Brian Dale

DNA methylation and gene expression in IVF

Recently, differences in DNA methylation patterns in placental and umbilical blood samples taken from children born after IVF and children conceived naturally have been reported. Since this may have an effect on gene expression, we highlight some of the biochemical/metabolic pathways in oocytes and embryos that might be relevant to methylation and imprinting during the process of human IVF. First, ovarian stimulation leads to elevated concentrations of follicular homocysteine which may have an effect on methylation. This should be compensated for by the systematic administration of folic acid and other B vitamins to patients. Second, there has been a trend to culture early human embryos in culture medium lacking essential amino acids. Consequently, methionine is not available during the first 3 days of in-vitro culture, a time when methylation is of major importance. We strongly recommend the use of culture medium with essential amino acids in human fertilization and early developmental stages. Finally, although all animals are, to some extent, a model for others, great caution should be exercised in extrapolating data; in particular, data from the mouse should not be assumed to be applicable to human embryology.

In-Vitro Fertilization: Gametes and gametogenesis

After a blastocyst has implanted in the uterus and begins to differentiate into the three primary germ layers, a special population of cells develops as primordial germ cells (PGCs). These are destined to become the gametes of the new individual: future reproduction of the organism is absolutely dependent upon the correct development of these unique populations of cells. They originate immediately behind the primitive streak in the extraembryonic mesoderm of the yolk sac; toward the end of gastrulation they move into the embryo via the allantois, and temporarily settle in the mesoderm and endoderm of the primitive streak. In humans, PGCs can be identified at about 3 weeks of gestation, close to the yolk sac endoderm at the root of the allantois.

In-Vitro Fertilization: Implantation and early stages of fetal development

During the transition from morula to blastocyst the embryo enters the uterus, where it is sustained by oxygen and a rich supply of metabolic substrates in uterine secretions. The subsequent sequence of events that lead to implantation is a crucial milestone in mammalian embryo development. Carefully orchestrated programs are set into action, which establish diverse cell lines, specify cell fate and major remodeling that will generate the embryo and its extraembryonic tissues: during gastrulation, the three primary germ layers that lead to body formation are formed. The critical conditions that are created in this early stage will pave the way to a successful pregnancy.

In-Vitro Fertilization: The clinical in-vitro fertilization laboratory

In the armory of medical technology available for alleviation of disease and quality of life enhancement, there is nothing to match the unique contribution of assisted reproductive technology (ART). There is no other life experience that matches the birth of a baby in significance and importance. The responsibility of nurturing and watching children grow and develop alters the appreciation of life and health, with a resulting long-term impact upon individuals, families and, ultimately, society. Thus, the combination of oocyte and sperm to create an embryo with the potential to develop into a unique individual cannot be regarded lightly, as merely another form of invasive medical technology, but must be treated with the respect and responsibility merited by the most fundamental areas of human life.

In-Vitro Fertilization: Review of cell and molecular biology

Gametogenesis, embryo development, implantation and in-vitro culture involve numerous complex pathways and interactions at the cellular and molecular level; a true understanding of their significance requires fundamental knowledge of the underlying principles. This chapter therefore provides a condensed overview and review of basic terminology and definitions, with particular emphasis on aspects relevant to reproductive biology and in-vitro fertilization.