ABSTRACT
The early embryo development represents a sequence of events including fertilization, oocyte activation and pronuclei formation, and embryo growth, which results in the formation of a competent embryo capable of attaching itself to the maternal endometrium and thus initiating the pregnancy. Fertilization is a dynamic and carefully orchestrated process that occurs in the fallopian tube in which haploid female and male gametes are involved in a timely and orderly sequence of events that culminates in the formation of the zygote and the development of a new independent individual. Preimplantation development, which represents the period between fertilization and implantation into the uterus, is characterized by a sequence of rapid cell divisions controlled by various cellular and molecular mechanisms. These mechanisms include intercellular communication regulated by autocrine, paracrine, and endocrine factors along with cell surface and extracellular matrix (ECM) protein
expression, which control migration and interaction among distinct cell groups. Selective expression and suppression of genes, responsible for cell differentiation, and a strict balance between proliferation and death of cells (apoptosis) are other important mechanisms and are essential to successful development.
