Studies on maxillofacial defects in fetal mice induced by methyl mercury chloride

Eighteen-day-old mouse embryos sequentialy treated with methyl mercury chloride (MMC) and tiopronin (TP, used to prevent cleft palate induced by MMC) on day 10 of gestation were examined for the presence of variant rugae. Nontreated mouse embryos served as controls.Variant rugae were classified into seven types (supernumerary, division, maldirection, bifurcation, shortness, cross and fusion). They were observed in MMC-treated embryos, and supernumerary was most frequent type. Division and shortness were ranked next. Variant rugae were also observed in nontreated embryos in low frequencies, although there were some differences between the control and MMC+TP treated embryos in the distribution of supernumerary rugae. The division in the MMC+TP group was characteristically found at the middle of the 2nd or 3 rd rugae. Division of the middle of the 2nd or 3 rd rugae may suggest teratogenicity.