Evolutionary aspects of “chloroplast-like” trnN and trnH expression in higher-plant mitochondria

Two identical “chloroplast-like” tRNA^Asn genes, trnN1 and trnN2, have been identified in the potato (Solanum tuberosum) mitochondrial genome. The flanking sequences of trnN1 are unrelated to the corresponding authentic potato chloroplast regions, whilst those of trnN2 are very similar to the chloroplast sequences. The trnN1 copy is present in the mitochondrial genome of various plants whereas the second copy, trnN2, is absent from all the other plant genomes studied so far. Interestingly, both trnN copies are expressed in potato mitochondria. Sequences flanking the chloroplast-like tRNA^His gene (trnH), present as a single copy in the potato mitochondrial DNA, are unrelated to the corresponding chloroplast sequences, whereas chloroplast-derived sequences have been maintained in the vicinity of the maize chloroplast-like mitochondrial trnH gene. However, both the potato and the maize trnH are expressed in mitochondria. Received: 10 April / 1 August 1997     

Unusual presentation and clinical variability in Belgian pedigrees with progressive external ophthalmoplegia and multiple deletions of mitochondrial DNA

We studied 14 patients from three unrelated Belgian pedigrees with a familial mitochondrial disorder and multiple deletions of mitochondrial DNA (mtDNA). In one family with an oculopharyngeal presentation there is a clear autosomal dominant inheritance. Progressive external ophthalmoplegia (PEO), “ragged red fibres” (RRF) and multiple deletions of mtDNA are common to all three families. Therefore a diagnosis of autosomal dominant progressive ophthalmoplegia with multiple deletions of mtDNA (adPEO) was made in one family at least. Our data confirm the previous observations that adPEO is a systemic disorder rather than a pure myopathy. In our pedigrees frequently associated features include axonal peripheral neuropathy, dysphagia, psychiatric illness, and sudden death. Mild ataxia, pes cavus and mitral valve prolapse with associated mitral insufficiency also occur. In some cases onset is atypical with neuropathy, adolescent onset myopathy or psychiatric illness. In such cases the common features of PEO and muscle weakness always complete the clinical phenotype later during the course of the disease. Biochemical studies on mitochondrial fractions prepared from one patient's muscle, revealed no abnormalities of respiratory chain enzyme activities.     

Mitochondrial DNA variability detected in a single wheat regenerant involves a rare recombination event across a short repeat

The mitochondrial genome of the selfed progeny of a plant regenerated from long-term somatic tissue culture displays specific structural rearrangements characterized by the appearance of novel restriction fragments. A mitochondrial DNA library was constructed from this selfed progeny in the SalI site of cosmid pHC79 and the novel fragments were subsequently studied. They were shown to arise from reciprocal recombination events involving DNA sequences present in the parental plant. The regions of recombination were sequenced and the nucleotide sequences were aligned with those of the presumptive parental fragments. We characterized an imperfect short repeated DNA sequence, 242 bp long, within which a 7-bb DNA repeat could act as a region of recombination. The use of PCR technology allowed us to show that these fragments were present in both parental plants and tissue cultures as low-abundance sequence arrangements.     

耐药性癫患者脑组织线粒体mMDHNDUFC_2基因表达异常

目的研究耐药性癫患者脑细胞线粒体mMDH、NDUFC2表达,探讨其在耐药性癫癎形成中的作用。方法分别提取48例耐药性癫癎患者、8例非耐药性癫患者及8例对照组脑组织标本的总RNA后,用基因芯片对其进行扫描,随后用荧光定量PCR技术进行验证。结果发现与线粒体功能有关的基因mMDH、NDUFC2在耐药性癫癎中显著下调,荧光定量RT—PCR验证结果与基因芯片一致。结论脑细胞线粒体基因mMDH、NDUFC2表达异常可能通过能量代谢及神经元坏死参与了耐药性癫癎的形成。     

线粒体脑肌病的MRI诊断价值

目的 探讨线粒体脑肌病的脑部MRI表现及其诊断价值。资料与方法 对13例线粒体脑肌病患者的临床、实验室及MRI表现进行回顾性分析。结果 13例头部MRI检查均显示异常，对病变的检出率为100％，主要MRI表现为3类：（1）大脑半球多发单侧或双侧病变（7例），4例呈对称性，病变呈片状等长T1、长T2信号，以一侧或两侧颞顶枕时皮层和皮层下白质最常受累。（2）大脑半球皮层和深部灰质核团同时出现片状等长T1、长T2信号2例。上述两类脑内病变有5例合并脑萎缩。（3）脑实质信号正常，但有脑萎缩4例，其中桥脑、延髓及小脑萎缩3例，大脑半球、脑干、小脑萎缩1例。结论 MRI对线粒体脑肌病的脑内病变显示敏感且准确，对其早期诊断、指导治疗、判断疗效和提示预后具有重要价值。     

