| Objective: Cleft of palate (CP) is one of the most common birth defects in humans, which brings huge suffering to patients and their families. Though People have been looking forward to finding the reason of CP, it is hard to tell the exact mechanism because many factors are involved. So it is important to establish a CP model in the process of etiology studying. The palate is sensitive to many teratogenic drugs because the development of palate is very complicated. Retinoic acid (RA) is a kind of drug with distinct teratogenic action. Now RA is used to therapy skin disease and leucocythemia since it can induce cell differentiation. It is known that RA can induce cell apoptosis, but the data are all about tumor cells and it has not been confirmed whether RA has a similar effect on embryonic cells especially on medial edge epithelial (MEE) cells. Bcl-2 has been thought to be a kind of protooncogene, and it can restrain cell apoptosis. It has been reported that RA can down-regulate the express of Bcl-2 in tumor tissue, which results in cell apoptosis. But little is known about what effect Bcl-2 has on palate development and what effect RA has on Bcl-2 in palate development. The present study is to establish CP model induced by RA, and to observe expression level of Bcl-2 in MEE cells, and then to analyze the effects RA has on Bcl-2 and reach the conclusion of teratogenic mechanism by RA. Method: Female C57BL/6J mice about 10 weeks of age were housed overnight with male C57BL/6J mice and checked for vaginal plugs the next morning, which was designated as day 0 of gestation, totally 36 pregnant females were obtained. All the pregnant mice were randomly divided into two groups: control group (n=12) and RA-treated group (n=24). Pregnant mice in RA-treated group received by gavage a single dose of RA at 100mg/kg body weight at 1 P.M. on GD10. Pregnant mice in control group received 0.2ml corn oil at the same time. 12 Pregnant mice in RA-treated group were killed in GD 16 to observe the malformation situation of the fetuses, and the rest of them were killed on GD13, GD13.5, GD14, GD14.5, GD15 and GD16 for histological and immunohistochemical study followed. 6 Pregnant mice in control group were killed in GD 16 to observe the development situation of the fetuses, and the rest of them were killed on GD13, GD13.5, GD14, GD14.5, GD15 and GD16 for histological and immunohistochemical study followed. In horizontal stage of palate development, the expression level of Bcl-2 in MEE cells was compared between control group and RA-treated group to make sure what kind of effect RA had on Bcl-2 and to make it clear how RA can result in CP. Result: 1.Of all the 79 fetuses (77 living and 2 dead) in RA-treated group 47 were found to get CP, the CP rate is 59.5%, and no fetus with CP was observed in control group (38 fetuses all living). 2.The expression of Bcl-2 in MEE cells in RA-treated group was lower than in control group in horizontal stage of palate development. Conclusion: 1.RA can induce CP in C57BL/6J mice, and the 100mg/kg body weight dose is safe and effective. 2.In horizontal stage of palate development RA can down-regulate the expression of Bcl-2 in MEE cells, which induces MEE cells apoptosisearlier, resulting in CP in the end.
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