Endonuclease G: a mitochondrial protein released in apoptosis and involved in caspase-independent DNA degradation.

A hallmark of apoptosis is the fragmentation of nuclear DNA. Although this activity involves the caspase-3-dependent DNAse CAD (caspase-activated DNAse), evidence exists that DNA fragmentation can occur independently of caspase activity. Here we report on the ability of truncated Bid (tBid) to induce the release of a DNAse activity from mitochondria. This DNAse activity was identified by mass spectrometry as endonuclease G, an abundant 30 kDa protein released from mitochondria under apoptotic conditions. No tBid-induced endonuclease G release could be observed in mitochondria from Bcl-2-transgenic mice. The in vivo occurrence of endonuclease G release from mitochondria during apoptosis was confirmed in the liver from mice injected with agonistic anti-Fas antibody and is completely prevented in Bcl-2 transgenic mice. These data indicate that endonuclease G may be involved in CAD-independent DNA fragmentation during cell death pathways in which truncated Bid is generated.     

Mitochondrial inner membrane permeabilisation enables mtDNA release during apoptosis

During apoptosis, pro‐apoptotic BAX and BAK are activated, causing mitochondrial outer membrane permeabilisation (MOMP), caspase activation and cell death. However, even in the absence of caspase activity, cells usually die following MOMP. Such caspase‐independent cell death is accompanied by inflammation that requires mitochondrial DNA (mtDNA) activation of cGAS‐STING signalling. Because the mitochondrial inner membrane is thought to remain intact during apoptosis, we sought to address how matrix mtDNA could activate the cytosolic cGAS‐STING signalling pathway. Using super‐resolution imaging, we show that mtDNA is efficiently released from mitochondria following MOMP. In a temporal manner, we find that following MOMP, BAX/BAK‐mediated mitochondrial outer membrane pores gradually widen. This allows extrusion of the mitochondrial inner membrane into the cytosol whereupon it permeablises allowing mtDNA release. Our data demonstrate that mitochondrial inner membrane permeabilisation (MIMP) can occur during cell death following BAX/BAK‐dependent MOMP. Importantly, by enabling the cytosolic release of mtDNA, inner membrane permeabilisation underpins the immunogenic effects of caspase‐independent cell death.     

Mitochondrial contact sites: their role in energy metabolism and apoptosis

The energy metabolism of the failing heart is characterised by a 30% decrease of the total adenine nucleotides content and what may be more important by a 60% loss of creatine and creatine phosphate [J.S. Ingwall, R.G. Weiss, Is the failing heart energy starved? On using chemical energy to support cardiac function, Circ. Res. 95 (2004) 35-145]. Besides the effect of these changes on the energy supply, failing heart is known to be more vulnerable to Ca2+ overload and apoptosis-inducing processes. Recent studies have pointed to the critical role of mitochondrial contact sites in controlling both the mitochondrial energy metabolism and Ca2+ homeostasis. This review focuses on the structure and function of protein complexes in mitochondrial contact sites and their regulatory role in the cellular bioenergetics, intra- and extra-mitochondrial Ca2+ levels, and release of apoptosis-inducing factors. Firstly, we review the compositions of different contact sites following by the discussion of experimental data obtained with isolated and reconstituted voltage-dependent anion channel-adenine nucleotide translocase complexes and consequences of the complex disassembling. Furthermore, we describe experiments involving the complex-stabilizing conditions in vitro and in intact cells. At the end, we discuss unsolved problems and opportunities for clinical application of the complex-stabilizing factors.     

Somatostatin: a historical perspective

Following the discovery and biochemical characterization of natural somatostatin its action profile has been thoroughly investigated. Although the name somatostatin was coined in virtue of its growth hormone release-inhibiting properties, a number of central and peripheral endocrine and paracrine actions have been ascribed to this peptide. Its inhibitory effect on a series of pituitary and gastrointestinal hormones has characterized somatostatin as a classical brain-gut hormone. Circulating and tissue levels of somatostatin and its possible physiological role are analyzed and clinical implications are drawn.     

