Digital anomalies of mouse limbs induced by treatment with urethan in vitro.

The effects of urethan on ICR/JCL mouse limbs were examined in forelimbs of day-11 embryos cultured in concentrations of 0, 50, and 100 mug/ml for one to four days, and in forelimbs of day-12 embryos and in fore- and hind limbs of day-13 embryos in 0, 10, 50, and 100 mug/ml for one to four days. Urethan did not cause digital malformations on day-11 limbs but induced syndactyly in day-12 forelimbs and polydactyly in day-12 forelimbs and day-13-fore- and hind limbs. The polydactyly may have been due to effects on mesenchymal cells producing localized cell proliferation, whereas syndactyly may have been due to effects on precartilage cells, resulting in excess migration of mesenchymal cells toward the digits, leaving the connective tissue at the interdigital space to develop inadequately.