Phylogeography of the harlequin beetle-riding pseudoscorpion and the rise of the Isthmus of Panamá

Molecular and geological evidence indicates that the emergence of the Isthmus of Panamá influenced the historical biogeography of the Neotropics in a complex, staggered manner dating back at least 9 Myr bp. To assess the influence of Isthmus formation on the biogeography of the harlequin beetle-riding pseudoscorpion, Cordylochernes scorpioides, we analysed mitochondrial COI sequence data from 71 individuals from 13 locations in Panamá and northern South America. Parsimony and likelihood-based phylogenies identified deep divergence between South American and Panamanian clades. In contrast to low haplotype diversity in South America, the Panamanian Cordylochernes clade is comprised of three highly divergent lineages: one clade consisting predominantly of individuals from central Panamá (PAN A), and two sister clades (PAN B1 and PAN B2) of western Panamanian pseudoscorpions. Breeding experiments demonstrated a strictly maternal mode of inheritance, indicating that our analyses were not confounded by nuclear-mitochondrial pseudogenes. Haplotype diversity is striking in western Atlantic Panamá, where all three Panamanian clades can occur in a single host tree. This sympatry points to the existence of a cryptic species hybrid zone in western Panamá, a conclusion supported by interclade crosses and coalescence-based migration rates. Molecular clock estimates yield a divergence time of approximately 3 Myr between the central and western Panamanian clades. Taken together, these results are consistent with a recent model in which a transitory proto-Isthmus enabled an early wave of colonization out of South America at the close of the Miocene, followed by sea level rise, inundation of the terrestrial corridor and then a second wave of colonization that occurred when the Isthmus was completed approximately 3 Myr bp.     

Survival of bowhead whales,Balaena mysticetus,estimated from 1981-1998 photoidentification data

Annual survival probability of bowhead whales, Balaena mysticetus, was estimated using both Bayesian and maximum likelihood implementations of Cormack and Jolly-Seber (JS) models for capture-recapture estimation in open populations and reduced-parameter generalizations of these models. Aerial photographs of naturally marked bowheads collected between 1981 and 1998 provided the data. The marked whales first photographed in a particular year provided the initial 'capture' and 'release' of those marked whales and photographs in subsequent years the 'recaptures'. The Cormack model, often called the Cormack-Jolly-Seber (CJS) model, and the program MARK were used to identify the model with a single survival and time-varying capture probabilities as the most appropriate for these data. When survival was constrained to be one or less, the maximum likelihood estimate computed by MARK was one, invalidating confidence interval computations based on the asymptotic standard error or profile likelihood. A Bayesian Markov chain Monte Carlo (MCMC) implementation of the model was used to produce a posterior distribution for annual survival. The corresponding reduced-parameter JS model was also fit via MCMC because it is the more appropriate of the two models for these photoidentification data. Because the CJS model ignores much of the information on capture probabilities provided by the data, its results are less precise and more sensitive to the prior distributions used than results from the JS model. With priors for annual survival and capture probabilities uniform from 0 to 1, the posterior mean for bowhead survival rate from the JS model is 0.984, and 95% of the posterior probability lies between 0.948 and 1. This high estimated survival rate is consistent with other bowhead life history data.     

Concerted integration of viral DNA termini by purified avian myeloblastosis virus integrase.

Concerted integration of retroviral DNA termini, which produces a characteristic duplication of sequences at the integration site and formation of the proviral state, is a necessary step of the retroviral life cycle. We investigated the pairwise integration reaction catalyzed by purified avian retrovirus integrase by measuring the response to solution parameters and how the sequences of the viral termini, which comprise the avian imperfect inverted repeat, affect the reaction. When we optimized the reaction, an efficiency was achieved which approached that measured in systems using cytoplasmic extracts from virus-infected cells. The response of purified avian integrase to solution parameters was similar to that of the integration activity derived from cellular extracts. For strand transfer, the U3 viral terminal sequences were preferred to those of the U5 termini, a result we previously showed for the trimming reaction. That the sequence preference was the same for trimming and strand transfer may be further evidence that only one catalytic site is used for both reactions. A significant number of integration sites were sequenced. Interesting trends were found for the fidelity of the host duplications to the avian 6-bp duplication size, the clustering of the integration sites in the nonessential region of the lambda host DNA, and the sequence characteristics of the duplication sites.     

