363 research outputs found
Central spindle self-organization and cytokinesis in artificially activated sea urchin eggs
Author Posting. © Marine Biological Laboratory, 2016. This article is posted here by permission of Marine Biological Laboratory for personal use, not for redistribution. The definitive version was published in Biological Bulletin 230, no.2 (2016): 85-95.The ability of microtubules of the mitotic apparatus
to control the positioning and initiation of the cleavage
furrow during cytokinesis was first established from
studies on early echinoderm embryos. However, the identity
of the microtubule population that imparts cytokinetic signaling
is unclear. The two main––and not necessarily mutually
exclusive–– candidates are the central spindle and the
astral rays. In the present study, we examined cytokinesis in
ammonia-activated sea urchin eggs, which lack paternally
derived centrosomes and undergo mitosis mediated by unusual
anastral, bipolar mini-spindles. Live cell imaging and
immunolabeling for microtubules and the centralspindlin
constituent and kinesin-related protein, MKLP1, demonstrated
that furrowing in ammonia-activated eggs was associated
with aligned arrays of centralspindlin-linked, opposed
bundles of antiparallel microtubules. These autonomous, zipper-
like arrays were not associated with a mitotic apparatus,
but did possess characteristics similar to the central spindle
region of control, fertilized embryos. Our results highlight the
self-organizing nature of the central spindle region and its
ability to induce cytokinesis-like furrowing, even in the absence
of a complete mitotic apparatus.This research was
supported by student/faculty summer research grants from
the Dickinson College Research and Development Committee
to JHH; Laura and Arthur Colwin Summer Research
Fellowships from the MBL to JHH and CBS; a National
Science Foundation Major Research Instrumentation grant
to JHH (MRI-0320606); and a NSF collaborative research
grant to JHH (MCB-1412688) and to CBS (MCB-
1412734)
Spiral Evolution in a Confined Geometry
Supported nanoscale lead crystallites with a step emerging from a
non-centered screw dislocation on the circular top facet were prepared by rapid
cooling from just above the melting temperature. STM observations of the top
facet show a nonuniform rotation rate and shape of the spiral step as the
crystallite relaxes. These features can be accurately modeled using curvature
driven dynamics, as in classical models of spiral growth, with boundary
conditions fixing the dislocation core and regions of the step lying along the
outer facet edge.Comment: 4 pages, 3 figures, to be published in Physical Review Letter
Shuttle Ground Support Equipment (GSE) T-0 Umbilical to Space Shuttle Program (SSP) Flight Elements Consultation
The NASA Engineering and Safety Center (NESC) was tasked with assessing the validity of an alternate opinion that surfaced during the investigation of recurrent failures at the Space Shuttle T-0 umbilical interface. The most visible problem occurred during the Space Transportation System (STS)-112 launch when pyrotechnics used to separate Solid Rocket Booster (SRB) Hold-Down Post (HDP) frangible nuts failed to fire. Subsequent investigations recommended several improvements to the Ground Support Equipment (GSE) and processing changes were implemented, including replacement of ground-half cables and connectors between flights, along with wiring modifications to make critical circuits quad-redundant across the interface. The alternate opinions maintained that insufficient data existed to exonerate the design, that additional data needed to be gathered under launch conditions, and that the interface should be further modified to ensure additional margin existed to preclude failure. The results of the assessment are contained in this report
Spatial analysis of individual- and village-level sociodemographic characteristics associated with age at marriage among married adolescents in rural Niger.
