Developmental pharmacology and the Ah locus: regulatory and temporal genes affecting teratogenesis.

The "Ah cluster" is a group of regulatory, temporal, and structural genes associated with the inducibility of numerous monooxygenase activities by polycyclic aromatic compounds such as 3-methylcholanthrene. Age- and tissue-specific differences in temporal control of these enzymes are shown to exist. These differences could be important in the age- and tissue-specific differences in one's susceptibility to cancer, drug toxicity, and birth defects. Allelic differences at the Ah locus are shown in the mouse to be associated with benzo[a]-pyrene-produced in utero toxicity: increased stillborns, resorptions, and dysmorphogenesis, plus decreased fetal weight.