INDUCTION OF ALTERED GENE-EXPRESSION IN EARLY EMBRYOS

This review focuses on known genes whose expression may be perturbed b y teratogens during early embryogenesis (preorganogenesis). Teratogens may disrupt embryogenesis by modifying positional information. Genes controlling positional information include those specifying the primar y body axes: anterior-posterior, dorsal-ventral, or left-right. These genes often encode transcription factors, whose regulation or activati on can stimulate aberrant tissue differentiation and morphogenesis. Al ternatively, teratogens may directly affect cell differentiation, prol iferation, or apoptosis. Hydrophilic signalling molecules such as grow th factors and hydrophobic molecules such as retinoids regulate these processes. The signalling pathways activated often induce the coordina te regulation of tissue specific gene expression. In addition to modif ying individual signalling pathways, teratogens can synergize with or antagonize the effects of other teratogens through inappropriate inter actions between signal transduction pathways. Since teratogens may oft en directly or indirectly perturb the expression of known or as yet un described developmentally critical genes, this review also provides a short description of techniques to identify genes whose expression is altered by teratogens. (C) 1997 Elsevier Science B.V.