Drosophila neuroblasts are a model system for studying stem cell self-renewal and the establishment of cortical polarity. Larval neuroblasts generate a large apical self-renewing neuroblast, and a ...small basal cell that differentiates. We performed a genetic screen to identify regulators of neuroblast self-renewal, and identified a mutation in sgt1 (suppressor-of-G2-allele-of-skp1) that had fewer neuroblasts. We found that sgt1 neuroblasts have two polarity phenotypes: failure to establish apical cortical polarity at prophase, and lack of cortical Scribble localization throughout the cell cycle. Apical cortical polarity was partially restored at metaphase by a microtubule-induced cortical polarity pathway. Double mutants lacking Sgt1 and Pins (a microtubule-induced polarity pathway component) resulted in neuroblasts without detectable cortical polarity and formation of “neuroblast tumors.” Mutants in hsp83 (encoding the predicted Sgt1-binding protein Hsp90), LKB1, or AMPKα all show similar prophase apical cortical polarity defects (but no Scribble phenotype), and activated AMPKα rescued the sgt1 mutant phenotype. We propose that an Sgt1/Hsp90–LKB1–AMPK pathway acts redundantly with a microtubule-induced polarity pathway to generate neuroblast cortical polarity, and the absence of neuroblast cortical polarity can produce neuroblast tumors.
► We used a novel sequence-capture genomic method to identify sgt1. ► Sgt1 is required for Bazooka localization in neuroblasts. ► Sgt1 is required for Scribble localization in neuroblasts. ► Sgt1 acts at the top of an Hsp90–LKB1–AMPK polarity pathway.
Mitochondrial diseases are among the most common and most complex of all inherited genetic diseases. The involvement of both the mitochondrial and nuclear genome presents unique challenges, but ...despite this there have been some remarkable advances in our knowledge of mitochondrial diseases over the past few years. A greater understanding of mitochondrial genetics has led to improved diagnosis as well as novel ways to prevent transmission of severe mitochondrial disease. These and other advances have had a major impact on patient care, but considerable challenges remain, particularly in the areas of therapies for those patients manifesting clinical symptoms associated with mitochondrial dysfunction and the tissue specificity seen in many mitochondrial disorders. This review highlights some important recent advances in mitochondrial disease but also stresses the areas where progress is essential.
Recent Advances in Mitochondrial Disease Craven, Lyndsey; Alston, Charlotte L; Taylor, Robert W ...
Annual review of genomics and human genetics,
08/2017, Letnik:
18, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Mitochondrial disease is a challenging area of genetics because two distinct genomes can contribute to disease pathogenesis. It is also challenging clinically because of the myriad of different ...symptoms and, until recently, a lack of a genetic diagnosis in many patients. The last five years has brought remarkable progress in this area. We provide a brief overview of mitochondrial origin, function, and biology, which are key to understanding the genetic basis of mitochondrial disease. However, the primary purpose of this review is to describe the recent advances related to the diagnosis, genetic basis, and prevention of mitochondrial disease, highlighting the newly described disease genes and the evolving methodologies aimed at preventing mitochondrial DNA disease transmission.
The human mitochondrial genome is extremely small compared with the nuclear genome, and mitochondrial genetics presents unique clinical and experimental challenges. Despite the diminutive size of the ...mitochondrial genome, mitochondrial DNA (mtDNA) mutations are an important cause of inherited disease. Recent years have witnessed considerable progress in understanding basic mitochondrial genetics and the relationship between inherited mutations and disease phenotypes, and in identifying acquired mtDNA mutations in both ageing and cancer. However, many challenges remain, including the prevention and treatment of these diseases. This review explores the advances that have been made and the areas in which future progress is likely.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Mitochondrial DNA and disease Greaves, Laura C; Reeve, Amy K; Taylor, Robert W ...
The Journal of pathology,
January 2012, Letnik:
226, Številka:
2
Journal Article
How mtDNA replication is terminated and the newly formed genomes are separated remain unknown. We here demonstrate that the mitochondrial isoform of topoisomerase 3α (Top3α) fulfills this function, ...acting independently of its nuclear role as a component of the Holliday junction-resolving BLM-Top3α-RMI1-RMI2 (BTR) complex. Our data indicate that mtDNA replication termination occurs via a hemicatenane formed at the origin of H-strand replication and that Top3α is essential for resolving this structure. Decatenation is a prerequisite for separation of the segregating unit of mtDNA, the nucleoid, within the mitochondrial network. The importance of this process is highlighted in a patient with mitochondrial disease caused by biallelic pathogenic variants in TOP3A, characterized by muscle-restricted mtDNA deletions and chronic progressive external ophthalmoplegia (CPEO) plus syndrome. Our work establishes Top3α as an essential component of the mtDNA replication machinery and as the first component of the mtDNA separation machinery.
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•Mitochondrial topoisomerase 3α separates mtDNA following replication•Mutations in TOP3A are a cause of human mitochondrial disease•mtDNA segregation proceeds via a hemicatenane formed at the origin of replication•Loss of Top3α impairs segregation of the mitochondrial nucleoid
Nicholls et al. identify a role for topoisomerase 3α in the separation of mtDNA following replication. Loss of Top3α activity impairs mtDNA segregation and, consequently, segregation of the mtDNA nucleoid within the mitochondrial network. Mutations in TOP3A cause human mitochondrial disease associated with mtDNA deletions and impaired mtDNA separation.
