Reliability Demonstration Approach for Advanced Stirling Radioisotope Generator

Developed for future space missions as a high-efficiency power system, the Advanced Stirling Radioisotope Generator (ASRG) has a design life requirement of 14 yr in space following a potential storage of 3 yr after fueling. In general, the demonstration of long-life dynamic systems remains difficult in part due to the perception that the wearout of moving parts cannot be minimized, and associated failures are unpredictable. This paper shows a combination of systematic analytical methods, extensive experience gained from technology development, and well-planned tests can be used to ensure a high level reliability of ASRG. With this approach, all potential risks from each life phase of the system are evaluated and the mitigation adequately addressed. This paper also provides a summary of important test results obtained to date for ASRG and the planned effort for system-level extended operation

Chromatin and transcriptional signatures for Nodal signaling during endoderm formation in hESCs

AbstractThe first stages of embryonic differentiation are driven by signaling pathways hardwired to induce particular fates. Endoderm commitment is controlled by the TGF-β superfamily member, Nodal, which utilizes the transcription factors, SMAD2/3, SMAD4 and FOXH1, to drive target gene expression. While the role of Nodal is well defined within the context of endoderm commitment, mechanistically it is unknown how this signal interacts with chromatin on a genome wide scale to trigger downstream responses. To elucidate the Nodal transcriptional network that governs endoderm formation, we used ChIP-seq to identify genomic targets for SMAD2/3, SMAD3, SMAD4, FOXH1 and the active and repressive chromatin marks, H3K4me3 and H3K27me3, in human embryonic stem cells (hESCs) and derived endoderm. We demonstrate that while SMAD2/3, SMAD4 and FOXH1 associate with DNA in a highly dynamic fashion, there is an optimal bivalent signature at 32 gene loci for driving endoderm commitment. Initially, this signature is marked by both H3K4me3 and H3K27me3 as a very broad bivalent domain in hESCs. Within the first 24h, SMAD2/3 accumulation coincides with H3K27me3 reduction so that these loci become monovalent marked by H3K4me3. JMJD3, a histone demethylase, is simultaneously recruited to these promoters, suggesting a conservation of mechanism at multiple promoters genome-wide. The correlation between SMAD2/3 binding, monovalent formation and transcriptional activation suggests a mechanism by which SMAD proteins coordinate with chromatin at critical promoters to drive endoderm specification

Transcriptional dynamics of transposable elements in the type I IFN response in Myotis lucifugus cells

Bats are a major reservoir of zoonotic viruses, and there has been growing interest in characterizing bat-specific features of innate immunity and inflammation. Recent studies have revealed bat-specific adaptations affecting interferon (IFN) signaling and IFN-stimulated genes (ISGs), but we still have a limited understanding of the genetic mechanisms that have shaped the evolution of bat immunity. Here we investigated the transcriptional and epigenetic dynamics of transposable elements (TEs) during the type I IFN response in little brown bat (Myotis lucifugus) primary embryonic fibroblast cells, using RNA-seq and CUT&amp;RUN. &nbsp;</p

A High-Light Sensitivity Optical Neural Silencer: Development and Application to Optogenetic Control of Non-Human Primate Cortex

