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Number of mitochondria and some properties of mitochondrial DNA in the mouse egg

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Abstract

The number of mitochondria stored in the 1-cell mouse egg was determined by electron microscopic morphometry. In the four eggs examined, the average mitochondrial number obtained per egg was 92,500 ± 7000 SD. The total DNA from 6600 unfertilized mouse eggs was isolated by buoyant density centrifugation in an ethidium bromide-CsCl gradient. A fluorometric assay performed on a sample of the purified DNA gave a value of about 8 pg for the DNA content of the unfertilized mouse egg (without the first polar body); it was estimated that about one-third of this amount, 2–3 pg, represented mitochondrial DNA (mtDNA). Electron microscopic visualization revealed that 11% of the mtDNA population consisted of catenated forms. About 30% of the mtDNA circles contained a D loop and 70% were clean duplex circles. No larger replicative intermediates of mtDNA were found, suggesting an absence of mtDNA replication in the unfertilized mouse egg.

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    This work was supported in part by Public Health Service Research Grant No. CA-16155 from the National Cancer Institute.

    Dr. Matsumoto was the recipient of a National Institutes of Health postdoctoral fellowship, No. CA-53287, from the National Cancer Institute.

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