Mitochondrial functions are intrinsically linked to their morphology and membrane ultrastructure. Characterizing abnormal mitochondrial structural features may thus provide insight into the ...underlying pathogenesis of inherited and acquired mitochondrial diseases. Following a systematic literature review on ultrastructural defects in mitochondrial myopathy, we investigated skeletal muscle biopsies from seven subjects with genetically defined mtDNA mutations. Mitochondrial ultrastructure and morphology were characterized using two complimentary approaches: transmission electron microscopy (TEM) and serial block face scanning EM (SBF-SEM) with 3D reconstruction. Six ultrastructural abnormalities were identified including i) paracrystalline inclusions, ii) linearization of cristae and abnormal angular features, iii) concentric layering of cristae membranes, iv) matrix compartmentalization, v) nanotunelling, and vi) donut-shaped mitochondria. In light of recent molecular advances in mitochondrial biology, these findings reveal novel aspects of mitochondrial ultrastructure and morphology in human tissues with implications for understanding the mechanisms linking mitochondrial dysfunction to disease.
Mitochondrial disease associated with the pathogenic m.3243A>G variant is a common, clinically heterogeneous, neurogenetic disorder. Using multiple linear regression and linear mixed modelling, we ...evaluated which commonly assayed tissue (blood N = 231, urine N = 235, skeletal muscle N = 77) represents the m.3243A>G mutation load and mitochondrial DNA (mtDNA) copy number most strongly associated with disease burden and progression. m.3243A>G levels are correlated in blood, muscle and urine (R2 = 0.61–0.73). Blood heteroplasmy declines by ~2.3%/year; we have extended previously published methodology to adjust for age. In urine, males have higher mtDNA copy number and ~20% higher m.3243A>G mutation load; we present formulas to adjust for this. Blood is the most highly correlated mutation measure for disease burden and progression in m.3243A>G‐harbouring individuals; increasing age and heteroplasmy contribute (R2 = 0.27, P < 0.001). In muscle, heteroplasmy, age and mtDNA copy number explain a higher proportion of variability in disease burden (R2 = 0.40, P < 0.001), although activity level and disease severity are likely to affect copy number. Whilst our data indicate that age‐corrected blood m.3243A>G heteroplasmy is the most convenient and reliable measure for routine clinical assessment, additional factors such as mtDNA copy number may also influence disease severity.
Synopsis
The m.3243A>G pathogenic mtDNA variant is associated with a highly heterogeneous multisystem disorder and varying mutation levels across tissues. In this study, mutation levels were characterised in three commonly sampled tissues ‐ blood, urine, skeletal muscle ‐ and correlated with disease burden.
Urine m.3243A>G heteroplasmy levels display more variability than blood levels and must be corrected for a ˜20% lower level in females.
Blood m.3243A>G heteroplasmy levels must be corrected for a decline of ˜2.3% per year.
Disease burden and progression are more strongly associated with blood m.3243A>G heteroplasmy levels than urine levels.
27% of the variance in disease burden can be attributed to blood m.3243A>G heteroplasmy and age.
Age, m.3243A>G heteroplasmy level and mtDNA copy number in skeletal muscle explain 40% of the variance in disease burden.
The m.3243A>G pathogenic mtDNA variant is associated with a highly heterogeneous multisystem disorder and varying mutation levels across tissues. In this study, mutation levels were characterised in three commonly sampled tissues ‐ blood, urine, skeletal muscle ‐ and correlated with disease burden.
Genetic and biochemical defects of mitochondrial function are a major cause of human disease, but their link to mitochondrial morphology in situ has not been defined. Here, we develop a quantitative ...three-dimensional approach to map mitochondrial network organization in human muscle at electron microscopy resolution. We establish morphological differences between human and mouse and among patients with mitochondrial DNA (mtDNA) diseases compared to healthy controls. We also define the ultrastructure and prevalence of mitochondrial nanotunnels, which exist as either free-ended or connecting membrane protrusions across non-adjacent mitochondria. A multivariate model integrating mitochondrial volume, morphological complexity, and branching anisotropy computed across individual mitochondria and mitochondrial populations identifies increased proportion of simple mitochondria and nanotunnels as a discriminant signature of mitochondrial stress. Overall, these data define the nature of the mitochondrial network in human muscle, quantify human-mouse differences, and suggest potential morphological markers of mitochondrial dysfunction in human tissues.
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•3D mitochondrial morphology is quantified by the mitochondrial complexity index (MCI)•Mouse mitochondria are larger and exhibit greater connectivity than human mitochondria•Non-adjacent mitochondria are connected by narrow mitochondrial nanotunnels•Multivariate morphology signatures distinguish mitochondrial disease patients from healthy controls
Vincent et al. use 3D electron microscopy to provide a quantitative morphometric assessment of human skeletal muscle mitochondria. They find that healthy human muscle mitochondria differ from mouse mitochondria and show that primary mtDNA defects are associated with a distinct morphological signature including increased abundance of mitochondrial nanotunnels.
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