Human cloning: can it be made safe?

There are continued claims of attempts to clone humans using nuclear transfer, despite the serious problems that have been encountered in cloning other mammals. It is known that epigenetic and genetic mechanisms are involved in clone failure, but we still do not know exactly how. Human reproductive cloning is unethical, but the production of cells from cloned embryos could offer many potential benefits. So, can human cloning be made safe?     

Marine microbial diversity: can it be determined?

Estimates of the order of magnitude for the total number of microbial species on Earth range from 10(3) to 10(9). Despite global dispersal of microorganisms, this number is probably rather large. The total biodiversity of an ecosystem is composed of two elements: first, a set of abundant taxa that carry out most ecosystem functions, grow actively and suffer intense losses through predation and viral lysis. These taxa are retrievable with molecular techniques but are difficult to grow in culture. Second, there is a seed bank of many rare taxa that are not growing or grow extremely slowly, do not experience viral lysis and predation is reduced. Such taxa are seldom retrieved by molecular techniques but many can be grown in culture, which explains the dictum 'everything is everywhere'.     

Doubly uniparental inheritance of mitochondrial DNA: Might it be simpler than we thought?

More than 100 species of bivalve mollusks are currently known to carry two highly diverged mitochondrial DNA (mtDNA) molecules, one of which is transmitted through the egg and the other through the sperm generation after generation, faithfully and uninterruptedly. This mtDNA system, which has become known as doubly uniparental inheritance (DUI), is most likely unique in eukaryotes and constitutes a striking deviation from the strictly maternal inheritance (SMI) of mtDNA that is the rule in the animal kingdom. Here, I present a model of how the paternal mtDNA may escape the mitochondrial destruction that occurs prior to sperm formation and enter the male germ line in the newly formed embryo. In essence, the model treats the sperm-transmitted mtDNA as a molecule that takes a ride with the sperm. The model can be easily tested and, if passed the tests, may open the way for the understanding of DUI at the molecular level and throw light on the mechanisms and evolution of mtDNA transmission in general. In addition, the model shifts attention from nuclear control of paternal mtDNA inheritance, whether systematic (as DUI) or leaky (as the cases reported in a wide variety of animal species), to the mtDNA itself as the protagonist of its own transmission. This possibility has been, so far, ignored in studies of paternal mtDNA transmission in other species including humans.     

2D protein electrophoresis: can it be perfected?

23 years after O'Farrel developed two-dimensional gel electrophoresis we still debate if the technique can be improved, or if there are other alternative separation technologies that can challenge its central position in proteomic projects. These questions are relevant as the pharmaceutical industry expects proteomic studies to provide novel protein targets for drug discovery and diagnostics. In our opinion, there are various aspects of the technology that can be improved, including resolution, sample preparation and detection, but so far there is no alternative technique(s) available, or any under development, that can replace it.     

Intramitochondrial recombination - is it why some mitochondrial genes sleep around?

A new paper by Kajander et al. undermines the general view that mitochondria do not recombine. The authors discovered the existence of 'sublimons', rearranged mitochondrial genomes present at very low levels in healthy human patients. Crucially, the different rearranged mitochondrial genomes can theoretically be interconverted through intramitochondrial recombination. The putative operation of intramitochondrial recombination should impact on our ideas of how mitochondrial genes evolve, particularly with respect to how mitochondrial genomes rearrange.     

Stomatal sensitivity to abscisic acid: can it be defined?

Abstract. Evidence is presented that the sensitivity of stomata to abscisic acid is greatly influenced by two factors which are known to vary in leaves, namely concentrations of potassium and of indol-3-ylacetic acid. It is suggested that the notion of 'quantitative tissue sensitivity', by which Trewavas explains the action of growth substances in developmental phenomena, may be applicable to stomatal responses to abscisic acid.     

D-loop mutations in mitochondrial DNA: link with mitochondrial DNA depletion?

Clinical presentation of the patients with mitochondrial DNA depletion is quite diverse and is suggestive of genetic heterogeneity. Autosomal recessive inheritance of the disease appears likely, thus implying the nuclear origin of the disease. This has been demonstrated recently in large families with neonatal presentation of the disease. Here, we report upon a family with one child having a late-onset disease associated with severe mitochondrial DNA depletion. The presence of mitochondrial alterations in the muscle of the patient's mother prompted us to extensively analyse the mitochondrial DNA in the family. We found mitochondrial DNA multiple deletions, but also three heteroplasmic point mutations of the D-loop region, two of which (T119C and T408A) affect conserved regions involved in the mtDNA replication process. These mutations were non-randomly distributed in the maternal lineage and, for one of them, among single muscle fibres. Involvement of the mitochondrial DNA in its own depletion appears therefore possible. It may act in close relationship with a hypothetical modified nuclear factor.     

Review: can diet influence the selective advantage of mitochondrial DNA haplotypes?

