A dynamical model of ommatidial crystal formation.

The crystalline photoreceptor lattice in the Drosophila eye is a paradigm for pattern formation during development. During eye development, activation of proneural genes at a moving front adds new columns to a regular lattice of R8 photoreceptors. We present a mathematical model of the governing activator-inhibitor system, which indicates that the dynamics of positive induction play a central role in the selection of certain cells as R8s. The "switch and template" patterning mechanism we observe is mathematically very different from the well-known Turing instability. Unlike a standard lateral inhibition model, our picture implies that R8s are defined before the appearance of the complete group of proneural cells. The model reproduces the full time course of proneural gene expression and accounts for specific features of the refinement of proneural groups that had resisted explanation. It moreover predicts that perturbing the normal template can lead to eyes containing stripes of R8 cells. We observed these stripes experimentally after manipulation of the Notch and scabrous genes. Our results suggest an alternative to the generally assumed mode of operation for lateral inhibition during development; more generally, they hint at a broader role for bistable switches in the initial establishment of patterns as well as in their maintenance.

Brain Death: Medical, Ethical, Cultural, and Legal Aspects.

The development of critical care stimulated brain death criteria formulation in response to concerns on treatment resources and unregulated organ procurement. The diagnosis centered on irreversible loss of brain function and subsequent systemic physiologic collapse and was subsequently codified into law. With improved critical care, physiologic collapse (while predominant) is not inevitable-provoking criticisms of the ethical and legal foundation for brain death. Other criteria have been unsuccessfully proposed, but irreversibility remains the conceptual foundation. Conflicts can arise when families reject the diagnosis-resulting in ethical, cultural, and communication challenges and implications for diversity, equity, and inclusion.

AcumenTM hypotension prediction index guidance for prevention and treatment of hypotension in noncardiac surgery: a prospective, single-arm, multicenter trial.

BACKGROUND: Intraoperative hypotension is common during noncardiac surgery and is associated with postoperative myocardial infarction, acute kidney injury, stroke, and severe infection. The Hypotension Prediction Index software is an algorithm based on arterial waveform analysis that alerts clinicians of the patient's likelihood of experiencing a future hypotensive event, defined as mean arterial pressure < 65 mmHg for at least 1 min. METHODS: Two analyses included (1) a prospective, single-arm trial, with continuous blood pressure measurements from study monitors, compared to a historical comparison cohort. (2) A post hoc analysis of a subset of trial participants versus a propensity score-weighted contemporaneous comparison group, using external data from the Multicenter Perioperative Outcomes Group (MPOG). The trial included 485 subjects in 11 sites; 406 were in the final effectiveness analysis. The post hoc analysis included 457 trial participants and 15,796 comparison patients. Patients were eligible if aged 18 years or older, American Society of Anesthesiologists (ASA) physical status 3 or 4, and scheduled for moderate- to high-risk noncardiac surgery expected to last at least 3 h. MEASUREMENTS: minutes of mean arterial pressure (MAP) below 65 mmHg and area under MAP < 65 mmHg. RESULTS: Analysis 1: Trial subjects (n = 406) experienced a mean of 9 ± 13 min of MAP below 65 mmHg, compared with the MPOG historical control mean of 25 ± 41 min, a 65% reduction (p < 0.001). Subjects with at least one episode of hypotension (n = 293) had a mean of 12 ± 14 min of MAP below 65 mmHg compared with the MPOG historical control mean of 28 ± 43 min, a 58% reduction (p< 0.001). Analysis 2: In the post hoc inverse probability treatment weighting model, patients in the trial demonstrated a 35% reduction in minutes of hypotension compared to a contemporaneous comparison group [exponentiated coefficient: - 0.35 (95%CI - 0.43, - 0.27); p < 0.001]. CONCLUSIONS: The use of prediction software for blood pressure management was associated with a clinically meaningful reduction in the duration of intraoperative hypotension. Further studies must investigate whether predictive algorithms to prevent hypotension can reduce adverse outcomes. TRIAL REGISTRATION: Clinical trial number: NCT03805217. Registry URL: https://clinicaltrials.gov/ct2/show/NCT03805217 . Principal investigator: Xiaodong Bao, MD, PhD. Date of registration: January 15, 2019.

Mapping the UDP-glucuronic acid binding site in UDP-glucuronosyltransferase-1A10 by homology-based modeling: confirmation with biochemical evidence.

