Maintenance of Metaphase in Colcemid-Treated Mouse Eggs by Distinct Calcium- and 6-Dimethylaminopurine (6-DMAP)-Sensitive Mechanisms

Abstract At fertilization in mice and humans, the activation of the egg is caused by a series of repetitive Ca2+ oscillations which are initiated by phospholipase-C(zeta)ζ that generates inositol-1-4-5-trisphophate (InsP3). Ca2+ oscillations and egg activation can be triggered in mature mouse eggs by incubation in Sr2+ containing medium, but this does not appear to be effective in human eggs. Here we have investigated the reason for this apparent difference using mouse eggs, and human eggs that failed to fertilize after IVF or ICSI. Mouse eggs incubated in Ca2+-free, Sr2+-containing medium immediately underwent Ca2+ oscillations but human eggs consistently failed to undergo Ca2+ oscillations in the same Sr2+ medium. We tested the InsP3-receptor (IP3R) sensitivity directly by photo-release of caged InsP3 and found that mouse eggs were about 10 times more sensitive to InsP3 than human eggs. There were no major differences in the Ca2+ store content between mouse and human eggs. However, we found that the ATP concentration was consistently higher in mouse compared to human eggs. When ATP levels were lowered in mouse eggs by incubation in pyruvate-free medium, Sr2+ failed to cause Ca2+ oscillations. When pyruvate was added back to these eggs, the ATP levels increased and Ca2+ oscillations were induced. This suggests that ATP modulates the ability of Sr2+ to stimulate IP3R-induced Ca2+ release in eggs. We suggest that human eggs may be unresponsive to Sr2+ medium because they have a lower level of cytosolic ATP.

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Selective and Continuous Elimination of Mitochondria Microinjected Into Mouse Eggs From Spermatids, but Not From Liver Cells, Occurs Throughout Embryogenesis

Genetics ◽

10.1093/genetics/156.3.1277 ◽

2000 ◽

Vol 156 (3) ◽

pp. 1277-1284 ◽

Cited By ~ 8

Author(s):

Hiroshi Shitara ◽

Hideki Kaneda ◽

Akitsugu Sato ◽

Kimiko Inoue ◽

Atsuo Ogura ◽

...

Keyword(s):

Early Stage ◽

Liver Mitochondria ◽

Blastocyst Stage ◽

Mus Musculus Domesticus ◽

Newborn Mice ◽

Selective Elimination ◽

Specific Factors ◽

Pcr Method ◽

Mammalian Eggs ◽

Mouse Eggs

Abstract Exclusion of paternal mitochondria in fertilized mammalian eggs is very stringent and ensures strictly maternal mtDNA inheritance. In this study, to examine whether elimination was specific to sperm mitochondria, we microinjected spermatid or liver mitochondria into mouse embryos. Congenic B6-mtspr strain mice, which are different from C57BL/6J (B6) strain mice (Mus musculus domesticus) only in possessing M. spretus mtDNA, were used as mitochondrial donors. B6-mtspr mice and a quantitative PCR method enabled selective estimation of the amount of M. spretus mtDNA introduced even in the presence of host M. m. domesticus mtDNA and monitoring subsequent changes of its amount during embryogenesis. Results showed that M. spretus mtDNA in spermatid mitochondria was not eliminated by the blastocyst stage, probably due to the introduction of a larger amount of spermatid mtDNA than of sperm mtDNA into embryos on fertilization. However, spermatid-derived M. spretus mtDNA was eliminated by the time of birth, whereas liver-derived M. spretus mtDNA was still present in most newborn mice, even though its amount introduced was significantly less than that of spermatid mtDNA. These observations suggest that mitochondria from spermatids but not from liver have specific factors that ensure their selective elimination and resultant elimination of mtDNA in them, and that the occurrence of elimination is not limited to early stage embryos, but continues throughout embryogenesis.

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PEROXYNITRITE (ONOO) MEDIATES DNA DAMAGE IN CYTOKINE/LEAD TREATED MOUSE HEPATOCYTES

The Japanese Journal of Pharmacology ◽

10.1016/s0021-5198(19)41812-x ◽

1997 ◽

Vol 75 ◽

pp. 104

Author(s):

Ruth E. Billings ◽

Susan M. LaRue ◽

David J. Sieg

Keyword(s):

Dna Damage ◽

Treated Mouse ◽

Mouse Hepatocytes

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