This review explores the potential for changes in dietary macronutrients to differentially influence mitochondrial bioenergetics and thereby the frequency of mtDNA haplotypes in natural populations. Such dietary modification may be seasonal or result from biogeographic or demographic shifts. Mechanistically, mtDNA haplotypes may influence the activity of the electron transport system (ETS), retrograde signalling to the nuclear genome and affect epigenetic modifications. Thus, differential provisioning by macronutrients may lead to selection through changes in the levels of ATP production, modulation of metabolites (including AMP, reactive oxygen species (ROS) and the NAD⁺/NADH ratio) and potentially complex epigenetic effects. The exquisite complexity of dietary influence on haplotype frequency is further illustrated by the fact that macronutrients may differentially influence the selective advantage of specific mutations in different life-history stages. In Drosophila, complex I mutations may affect larval growth because dietary nutrients are fed through this complex in immaturity. In contrast, the majority of electrons are provided to complex III in adult flies. We conclude the review with a case study that considers specific interactions between diet and complex I of the ETS. Complex I is the first enzyme of the mitochondrial ETS and co-ordinates in the oxidation of NADH and transfer of electrons to ubiquinone. Although the supposition that mtDNA variants may be selected upon by dietary macronutrients could be intuitively consistent to some and counter intuitive to others, it must face a multitude of scientific hurdles before it can be recognized.     

Remission in psoriatic arthritis: is it possible and how can it be predicted?

Introduction

Since remission is now possible in psoriatic arthritis (PsA) we wished to examine remission rates in PsA patients following anti tumour necrosis factor alpha (TNFα) therapy and to examine possible predictors of response.

Methods

Analysis of a prospective patient cohort attending a biologic clinic, between November 2004 and March 2008, was performed prior to commencing therapy and at regular intervals. Baseline clinical characteristics including demographics, previous disease-modifying antirheumatic drug (DMARD) response, tender and swollen joint counts, early morning stiffness, pain visual analogue score, patient global assessment, C reactive protein (CRP) and health assessment questionnaire (HAQ) were collected.

Results

A total of 473 patients (152 PsA; 321 rheumatoid arthritis (RA)) were analyzed. At 12 months remission, defined according to the disease activity score using 28 joint count and CRP (DAS28-CRP), was achieved in 58% of PsA patients compared to 44% of RA patients, significant improvement in outcome measures were noted in both groups (P < 0.05). Analysis of a subgroup of PsA and RA patients matched for DAS28-CRP at baseline also showed higher numbers of PsA patients achieving remission. Linear regression analysis identified the HAQ at baseline as the best predictor of remission in PsA patients (P < 0.001).

Conclusions

DAS28 remission is possible in PsA patients at one year following anti-TNF therapy, at higher rates than in RA patients and is predicted by baseline HAQ.     

Human stem cell aging: do mitochondrial DNA mutations have a causal role?

A decline in the replicative and regenerative capacity of adult stem cell populations is a major contributor to the aging process. Mitochondrial DNA (mtDNA) mutations clonally expand with age in human stem cell compartments including the colon, small intestine, and stomach, and result in respiratory chain deficiency. Studies in a mouse model with high levels of mtDNA mutations due to a defect in the proofreading domain of the mtDNA polymerase γ (mtDNA mutator mice) have established causal relationships between the accumulation of mtDNA point mutations, stem cell dysfunction, and premature aging. These mtDNA mutator mice have also highlighted that the consequences of mtDNA mutations upon stem cells vary depending on the tissue. In this review, we present evidence that these studies in mice are relevant to normal human stem cell aging and we explore different hypotheses to explain the tissue‐specific consequences of mtDNA mutations. In addition, we emphasize the need for a comprehensive analysis of mtDNA mutations and their effects on cellular function in different aging human stem cell populations.     

Diphtheria-tetanus overimmunization in children with no records: can it be prevented?

A pilot study was undertaken to assess the validity of two new tests for predicting the immune response of Toronto schoolchildren with no acceptable evidence of prior administration of diphtheria or tetanus toxoid to a routine booster injection of diphtheria and tetanus (DT) toxoid. The tests, an inexpensive enzyme-linked immunosorbent assay (ELISA) fingerprick test for tetanus antibodies and a modification of the Schick skin test for susceptibility to diphtheria, were administered before the booster injection. One week later the ELISA test was repeated and the result of the modified Schick test read. On both occasions a diphtheria microneutralization assay was done for "gold standard" evidence of prior exposure to diphtheria toxoid or toxin. The results were used to determine the sensitivity and specificity of a single prebooster tetanus ELISA test or a modified Schick test for predicting which children with no records could be safely protected with only one DT booster dose instead of the primary series of three or four doses usually given to such children. Only 6 of the 34 subjects (18%) were totally without prior exposure to tetanus toxoid. Two of the six (6% of 33 subjects) appeared to mount a primary immune response to diphtheria toxoid as well. An initial ELISA titre of 0.01 IU/ml or lower correctly identified all six children needing a full series of tetanus toxoid (sensitivity for a primary immune response 100%) and falsely identified only 3 of 28 immune children as needing the series (specificity for immunity 89.3%). The modified Schick test appeared to have even greater accuracy for identifying children needing a full series of diphtheria toxoid. However, its use, entailing the costs of an extra nurse visit, would have prevented only seven more children from receiving an unnecessary full series of diphtheria toxoid than use of the baseline tetanus ELISA test alone.