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Assisted reproductive technology (ART), most notably in vitro fertilization embryo transfer (IVF-ET), has dramatically progressed during the approximately 30 years since its introduction in 1978. It is extremely important to know the hereditary safety ART. However, detailed follow-up studies of children conceived and born by IVF have rarely been conducted. In the present study, we reviewed data at our clinic in addition to the literature regarding congenital abnormalities in children conceived and born by conventional IVF and intracytoplasmic sperm injection (ICSI). Several studies have reported no statistically significant differences in the frequency of congenital abnormalities between natural conception and conception using ART. However, since other studies have in fact indicated increases in congenital abnormalities, it is important to accurately inform patients of these data prior to treatment. In addition, since the field of reproductive medicine has recently become more complex due to the addition of genetic elements, it is essential that those providing treatment possess the relevant knowledge.
Oocyte donation is the last hope for the infertile women who lack their own eggs. Oocyte donation is not still admitted in Japan, and there are groups who are trying to establish new rules for a system that enables oocyte donation in Japan. In this paper, we discuss about the problems concerning the rights of the oocyte donors, recipients and their coming children.
Concept of the fertilizing ability of human spermatozoa has been drastically changed since intracytoplasmic sperm injection (ICSI) played an important role of modern reproductive medicine. Recent studies on the qualities of sperm nucleus revealed that the fertilization and embryo development in vitro should be related to the structure of sperm nuclear chromatin, especially in case of ICSI procedure. It has been suggested that oocytes injected with sperm nuclei with poor S-S bonds have more developmental potency than that with S-S rich sperm nuclei. Moreover, it has been pointed out from the assessment of DNA fragmentation that oocytes injected with genetically impaired nuclei have little potency to develop beyond 8 cell stage embryo. Hereafter, the more definitive assessments of sperm nuclear chromatin should be needed to select the best nuclei for ICSI procedure.
We previously reported that 2-cell embryos obtained after administering cadmium (Cd) to mice immediately before ovulation already demonstrated reduced developmental ability. To determine when this Cd toxicity appears in mouse oocytes before the 2-cell stage, we exposed oocytes to Cd at maturation and during the fertilization period using IVM and IVF techniques. Four experimental groups were defined by the period of Cd exposure: IVM group, exposure at the maturation period; IVF group, exposure at the fertilization period; IVM · IVF group, exposure during both periods; Control group, no exposure. Oocytes obtained from the ovaries were subjected to IVM and IVF, and the fertilization and developmental rates were investigated in all groups. As a result, Cd exposure during the maturation period disturbed fertilization of oocytes, and Cd exposure during the fertilization period disrupted the normal development of embryos after fertilization. This suggested that the manifestation of Cd toxicity in oocytes clearly differed with the exposure period. In addition, it was shown that Cd exposure during the maturation or fertilization period influenced the early development (including the fertilization) at a lower concentration than exposure after the 2-cell stage.
It has been reported that zona-free mammalian oocytes treated with a cytoskeleton inhibitor are separated into several fragments with or without the chromatin by centrifugation. The utilization of these fragments for nuclear or cytoplasmic transfer would increase the efficiency of preparing recipient or donor cytoplasts. In the present study, the separation of mouse oocyte fragments by centrifugation was examined, and the characteristics of these fragments were evaluated. Zona-free mouse oocytes were treated with cytochalasin D, loaded individually onto a discontinuous Percoll gradient in a capillary tube, and centrifuged at 9,500 g for 1–3 min. Oocyte fragments were recovered and examined for the distributions of chromatin, lipids, and mitochondria. After centrifugation for 1 min, 57% of the oocytes treated with cytochalasin D at 4–8°C were divided into pairs of small (diameter: 27.6 ± 7.2 μm) and large (diameter: 73.5 ± 2.4 μm) fragments. Most of the large fragments did not contain any chromatin (92–100%) and showed strong and homogeneous mitochondrial fluorescence. The lipids in the oocytes moved to the centripetal side, and a part of the lipids might have been expelled to the small fragments. The present results suggest that the large fragments derived from the oocytes by centrifugation may be available as a potential source of recipient cytoplasts that are necessary for the nuclear transfer technique.