Cell Signaling During Mammalian Early Embryo Development

D. Randall Armant, Armant, D. Randall

The key, versatile role of intracellular Ca(2+) signaling during egg activation after fertilization has been appreciated for several decades. More recently, evidence has accumulated supporting the concept that cytoplasmic Ca(2+) is also a major signaling nexus during subsequent development of the fertilized ovum. This chapter will review the molecular reactions that regulate intracellular Ca(2+) levels and cell function, the role of Ca(2+) signaling during egg activation and specific examples of repetitive Ca(2+) signaling found throughout pre- and peri-implantation development. Many of the upstream and downstream pathways utilized during egg activation are also critical for specific processes that take place during embryonic development. Much remains to be done to elucidate the full complexity of Ca(2+) signaling mechanisms in preimplantation embryos to the level of detail accomplished for egg activation. However, an emerging concept is that because this second messenger can be modulated downstream of numerous receptors and is able to bind and activate multiple cytoplasmic signaling proteins, it can help the coordination of development through up- and downstream pathways that change with each embryonic stage.