Dimensions and Global Twist of Single-Layer DNA Origami Measured by Small-Angle X-ray Scattering

The rational design of complementary DNA sequences can be used to create nanostructures that self-assemble with nanometer precision. DNA nanostructures have been imaged by atomic force microscopy and electron microscopy. Small-angle X-ray scattering (SAXS) provides complementary structural information on the ensemble-averaged state of DNA nanostructures in solution. Here we demonstrate that SAXS can distinguish between different single-layer DNA origami tiles that look identical when immobilized on a mica surface and imaged with atomic force microscopy. We use SAXS to quantify the magnitude of global twist of DNA origami tiles with different crossover periodicities: these measurements highlight the extreme structural sensitivity of single-layer origami to the location of strand crossovers. We also use SAXS to quantify the distance between pairs of gold nanoparticles tethered to specific locations on a DNA origami tile and use this method to measure the overall dimensions and geometry of the DNA nanostructure in solution. Finally, we use indirect Fourier methods, which have long been used for the interpretation of SAXS data from biomolecules, to measure the distance between DNA helix pairs in a DNA origami nanotube. Together, these results provide important methodological advances in the use of SAXS to analyze DNA nanostructures in solution and insights into the structures of single-layer DNA origami

Stroke genetics informs drug discovery and risk prediction across ancestries

Previous genome-wide association studies (GWASs) of stroke — the second leading cause of death worldwide — were conducted predominantly in populations of European ancestry1,2. Here, in cross-ancestry GWAS meta-analyses of 110,182 patients who have had a stroke (five ancestries, 33% non-European) and 1,503,898 control individuals, we identify association signals for stroke and its subtypes at 89 (61 new) independent loci: 60 in primary inverse-variance-weighted analyses and 29 in secondary meta-regression and multitrait analyses. On the basis of internal cross-ancestry validation and an independent follow-up in 89,084 additional cases of stroke (30% non-European) and 1,013,843 control individuals, 87% of the primary stroke risk loci and 60% of the secondary stroke risk loci were replicated (P < 0.05). Effect sizes were highly correlated across ancestries. Cross-ancestry fine-mapping, in silico mutagenesis analysis3, and transcriptome-wide and proteome-wide association analyses revealed putative causal genes (such as SH3PXD2A and FURIN) and variants (such as at GRK5 and NOS3). Using a three-pronged approach4, we provide genetic evidence for putative drug effects, highlighting F11, KLKB1, PROC, GP1BA, LAMC2 and VCAM1 as possible targets, with drugs already under investigation for stroke for F11 and PROC. A polygenic score integrating cross-ancestry and ancestry-specific stroke GWASs with vascular-risk factor GWASs (integrative polygenic scores) strongly predicted ischaemic stroke in populations of European, East Asian and African ancestry5. Stroke genetic risk scores were predictive of ischaemic stroke independent of clinical risk factors in 52,600 clinical-trial participants with cardiometabolic disease. Our results provide insights to inform biology, reveal potential drug targets and derive genetic risk prediction tools across ancestries