内毒素、失血性休克大鼠线粒体质子跨膜转运和H~ -ATP酶的改变

目的研究内毒素、失血性休克大鼠肝线粒体质子跨膜转运和Ｈ＋－ＡＴＰ酶的变化。方法大肠杆菌内毒素休克模型和失血性休克模型。采用荧光探针ＡＣＭＡ测定质子跨膜转运。结果（１）内毒素休克５小时亚线粒体在以ＡＴＰ、ＮＡＤＨ和ｓｕｃｃｉｎａｔｅ为底物时引起的ＡＣＭＡ最大荧光淬灭值显著减少（Ｐ＜０．０５）；最大荧光淬灭时间和半数荧光淬灭时间非常显著延长（Ｐ＜０．０１）。（２）内毒素休克早期，线粒体Ｈ＋－ＡＴＰ酶活性显著升高（Ｐ＜０．０５），晚期非常显著下降。（３）内毒素休克大鼠肝线粒体膜结合ＰＬＡ２、血浆和线粒体ＭＤＡ升高（Ｐ＜０．０５）。（４）失血性休克时Ｈ＋－ＡＴＰ酶和质子转运无显著改变。结论内毒素休克时线粒体跨膜质子转运和Ｈ＋－ＡＴＰ酶活性显著下降，失血性休克时变化不大     

A retrospective study of patients with the hereditary syndrome of congenital cataract,mitochondrial myopathy of heart and skeletal muscle and lactic acidosis

The objectives of this study were to describe the course of two forms of an hereditary syndrome characterised by congenital cataract, mitochondrial myopathy of heart and skeletal muscle and lactic acidosis. We also sought to determine clinical, physicochemical and histopathological data which might allow early distinction between the two forms. We compared the ages at which clinical and physicochemical signs appeared in 16 patients. In 5 patients, enzyme-histochemical and ultrastructural data of skeletal muscle were available and muscle fibre composition analysed morphometrically. In any particular family only one form of the syndrome occurred. Amongst the patients who did not survive (range 14–34 years) 4 patients died in the neonatal period and 7 died at a median age of 23 years. The median age of the survivors was 19 years (range 15–42 years). Outflow obstruction of the left ventricle was noted in four deceased patients at variable times prior to death. The other deceased patients were not examined, but the cause of death was invariably heart failure. In none of the surviving patients was outflow obstruction noted. Enzyme-histochemical and ultrastructural findings were not specific for the course of the disease. In one biopsy, taken at the age of 3.5 months from a patient who survived, strong lipid accumulation was noted. Morphometric analysis showed proliferation of the mitochondria in muscle fibres, which increased during the course of the disease.     

Applications of magnetic resonance spectroscopy to diagnosis and monitoring of mitochondrial disease

Magnetic resonance spectroscopy (MRS) can now be performed on routine high-field clinical magnetic resonance imaging systems. Over the last decade it has provided several useful insights into the pathophysiology of mitochondrial disorders. More recently, the feasibility of applications to clinical diagnosis and monitoring have been demonstrated. Exciting new work suggests that carefully supervised physical conditioning in conjunction with sodium dichloroacetate administration can markedly enhance both biochemical measures of aerobic metabolism and functional performance of patients with mitochondrial myopathies.

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Sommario La risonanza magnetica spettroscopica (MRS) può oggi essere effettuata di routine in apparecchi clinici di risonanza magnetica. Nell'ultima decade essa ha fornito importanti informazioni nella patofisiologia dei disordini mitocondriali. Più recentemente sono state dimostrate le sue possibilità di applicazione nella diagnosi clinica e nel monitoraggio di pazienti neurologici. Nuovi ed interessanti studi suggeriscono che un allenamento attentamente supervisionato in congiunzione con trattamento con dicloroacetato è capace di migliorare i parametri biochimici e la performance di pazienti con miopatie mitocondriali.

     

Self-splicing activity of the mitochondrial group-I introns from Aspergillus nidulans and related introns from other species

The mitochondrial genome of Aspergillus nidulans contains several group-I introns. Each one has been assayed for its ability to self-splice in vitro in the absence of proteins. The intron from the apocytochrome b gene is unusual among subgroup IB4 introns in being able to self-splice, unlike a similar intron from Saccharomyces cerevisiae. The first intron in the cytochrome oxidase subunit-1 gene self-splices but only correctly completes the first step of splicing; cryptic 3′ splice-sites are recognized instead and these are also used at a low frequency in vivo. The highly homologous intron from Podospora anserina completes both steps in vitro. The remaining introns do not self-splice. The correlation between subgroup category, the likely presence of specific tertiary interactions, and self-splicing activity is discussed. Received: 16 May / 25 August 1997     

Mitochondrial genome of the dimorphic zygomycete Mucor racemosus

Mitochondria were isolated from the dimorphic zygomycete Mucor racemosus by differential centrifugation. DNA from the organelles was purified by cesium chloride-ethidium bromide isopycnic centrifugation. Examination of the mitochondrial DNA by electron microscopy revealed a circular chromosome approximately 63.8 kbp in circumference. The chromosome was digested with restriction endonucleases and the resulting DNA fragments were separated by agarose-gel electrophoresis. Electrophoretic mobilities and stoichiometry of the fragments indicated a mixed population of mtDNA molecules each with a size of about 63.4 kbp. Physical maps were constructed from analyses of fragments generated in single and double restriction digests and from the hybridization of fragments to probes for the large and small mitochondrial rRNA genes from Saccharomyces cerevisiae. The Mucor mitochondrial chromosome was found to exist in the form of two flip-flop isomers with inverted repeat sequences encoding both rRNA genes.