PhiC31 integrase induces a DNA damage response and chromosomal rearrangements in human adult fibroblasts

<p>Abstract</p> <p>Background</p> <p>PhiC31 integrase facilitates efficient integration of transgenes into human and mouse genomes and is considered for clinical gene therapy. However recent studies have shown that the enzyme can induce various chromosomal abnormalities in primary human embryonic cells and mammalian cell lines. The mechanisms involved are unknown, but it has been proposed that PhiC31 attachment sites in the host genome recombine leading to chromosomal translocations.</p> <p>Results</p> <p>We have studied possible effects of the PhiC31 integrase expression in human adult fibroblasts by karyotyping. All control cells were cytogenetically normal, whereas cells expressing PhiC31 integrase show chromosomal abnormalities confirming our previous results using primary embryonic fibroblasts. In order to study the early mechanisms involved we measured H2AX phosphorylation – a primary event in the response to DNA double-strand-breaks. Transient transfection with PhiC31 integrase encoding plasmids lead to an elevated number of cells positive for H2AX phosphorylation detected by immunofluorescence. Western blot analysis confirmed the upregulated H2AX phosphorylation, whereas markers for apoptosis as well as p53 and p21 were not induced. Cells transfected with plasmids encoding the Sleeping Beauty transposase remained cytogenetically normal, and in these cells less upregulation of H2AX phosphorylation could be detected.</p> <p>Conclusion</p> <p>In primary human fibroblasts expression of PhiC31 integrase leads to a DNA damage response and chromosomal aberrations.</p

Divalent metal transporter 1 (DMT1) in the brain:implications for a role in iron transport at the blood-brain barrier, and neuronal and glial pathology

Iron is required in a variety of essential processes in the body. In this review, we focus on iron transport in the brain and the role of the divalent metal transporter 1 (DMT1) vital for iron uptake in most cells. DMT1 locates to cellular membranes and endosomal membranes, where it is a key player in non-transferrin bound iron uptake and transferrin-bound iron uptake, respectively. Four isoforms of DMT1 exist, and their respective characteristics involve a complex cell-specific regulatory machinery all controlling iron transport across these membranes. This complexity reflects the fine balance required in iron homeostasis, as this metal is indispensable in many cell functions but highly toxic when appearing in excess. DMT1 expression in the brain is prominent in neurons. Of serious dispute is the expression of DMT1 in non-neuronal cells. Recent studies imply that DMT1 does exist in endosomes of brain capillary endothelial cells denoting the blood-brain barrier. This supports existing evidence that iron uptake at the BBB occurs by means of transferrin-receptor mediated endocytosis followed by detachment of iron from transferrin inside the acidic compartment of the endosome and DMT1-mediated pumping iron into the cytosol. The subsequent iron transport across the abluminal membrane into the brain likely occurs by ferroportin. The virtual absent expression of transferrin receptors and DMT1 in glial cells, i.e., astrocytes, microglia and oligodendrocytes, suggest that the steady state uptake of iron in glia is much lower than in neurons and/or other mechanisms for iron uptake in these cell types prevail

Exon duplications in the ATP7A gene: Frequency and Transcriptional Behaviour

<p>Abstract</p> <p>Background</p> <p>Menkes disease (MD) is an X-linked, fatal neurodegenerative disorder of copper metabolism, caused by mutations in the <it>ATP7A </it>gene. Thirty-three Menkes patients in whom no mutation had been detected with standard diagnostic tools were screened for exon duplications in the <it>ATP7A </it>gene.</p> <p>Methods</p> <p>The <it>ATP7A </it>gene was screened for exon duplications using multiplex ligation-dependent probe amplification (MLPA). The expression level of <it>ATP7A </it>was investigated by real-time PCR and detailed analysis of the <it>ATP7A </it>mRNA was performed by RT-PCR followed by sequencing. In order to investigate whether the identified duplicated fragments originated from a single or from two different X-chromosomes, polymorphic markers located in the duplicated fragments were analyzed.</p> <p>Results</p> <p>Partial <it>ATP7A </it>gene duplication was identified in 20 unrelated patients including one patient with Occipital Horn Syndrome (OHS). Duplications in the <it>ATP7A </it>gene are estimated from our material to be the disease causing mutation in 4% of the Menkes disease patients. The duplicated regions consist of between 2 and 15 exons. In at least one of the cases, the duplication was due to an intra-chromosomal event. Characterization of the <it>ATP7A </it>mRNA transcripts in 11 patients revealed that the duplications were organized in tandem, in a head to tail direction. The reading frame was disrupted in all 11 cases. Small amounts of wild-type transcript were found in all patients as a result of exon-skipping events occurring in the duplicated regions. In the OHS patient with a duplication of exon 3 and 4, the duplicated out-of-frame transcript coexists with an almost equally represented wild-type transcript, presumably leading to the milder phenotype.</p> <p>Conclusions</p> <p>In general, patients with duplication of only 2 exons exhibit a milder phenotype as compared to patients with duplication of more than 2 exons. This study provides insight into exon duplications in the <it>ATP7A </it>gene.</p

