Alternative splicing of human G6PD messenger RNA in K562 cells but not in cultured erythroblasts

Abstract. The biochemical properties of glucose-6-phosphate dehydrogenase (G6PD) vary in different tissues, and different protein isoforms of the enzyme have been described. Alternative splicing of G6PD intron VII has been detected in transformed lympho-blasts, granulocytes and spermatocytes; the function of this mRNA species is still unknown. We developed a PCR for detecting alternatively spliced G6PD mRNA in K562 and in erythroblasts at different stage of maturation obtained from human peripheral BFU-E in order to evaluate a possible physiological role during erythroid maturation. Trace events of alternative splicing of G6PD intron VII sequences were observed in K562 cells but not in BFU-E-derived erythroid precursors; we consider this phenoemenon a non-functional activity in the cells analysed.     

葡萄糖-6-磷酸脱氢酶eDNA1311C→T复合11内含子93T→C突变

目的 探讨葡萄糖-6-磷酸脱氢酶(G6PD)基因eDNA1311C→T复合11内含子93T→C的突变与G6PD缺乏的关系。方法 运用硝基四氮唑蓝纸片法筛查G6PD患，以定量法确诊，运用PCR-SSCP筛查11外显子异常的标本，以突变特异性扩增系统(ARMS)法鉴定1311C→T突变，DNA直接测序1311突变标本的11外显子和11内含子。结果 在12例1311突变的标本中，在11内含子的93位均发现有T→C突变。结论 eDNA1311C→T突变同时合并11内含子的93位T→C突变可能是G6PD缺乏患酶活性降低的原因。     

深圳盐田地区G6PD缺乏症发病率与基因突变调查

目的了解深圳盐田区G6PD缺乏症的流行现状、基因突变谱,探讨其诊断方法及流程。方法采用G6PD／6PGD定量比值法检测G6PD酶活性,反向点杂交及DNA测序检测G6PD基因突变。结果该区G6PD基因突变人群携带率为4．50％,基因突变以C．1388G〉A、c．1376G〉T和c．95A〉G为主。结论该区为包含其他罕见或少见突变类型的复杂G6PD基因突变谱,基于G6PD酶活性的表型筛查有明显的漏检率,基因检测结合表型筛查可大大提高诊断准确性与可靠性。     

福建畲族葡萄糖-6-磷酸脱氢酶基因突变型

目的研究福建畲族葡萄糖-6-磷酸脱氢酶（G6PD）基因突变型特点，调查其G6PD缺乏症发生率及基因频率。方法用硝基四氮唑蓝（NBT）纸片法进行G6PD缺乏症定性筛查，用突变特异性扩增系统、错配碱基PCR介导酶切位点／限制性内切酶图谱分析、聚合酶链反应．单链构象多态性分析（PCR-SSCP）和DNA测序进行基因突变型鉴定结果在1820名青水畲族和764名穆云畲族人中，分别发现101例和104例酶活性异常，两地的致病基因频率分别为0．0607和0．1706。在穆云乡54例纯畲族血缘的样本中，共检出nt1376G→T突变38例、nt1388G→A突变12例、nt95A→G突变6例，三种基因突变型分别占70．3％，18．5％和11．1％；并发现1例nt1376G→T复合nt95A→G突变、1例nt1376G→T复合nt1388G→A突变。在青水畲族中发现6例nt1024C→T突变，占8．6％；发现1例392G→T突变，结论①nt1376G→T、nt1388G→A是幅建畲族中主要的基因突变型，中华民族具有共同的G6PD基因突变型，因而可能源于共同的祖先。②在畲族人群中发现nt1376G→T、nt1388G→A、nt95A→G、nt1024C→T和nt392G→T 5种基因突变型。③发现nt1376G→T复合nt95A→G突变、nt1376G→T复合nt1388G→A突变④nt95A→G是穆云畲族中另一种常见的基因突变型；1024C→T是青水畲族中常见的一种G6PD基因突变型。⑤明确青水畲族中G6PD基因频率为0．0607，穆云畲族中为0．1706，为上述地区G6PD缺乏症的防治提供决策参考。     

葡萄糖—6—磷酸脱氢酶基因突变与NlaⅢ多态性位点连锁关系 …

目的 研究葡萄糖－６－磷酸脱氢酶（Ｇ６ＰＤ）基因内的特定多态性位点与Ｇ６ＰＤ缺陷基因突变的连锁关系,进一步揭示Ｇ６ＰＤ缺陷症分子病理学本质及Ｇ６ＰＤ基因斩多态性位点在人类学和人类迁移研究中的意义。方法 应用变性梯度凝胶电泳和ＤＮＡ点杂交技术检测５４例Ｇ６ＰＤ活性正常男性对照者及６６例男笥Ｇ６ＰＤ缺陷者Ｇ６ＰＤ基因中距离１２外显子上游１３ｂｐ的ＮｌａⅢ多态性位点。     

