Using high-throughput barcode sequencing to efficiently map connectomes

The function of a neural circuit is determined by the details of its synaptic connections. At present, the only available method for determining a neural wiring diagram with single synapse precision-a 'connectome'-is based on imaging methods that are slow, labor-intensive and expensive. Here, we present SYNseq, a method for converting the connectome into a form that can exploit the speed and low cost of modern high-throughput DNA sequencing. In SYNseq, each neuron is labeled with a unique random nucleotide sequence-an RNA 'barcode'-which is targeted to the synapse using engineered proteins. Barcodes in pre- and postsynaptic neurons are then associated through protein-protein crosslinking across the synapse, extracted from the tissue, and joined into a form suitable for sequencing. Although our failure to develop an efficient barcode joining scheme precludes the widespread application of this approach, we expect that with further development SYNseq will enable tracing of complex circuits at high speed and low cost

Development of an In Vitro Compartmentalization Screen for High-Throughput Directed Evolution of [FeFe] Hydrogenases

BACKGROUND: [FeFe] hydrogenase enzymes catalyze the formation and dissociation of molecular hydrogen with the help of a complex prosthetic group composed of common elements. The development of energy conversion technologies based on these renewable catalysts has been hindered by their extreme oxygen sensitivity. Attempts to improve the enzymes by directed evolution have failed for want of a screening platform capable of throughputs high enough to adequately sample heavily mutated DNA libraries. In vitro compartmentalization (IVC) is a powerful method capable of screening for multiple-turnover enzymatic activity at very high throughputs. Recent advances have allowed [FeFe] hydrogenases to be expressed and activated in the cell-free protein synthesis reactions on which IVC is based; however, IVC is a demanding technique with which many enzymes have proven incompatible. METHODOLOGY/PRINCIPAL FINDINGS: Here we describe an extremely high-throughput IVC screen for oxygen-tolerant [FeFe] hydrogenases. We demonstrate that the [FeFe] hydrogenase CpI can be expressed and activated within emulsion droplets, and identify a fluorogenic substrate that links activity after oxygen exposure to the generation of a fluorescent signal. We present a screening protocol in which attachment of mutant genes and the proteins they encode to the surfaces of microbeads is followed by three separate emulsion steps for amplification, expression, and evaluation of hydrogenase mutants. We show that beads displaying active hydrogenase can be isolated by fluorescence-activated cell-sorting, and we use the method to enrich such beads from a mock library. CONCLUSIONS/SIGNIFICANCE: [FeFe] hydrogenases are the most complex enzymes to be produced by cell-free protein synthesis, and the most challenging targets to which IVC has yet been applied. The technique described here is an enabling step towards the development of biocatalysts for a biological hydrogen economy

Enhancing Protease Activity Assay in Droplet-Based Microfluidics Using a Biomolecule Concentrator

We introduce an integrated microfluidic device consisting of a biomolecule concentrator and a microdroplet generator, which enhances the limited sensitivity of low-abundance enzyme assays by concentrating biomolecules before encapsulating them into droplet microreactors. We used this platform to detect ultralow levels of matrix metalloproteinases (MMPs) from diluted cellular supernatant and showed that it significantly (~10-fold) reduced the time required to complete the assay and the sample volume used.National Institutes of Health (U.S.) (Grant GM68762)National Institutes of Health (U.S.) (Grant U54-CA112967)National Institutes of Health (U.S.) (Grant R01-EB010246)National Institutes of Health (U.S.) (Grant R01-GM081336)National Science Foundation (U.S.) (Graduate Fellowship)United States. Defense Advanced Research Projects Agency (Cipher Program

Sotatercept, a novel transforming growth factor beta ligand trap, improves anemia in beta-thalassemia: a phase 2, open-label, dose-finding study

\u3b2-thalassemia, a hereditary blood disorder caused by defective synthesis of hemoglobin \u3b2 globin chains, leads to ineffective erythropoiesis and chronic anemia that may require blood transfusions. Sotatercept (ACE-011) acts as a ligand trap to inhibit negative regulators of late-stage erythropoiesis in the transforming growth factor beta superfamily, correcting ineffective erythropoiesis. In this phase II, open-label, dose-finding study, 16 patients with transfusion-dependent \u3b2-thalassemia and 30 patients with non-transfusion-dependent \u3b2 thalassemia were enrolled at 7 centers in 4 countries from November 2012 to November 2014. Patients were treated with sotatercept at 0.1, 0.3, 0.5, 0.75, or 1.0 mg/kg to determine a safe and effective dose. Doses were administered by subcutaneous injection every 3 weeks. Patients were treated for 6422 months. Response was assessed as a 6520% reduction in transfusion burden sustained for 24 weeks in transfusion-dependent \u3b2-thalassemia patients, and an increase in hemoglobin level of 651.0 g/dL sustained for 12 weeks in non-transfusion-dependent \u3b2-thalassemia patients. Sotatercept was well tolerated. After a median treatment duration of 14.4 months (range 0.6-35.9), no severe life-threatening adverse events were observed; 13% of patients reported serious but manageable adverse events. The active dose of sotatercept was 650.3 mg/kg for non-transfusion-dependent \u3b2-thalassemia and 650.5 mg/kg for transfusion-dependent \u3b2-thalassemia patients. Of 30 non-transfusion-dependent \u3b2-thalassemia patients treated with 650.1 mg/kg sotatercept, 18 (60%) achieved a mean hemoglobin increase 651.0 g/dL, and 11 (37%) an increase 651.5 g/dL, sustained for 6512 weeks. Four (100%) transfusion-dependent \u3b2-thalassemia patients treated with 1.0 mg/kg sotatercept achieved a transfusion-burden reduction of 6520%. Sotatercept was effective and well tolerated in patients with \u3b2-thalassemia. Most non-transfusion-dependent \u3b2-thalassemia patients treated with higher doses achieved sustained increases in hemoglobin level. Transfusion-dependent \u3b2-thalassemia patients treated with higher doses of sotatercept achieved notable reductions in transfusion requirement. The registration number at ClinicalTrials.gov was NCT01571635

Highly Parallel Genome-Wide Expression Analysis of Single Mammalian Cells

We have developed a high-throughput amplification method for generating robust gene expression profiles using single cell or low RNA inputs.The method uses tagged priming and template-switching, resulting in the incorporation of universal PCR priming sites at both ends of the synthesized cDNA for global PCR amplification. Coupled with a whole-genome gene expression microarray platform, we routinely obtain expression correlation values of R(2)~0.76-0.80 between individual cells and R(2)~0.69 between 50 pg total RNA replicates. Expression profiles generated from single cells or 50 pg total RNA correlate well with that generated with higher input (1 ng total RNA) (R(2)~0.80). Also, the assay is sufficiently sensitive to detect, in a single cell, approximately 63% of the number of genes detected with 1 ng input, with approximately 97% of the genes detected in the single-cell input also detected in the higher input.In summary, our method facilitates whole-genome gene expression profiling in contexts where starting material is extremely limiting, particularly in areas such as the study of progenitor cells in early development and tumor stem cell biology

Single-cell analysis tools for drug discovery and development

The genetic, functional or compositional heterogeneity of healthy and diseased tissues presents major challenges in drug discovery and development. Such heterogeneity hinders the design of accurate disease models and can confound the interpretation of biomarker levels and of patient responses to specific therapies. The complex nature of virtually all tissues has motivated the development of tools for single-cell genomic, transcriptomic and multiplex proteomic analyses. Here, we review these tools and assess their advantages and limitations. Emerging applications of single cell analysis tools in drug discovery and development, particularly in the field of oncology, are discussed