Functional DNA nanotechnology

This thesis sets out to further the field of functional DNA nanotechnology through the design of novel functional DNA scaffolds, and investigates their applications and efficacy. The work presented here comprises two parts: The design of a chiral DNA nanotube that acts as a scaffold for motor motion and for an enzyme cascade; and the design of two different tetrahedral scaffolds for selection of a combination of three ligands, which together have a greater binding effect than the sum of the individual components. It begins by proposing the design of a DNA origami nanotube which distinguishes between the inside and outside face of the tube at the design stage, which most previous designs reported do not. The previous designs in the literature result in a distribution of 50:50, of one face forming the inside surface on one tube and the same face forming the outside surface of a different tube. In the design presented in this thesis, this distinction results from making the tube chiral, which forces it to roll up in a predetermined manner. Chirality is introduced by varying the positions of staple crossovers and this process is explained. The chiral tubes may stack end-to-end to form long polymers, or exist in monomeric form with stacking suppressed, by inclusion of different sets of staples at the ends of the tubes. We confirm tube formation and right-handed chirality with AFM and CD respectively. The efficacy of the tube as a scaffold for an enzyme cascade is tested and discussed in context of the wider field. No significant enhancement is observed when enzymes are tethered to the inside of the tubes, compared to when they are tethered to the outside or are free in solution, although the same slight trend is always observed. Suggestions are made to better this experiment and further understand the underlying physics of such systems. We propose using the tube as a scaffold for a DNA track, upon which a DNA motor may walk. DNA motors are introduced and we attempt to observe micron-scale, inter-tube motion within the confines of our origami tube. Initial experiments show the motor moving and we propose methods of fluorescent labeling via PAINT to better the experimental set-up for TIRF microscopy, which currently is limited by photobleaching. The second part of this thesis proposes systems for selection of a combination of three ligands, which together have a greater binding effect than the sum of the individual components. Here we design two tetrahedral systems where either three ligands or three aptamers are brought together at a vertex of the tetrahedron to form a binding domain. The aptameric system allows for selection, amplification and reassembly of the strongest binders, because the functional and structural sequences are on one strand of DNA, following ligation. This design betters the initial tetrahedral system, where the coding/record strands for amplification are separate from the functional binding domain strands the ligands are attached to. This means it is not possible to reassemble this particular structure after amplification of the record strand.</p

Report of Proceedings of the Seventeenth Annual Meeting of the Alumnae Association of the Woman's Medical College of Pennsylvania, May 6 and 7, 1892.

Report of Proceedings of the Seventeenth Annual Meeting of the Alumnae Association of the Woman's Medical College of Pennsylvania, May 6 and 7, 1892. THree articles relate to the topical category Missionary Work and Public Health: a letter by Elizabeth M. Reifsnyder to Dr. Allen on pp.20-22 (Reifsnyder graduated from the Woman's Medical College of Pennsylvania in 1881); A glimpse of Chinese obstetrics by Rachel R. Benn-Bunkle on pp.22-24, who graduated from the Woman's Medical College of Pennsylvania in 1890; a necrology report on Sarah C. Seward, a medical missionary to India, on pp. 26-27

Non-invasive prenatal testing for aneuploidy and beyond: challenges of responsible innovation in prenatal screening

This paper contains a joint ESHG/ASHG position document with recommendations regarding responsible innovation in prenatal screening with non-invasive prenatal testing (NIPT). By virtue of its greater accuracy and safety with respect to prenatal screening for common autosomal aneuploidies, NIPT has the potential of helping the practice better achieve its aim of facilitating autonomous reproductive choices, provided that balanced pretest information and non-directive counseling are available as part of the screening offer. Depending on the health-care setting, different scenarios for NIPT-based screening for common autosomal aneuploidies are possible. The trade-offs involved in these scenarios should be assessed in light of the aim of screening, the balance of benefits and burdens for pregnant women and their partners and considerations of cost-effectiveness and justice. With improving screening technologies and decreasing costs of sequencing and analysis, it will become possible in the near future to significantly expand the scope of prenatal screening beyond common autosomal aneuploidies. Commercial providers have already begun expanding their tests to include sex-chromosomal abnormalities and microdeletions. However, multiple false positives may undermine the main achievement of NIPT in the context of prenatal screening: the significant reduction of the invasive testing rate. This document argues for a cautious expansion of the scope of prenatal screening to serious congenital and childhood disorders, only following sound validation studies and a comprehensive evaluation of all relevant aspects. A further core message of this document is that in countries where prenatal screening is offered as a public health programme, governments and public health authorities should adopt an active role to ensure the responsible innovation of prenatal screening on the basis of ethical principles. Crucial elements are the quality of the screening process as a whole (including non-laboratory aspects such as information and counseling), education of professionals, systematic evaluation of all aspects of prenatal screening, development of better evaluation tools in the light of the aim of the practice, accountability to all stakeholders including children born from screened pregnancies and persons living with the conditions targeted in prenatal screening and promotion of equity of access