The developmental competence of mammalian oocytes: a convenient but biologically fuzzy concept.

Oocyte developmental competence is often used to qualify in vitro procedures for embryo production. It supposedly accounts for the oocyte's ability to develop into a normal, viable and fertile offspring after fertilization, but for practical reasons it often characterizes the ability of such oocytes to develop to the blastocyst stage in vitro. Molecular tools compatible with the analysis of very small amounts of material have resulted in research aimed at designing molecular criteria to define this competence. However we feel that such research strategies easily lead to misunderstanding of the regulative processes that drive embryo development. Artificially induced blastocyst stage is a poor predictor of oocyte developmental competence. However preimplantation stages also appear to be sensitive to environmental conditions that can induce long-lasting detrimental effects. Larger scale analysis now made available by a functional genomics approach provides a more accurate understanding of the complex regulative networks that sustain the molecular mechanisms responsible for normal development. We propose that the concept of developmental competence should be used more cautiously and also should refer more explicitly to the experimental context it intends to enlighten.