Eggs in the balance

Polycyclic aromatic hydrocarbons (PAH), found in cigarette smoke and air po llution, interact with the aryl hydrocarbon receptor (Ahr) to cause reprodu ctive defects. Mice lacking either Ahr or the pro-apoptotic protein Bax hav e an increased number of primordial follicles, and these mutant oocytes are resistant to PAH toxicity. A new study shows that the Bax promoter contain s two core Ahr response elements, which are required for PAH stimulation of Bax promoter activity in oocytes. Thus, the toxic effects of PAH in oocyte s are mediated directly by Ahr induction of the Bax pathway.