Mitochondrial DNA variant 11719G is a marker for the mtDNA haplogroup cluster HV

Based on sequencing data and results obtained from applying a tailored mismatch polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, we report that the G allele of the mitochondrial DNA (mtDNA) polymorphism at nucleotide position 11719 is associated with the European mtDNA haplogroup cluster HV, and that 11719A is therefore the ancestral allele.     

BioMetals: a historical and personal perspective

Understanding of BioMetals developed basically from a starting point about 60 years ago to current mechanistic understanding of the biological behavior of many metal ions from protein structural and functional studies. Figure 1 shows a Biochemical Periodic Table, element by element, with requirements, roles and biochemistry of the specific ions indicated. With few exceptions, the biology is of the ions formed and not of the elemental state of each. Early BioMetals efforts defined nutritional growth needs for animals, plants and microbes for inorganic “macro-nutrients” such as magnesium, calcium, potassium, sodium, and phosphate and of “micronutrients” such as copper, iron, manganese and zinc. Surprises came early with regard to microbes, for example the finding that Escherichia coli (then and now the standard microbial model) grows happily in the apparent total absence of calcium, sodium, and chloride, which are certainly major animal nutrients. Some elements such as mercury and arsenic are never required by living cells, but are always toxic, often at very low levels. Therefore, the division into nutrient elements and toxic elements came soon. For most inorganic nutrients, excessive amounts can be toxic as well, for example for copper and iron.     

线粒体DNA及其提取方法

线粒体是存在于绝大多数真核细胞内的一种基本的重要的细胞器,其具有相对独立的遗传系统。线粒体基因在真核生物具有高保守性,线粒体DNA(mtDNA)已被广泛应用于发病机理、临床诊断、遗传变异、生物进化等多方面的研究。1981年,Anderson用氯化铯密度梯度分离得到线粒体DNA(mtDNA),进行了全序列分析。此后,mtDNA的研究日益得到重视。已有的mtDNA提取方法概括起来可分为密度梯度离心法、酶消化法、柱层析法、氯化铯超速离心法、碱变性法和改进高盐沉淀法等,通过对以上方法的比较,发现改进高盐沉淀法具有简便、经济、易重复等优点。     

Intermediate filaments: a historical perspective

Intracellular protein filaments intermediate in size between actin microfilaments and microtubules are composed of a surprising variety of tissue specific proteins commonly interconnected with other filamentous systems for mechanical stability and decorated by a variety of proteins that provide specialized functions. The sequence conservation of the coiled-coil, alpha-helical structure responsible for polymerization into individual 10 nm filaments defines the classification of intermediate filament proteins into a large gene family. Individual filaments further assemble into bundles and branched cytoskeletons visible in the light microscope. However, it is the diversity of the variable terminal domains that likely contributes most to different functions. The search for the functions of intermediate filament proteins has led to discoveries of roles in diseases of the skin, heart, muscle, liver, brain, adipose tissues and even premature aging. The diversity of uses of intermediate filaments as structural elements and scaffolds for organizing the distribution of decorating molecules contrasts with other cytoskeletal elements. This review is an attempt to provide some recollection of how such a diverse field emerged and changed over about 30 years.     

Neutral theory: a historical perspective

To resolve a panselectionist paradox, the population geneticist Kimura invented a neutral theory, where each gene is equally likely to enter the next generation whatever its allelic type. To learn what could be explained without invoking Darwinian adaptive divergence, Hubbell devised a similar neutral theory for forest ecology, assuming each tree is equally likely to reproduce whatever its species. In both theories, some predictions worked; neither theory proved universally true. Simple assumptions allow neutral theorists to treat many subjects still immune to more realistic theory. Ecologists exploit far fewer of these possibilities than population geneticists, focussing instead on species abundance distributions, where their predictions work best, but most closely match non-neutral predictions. Neutral theory cannot explain adaptive divergence or ecosystem function, which ecologists must understand. By addressing new topics and predicting changes in time, however, ecological neutral theory can provide probing null hypotheses and stimulate more realistic theory.     

