WRN helicase and mismatch repair complexes independently and synergistically disrupt cruciform DNA structures.

The Werner Syndrome helicase, WRN, is a promising therapeutic target in cancers with microsatellite instability (MSI). Long-term MSI leads to the expansion of TA nucleotide repeats proposed to form cruciform DNA structures, which in turn cause DNA breaks and cell lethality upon WRN downregulation. Here we employed biochemical assays to show that WRN helicase can efficiently and directly unfold cruciform structures, thereby preventing their cleavage by the SLX1-SLX4 structure-specific endonuclease. TA repeats are particularly prone to form cruciform structures, explaining why these DNA sequences are preferentially broken in MSI cells upon WRN downregulation. We further demonstrate that the activity of the DNA mismatch repair (MMR) complexes MutSα (MSH2-MSH6), MutSß (MSH2-MSH3), and MutLα (MLH1-PMS2) similarly decreases the level of DNA cruciforms, although the mechanism is different from that employed by WRN. When combined, WRN and MutLα exhibited higher than additive effects in in vitro cruciform processing, suggesting that WRN and the MMR proteins may cooperate. Our data explain how WRN and MMR defects cause genome instability in MSI cells with expanded TA repeats, and provide a mechanistic basis for their recently discovered synthetic-lethal interaction with promising applications in precision cancer therapy.

Effects of iron supplementation on dominant bacterial groups in the gut, faecal SCFA and gut inflammation: a randomised, placebo-controlled intervention trial in South African children.

Fe supplementation is a common strategy to correct Fe-deficiency anaemia in children; however, it may modify the gut microbiota and increase the risk for enteropathogenic infection. In the present study, we studied the impact of Fe supplementation on the abundance of dominant bacterial groups in the gut, faecal SCFA concentration and gut inflammation in children living in rural South Africa. In a randomised, placebo-controlled intervention trial of 38 weeks, 6- to 11-year-old children with Fe deficiency received orally either tablets containing 50 mg Fe as FeSO4 (n 22) for 4 d/week or identical placebo (n 27). In addition, Fe-sufficient children (n 24) were included as a non-treated reference group. Faecal samples were analysed at baseline and at 2, 12 and 38 weeks to determine the effects of Fe supplementation on ten bacterial groups in the gut (quantitative PCR), faecal SCFA concentration (HPLC) and gut inflammation (faecal calprotectin concentration). At baseline, concentrations of bacterial groups in the gut, faecal SCFA and faecal calprotectin did not differ between Fe-deficient and Fe-sufficient children. Fe supplementation significantly improved Fe status in Fe-deficient children and did not significantly increase faecal calprotectin concentration. Moreover, no significant effect of Fe treatment or time × treatment interaction on the concentrations of bacterial groups in the gut or faecal SCFA was observed compared with the placebo treatment. Also, there were no significant differences observed in the concentrations of any of the bacterial target groups or faecal SCFA at 2, 12 or 38 weeks between the three groups of children when correcting for baseline values. The present study suggests that in African children with a low enteropathogen burden, Fe status and dietary Fe supplementation did not significantly affect the dominant bacterial groups in the gut, faecal SCFA concentration or gut inflammation.

Efficient generation of rat induced pluripotent stem cells using a non-viral inducible vector.

Current methods of generating rat induced pluripotent stem cells are based on viral transduction of pluripotency inducing genes (Oct4, Sox2, c-myc and Klf4) into somatic cells. These activate endogenous pluripotency genes and reprogram the identity of the cell to an undifferentiated state. Epigenetic silencing of exogenous genes has to occur to allow normal iPS cell differentiation. To gain more control over the expression of exogenous reprogramming factors, we used a novel doxycycline-inducible plasmid vector encoding Oct4, Sox2, c-Myc and Klf4. To ensure efficient and controlled generation of iPS cells by plasmid transfection we equipped the reprogramming vector with a bacteriophage φC31 attB site and used a φC31 integrase expression vector to enhance vector integration. A series of doxycycline-independent rat iPS cell lines were established. These were characterized by immunocytochemical detection of Oct4, SSEA1 and SSEA4, alkaline phosphatase staining, methylation analysis of the endogenous Oct4 promoter and RT-PCR analysis of endogenous rat pluripotency genes. We also determined the number of vector integrations and the extent to which reprogramming factor gene expression was controlled. Protocols were developed to generate embryoid bodies and rat iPS cells demonstrated as pluripotent by generating derivatives of all three embryonic germ layers in vitro, and teratoma formation in vivo. All data suggest that our rat iPS cells, generated by plasmid based reprogramming, are similar to rat ES cells. Methods of DNA transfection, protein transduction and feeder-free monolayer culture of rat iPS cells were established to enable future applications.