Under normal milieu, mammalian oocytes are fertilized, and the zygotes develop into blastocysts in the female reproductive tract. After pick-up of oocytes, exposure to light during in vitro manipulation is unavoidable. Development of mouse zygotes to blastocysts is unaffected by exposure to cool white fluorescent light for 15 min, but the incidence of apoptotic cells in blastocysts is significantly increased by the light exposure. The blastocysts that develop from zygotes exposed to light develop to term fetuses at a lower rate than those developed from zygotes shielded from light. The incidence of apoptoic cells in blastocysts is significantly decreased by addition of SB20358, p38MAPK inhibitor, or Q-VD-Oph, caspase inhibitor. Furthermore, when HB-EGF is added to the culture medium, the total cell number of blastocysts developing from zygotes exposed to light increases, and the incidence of apoptotic cells in blastocysts decreases. These blastocysts develop to term fetuses at the same rate as those developed from zygotes shielded from light. In vitro conditions are stressful, and are not the best environment for eggs. Light is one of the physical factors affecting the function of mammalian embryos and extreme care should be taken concerning its effects.

It seems that ICSI is well investigated basically and clinically, as more than 20 years have passed from the first report of success in human's ICSI. However, the study is still insufficient in practice. We need discussion about the unknown points in ICSI procedure, for example the in vitro ageing of retrieved oocytes, non-physiological treatment removing the cumulus cells from COC by hyaluronidase, the method of selection of good sperm, the method of immobilization of sperm, the effect of polyvinylpyrrolidone and acrosome enzyme that are brought in the oocyte. We must practice good treatments for oocytes and embryos. It is important that we continue carrying out that it is thought to be right scientifically and theoretically in ICSI procedure to improve quality of ICSI. It leads to improvement of the quality of ART and seems to be the mission of a stuff engaged in reproductive medicine.

Azoospermia is caused by abnormality in the various genes involved in spermatogenesis. However, the crucial genes for spermatogenesis have not yet been identified. Recently, targeted knockout and transgenic mice have been generated and considerable knowledge has been accumulated about their phenotype patterns, and a wide variety of genes are known to be associated with sperm formation. First, we review the meiotic and post-meiotic phases and genes expressed during spermatogenesis. Many genes corresponding to various clinical features of azoospermia exist, and we also review azoospermia related genes from clinical aspects. The AZF (azoospermia factor) regions on the Y chromosome long arm are thought to show a major correlation with spermatogenesis. From the genomic point of view, their deletion due to intrachromosomal recombimation is reviewed as a constitutional feature of the Y chromosome. Moreover, we explain how to use a detection kit for the Y chromosome micro deletion which we developed.

Chromosomal abnormalities arising after fertilization, are observed at a relatively high rate at the cleavage stage. To evaluate the aneuploidy and mosaicism, microarray comparative genomic hybridization (CGH) of trophectoderm cells from blastocysts has been considered in preimplantation screening. However, 1% or less of live births are children with chromosomal abnormalities. In this paper, cytogenetic features of patients with chromosomal abnormalities and methods for detecting the disorders are described. Consideration of the utilities and limitations of cytogenetic techniques is essential in the clinical setting.

Louise Brown, who in 1978 was the first person born via ART (assisted reproductive technology), gave birth herself by natural pregnancy. Although it has been the subject of many ethical and scientific arguments, various kinds of ART have been developed and advanced. ART does not affect a child's health but can cause a slightly higher occurrence of congenital anomalies because of male and/or female infertility factors including chromosomal abnormalities. However, there is no difference in offspring resulting from ICSI (intracytoplasmic sperm injection) or IVF (In vitro fertilization).

It is a challenge to induce spermatogenesis in vitro, because it involves a complicated process of sequential cell proliferation and differentiation, from spermatogonial stem cells to sperm formation. Recently, we have succeeded, using a classical organ culture method, to produce sperm from spermatogonial stem cells, using several modifications. The produced spermatids and sperm were fertile, giving rise to healthy progeny. This new in vitro system for spermatogenesis could be useful for addressing the issue of sperm quality that is becoming more important in this ICSI era. We also hope that an in vitro system of human spermatogenesis will be developed in the near future.

Microinsemination, also referred to as intracytoplasmic sperm injection (ICSI), is a technique used to fertilize oocytes by delivering spermatozoa into ooplasm using micromanipulation devices. Microinsemination dose not need some of the sperm-specific properties, such as motility, acrosome reaction, or sperm-oocyte membrane fusion. So we can obtain normal offspring not only with spermatozoa but also with male germ cells that are unable to fertilize oocytes under conventional in vivo and in vitro conditions. ICSI has been widely used as an assisted reproduction technique to study the mechanisms of mammalian fertilization and to rescue male-factor infertility in humans and animals. This review describes how to apply ICSI referring to many studies and discusses future applications.