To determine whether spermatozoa must be structurally intact before microsurgical injection into oocytes for normal fertilization, intact spermatozoa, as well as sperm heads separated from tails by sonication, were individually injected into oocytes. When whole spermatozoa were injected immediately after their immobilization, the majority of the oocytes were fertilized and developed normally. Sonication in the presence or absence of Triton X-100 decapitated more than 95% of spermatozoa. Although all decapitated spermatozoa were diagnosed as "dead" by live/dead sperm staining, separated sperm heads (nuclei) could participate in normal embryo development when injected into the oocytes. The ability of isolated sperm heads (nuclei) to participate in normal embryo development was maintained under cryopreservation conditions that were not suitable for the survival of plasma membrane-intact spermatozoa. These results indicate that 1) spermatozoa do not need to be structurally intact for intracytoplasmic injection, 2) the plasma and acrosomal membranes and all tail components are not essential for normal embryo development, at least in the mouse, and 3) the cryopreservation conditions required for maintenance of the genetic integrity of sperm nuclei are less stringent than those necessary for keeping plasma membrane-intact spermatozoa alive.
Prostate cancer has become the most common cancer among men in the United States. Although milk consumption is considered to be a risk factor in some epidemiological studies, the results are inconsistent. A meta-analysis method was conducted to estimate the combined odds ratio (OR) between milk consumption and prostate cancer from case-control studies published between 1984 and 2003 using commercial software (comprehensive meta-analysis). The combined OR was 1.68 (95% confidence interval = 1.34-2.12) in the 11 published case-control studies. The combined OR varied little by study stratification. Additionally, we evaluated the possible risk factors in milk for prostate cancer. In conclusion, we found a positive association between milk consumption and prostate cancer. The underlying mechanisms, including fat, calcium, hormones, and other factors, should be investigated further.
Selection of good quality oocytes is important for improvement of assisted reproductive technology. Here, we studied the relationship of the mitochondrial distribution in metaphase II stage (MII) oocytes with fertility, since mitochondria in ooplasm are essential for energy production required for fertilization and embryo development. To observe mitochondria non-invasively, we used oocytes from a transgenic mouse, in which enhanced green fluorescent protein is targeted to the mitochondrial matrix and thus fluorescence is observed exclusively in the mitochondria. Control oocytes with mitochondria distributed around the nucleus showed normal embryo developmental competence, whereas oocytes with abnormal diffuse and fragmented mitochondria showed a significantly lower rate of embryo development after activation by intracytoplasmic sperm injection or strontium, which is a very effective agent for activation of mouse oocytes. Also, we showed that the reduced developmental competence of oocytes with diffuse and fragmented mitochondria caused by vitrification and thawing is similar to that of oocytes with abnormal mitochondrial foci obtained naturally. These findings suggest that abnormal mitochondrial distribution in oocytes at MII is a cause of developmental retardation and therefore normal mitochondrial distribution could be used as a criterion for selection of good oocytes.
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