Immunohistochemical Study on Early Odontogenesis in Hsp70 Knock-out Mice Fetuses Exposed by Maternal Hyperthermia

Yoo, Jin Young; Shim, Yun Tak; Lee, Jin; Ahn, Sangil; Kim, Jong Ryong; Kim, Won Kyu

Abstract

To investigate the effects of maternal hyperthermia on early odontogenesis,pregnant Hsp70 knock-out and wild type mice at embryonic day (ED)8.5 were immersed in a 43 degrees C water bath until their core body temperature reached that temperature,and then given a further 5 min of hyperthermia.Untreated Hsp70 WT mice fetuses were used as the control group.Fetuses were collected at EDs 13.5,15.5 and 17.5.Developing teeth in the mandible were processed for histological and immunohistochemical studies.Tissue sections were immunostained for FGF-8 and FGF -4 and observed using light microscopy.In the controls, FGF-8 immunolocalization was observed in cells within the dental lamina and in apically located dental epithelium at ED 13.5.However,a few cells were immunopositive in the heat shocked (HS)group.At EDs 15.5 and 17.5 of the control group,the basal lamina adjacent to the dental pulp showed positive immunostaining.In contrast,most of the dental epithelium was immunopositive at ED 15.5 in the HS group and inner and outer dental epithelial cells were continuously immunopositive by ED 17.5.FGF-4 immunolocalization was found in apical dental epithelium at ED 13.3 in the control group,but no such positive reaction was observed in the HS group.At ED 15.5 in the controls,basal lamina and dental epithelium near the cervical loop were immunopositive.In contrast,early cap-stage teeth had cells near the mouth of the dental bud and cervical loop that were immunopositive to FGF-4 in the HS group.In controls at ED 17.5,cells near the future secondary enamel knot were immunopositive,whereas most of the dental epithelium except for cells in the mouth of the dental lamina was negative in the HS group.Thus,maternal hyperthermia may inhibit normal odontogenesis through sustained production of FGF-8 and downregulation of FGF-4.