The Proapoptotic Protein BNIP3 Interacts with VDAC to Induce Mitochondrial Release of Endonuclease G

BNIP3 is a proapoptotic protein that induces cell death through a mitochondria-mediated pathway. We reported previously that mitochondrial localization of BNIP3 and translocation of EndoG from mitochondria to the nucleus are critical steps of the BNIP3 pathway. It is not clear, however, that how BNIP3 interacts with mitochondria. Here we show that expression of BNIP3 resulted in mitochondrial release and nuclear translocation of EndoG. Incubation of a recombinant GST-BNIP3 protein with freshly isolated mitochondria led to the integration of BNIP3 into mitochondria, reduction in the levels of EndoG in mitochondria and the presence of EndoG in the supernatant that was able to cleave chromatin DNA. Co-immunoprecipitation and mass spectrometry analysis reveals that BNIP3 interacted with the voltage-dependent anion channel (VDAC) to increase opening probabilities of mitochondrial permeability transition (PT) pores and induce mitochondrial release of EndoG. Blocking VDAC with a VDAC antibody largely abolished mitochondrial localization of BNIP3 and prevented EndoG release. Together, the data identify VDAC as an interacting partner of BNIP3 and support endonuclease G as a mediator of the BNIP3 pathway.     

The Tinel sign: a historical perspective

The Tinel sign is one of the most well-known and widely used clinical diagnostic tools in medicine. Aside from Jules Tinel, after whom the sign is named, several authors have described the famous "tingling" sign seen in regenerating injured nerves. In fact, Tinel was not the first to present the sign to the scientific community. The clinical value and utility of the Tinel sign have remained in question since its introduction; many may misinterpret the sign as a prelude to complete functional recovery of injured nerves, when in fact it only signals the progress of nerve regeneration. Today the Tinel sign is widely associated with the diagnosis of carpal tunnel syndrome and in the evaluation of regenerating peripherally injured nerves. Knowledge of the history and misconceptions surrounding the sign provides clinicians today with a greater appreciation of current debates on the use of the Tinel sign.     

Mitochondrial dynamics and apoptosis: a painful separation

Reporting in Molecular Cell, Sheridan et al. (2008) and Breckenridge et al. (2008) show that mitochondrial fragmentation is not required to induce cell death. Meanwhile, Yamaguchi et al. show that proapoptotic Bcl-2 family members promote cytochrome c mobilization through Opa1-mediated cristae remodeling. Therefore, the connection between mitochondrial structure and apoptosis is more complex than previously imagined.     

Born in a follicle--a historical perspective

A review of major studies of tetrapod skin development since the 1870s illustrates how knowledge of structure and mechanism progressed through phases emphasizing Natural History, morphology, endocrinology, and tissue manipulation prior to the prevailing "molecular era." Each successive phase of investigation, while suffering from its own limitations and constraints, has produced conceptual advances. At various times, different systems in various organisms have been research models of choice for practical and/or technical reasons. Comparative studies of scaled and non-scaled integuments and appendages thereof, e.g., nails, claws, glands, hair, and especially feathers, revealed data that suggested new directions for research programs. Some non-mammalian models still offer unique opportunities for pursuit of specific questions pertinent to studies of hair: arguments between American and British schools concerning feather development that originated in the 1930s remain unresolved and may thus affect interpretation of recent investigations. The current emphasis on the study of diffusible molecules involved in papilla-follicle interactions in hair development and replacement can only be understood in the context of the interwoven history of questions relating sequentially to evolutionary homology, physiological controls of tissue homeostasis, embryonic induction, and, most recently, molecular genetics.