Epigenetic and experimental modifications in early mammalian development: Part II - Culture of preimplantation embryos and its long-term effects on gene expression and phenotype

A growing number of medical, scientific and biotechnological procedures rel y on culture of mammalian preimplantation embryos. This review presents cur rently available data on aberrant offspring development that sometimes aris es from commonly applied in-vitro procedures in humans, ruminant species an d mice. Comparison between mammalian species reveals similarities in the ph enotypic abnormalities that are observed at fetal and perinatal stages of d evelopment. In particular, aberrant effects on fetal growth have been obser ved in multiple studies in which serum complemented the preimplantation cul ture medium. Although it remains to be determined whether there is a common causal mechanism(s) involved, several hypotheses have been put forward to account for the variety of the observed developmental abnormalities. One of these postulates that culture can result in the epigenetic deregulation of developmentally important genes, and that such epigenetic alterations woul d affect in particular the expression of genes that are subject to genomic imprinting. Imprinted genes play key roles in the control of fetal growth, and altered imprinting can cause growth defects. Some recent in-vitro cultu re studies on mice and ruminant species now lend support to this hypothesis .