The Preliminary Study On The Mechanism Of Craniomaxillofacial Dysplasia Induced By The Overexpression Of Fgf18 In Cranial Neural Crest Cells In Mice

Cleft palate is one of the most common congenital defects in the craniomaxillofacial region.It has complicated pathogenesis and affects patients’ swallowing function,phonetic function and the germination and arrangement of the teeth.The previous studies found that there are several different signaling pathways which play a crucial role during the development of palatal shelf,including FGF signaling pathway,WNT signaling pathway,SHH signaling pathway and BMP signaling pathway.In recent years,genome-wide association studies of cleft lip and palate in humans have shown disease association with the FGF18 which is one of FGF family members.In order to research the mechanism of FGF18 on cleft palate in humans,we constructed Wntl-Cre;pMes-Fgf18 mice and studied the effects of Fgf18 on the craniomaxillofacial development of mice with overexpression of Fgf18 in the mesenchyme.Firstly,we successfully constructed pMes-Fgfl8 mice by prokaryotic microinjection technology.And the mice with overexpression of Fgf18 in the mesenchyme were obtained by crossing pMes-Fgf18 mice with Wnll-Cre mice.Afterwards,we found that Wnt1-Cre;pMes-Fgf18 mice had a cleft palate and died about 24 hours after birth.Secondly,we tested the cell proliferation rate of palatal shelves and cultured palatal shelves in vitro.And it indicates that the cleft palate in Wntl-Cre;pMes-Fgf18 mice has no direct connection with palatal shelves.Next,we measured the height of tongues and stained the bone of heads in Wntl-Cre;pMes-Fgfl8 mice,and it shown that the tongues abnormally heighten and mandibles shorten.So the cleft palate in Wntl-Cre;pMes-Fgf18 mouse is caused by the abnormal growth of both tongue and mandible.Finally,we examined the expression of four intracellular transduciton pathways in the FGF signaling network by immunohistochemistry technology.The conclusion dedicates that Fgf18 may activate the Erkl/2 pathway and P38 pathway to increase the cell proliferation rate of the tongue and mandible in Wnt1-Cre;pMes-Fgf18 mouse.So the tongue unusually heightens,and the mandible becomes hypertrophic and shorter.Then the mandible cannot normally extend and grow down,which causes the tongue cannot fall into oral cavity but occupy much more space of the oral cavity.Therefore both the towering tongue and curtate mandible hinder the palatal shelf elevation,and it eventually leads to cleft palate in Wntl-Cre,pMes-Fgf18 mouse.This phenotype in mice resembles human Pierre Robin Syndrome,so deep understanding of the relationship between Fgf18 and cleft palate can greatly promote the clinical medicine research of cleft lip and palate in humans.