A polymorphic marker for the human cathepsin B gene

Human cathepsin B (CTSB) is a proteolytic enzyme implicated in tumor invasion and metastasis. We describe a PCR-based polymorphic marker for this gene comprising two amplimers differing in length by 19 consecutive nucleotides in intron 7, near the exon 8 splice acceptor site, identifying two gene alleles (A and B). Allele frequencies were 0.614 for A and 0.386 for the B allele, with an observed heterozygosity of 0.457 in a cohort of 70 non-related Australian blood donors. One additional nucleotide difference was also revealed through sequencing. The human CTSB gene is located on chromosome 8 and the alleles described here can potentially be used as markers in linkage and association studies of cancers and other diseases.     

Hyperinsulinemia is associated with altered insulin receptor mRNA splicing in muscle of the spontaneously obese diabetic rhesus monkey.

The human insulin receptor has two isoforms derived from alternative splicing of exon 11 of the insulin receptor gene. The type B (containing exon 11, or exon 11+) isoform binds insulin with twofold lower affinity than the type A (lacking exon 11, or exon 11-) isoform. In efforts to resolve the controversy over whether altered splicing is involved in the development of insulin resistance and non-insulin-dependent diabetes mellitus (NIDDM), the spontaneously obese diabetic rhesus monkey, a unique model that is extraordinarily similar to human NIDDM, was used. Cross-sectional studies of insulin receptor mRNA splicing variants in vastus lateralis muscle were performed on 19 rhesus monkeys. When monkeys were divided into four groups based upon the known stages of progression to NIDDM: normal (normoglycemic/normoinsulinemic), prediabetic (normoglycemic/hyperinsulinemic), early NIDDM (hyperglycemic/hyperinsulinemic), and late NIDDM (hyperglycemic/hypoinsulinemic), both hyperinsulinemic groups had significantly higher percentages of the exon 11- mRNA splicing variant compared to the normal (74.8 +/- 1.7 vs 59.0 +/- 2.3%; P < 0.005) and late NIDDM groups (74.8 +/- 1.7 vs 64.2 +/- 3.9%; P < 0.05). Our findings provide the first direct evidence linking hyperinsulinemia to alterations in insulin receptor mRNA splicing, and suggest that alterations of insulin receptor mRNA splicing in muscle is an early molecular marker that may play an important role in NIDDM.     

Identification of amino acids at the junction of exons 3 and 7 that are used for the generation of glycosylation-related human CD45RO and CD45RO-like antigen specificities

The CD45 transmembrane protein tyrosine phosphatase plays an essential role in lymphocyte activation. In humans, CD45 is composed of five isoforms that are generated by alternative splicing of three exons of a common precursor mRNA. Expression of the smallest molecular mass 180-kD CD45 isoform (CD45-O) results from splicing out of exons 4(A), 5(B), and 6(C), which encode peptide regions near the NH2 terminus, and is regulated during T cell maturation and activation. Two monoclonal antibodies (mAb), UCHL1 (anti-CD45RO) and A6 (anti-CD45RO-like), were studied that selectively bind to murine transfectant cells expressing the human CD45-O isoform. The anti-CD45RO-like A6 mAb, but not the anti- CD45RO UCHL1 mAb, also weakly reacted with transfectant cells expressing the human CD45 isoforms that contained exons 4 and 5(AB), or exon 5(B) encoded sequences. The structural basis of the antigen specificities of these two different human anti-CD45RO mAbs was investigated at the molecular level by using potential glycosylation- defective CD45-O isoform variants containing amino acid substitutions at the junction of exons 3 and 7. Replacement of the threonine residue at position 8 (last amino acid encoded in exon 3 and a putative O- linked carbohydrate anchorage site) by an alanine, completely abrogated the reactivity of the UCHL1 mAb, but did not affect that of the A6 mAb. Conversely, replacement of either the asparagine at position 174 or the serine at position 176 (the first two putative carbohydrate anchorage sites in exon 7) by alanine, abrogated the reactivity of the A6 mAb, but not that of the UCHL1 mAb. Both the UCHL1 and A6 epitopes were dependent on the presence of O-linked carbohydrates; and the UCHL1, but not the A6 epitope, was dependent on the presence of sialic acid. These results demonstrate a pivotal role for the amino acids encoded at the junction of exons 3 and 7 for the generation of glycosylation-related CD45RO epitopes that are expressed in a cell lineage- and activation- regulated fashion.     