Technologies for silencing the electrical activity of genetically targeted neurons in the brain are important for assessing the contribution of specific cell types and pathways toward behaviors and pathologies. Recently we found that archaerhodopsin-3 from Halorubrum sodomense (Arch), a light-driven outward proton pump, when genetically expressed in neurons, enables them to be powerfully, transiently, and repeatedly silenced in response to pulses of light. Because of the impressive characteristics of Arch, we explored the optogenetic utility of opsins with high sequence homology to Arch, from archaea of the Halorubrum genus. We found that the archaerhodopsin from Halorubrum strain TP009, which we named ArchT, could mediate photocurrents of similar maximum amplitude to those of Arch (∼900 pA in vitro), but with a >3-fold improvement in light sensitivity over Arch, most notably in the optogenetic range of 1–10 mW/mm2, equating to >2× increase in brain tissue volume addressed by a typical single optical fiber. Upon expression in mouse or rhesus macaque cortical neurons, ArchT expressed well on neuronal membranes, including excellent trafficking for long distances down neuronal axons. The high light sensitivity prompted us to explore ArchT use in the cortex of the rhesus macaque. Optical perturbation of ArchT-expressing neurons in the brain of an awake rhesus macaque resulted in a rapid and complete (∼100%) silencing of most recorded cells, with suppressed cells achieving a median firing rate of 0 spikes/s upon illumination. A small population of neurons showed increased firing rates at long latencies following the onset of light stimulation, suggesting the existence of a mechanism of network-level neural activity balancing. The powerful net suppression of activity suggests that ArchT silencing technology might be of great use not only in the causal analysis of neural circuits, but may have therapeutic applications

Monitoring Deformation in Graphene Through Hyperspectral Synchrotron Spectroscopy to Inform Fabrication

The promise from graphene to produce devices with high mobilities and detectors with fast response times is truncated in practice by strain and deformation originating during growth and subsequent processing. This work describes effects from graphene growth, multiple layer transfer, and substrate termination on out of plane deformation, critical to device performance. Synchrotron spectroscopy data was acquired with a state-of-the-art hyperspectral large-area detector to describe growth and processing with molecular sensitivity at wafer length scales. A study of methodologies used in data analysis discouraged dichroic ratio approaches in favor of orbital vector approximations and data mining algorithms. Orbital vector methods provide a physical insight into mobility-detrimental rippling by identifying ripple frequency as main actor, rather than intensity; which was confirmed by data mining algorithms, and in good agreement with electron scattering theories of corrugation in graphene. This work paves the way to efficient information from mechanical properties in graphene in a high throughput mode throughout growth and processing in a materials by design approach

Independent optical excitation of distinct neural populations

Optogenetic tools enable examination of how specific cell types contribute to brain circuit functions. A long-standing question is whether it is possible to independently activate two distinct neural populations in mammalian brain tissue. Such a capability would enable the study of how different synapses or pathways interact to encode information in the brain. Here we describe two channelrhodopsins, Chronos and Chrimson, discovered through sequencing and physiological characterization of opsins from over 100 species of alga. Chrimson's excitation spectrum is red shifted by 45 nm relative to previous channelrhodopsins and can enable experiments in which red light is preferred. We show minimal visual system–mediated behavioral interference when using Chrimson in neurobehavioral studies in Drosophila melanogaster. Chronos has faster kinetics than previous channelrhodopsins yet is effectively more light sensitive. Together these two reagents enable two-color activation of neural spiking and downstream synaptic transmission in independent neural populations without detectable cross-talk in mouse brain slice.PostprintPeer reviewe

Transgenic Mice for Intersectional Targeting of Neural Sensors and Effectors with High Specificity and Performance

SummaryAn increasingly powerful approach for studying brain circuits relies on targeting genetically encoded sensors and effectors to specific cell types. However, current approaches for this are still limited in functionality and specificity. Here we utilize several intersectional strategies to generate multiple transgenic mouse lines expressing high levels of novel genetic tools with high specificity. We developed driver and double reporter mouse lines and viral vectors using the Cre/Flp and Cre/Dre double recombinase systems and established a new, retargetable genomic locus, TIGRE, which allowed the generation of a large set of Cre/tTA-dependent reporter lines expressing fluorescent proteins, genetically encoded calcium, voltage, or glutamate indicators, and optogenetic effectors, all at substantially higher levels than before. High functionality was shown in example mouse lines for GCaMP6, YCX2.60, VSFP Butterfly 1.2, and Jaws. These novel transgenic lines greatly expand the ability to monitor and manipulate neuronal activities with increased specificity.Video Abstrac