BACKGROUND: Niger has the highest prevalence of child marriage in the world. While child marriage in Niger is clearly normative in the sense that it is commonly practiced, the social and contextual factors that contribute to it are still unclear. METHODS: Here, we tested the importance of village-level factors as predictors of young age at marriage for a group of married adolescent girls (N = 1031) in the Dosso district of rural Niger, using multi-level and geographic analyses. We aggregated significant individual level factors to determine whether, independent of a girl's own sociodemographic characteristics, the impact of each factor is associated at the village level. Finally, we tested for spatial dependence and heterogeneity in examining whether the village-level associations we find with age at marriage differ geographically. RESULTS: The mean age of marriage for girls in our study was 14.20 years (SD 1.8). Our statistical results are consistent with other literature suggesting that education is associated with delayed marriage, even among adolescent girls. Younger ages at marriage are also associated with a greater age difference between spouses and with a greater likelihood of women being engaged in agricultural work. Consistent with results at the individual level, at the village level we found that the proportion of girls who do agricultural work and the mean age difference between spouses were both predictive of a lower age at marriage for individual girls. Finally, mapping age at marriage at the village level revealed that there is geographical variation in age at marriage, with a cluster of hot spots in the Hausa-dominated eastern area where age at marriage is particularly low and a cluster of cold spots in the Zarma-dominated western areas where age at marriage is relatively high. CONCLUSIONS: Our findings suggest that large-scale approaches to eliminating child marriage in these communities may be less successful if they do not take into consideration geographically and socially determined contextual factors at the village level
Arp2/3 complex inhibition radically alters lamellipodial actin architecture, suspended cell shape, and the cell spreading process
© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Molecular Biology of the Cell 26 (2015): 887-900, doi:10.1091/mbc.E14-07-1244.Recent studies have investigated the dendritic actin cytoskeleton of the cell edge's lamellipodial (LP) region by experimentally decreasing the activity of the actin filament nucleator and branch former, the Arp2/3 complex. Here we extend these studies via pharmacological inhibition of the Arp2/3 complex in sea urchin coelomocytes, cells that possess an unusually broad LP region and display correspondingly exaggerated centripetal flow. Using light and electron microscopy, we demonstrate that Arp2/3 complex inhibition via the drug CK666 dramatically altered LP actin architecture, slowed centripetal flow, drove a lamellipodial-to-filopodial shape change in suspended cells, and induced a novel actin structural organization during cell spreading. A general feature of the CK666 phenotype in coelomocytes was transverse actin arcs, and arc generation was arrested by a formin inhibitor. We also demonstrate that CK666 treatment produces actin arcs in other cells with broad LP regions, namely fish keratocytes and Drosophila S2 cells. We hypothesize that the actin arcs made visible by Arp2/3 complex inhibition in coelomocytes may represent an exaggerated manifestation of the elongate mother filaments that could possibly serve as the scaffold for the production of the dendritic actin network.This research was supported by National Science Foundation STEP grant 0856704 to Dickinson College, student/faculty summer research grants from the Dickinson College Research and Development Committee, Laura and Arthur Colwin Summer Research Fellowships from the Marine Biological Laboratory to J.H.H. and C.B.S., National Institutes of Health Grant EB002583 to R.O., and National Science Foundation collaborative research grants to J.H.H. (MCB-1412688) and C.B.S. (MCB-1412734)
Final Report of the AFIT Quality Initiative Internal Discovery Committee
This document contains results of a study designed to document the key elements for student success at AFIT in our continuing education and graduate programs and discover to what degree they exist at AFIT. The effort represents an attempt to guide improvement of our graduate and continuing education programs through experience available from our faculty, staff and students. The process outlined herein was designed to achieve success by allowing the participants to define what it means to succeed and then self-assess the presence of these factors at AFIT. It’s therefore a true internal discovery process since its output reflects the state of our internal understanding of teaching and learning excellence. This inclusive approach, which garnered participation from 400 people across AFIT’s schools, will be used in conjunction with the external committee\u27s recommendations to determine a course of action to invest into AFIT\u27s instructional capabilities
The powers in PowerPoint: Embedded authorities, documentary tastes, and institutional (second) orders in corporate Korea
