Helmken C, Wetter A, Rudnik-Schöneborn S, Liehr T, Zerres K, Wirth B
Institute of Human Genetics, Bonn, Germany.
Eur J Hum Genet. 2000 Jul;8(7):493-9. doi: 10.1038/sj.ejhg.5200479.
The survival motor neuron (SMN) protein and the SMN interacting protein 1 (SIP1) are part of a 300 kD protein complex with a crucial role in snRNP biogenesis and pre-mRNA splicing. Both proteins are colocalised in nuclear structures called gems and in the cytoplasm. Approximately 96% of patients with autosomal recessive spinal muscular atrophy (SMA) show mutations in the SMN1 gene, while about 4% fail to show any mutation, despite a typical SMA phenotype. Additionally, sibs with identical 5q13 homologs and homozygous absence of SMN1 can show variable phenotypes which suggest that SMA is modified by other, yet unknown factors. Since both genes, SMN1 and SIP1, belong to the same pathway and are part of the same protein complex, it is obvious to ask whether mutations within SIP1 are responsible for both the phenotypic variability and the appearance of non-SMN mutated SMA patients. First, we identified the chromosomal location of SIP1 and assigned it to chromosomal region 14q13-q21 by fluorescence in situ hybridisation. No SMA related disorder has yet been assigned to this chromosomal region. Next, we determined the exon-intron structure of the SIP1 gene which encompasses 10 exons and identified five transcription isoforms. We sequenced either RT-PCR products or genomic DNA covering the complete coding region from 23 typical SMA patients who had failed to show any SMN1 mutation. No mutation and no polymorphism was found within SIP1. Additionally, we sequenced RT-PCR products or genomic fragments of the entire SIP1 coding region from 26 sibs of 11 SMA families with identical genotypes (delta7SMN/delta7SMN or delta7SMN/other mutation) but different phenotypes and again no mutation was found. Finally, we performed quantitative analysis of RT-PCR products from the same 26 sibs. No difference in expression level of the five isoforms among phenotypically variable sibs was observed. Based on these data, we suggest that neither the phenotypic variability nor the 5q-unlinked SMA are caused by mutations within SIP1.
生存运动神经元（SMN）蛋白和SMN相互作用蛋白1（SIP1）是一个300 kD蛋白复合物的组成部分，该复合物在小核核糖核蛋白（snRNP）生物合成和前体mRNA剪接中起关键作用。这两种蛋白都共定位于称为宝石小体的核结构和细胞质中。约96%的常染色体隐性脊髓性肌萎缩症（SMA）患者在SMN1基因中存在突变，而约4%的患者尽管具有典型的SMA表型，但未显示任何突变。此外，具有相同5q13同源物且SMN1纯合缺失的同胞可表现出可变的表型，这表明SMA受到其他未知因素的影响。由于SMN1和SIP1这两个基因属于同一途径且是同一蛋白复合物的组成部分，因此很自然会问SIP1内的突变是否导致了表型变异性以及非SMN突变的SMA患者的出现。首先，我们确定了SIP1的染色体定位，并通过荧光原位杂交将其定位到染色体区域14q13 - q21。尚未有与SMA相关的疾病被定位到该染色体区域。接下来，我们确定了SIP1基因的外显子 - 内含子结构，该基因包含10个外显子，并鉴定出五种转录异构体。我们对23名未显示任何SMN1突变的典型SMA患者的RT - PCR产物或覆盖完整编码区的基因组DNA进行了测序。在SIP1内未发现突变和多态性。此外，我们对11个具有相同基因型（delta7SMN/delta7SMN或delta7SMN/其他突变）但表型不同的SMA家族的26名同胞的整个SIP1编码区的RT - PCR产物或基因组片段进行了测序，同样未发现突变。最后，我们对相同的26名同胞的RT - PCR产物进行了定量分析。在表型可变的同胞中，未观察到五种异构体的表达水平存在差异。基于这些数据，我们认为表型变异性和5q非连锁SMA均不是由SIP1内的突变引起的。
