This review examines the place of mitochondria in the life cycle through oogenesis, ovulation and early embryogenesis. Mitochondria are semi-autonomous organelles responsible for the bulk of oxidative energy production in the body. They play central roles in ageing, in apoptosis and in many non-Mendelian-inherited bioenergetic and neurological diseases. Originating as free alpha-proteobacteria that entered into a symbiotic relationship with the ancestral eukaryotic organisms, they now have a highly restricted genome of ~16 kb, encoding for 37 genes of the oxidative phosphorylation pathway. Mitochondria are inherited through the mother and special mechanisms have evolved to eliminate the contribution of the spermatozoon in early embryonic development. Most mitochondrial genes have become translocated to the nucleus, and nuclear and mitochondrial genes have co-evolved. This, coupled with a high mutation rate in the remaining mitochondrial DNA, has resulted in a high degree of concordance between them. Disharmony between nuclear and mitochondrial genes is thus likely to complicate cloning technology and the experimental reconstruction of chimeric embryos by cytoplasmic or nuclear transfer.

Animals↗

PubMedDate not supplied

Mitochondria: potential roles in embryogenesis and nucleocytoplasmic transfer.

This review examines current understanding of mammalian mitochondria and mitochondrial DNA in the light of new reproductive technologies. Mitochondria are central to ageing, apoptosis, metabolism and many diseases. They are controlled by a dual genome system, with cooperation between endogenous mitochondrial genes and mitochondrial genes translocated to the nucleus over the course of evolution. This translocation has been accompanied by extreme compression of the mitochondrial genome, with little tolerance for mutations or heteroplasmy (multiple genomes). The highly compact mitochondrial genome appears to be maintained by a stringent numerical bottleneck in embryogenesis and oogenesis, followed by clonal expansion from a highly selected subset of precursor molecules. The dual nature of control between nucleus and cytoplasm sets up potential conflicts, which are normally resolved by natural selection. Such potentially opposing interests and mechanisms are probably partly to blame for the poor rates of success in cloning animals by nuclear transfer. The ability to construct cell systems and animal embryos with novel combinations and permutations of nuclear and cytoplasmic genes will provide powerful tools for examining these fundamental biological questions. Clinically, attempts to 'rescue' abnormal human oocytes or embryos by cytoplasmic transfer risk complex and unpredictable outcomes emerging from disharmonious nuclear-cytoplasmic interactions.

Aging↗

PubMedDate not supplied

Pentoxifylline increases sperm penetration into zona-free hamster oocytes without increasing the acrosome reaction.

Several drugs have been used to stimulate human sperm motility, including 3-deoxy-adenosine, caffeine, and pentoxifylline. Pentoxifylline is an inhibitor of the phosphodiesterase and may stimulate sperm motility by increasing the intracellular levels of cAMP. In this study we have evaluated the effect of pentoxifylline in the outcome of the sperm penetration assay into zona-free hamster oocytes. Twenty-seven semen samples, obtained for diagnostic purposes, were used. After the motile sperm were selected by the swim-up technique, the samples were divided into two aliquots. One aliquot was incubated with 1 mg ml-1 of pentoxifylline at 37 degrees C, 5% CO2 for 30 min. The control aliquot was incubated with culture medium. The samples were then washed and resuspended in fresh, pentoxifylline-free medium, at a sperm concentration of 10 x 10(6) cells ml-1. One hundred microlitres of each sperm suspension was then deposited under oil and 30-40 zona-free hamster oocytes were added. After 6 h of gamete coincubation, the percentage of penetrated oocytes and the number of decondensed sperm heads were evaluated. The percentage of acrosome-reacted sperm was evaluated using the Pisum sativum lectin. The percentage of zona-free hamster oocytes penetrated was increased after pentoxifylline-treatment. The percentage of acrosome reacted sperm and the number of decondensed sperm heads per egg were not different between the control and the pentoxifylline-treated groups. The results suggest that the beneficial effect of pentoxifylline upon the sperm cells is not mediated by stimulation of the acrosome reaction.

Acrosome↗

PubMedDate not supplied

Computers in toxicological education: an overview.

Explore the source record for details and available documents.

Animals↗

PubMedDate not supplied

A test of the human sperm acrosome reaction following ionophore challenge. Relationship to fertility and other seminal parameters.

Acrosome reaction capacity was tested on semen samples from 53 fertile and 26 subfertile men. Preparations were divided into two aliquots after 3 or 24 hours of culture. One aliquot received 10 mumol/L calcium ionophore A23187 in dimethyl sulfoxide (DMSO) and the other received DMSO alone. Acrosome reactions were scored on ethanol-permeabilized smears using fluorescein isothiocyanate (FITC)-conjugated Pisum sativum lectin. The following factors were analyzed: the spontaneous reaction rates (control); induced reaction rates (ionophore-challenged); and the difference between the two, being the proportion of spermatozoa in the population capable of reacting in response to calcium influx (acrosome reaction to ionophore challenge [ARIC]). While spontaneous reactions bore no relation to fertility, induced reactions and ARICs were significantly reduced or absent in subfertile men, indicating acrosomal dysfunction as a likely cause of fertilization failure. The test was shown to have a predictive value for fertility comparable to that of the hamster ovum sperm penetration assay and to be a simple and cost-effective addition to existing semenology.

Acrosome↗