Microsoft PowerPoint is both the bane and banality of contemporary South Korean office work. Corporate workers spend countless hours refining and crafting plans, proposals, and reports in PowerPoint that often lead to conflicts with coworkers and overtime work. This article theorizes the excessive attention to documents in modern office contexts. Where scholars have been under the impression that institutional documents align with institutional purposes, I describe a context in which making documents for individual purposes and making them for work exist under a basic tension. Based on fieldwork in corporate Korea between 2013 and 2015, I describe how Korean office workers calibrate documents to the tastes of superiors who populate the managerial chain. These practices leave little trace of real "work" on paper, but they are productive for navigating complex internal labor markets and demonstrating a higher order value of attention toward others. These findings suggest that institutional and individual authorities are not competing projects inside organizations but become entangled in increasingly complex participatory encounters, even as they are channeled through a seemingly simple software like PowerPoint. [documents, expertise, authority, technology, South Korea
Ordered subset linkage analysis supports a susceptibility locus for age-related macular degeneration on chromosome 16p12
BACKGROUND: Age-related macular degeneration (AMD) is a complex disorder that is responsible for the majority of central vision loss in older adults living in developed countries. Phenotypic and genetic heterogeneity complicate the analysis of genome-wide scans for AMD susceptibility loci. The ordered subset analysis (OSA) method is an approach for reducing heterogeneity, increasing statistical power for detecting linkage, and helping to define the most informative data set for follow-up analysis. OSA assesses the linkage evidence in subsets of potentially more homogeneous families by rank-ordering family-specific lod scores with respect to trait-associated covariates or phenotypic features. Here, we present results of incorporating five continuous covariates into our genome-wide linkage analysis of 389 microsatellite markers in 62 multiplex families: Body mass index (BMI), systolic (SBP) and diastolic (DBP) blood pressure, intraocular pressure (IOP), and pack-years of cigarette smoking. Chromosome-wide significance of increases in nonparametric multipoint lod scores in covariate-defined subsets relative to the overall sample was assessed by permutation. RESULTS: Using a correction for testing multiple covariates, statistically significant lod score increases were observed for two chromosomal regions: 14q13 with a lod score of 3.2 in 28 families with average IOP ≤ 15.5 (p = 0.002), and 6q14 with a lod score of 1.6 in eight families with average BMI ≥ 30.1 (p = 0.0004). On chromosome 16p12, nominally significant lod score increases (p ≤ 0.05), up to a lod score of 2.9 in 32 families, were observed with several covariate orderings. While less significant, this was the only region where linkage evidence was associated with multiple clinically meaningful covariates and the only nominally significant finding when analysis was restricted to advanced forms of AMD. Families with linkage to 16p12 had higher averages of SBP, IOP and BMI and were primarily affected with neovascular AMD. For all three regions, linkage signals at or very near the peak marker have previously been reported. CONCLUSION: Our results suggest that a susceptibility gene on chromosome 16p12 may predispose to AMD, particularly to the neovascular form, and that further research into the previously suggested association of neovascular AMD and systemic hypertension is warranted
A quantitative theory of current-induced step bunching on Si(111)
We use a one-dimensional step model to study quantitatively the growth of
step bunches on Si(111) surfaces induced by a direct heating current.
Parameters in the model are fixed from experimental measurements near 900 deg C
under the assumption that there is local mass transport through surface
diffusion and that step motion is limited by the attachment rate of adatoms to
step edges. The direct heating current is treated as an external driving force
acting on each adatom. Numerical calculations show both qualitative and
quantitative agreement with experiment. A force in the step down direction will
destabilize the uniform step train towards step bunching. The average size of
the step bunches grows with electromigration time as t^beta, with beta = 0.5,
in agreement with experiment and with an analytical treatment of the steady
states. The model is extended to include the effect of direct hopping of
adatoms between different terraces. Monte-Carlo simulations of a solid-on-solid
model, using physically motivated assumptions about the dynamics of surface
diffusion and attachment at step edges, are carried out to study two
dimensional features that are left out of the present step model and to test
its validity. These simulations give much better agreement with experiment than
previous work. We find a new step bending instability when the driving force is
along the step edge direction. This instability causes the formation of step
bunches and antisteps that is similar to that observed in experiment.Comment: 11 pages, 7 figure
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