Transient stress and stress enzyme responses have practical impacts on parameters of embryo development, from IVF to directed differentiation of stem cells.

In this review, we discuss the expression, regulation, downstream mechanisms, and function of stress-induced stress enzymes in mammalian oocytes, peri-implantation embryos, and the stem cells derived from those embryos. Recent reports suggest that stress enzymes mediate developmental functions during early mammalian development, in addition to the homeostatic functions shared with somatic cells. Stress-induced enzymes appear to insure that necessary developmental events occur: many of these events may occur at a slower rate, although some may occur more rapidly. Developmental events induced by stress may be mediated by a single dominant enzyme, but there are examples of responses that require the integration of more than one stress enzyme. The discussion focuses on the consequences of stress as a function of duration and magnitude, and this includes an emerging understanding of the threshold levels of duration and magnitude that lead to pathology. Other topics discussed are the reversibility of the developmental as well as homeostatic consequences of stress, the further problems with readaptation after stress subsides, and the mechanisms and functions of stress enzymes during early mammalian development. The analyses are done with specific concern for their practical impact in assisted reproductive technology (ART) and stem cell technologies. (c) 2007 Wiley-Liss, Inc.