Noninvasive optical inhibition with a red-shifted microbial rhodopsin

Optogenetic inhibition of the electrical activity of neurons enables the causal assessment of their contributions to brain functions. Red light penetrates deeper into tissue than other visible wavelengths. We present a red-shifted cruxhalorhodopsin, Jaws, derived from Haloarcula (Halobacterium) salinarum (strain Shark) and engineered to result in red light–induced photocurrents three times those of earlier silencers. Jaws exhibits robust inhibition of sensory-evoked neural activity in the cortex and results in strong light responses when used in retinas of retinitis pigmentosa model mice. We also demonstrate that Jaws can noninvasively mediate transcranial optical inhibition of neurons deep in the brains of awake mice. The noninvasive optogenetic inhibition opened up by Jaws enables a variety of important neuroscience experiments and offers a powerful general-use chloride pump for basic and applied neuroscience.McGovern Institute for Brain Research at MIT (Razin Fellowship)United States. Defense Advanced Research Projects Agency. Living Foundries Program (HR0011-12-C-0068)Harvard-MIT Joint Research Grants Program in Basic NeuroscienceHuman Frontier Science Program (Strasbourg, France)Institution of Engineering and Technology (A. F. Harvey Prize)McGovern Institute for Brain Research at MIT. Neurotechnology (MINT) ProgramNew York Stem Cell Foundation (Robertson Investigator Award)National Institutes of Health (U.S.) (New Innovator Award 1DP2OD002002)National Institute of General Medical Sciences (U.S.) (EUREKA Award 1R01NS075421)National Institutes of Health (U.S.) (Grant 1R01DA029639)National Institutes of Health (U.S.) (Grant 1RC1MH088182)National Institutes of Health (U.S.) (Grant 1R01NS067199)National Science Foundation (U.S.) (Career Award CBET 1053233)National Science Foundation (U.S.) (Grant EFRI0835878)National Science Foundation (U.S.) (Grant DMS0848804)Society for Neuroscience (Research Award for Innovation in Neuroscience)Wallace H. Coulter FoundationNational Institutes of Health (U.S.) (RO1 MH091220-01)Whitehall FoundationEsther A. & Joseph Klingenstein Fund, Inc.JPB FoundationPIIF FundingNational Institute of Mental Health (U.S.) (R01-MH102441-01)National Institutes of Health (U.S.) (DP2-OD-017366-01)Massachusetts Institute of Technology. Simons Center for the Social Brai

AI is a viable alternative to high throughput screening: a 318-target study

: High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that our AtomNet® convolutional neural network successfully finds novel hits across every major therapeutic area and protein class. We address historical limitations of computational screening by demonstrating success for target proteins without known binders, high-quality X-ray crystal structures, or manual cherry-picking of compounds. We show that the molecules selected by the AtomNet® model are novel drug-like scaffolds rather than minor modifications to known bioactive compounds. Our empirical results suggest that computational methods can substantially replace HTS as the first step of small-molecule drug discovery

The placenta goes viral: Retroviruses control gene expression in pregnancy.

The co-option of endogenous retroviruses (ERVs) is increasingly recognized as a recurrent theme in placental biology, which has far-reaching implications for our understanding of mammalian evolution and reproductive health. Most research in this area has focused on ERV-derived proteins, which have been repeatedly co-opted to promote cell-cell fusion and immune modulation in the placenta. ERVs also harbor regulatory sequences that can potentially control placental gene expression, but there has been limited evidence to support this role. In a recent study, Dunn-Fletcher and colleagues discover a striking example of an ERV-derived enhancer element that has been co-opted to regulate a gene important for human pregnancy. Using genomic and experimental approaches, they firmly establish that a primate-specific ERV functions as a placenta-specific enhancer for corticotropin-releasing hormone (CRH), a hormone linked to the control of birth timing in humans. Their findings implicate an extensive yet understudied role for retroviruses in shaping the evolution of placental gene regulatory networks