Splice Site Mutations in the ATP7A Gene

Menkes disease (MD) is caused by mutations in the ATP7A gene. We describe 33 novel splice site mutations detected in patients with MD or the milder phenotypic form, Occipital Horn Syndrome. We review these 33 mutations together with 28 previously published splice site mutations. We investigate 12 mutations for their effect on the mRNA transcript in vivo. Transcriptional data from another 16 mutations were collected from the literature. The theoretical consequences of splice site mutations, predicted with the bioinformatics tool Human Splice Finder, were investigated and evaluated in relation to in vivo results. Ninety-six percent of the mutations identified in 45 patients with classical MD were predicted to have a significant effect on splicing, which concurs with the absence of any detectable wild-type transcript in all 19 patients investigated in vivo. Sixty-seven percent of the mutations identified in 12 patients with milder phenotypes were predicted to have no significant effect on splicing, which concurs with the presence of wild-type transcript in 7 out of 9 patients investigated in vivo. Both the in silico predictions and the in vivo results support the hypothesis previously suggested by us and others, that the presence of some wild-type transcript is correlated to a milder phenotype

Iron deficiency and iron treatment in the fetal developing brain – a pilot study introducing an experimental rat model

Abstract Background Iron deficiency is especially common in women during the reproductive age and it is estimated that 52% of pregnant women have iron deficiency anemia. Maternal iron deficiency with or without anemia in pregnancy may have consequences for the fetus, where it may have an impact on the cerebral development of the brain. Both animals and adult human studies support that iron deficiency affects psychomotor development, behavioral traits, and cognitive functions in the offspring. However, it has not yet been established whether the availability of sufficient iron is particularly important in certain phases during brain development, and whether possible damages are reversible if iron supplementation is provided during pregnancy. Here we report results from a pilot study in an experimental rat model suitable for introducing iron deficiency in the fetal rat brain. Methods The model was utilized for examination of the potential to reverse changes in fetal brain iron by maternal parenteral iron administration. Fertilized females subjected to iron deficiency without anemia were subcutaneously injected with iron isomaltoside at the day of mating (E0), 14 days into pregnancy (E14), or at the day of birth (Postnatal (P) 0). Blood, brain and liver in the offspring were examined on P0 or in adulthood on postnatal day P70. Results Maternal iron restriction during pregnancy led to significantly lower levels of iron in the brains of newborn rats compared to levels in pups of iron sufficient mothers. Females fed ID diet (5.2 mg/kg Fe) had offspring with significantly lower cerebral iron compared to a control group fed a standard diet (158 mg/kg Fe). Injection of IIM to pregnant ID females on E0 or E14 yielded normalization of Fe in the developing brain known to express elevated levels of capillary transferrin receptors, indicating that the administered iron passed the placenta and fetal blood brain barrier. Conclusions In future studies, this translational model may be applied to examine morphological and biochemical consequences of iron deficiency and iron deficiency treatment in the developing fetal brain

Impairment of interrelated iron- and copper homeostatic mechanisms in brain contributes to the pathogenesis of neurodegenerative disorders

Iron and copper are important co-factors for a number of enzymes in the brain, including enzymes involved in neurotransmitter synthesis and myelin formation. Both shortage and an excess of iron or copper will affect the brain. The transport of iron and copper into the brain from the circulation is strictly regulated, and concordantly protective barriers, i.e., the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCB) have evolved to separate the brain environment from the circulation. The uptake mechanisms of the two metals interact. Both iron deficiency and overload lead to altered copper homeostasis in the brain. Similarly, changes in dietary copper affect the brain iron homeostasis. Moreover, the uptake routes of iron and copper overlap each other which affect the interplay between the concentrations of the two metals in the brain. The divalent metal transporter-1 (DMT1) is involved in the uptake of both iron and copper. Furthermore, copper is an essential co-factor in numerous proteins that are vital for iron homeostasis and affects the binding of iron-response proteins to iron-response elements in the mRNA of the transferrin receptor, DMT1, and ferroportin, all highly involved in iron transport. Iron and copper are mainly taken up at the BBB, but the BCB also plays a vital role in the homeostasis of the two metals, in terms of sequestering, uptake, and efflux of iron and copper from the brain. Inside the brain, iron and copper are taken up by neurons and glia cells that express various transporters

<i>In silico</i> splice site predictions.

<p>A comprehensive overview of identified splice site mutations in donor sites (DS) and acceptor sites (AS) of the <i>ATP7A</i> gene. The mutations are located in exon-intron boundaries in either the intervening sequence (IVS) or in the exon sequence (E). The various mutations lead to different MD phenotypes classified as classical MD (C), atypical MD (A), OHS (O) or unknown (−). The mutations were analysed with the online bioinformatics tool, Human Splicing Finder (HSF), to predict the splicing signals in wild-type and mutated DNA sequences. The strength of the splice sites is indicated by the consensus value (CV) and the CV variation (ΔCV). Potential cryptic splice sites predicted with HSF are given. Effects on pre-mRNA splicing that have been identified <i>in vivo</i> are listed.</p>*<p>Found in this study.</p

CV and ΔCV in relation to MD patient phenotypes.

<p>Using HSF, each mutation is analysed for the effect on the given splice site based on the two parameters CV and ΔCV. Mutated splice sites with CVs above 70 are likely to retain some activity. Conversely, splice sites with CVs below 70 are considered inactive. ΔCV-reductions of less than 10% (or * less than 7% at position +4) are likely to retain some wild-type splice site activity, whereas ΔCV-reductions of more than 10% (7% at position +4) are considered broken and inactive <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018599#pone.0018599-Desmet1" target="_blank">[10]</a>. The mutations are categorized based on the CV- and ΔCV-values obtained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018599#pone-0018599-t001" target="_blank">Table 1</a> “Mild MD” covers atypical MD and OHS phenotypes. Patients with unknown clinical phenotype are not included.</p