AMOLECULAR BIOLOGICAL STUDY FOR THE SPONTANEOUSLY EPILEPTIC RATS

采用定位克隆的方法，对自发性癫痫大鼠癫痫合并自发性脑病的致病基因--震颤(TM)和震颤(Zi)突变基因进行了研究。遗传连锁分析表明，Tm和Zi基因分别与突触小泡中编码完整膜蛋白的SYB2基因和第3染色体上的PrNP基因紧密连锁，使它们成为突变基因的候选基因。TRM大鼠品系(TM纯合子)的SYB2基因和ZI大鼠品系(ZI纯合子)PRNP基因外显子2的基因组DNA序列与对照品系WTC相同。此外，在TRM、ZI和WTC脑组织的Northern杂交分析中，SYB2和PRNP基因的表达没有差异，表明SYB2和PRNP基因分别不是TM和PRNP基因。尽管有这一发现，我们仍希望保留这两个基因作为候选基因，因为SYB2和PRNP基因的生物学功能尚不完全清楚。Tm和Zi基因在大鼠染色体10q24和3q35上的分配将是克隆Tm和Zi基因的第一步。

A positional cloning approach is taken for the study of tremor (TM) and zitter (ZI) mutant genes, causative genes for epilepsy with spongiform encephalopathy in spontaneously epileptic rat (SER, a homozygote for zitter (ZI) and tremor (TM) mutant genes). Genetic linkage analysys revealed that the TM and ZI genes were tightly linked to the synaptobrevin-2 (SYB2) gene, coding an integral membrane protein in synaptic vesicles, on chromosome 10, and the prion protein (PRNP) gene, coding a key membrane molecule of prion diseases, on chromosome 3, respectively, making them candidates for the mutant genes. The genomic DNA sequence of the SYB2 gene of the TRM rat strain (homozygote for the TM) and the exon 2 of the PRNP gene of the ZI rat strain (homozygote for the ZI) were identical to those of a control strain WTC.In addition, no difference was detected for expression of the SYB2 and the PRNP genes on the Northern blot analyzes of TRM, ZI and WTC brain, suggesting that the SYB2 and PRNP genes are not the TM and the ZI, respectively. Despite this finding, we would like to retain the two genes as candidates, since the biological functions of the SYB2 and PRNP genes are not yet perfectly understood. The assignments of the TM and ZI genes to rat chromosome 10q24 and 3q35 will be the first step towards the cloning of the TM and ZI genes.