The UDP-glucuronosyltransferase (UGT) isozyme system is critical for protecting the body against endogenous and exogenous chemicals by linking glucuronic acid donated by UDP-glucuronic acid to a lipophilic acceptor substrate. UGTs convert metabolites, dietary constituents, and environmental toxicants to highly excretable glucuronides. Because of difficulties associated with purifying endoplasmic reticulum-bound UGTs for structural studies, we carried out homology-based computer modeling to aid analysis. The search found structural homology in Escherichia coli UDP-galactose 4-epimerase. Consistent with predicted similarities involving the common UDP moiety in substrate/inhibitor, UDP-glucose and UDP-hexanol amine caused competitive inhibition by Lineweaver-Burk plots. Among predicted binding sites N292, K314, K315, and K404 in UGT1A10, two informative sets of mutants K314R/Q/A/E/G and K404R/E had null activities or 2.7-fold higher/50% less activity, respectively. Scatchard analysis of binding data of the affinity ligand, 5-azidouridine-[beta- (32)P]diphosphoglucuronic acid, to purified UGT1A10-His or UGT1A7-His revealed high- and low-affinity binding sites. 2-Nitro-5-thiocyanobenzoic acid-digested UGT1A10-His bound with the radiolabeled affinity ligand revealed an 11.3 and 14.3 kDa peptide associated with K314 and K404, respectively, in a discontinuous SDS-PAGE system. Similar treatment of 1A10His-K314A bound with the ligand lacked both peptides; 1A10-HisK404R- and 1A10-HisK404E showed 1.3-fold greater and 50% less label in the 14.3 kDa peptide, respectively, compared to 1A10-His without affecting the 11.3 kDa peptide. Scatchard analysis of binding data of the affinity ligand to 1A10His-K404R and -K404E showed a 6-fold reduction and a large increase in K d, respectively. Our results indicate that K314 and K404 are required UDP-glcA binding sites in 1A10, that K404 controls activity and high-affinity sites, and that K314 and K404 are strictly conserved in 70 aligned UGTs, except for S321, equivalent to K314, in UGT2B15 and 2B17 and I321 in the inactive UGT8, which suggests UGT2B15 and 2B17 contain suboptimal activity. Hence our data strongly support UDP-glcA binding to K314 and K404 in UGT1A10.

A Technique to Allow Prone Positioning in the Spine Surgery Patient With Unstable Spine Fracture and Flail Segment Rib Fractures.

Two patients with unstable thoracic spine and flail segment rib fractures initially failed prone positioning on a Jackson spinal table used for posterior spinal instrumentation and fusion surgery. Both patients experienced rapid hemodynamic collapse. We developed a solution using the anterior portions of a thoracolumbosacral orthosis brace as chest supports to use during prone positioning, allowing both patients to undergo uncomplicated posterior spinal instrumentation and fusion surgeries with greater hemodynamic stability.

Do femtonewton forces affect genetic function? A review.

Protein-Mediated DNA looping is intricately related to gene expression. Therefore any mechanical constraint that disrupts loop formation can play a significant role in gene regulation. Polymer physics models predict that less than a piconewton of force may be sufficient to prevent the formation of DNA loops. Thus, it appears that tension can act as a molecular switch that controls the much larger forces associated with the processive motion of RNA polymerase. Since RNAP can exert forces over 20 pN before it stalls, a 'substrate tension switch' could offer a force advantage of two orders of magnitude. Evidence for such a mechanism is seen in recent in vitro micromanipulation experiments. In this article we provide new perspective on existing theory and experimental data on DNA looping in vitro and in vivo. We elaborate on the connection between tension and a variety of other intracellular mechanical constraints including sequence specific curvature and supercoiling. In the process, we emphasize that the richness and versatility of DNA mechanics opens up a whole new paradigm of gene regulation to explore.

Three-dimensional characterization of tethered microspheres by total internal reflection fluorescence microscopy.

Tethered particle microscopy is a powerful tool to study the dynamics of DNA molecules and DNA-protein complexes in single-molecule experiments. We demonstrate that stroboscopic total internal reflection microscopy can be used to characterize the three-dimensional spatiotemporal motion of DNA-tethered particles. By calculating characteristic measures such as symmetry and time constants of the motion, well-formed tethers can be distinguished from defective ones for which the motion is dominated by aberrant surface effects. This improves the reliability of measurements on tether dynamics. For instance, in observations of protein-mediated DNA looping, loop formation is distinguished from adsorption and other nonspecific events.