Engineering of cysteine and methionine biosynthesis in potato

Summary. Methionine and cysteine, two amino acids containing reduced sulfur, are not only an important substrate of protein biosynthesis but are also precursors of various other metabolites such as glutathione, phytochelatines, S-adenosylmethionine, ethylene, polyamines, biotin, and are involved as methyl group donor in numerous cellular processes. While methionine is an essential amino acid due to an inability of monogastric animals and human beings to synthesise this metabolite, animals are still able to convert methionine consumed with their diet into cysteine. Thus, a balanced diet containing both amino acids is necessary to provide a nutritionally favourable food or feed source. Because the concentrations of methionine and cysteine are often low in edible plant sources, e.g. potato, considerable efforts in plant breeding and research have been and are still performed to understand the physiological, biochemical, and molecular mechanisms that contribute to their synthesis, transport, and accumulation in plants. During the last decade molecular tools have enabled the isolation of most of the genes involved in cysteine and methionine biosynthesis, and the efficient plant transformation technology has allowed the creation of transgenic plants that are altered in the activity of individual genes. The physiological analysis of these transgenic plants has contributed considerably to our current understanding of how amino acids are synthesised. We focused our analysis on potato (Solanum tuberosum cv. Désirée) as this plant provides a clear separation of source and sink tissues and, for applied purposes, already constitutes a crop plant. From the data presented here and in previous work we conclude that threonine synthase and not cystathionine gamma-synthase as expected from studies of Arabidopsis constitutes the main regulatory control point of methionine synthesis in potato. This article aims to cover the current knowledge in the area of molecular genetics of sulfur-containing amino acid biosynthesis and will provide new data for methionine biosynthesis in solanaceous plants such as potato. Received December 19, 2001 Accepted January 7, 2002     

The regulation of mitochondrial DNA copy number in glioblastoma cells

As stem cells undergo differentiation, mitochondrial DNA (mtDNA) copy number is strictly regulated in order that specialized cells can generate appropriate levels of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) to undertake their specific functions. It is not understood whether tumor-initiating cells regulate their mtDNA in a similar manner or whether mtDNA is essential for tumorigenesis. We show that human neural stem cells (hNSCs) increased their mtDNA content during differentiation in a process that was mediated by a synergistic relationship between the nuclear and mitochondrial genomes and results in increased respiratory capacity. Differentiating multipotent glioblastoma cells failed to match the expansion in mtDNA copy number, patterns of gene expression and increased respiratory capacity observed in hNSCs. Partial depletion of glioblastoma cell mtDNA rescued mtDNA replication events and enhanced cell differentiation. However, prolonged depletion resulted in impaired mtDNA replication, reduced proliferation and induced the expression of early developmental and pro-survival markers including POU class 5 homeobox 1 (OCT4) and sonic hedgehog (SHH). The transfer of glioblastoma cells depleted to varying degrees of their mtDNA content into immunocompromised mice resulted in tumors requiring significantly longer to form compared with non-depleted cells. The number of tumors formed and the time to tumor formation was relative to the degree of mtDNA depletion. The tumors derived from mtDNA depleted glioblastoma cells recovered their mtDNA copy number as part of the tumor formation process. These outcomes demonstrate the importance of mtDNA to the initiation and maintenance of tumorigenesis in glioblastoma multiforme.     

Mitochondrial quality control mediated by PINK1 and PRKN: links to iron metabolism and tumor immunity

Mitochondrial quality control is an essential process required to maintain cellular homeostasis and functions. Mutations of PINK1 and PRKN/PARK2 contribute to the risk of Parkinson disease. Our recent findings indicate that depletion of Pink1 and Prkn promotes pancreatic tumorigenesis in KRAS-driven engineered mouse models. Mechanistically, PINK1- and PRKN-mediated autophagic degradation of mitochondrial iron importers (e.g., SLC25A37 and SLC25A28) suppresses pancreatic tumor growth by attenuating mitochondrial iron accumulation, inflammasome activation, HMGB1 release, and subsequent immune checkpoint expression. Consequently, pharmacological or genetic inhibition of mitochondrial iron-dependent signals prolongs animal survival and reverses pancreatic tumor phenotype in vivo. Thus, PINK1- and PRKN-mediated immunometabolism provides new insights into the tumor microenvironment and could be a suitable target for new pancreatic cancer treatments.     

High Mobility Group Box 1 (HMGB1) Phenotypic Role Revealed with Stress

High mobility group box 1 (HMGB1) is an evolutionarily ancient protein that is present in one form or another in all eukaryotes. It fundamentally resides in the nucleus but translocates to the cytosol with stress and is subsequently released into the extracellular space. HMGB1 global knockout mice exhibit lethal hypoglycemia, whereas tissues and cells from conditional knockout or knock-in mice are born alive without apparent significant functional deficit. An aberrant response to targeted stress in the liver, pancreas, heart or myeloid cells is consistent with a protective role for HMGB1 in sustaining nuclear homeostasis and enabling other stress responses, including autophagy. Under some conditions, HMGB1 is not required for liver and heart function. Many challenges remain with respect to understanding the multiple roles of HMGB1 in health and disease.     

Cell Death and DAMPs in Acute Pancreatitis

Cell death and inflammation are key pathologic responses of acute pancreatitis (AP), the leading cause of hospital admissions for gastrointestinal disorders. It is becoming increasingly clear that damage-associated molecular pattern molecules (DAMPs) play an important role in the pathogenesis of AP by linking local tissue damage to systemic inflammation syndrome. Endogenous DAMPs released from dead, dying or injured cells initiate and extend sterile inflammation via specific pattern recognition receptors. Inhibition of the release and activity of DAMPs (for example, high mobility group box 1, DNA, histones and adenosine triphosphate) provides significant protection against experimental AP. Moreover, increased serum levels of DAMPs in patients with AP correlate with disease severity. These findings provide novel insight into the mechanism, diagnosis and management of AP. DAMPs might be an attractive therapeutic target in AP.