Induction of altered gene expression in early embryos

This review focuses on known genes whose expression may be perturbed by teratogens during early embryogenesis (preorganogenesis). Teratogens may disrupt embryogenesis by modifying positional information. Genes controlling positional information include those specifying the primary body axes: anterior-posterior, dorsal-ventral, or left-right. These genes often encode transcription factors, whose regulation or activation can stimulate aberrant tissue differentiation and morphogenesis. Alternatively, teratogens may directly affect cell differentiation, proliferation, or apoptosis. Hydrophilic signalling molecules such as growth factors and hydrophobic molecules such as retinoids regulate these processes. The signalling pathways activated often induce the coordinate regulation of tissue specific gene expression. In addition to modifying individual signalling pathways, teratogens can synergize with or antagonize the effects of other teratogens through inappropriate interactions between signal transduction pathways. Since teratogens may often directly or indirectly perturb the expression of known or as yet undescribed developmentally critical genes, this review also provides a short description of techniques to identify genes whose expression is altered by teratogens.