Teratogen responsive signaling pathways in organogenesis stage mouse limbs

Teratogen exposure activates damage response pathways during organogenesis that determine the fate of the embryo. Cyclophosphamide, an alkylating agent, induces growth reduction defects in organogenesis stage mouse limbs. Here we identify components of the signaling network triggered by in vitro exposure of CD-1 murine limbs to 4-hydroperoxycyclophosphamide (4-OOHCPA), a preactivated analog of cyclophosphamide. The predominant response was downregulation of gene expression; many of the affected genes were transcription factors, transcription regulators, or oncogenes. Pathway analysis of the genes regulated by 4-OOHCPA exposure revealed a novel damage response pathway in limbs comprised of basic transcription factors, Hif1a, Ndn, Hes1 and Myog, transcription activators and repressors, Egr1 and E2f1, intracellular transducers, effectors and modulators, Bmpr1b and Pea15, and oncogenes and tumor suppressors, Hras1, Abl1, Smad1, and Ttf1. Thus, teratogen exposure triggers both developmentally specific signaling pathways and a general damage response. We hypothesize that hypoxia signaling plays a central role in integrating these responses.