임신 중 고열이 Hsp70 KO 생쥐의 초기 치아발생에서 FGF-8과 BMP-4의 발현에 미치는 영향
The Effects of Hyperthermia on FGF-8 and BMP-4 Expression during Early Odontogenesis in Hsp70 Knock-out Mice Fetuses
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치아의 초기발생과정에는 여러 신호전달물질이 치아판에서 발현되어 치아 중간엽을 유도한다. 이러한 여 러 물질 중 FGF-8은 초기 치아상피에서 발현하며 BMP-4는 치아상피의 유도에 의해 치아 중간엽에서 발현되어 치아의 형태발생을 조절한다. 한편, 임신 중 고열은 조직 및 기관의 정상발생을 방해하여, 심한 경우 선천성기형을 유발하는 요인의 하나로 인정받고 있다. 임신 중 고열에 노출되는 경우 보호 기전으로서 열충격단백질이 분비되 며, 이 중 Hsp 70이 중추적인 역할을 하는 것으로 알려져 있다. 이에 본 연구에서는 유전자 변형기법을 이용하여 제작된 Hsp70 KO 생쥐를 실험동물로 사용하여 치아 초기발생과정에 중요한 역할을 수행하는 FGF-8 와 BMP-4의 발현양상을 면역조직화학법으로 연구하고자 하였다. 실험군은 고열에 노출된 Hsp70 KO 생쥐 태아를, 대조군으로 고열에 노출되지 않은 Hsp70 KO 생쥐 태아를 사 용하였다. 실험군은 임신 제8일에 43C 수조에서 5분간 열충격을 주었고, 대조군에는 아무런 조작도 가하지 않았 다. 임신 제13, 15, 17일에 자궁 속의 태아를 적출한 후 머리를 절취하였다. 머리에서 아래턱을 절취하여 통상적인 조직 제작법에 따라 파라핀에 포매한 후 조직표본을 제작하여 FGF-8 및 BMP-4 면역조직화학염색을 시행하고 광 학현미경으로 관찰하여 다음과 같은 결과를 얻었다. 임신 시기에 따른 치아의 발생은 실험군이 대조군보다 지연되어 있었다. 치아의 FGF-8은 대조군의 경우 발생 이 진행됨에 따라 치아상피에서 발현이 감소되었지만 실험군에서는 지속적으로 발현하였다. BMP-4는 대조군에서 는 상아질모세포로 분화할 치아속질 중간엽세포에서 양성반응이 나타났지만 실험군의 중간엽세포는 반응을 보이 지 않았다. 이상의 결과에서 임신 중 고열은 치아판 성장을 억제하고, 치아상피에서 FGF-8의 발현을 지연시키며, 치아속질 내 중간엽세포에서 BMP-4 발현을 저해하여 치아의 정상적인 발생 중 나타나는 상피-중간엽 상호작용을 방해하는 것으로 생각된다.
Abstract
During early tooth development, multiple signaling molecules are expressed in the dental lamina and induce the dental mesenchyme. One signal, FGF-8, is expressed in the early dental epithelium, another one, BMP-4, has been shown to induce morphologic changes in dental mesenchyme. Meanwhile, hyperthermic exposure during pregnancy, as one of teratogens, is known to disturbe normal development and induce several congenital anomalies. This study is aimed to investigate the effects of maternal hyperthermia on the expressions of FGF-8 and BMP-4 in early odontogenesis. The pregnant Hsp70 knock-out at gestational day 8 were immersed in 43C water bath until their body core temperature reached at 43C. Thereafter, pregnant mice were given more 5 minutes hyperthermic exposure. Heat-untreated Hsp70 KO mice fetuses were used as the control group. Fetuses were collected at embryonic day (ED) 13, 15 and 17. Developing tooth in the mandible was processed for immunohistochemical study. Tissue sections were immunostained for FGF-8 and BMP-4 and observed with light microscope. The obtained results were as follows: Tooth development in the heat shocked (HS) group is delayed rather than the control group in the given developmental period. FGF-8 immunolocalization in control group at ED 13 was gradually decreased compared to the HS group which showed continuously positive immunoreaction. BMP-4 immunolocalization was detected in dental mesenchyme, however, there was no positive immunoreaction found in HS group. These results suggest that maternal hyperthermia should induce the early odontogenesis, delay the expression of FGF-8 in dental epithelium, and disturbe the expression of BMP-4 in dental mesenchyme. Consequently, hyperthermic exposure during pregnancy affects epithelial-mesenchymal interactions.
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