方舟子：更正一下精子中线粒体的命运
以前普遍认为，精子中的线粒体DNA之所以没能遗传下来，是因为在受精时只有精子头部（不含线粒体）进入卵子，而含线粒体的中部（称为线粒体鞘）被排除在外。1996年有两项研究发现这种曾被普遍接受的观点并不准确。在受精时，精子的线粒体鞘也进入了卵子，但是在随后的两次细胞分裂中，精子线粒体消失。所以受精卵中的线粒体完全来自卵子，但我前面说的“在受精时只有精子头部进入卵子，而精子头部不含线粒体”是过时观点，应该删去。
附文献：
Proc Natl Acad Sci U S A. 1996 Nov 26;93(24):13859-63.
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Misconceptions about mitochondria and mammalian fertilization:implications for theories on human evolution.
Ankel-Simons F, Cummins JM.
Duke University Primate Center, Durham, NC 27705, USA.
In vertebrates, inheritance of mitochondria is thought to bepredominantly maternal, and mitochondrial DNA analysis has become astandard taxonomic tool. In accordance with the prevailing view ofstrict maternal inheritance, many sources assert that duringfertilization, the sperm tail, with its mitochondria, gets excludedfrom the embryo. This is incorrect. In the majority ofmammals-including humans-the midpiece mitochondria can beidentified in the embryo even though their ultimate fate isunknown. The "missing mitochondria" story seems to havesurvived--and proliferated-unchallenged in a time of contentionbetween hypotheses of human origins, because it supports the"African Eve" model of recent radiation of Homo sapiens out ofAfrica. We will discuss the infiltration of this mistake intoconcepts of mitochondrial inheritance and human evolution.
PMID: 8943026 [PubMed - indexed for MEDLINE]
PMCID: PMC19448
Biol Reprod. 1996 Dec;55(6):1195-205.
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Fate of the sperm mitochondria, and the incorporation, conversion,and disassembly of the sperm tail structures during bovinefertilization.
Sutovsky P, Navara CS, Schatten G.
Department of Zoology, University of Wisconsin, Madison 53706,USA.
Sperm incorporation and the conversion of the sperm-derivedcomponents into zygotic structures during in vitro fertilization ofbovine oocytes was explored by combining ultrastructural studieswith observations of the fertilizing sperm tagged with amitochondrion-specific vital dye MitoTracker green FM. The zygotesfertilized by the MitoTracker-labeled sperm were fixed at varioustimes after fertilization and then processed forimmunocytochemistry to examine the distribution of DNA,microtubules, and sperm tail components, including the fibroussheath and axonemal microtubules. We show here that the completeincorporation of the sperm, but not sperm-oocyte binding and oocyteactivation, depends upon the integrity of oocyte microfilaments andis inhibited by the microfilament disrupter cytochalasin B. Aftersperm incorporation, the mitochondria are displaced from thesperm's connecting piece, and the sperm centriole is exposed to theegg cytoplasm. This event is followed by the formation of themicrotubule-based sperm aster, which is responsible for the unionof male and female pronuclei. Concomitantly, the major structure ofthe sperm principal piece, the fibrous sheath, disappears. Afterthe first mitosis, the compact mitochondrial sheath can be seen inone of the blastomeres. An aggregate of the sperm mitochondria isobserved at the entry of the second mitosis, although they remainin the vicinity of the nucleus and can later be seen at one pole ofthe metaphase spindle. The mitochondrial cluster is occasionallyfound in one of the blastomeres in the early-stage four-cellembryos, but it is no longer detected by the beginning of the thirdmitotic cycle. These data suggest that the disassembly of the spermtail during bovine fertilization occurs as a series of preciselyorchestrated events involving the destruction (fibrous sheath andmitochondrial sheath) and transformation (DNA, sperm centriole) ofparticular sperm structures into zygotic and embryoniccomponents.
Publication Types:
" ResearchSupport, U.S. Gov't, Non-P.H.S.
" ResearchSupport, U.S. Gov't, P.H.S.
PMID: 8949874 [PubMed - indexed for MEDLINE]
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