Pathogenesis of Limb Malformations in Mice Induced by Methoxyacetic Acid

The present study was performed to reveal the pathogenesis of limb malformations induced by methoxyacetic acid (MAA) in developing mouse limbs. Pregnant Jcl:ICR mice were orally given at gestational day (gd) 10.5, 11.0, or 11.5 (vaginal plug = gd 0) a single dose of MAA 10 mmol/kg of body weight. Various patterns of cell death in limb buds were observed by vital dye staining with Nile blue A. Under a light microscope and transmission electron microscope, excessive cell death was observed in the mesenchyme as well as in the apical ectodermal ridge (AER) 2 hr after MAA treatment, reaching a maximum after 6 hr. Scanning electron microscopic examinations showed hypoplasia of the AER and small hand plates 24 hr after treatment. Small hand plates and delayed digital ray formation were noted at 48 hr. Neither detachment nor massive necrosis was detected in the periderm covering the limb bud. The distribution of cell death 6 hr after treatment was similar in limb buds treated either at gd 10.5, 11.0 or 11.5, but the final pattern of limb defects was different in fetuses treated at different stages. This study indicates that variations in the pattern of limb defects induced by MAA are due to differences in the amount and distribution of cell death, together with differences in the regenerative capacity of surviving cells.