Synthetic intron improves transduction efficiency of trans-splicing adeno-associated viral vectors

Trans-splicing adeno-associated viral (AAV) vectors hold great promise in many gene therapy applications. We have shown that rational selection of the gene-splitting site in a therapeutic target gene can lead to extremely efficient trans-splicing vectors [Lai, Y., Yue, Y., Liu, M., Ghosh, A., Engelhardt, J.F., Chamberlain, J.S., and Duan, D. (2005). Nat. Biotechnol. 23, 1435-1439]. Our original strategy requires the screening of endogenous introns that are capable of overcoming the mRNA accumulation barrier. To further develop transsplicing vectors, we have tested whether the use of a generic synthetic intron can bypass the labor-intensive intron-screening process. Two previously characterized exon/intron/exon junctions (60/60/61 and 63/63/64, respectively) in the 6 kb minidystrophin gene were used as templates to represent highly efficient (60/60/61) and relatively poor (63/63/64) gene-splitting sites. We compared RNA production from the reconstituted viral genome and transduction efficiency of the trans-splicing vectors in dystrophin-null mdx mouse skeletal muscle. Our results suggest that a synthetic intron can successfully overcome the mRNA accumulation barrier at the exon 63/64 junction. Furthermore, when the gene was split at the exon 63/64 junction, the synthetic intronbased vectors performed better than the endogenous intron-based vectors. When the gene was split at the exon 60/61 junction, we observed only nominal improvement in mRNA production. Nevertheless, vectors based on the exon 60/61 junction remain the best set in transduction efficiency. Taken together, our results suggest that optimizing intron sequence may boost the transduction efficiency of trans-splicing AAV vectors.     

贵州三都水族居民葡萄糖-6-磷酸脱氢酶缺乏症基因突变研究

为了了解贵州省少数民族居民葡萄糖-6-磷酸脱氢酶(glucose-6-phosphate dehydrogenase，G6PD)缺乏症的发病率、基因突变类型特点及分布特征，进一步从分子水平揭示G6PD基因突变的异质性，对贵州省三都水族自治县1090名当地水族居民采用噻唑蓝定性法、G6PD／6PGD活性比值法进行G6PD缺乏症的筛查，再经错配引物介导的聚合酶链反应/限制性酶切分析法检测中国人中最常见的3种G6PD基因突变型：1376G→T、1388G→A、95A→G。结果表明：在受检的1090人中，共检出G6PD缺乏症98例，检出率8．99％，在G6PD缺乏症中检出最常见的3种G6PD基因突变型：1376G→T24例；1388G→A12例；95A→G9例；并在国内首次检出1376G→T、95A→G复合型突变1例。1376G→T突变频率为0．245；1388G→A突变频率为0．122；95A→G突变频率为0．092。结论：1376G→T、1388G→A、95A→G为贵州省三都水族居民的常见G6PD突变型，这个结果提示贵州三都水族与中国其它少数民族在起源上可能有共同的渊源。     

Dysbindin-1, a Schizophrenia-Related Protein, Functionally Interacts with the DNA- Dependent Protein Kinase Complex in an Isoform-Dependent Manner

DTNBP1 has been recognized as a schizophrenia susceptible gene, and its protein product, dysbindin-1, is down-regulated in the brains of schizophrenic patients. However, little is known about the physiological role of dysbindin-1 in the central nervous system. We hypothesized that disruption of dysbindin-1 with unidentified proteins could contribute to pathogenesis and the symptoms of schizophrenia. GST pull-down from human neuroblastoma lysates showed an association of dysbindin-1 with the DNA-dependent protein kinase (DNA-PK) complex. The DNA-PK complex interacts only with splice isoforms A and B, but not with C. We found that isoforms A and B localized in nucleus, where the kinase complex exist, whereas the isoform C was found exclusively in cytosol. Furthermore, results of phosphorylation assay suggest that the DNA-PK complex phosphorylated dysbindin-1 isoforms A and B in cells. These observations suggest that DNA-PK regulates the dysbindin-1 isoforms A and B by phosphorylation in nucleus. Isoform C does not contain exons from 1 to 6. Since schizophrenia-related single nucleotide polymorphisms (SNPs) occur in these introns between exon 1 and exon 6, we suggest that these SNPs might affect splicing of DTNBP1, which leads to impairment of the functional interaction between dysbindin-1 and DNA-PK in schizophrenic patients.     

Jk(a-b-)表型分子机理的初步研究

目的　研究Jk(a-b - )表型的分子机理。方法　在标准血清学鉴定的基础上 ,对Jk(a -b - )表型进行第 4～ 11外显子及部分内含子DNA扩增 ,PCR产物经割胶纯化后直接进行测序分析。结果　Jk(a -b - )表型在第 5内含子 3’端拼接接受位点G突变为A ;第 3内含子 3’端第 78位A→G ;第 8内含子 5’端第 84位C→T ;外显子第 5 88位A→G(第 7外显子内 ) ;第 838位G→A(第 9外显子内 )。其中第 5内含子 3’端拼接接受位点G突变为A导致转录后外显子 6的缺失。结论　第 5内含子 3’端拼接接受位点的碱基G突变为A可能是Jk(a -b - )表型的分子遗传机理之一。