Developmental genetic analysis of mouse dysmyelination mutant, quaking.

为了了解共济失调的病因，我们寻找并分析了引起小鼠共济失调表型突变的负责基因。[结果]qkl基因横跨约70kb的基因组区域，由至少10个外显子组成。它产生了六种不同的转录本，理论上，编码五种不同的蛋白质同种异构体。所有转录本共享外显子1至4，而编码外显子和外显子4下游的两个不同的3'- utr被不同地利用。一种同工异构体具有截断的KH结构域，可以作为其他异构体的拮抗剂。这些mRNA似乎编码了一个假定的RNA结合蛋白，其中含有RNA结合活性所需的一个KH基序。我们制作了三种qkl基因敲除小鼠，并对其中两种进行了详细的分析。KO等位基因杂合的小鼠表现正常。然而，与原qk等位基因（=qkv）结合的双杂合子表现出快速震颤，清楚地表明qkl基因是引起震颤突变的原因。此外，与qkv/qkv小鼠相比，这种双杂合子复合小鼠表现出更严重的表型；早期发作的抽搐、步态异常或生长迟缓。在许多方面，这种表型类似于一些人类白质营养不良症。这种严重的表型可能是由于髓鞘形成的过早停止：少突胶质细胞过程不能正确地与轴突相互作用以形成致密的髓鞘。qkl在qkv纯合子中的表达显著降低，在qkv/qklO复合物中的表达更低。因此，髓鞘形成似乎对qkl的剂量很敏感。事实上，当引入含qkl全基因的BAG克隆提高qkl水平时，震颤表型完全恢复。在qk突变体中，PLP、MBP等髓磷脂基因的mRNA表达减少，且这些基因几乎没有蛋白产物。此外，qkl表达的降低改变了MAG、PLP和MBP的mRNA剪接。这些结果表明，qkl是中枢神经系统髓鞘形成的重要调控因子，可能在髓鞘基因的转录后调控中发挥重要作用。少

A responsible gene for mouse mutation showing ataxic phenotype was sought and analyzed in order to understand the etiology of the ataxia. [Results] It was found that qkl gene was spanning about 70 kb of genomic region, and consists of at least 10 exons. It gives rise to six distinct transcripts encoding, theoretically, five different protein isoforms. Exons 1 through 4 are shared by all the transcripts, whereas coding exons and two distinct 3'-UTRs downstream to the exon 4 are differentially utilized. One isoform has a truncated KH domain and may act as an antagonist to the others. These mRNA appear to encode a putative RNA binding protein containing one KH motif required for RNA binding activity. We have made three lines of qkl knockout mouse, of which two were analyzed in detail. Mice heterozygous for the KO allele behave normally. However, double heterozygotes in combination with the original qk allele (=qkv) showed rapid tremor, clearly demonstrating that qkl gene is the responsibl … More e gene for the quaking mutation. Furthermore, this double heterozygote compound mice showed even more severe phenotype compared to the qkv/qkv mice ; early onset of convulsion, gait abnormality, or growth retardation. In many ways this phenotype resembles that of some of the human leukodystrophies. This severe phenotype is probably due to premature arrest of myelination : the oligodendrocyte processes fail to properly interact with the axons to form compacted myelin. qkl expression was found to be significantly reduced in qkv homozygotes and was even less in the compound, qkv/qklO.Thus myelination appears to be sensitive to the dosage of qkl. In fact, when qkl level is increased by introduction of BAG clone containing the whole qkl gene, the tremor phenotype was completely recovered. mRNA expression of other myelin genes including PLP, MBP were reduced in the qk mutants, and there were almost no protein products for these genes. Furthermore, mRNA splicing of MAG, PLP and probably MBP is altered by the reduced qkl expression. These results sugegst that qkl is an essential regulator of myelination in CNS, and probably plays important role in post-transcriptional regulation of the myelin genes. Less