave velocity during syncytial division cycles from cycles 9–12. The wave speed slows with each cycle, decreasing from 0.45 to 0.29 μm/s. As the nuclear division cycle time slows, the wave becomes progressively slower; the product of wave speed and cycle time remains constant, which is a further indication of the entrainment of calcium wave and nuclear cycle. Fig. 2 C shows a single [Cai] wave in a cycle 8 embryo before the nuclei have reached the cortex. As the wave progresses toward the equator, it is followed by a cortical constriction that represents a cortical contraction travelling at the same velocity. The constriction can be seen in the confocal section, as the movement of the plasma membrane away from the vitelline membrane creates a dye-free perivitelline space that appears black beneath the autofluorescent vitelline membrane. The time that elapsed between the leading edge of the calcium wave and the leading edge of the constriction is ∼90 s. We observed the association between wave and constriction in three of three embryos, suggesting that the [Cai] increase causes the cortical contraction.


Microdomains bounded by endoplasmic reticulum segregate cell cycle calcium transients in syncytial Drosophila embryos.

Parry H, McDougall A, Whitaker M - J. Cell Biol. (2005)

The [Cai] increases are slow, periodic calcium waves that originate at both poles of the embryo and annihilate upon collision. (A) The images display the CaGr/TMR confocal ratio of a section through an embryo in cycle 9. Slow calcium waves are seen moving toward the equator of the embryo from the poles and annihilating upon collision. The calcium wave speed in this cycle is ∼0.4 μm/s (Table II). (B) Topographical representation of another slow calcium wave during cycle 10. The polar origin of the calcium wave is evident. The waves propagate cortically toward the equator of the embryo. (C) The slow calcium waves precede the wave of cortical contraction, which is seen as retraction of the plasma membrane away from the vitelline membrane. The images display CaGr/TMR confocal ratio images in a cycle 8 embryo. The slow cortical calcium wave moves vertically downwards away from the anterior pole, as indicated by the movement of arrowheads. The displacement of both the calcium wave and the cortical contraction are progressive. The arrowheads mark the region of highest calcium increase in each successive image, and the white arrow marks the starting position of the calcium increase at time = 0. The leading edge of the cortical contraction is marked by a yellow dot. Note that in this image, the embryo equator is beyond the bottom of the images and that the widest part of the image at the top is a property of the confocal section; it is not the embryo equator, which lies beyond the bottom of the images. Temperature is 18°C.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171230&req=5

fig2: The [Cai] increases are slow, periodic calcium waves that originate at both poles of the embryo and annihilate upon collision. (A) The images display the CaGr/TMR confocal ratio of a section through an embryo in cycle 9. Slow calcium waves are seen moving toward the equator of the embryo from the poles and annihilating upon collision. The calcium wave speed in this cycle is ∼0.4 μm/s (Table II). (B) Topographical representation of another slow calcium wave during cycle 10. The polar origin of the calcium wave is evident. The waves propagate cortically toward the equator of the embryo. (C) The slow calcium waves precede the wave of cortical contraction, which is seen as retraction of the plasma membrane away from the vitelline membrane. The images display CaGr/TMR confocal ratio images in a cycle 8 embryo. The slow cortical calcium wave moves vertically downwards away from the anterior pole, as indicated by the movement of arrowheads. The displacement of both the calcium wave and the cortical contraction are progressive. The arrowheads mark the region of highest calcium increase in each successive image, and the white arrow marks the starting position of the calcium increase at time = 0. The leading edge of the cortical contraction is marked by a yellow dot. Note that in this image, the embryo equator is beyond the bottom of the images and that the widest part of the image at the top is a property of the confocal section; it is not the embryo equator, which lies beyond the bottom of the images. Temperature is 18°C.
Mentions: When displayed at higher temporal resolution, the [Cai] changes have a spatial substructure. Fig. 2 A shows two examples of the spatial pattern of [Cai] increase. In the top panel, two [Cai] waves are arriving from poles at the equator of the embryo and are annihilating there. In Fig. 2 B, the initiation of a calcium wave at the anterior pole is followed by progression of the wave toward the equator and out of the frame. Thus, the calcium signal shows the same behavior as mitotic waves, originating at both embryonic poles and moving toward the equator. Table II gives the mean wave velocity during syncytial division cycles from cycles 9–12. The wave speed slows with each cycle, decreasing from 0.45 to 0.29 μm/s. As the nuclear division cycle time slows, the wave becomes progressively slower; the product of wave speed and cycle time remains constant, which is a further indication of the entrainment of calcium wave and nuclear cycle. Fig. 2 C shows a single [Cai] wave in a cycle 8 embryo before the nuclei have reached the cortex. As the wave progresses toward the equator, it is followed by a cortical constriction that represents a cortical contraction travelling at the same velocity. The constriction can be seen in the confocal section, as the movement of the plasma membrane away from the vitelline membrane creates a dye-free perivitelline space that appears black beneath the autofluorescent vitelline membrane. The time that elapsed between the leading edge of the calcium wave and the leading edge of the constriction is ∼90 s. We observed the association between wave and constriction in three of three embryos, suggesting that the [Cai] increase causes the cortical contraction.

Bottom Line: Cell. 92:193-204).Constructs that chelate InsP3 also prevent nuclear division.An analysis of nuclear calcium concentrations demonstrates that they are differentially regulated.

View Article: PubMed Central - PubMed

Affiliation: Institute for Cell and Molecular Biosciences, University of Newcastle upon Tyne Medical School, Newcastle upon Tyne NE2 4HH, England, UK.

ABSTRACT
Cell cycle calcium signals are generated by the inositol trisphosphate (InsP3)-mediated release of calcium from internal stores (Ciapa, B., D. Pesando, M. Wilding, and M. Whitaker. 1994. Nature. 368:875-878; Groigno, L., and M. Whitaker. 1998. Cell. 92:193-204). The major internal calcium store is the endoplasmic reticulum (ER); thus, the spatial organization of the ER during mitosis may be important in shaping and defining calcium signals. In early Drosophila melanogaster embryos, ER surrounds the nucleus and mitotic spindle during mitosis, offering an opportunity to determine whether perinuclear localization of ER conditions calcium signaling during mitosis. We establish that the nuclear divisions in syncytial Drosophila embryos are accompanied by both cortical and nuclear localized calcium transients. Constructs that chelate InsP3 also prevent nuclear division. An analysis of nuclear calcium concentrations demonstrates that they are differentially regulated. These observations demonstrate that mitotic calcium signals in Drosophila embryos are confined to mitotic microdomains and offer an explanation for the apparent absence of detectable global calcium signals during mitosis in some cell types.

Show MeSH
Related in: MedlinePlus