| Research Abstract |
To identify the candidate chromosome and to detect the region that included causative gene(s) causing absence of the third molars in EL mice, all chromosomes were examined by the individual genotyping of the F2 (EL x MSM) mice. The gene causing absence of the third molars in EL mice was mapped on the region from D3Mit141 to D3Mit290 (x 2 =22.8, p<0.0001). Gene such as Lef1, Egf and CSF-1 that have been shown to be associated with tooth development, are located in this region. To determine whether the congenital absence of the third molars in EL mice occurs due to failure of initiation or subsequent arrest in development, I analyzed H ＆ E stained serial sagittal sections of normal and EL mice. Compared to normal mice, third molars development in EL mice progressed from early cap to cap stage from P3 to P5, but did not progress beyond the cap stage and the developing tooth gradually regressed to complete elimination. I examined whether the absence of the third molars in EL mice occurred due to lack of Lef1 expression. Lef1 expression in EL mice was not different from that observed in normal mice. From these data, it was concluded that Lef1 is not a likely candidate gene involved in the congenital absence of the third molars in EL mice. On the other hand, the candidate chromosomal analysis was also performed on genetic crosses using two strains of mice, EL and DDY. The highest scores were found at D13Mit78 and D13Mit35 markers (x2 =11.8, p<0.01). Based on these results, there was a possibility that a candidate gene causing absence of the third molars might be existed on mouse chromosome 3.
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