196 research outputs found
Plant stem cell maintenance by transcriptional cross-regulation of related receptor kinases
The CLAVATA3 (CLV3)-CLAVATA1 (CLV1) ligand-receptor kinase pair negatively regulates shoot stem cell proliferation in plants. clv1 null mutants are weaker in phenotype than clv3 mutants, but the clv1 null phenotype is enhanced by mutations in the related receptor kinases BARELY ANY MERISTEM 1, 2 and 3 (BAM1, 2 and 3). The basis of this genetic redundancy is unknown. Here, we demonstrate that the apparent redundancy in the CLV1 clade is in fact due to the transcriptional repression of BAM genes by CLV1 signaling. CLV1 signaling in the rib meristem (RM) of the shoot apical meristem is necessary and sufficient for stem cell regulation. CLV3-CLV1 signaling in the RM represses BAM expression in wild-type Arabidopsis plants. In clv1 mutants, ectopic BAM expression in the RM partially complements the loss of CLV1. BAM regulation by CLV1 is distinct from CLV1 regulation of WUSCHEL, a proposed CLV1 target gene. In addition, quadruple receptor mutants are stronger in phenotype than clv3, pointing to the existence of additional CLV1/BAM ligands. These data provide an explanation for the genetic redundancy seen in the CLV1 clade and reveal a novel feedback operating in the control of plant stem cells
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Development of an Objective Structured Clinical Examination as a Component of Assessment for Initial Board Certification in Anesthesiology.
With its first administration of an Objective Structured Clinical Examination (OSCE) in 2018, the American Board of Anesthesiology (ABA) became the first US medical specialty certifying board to incorporate this type of assessment into its high-stakes certification examination system. The fundamental rationale for the ABA's introduction of the OSCE is to include an assessment that allows candidates for board certification to demonstrate what they actually "do" in domains relevant to clinical practice. Inherent in this rationale is that the OSCE will capture competencies not well assessed in the current written and oral examinations-competencies that will allow the ABA to judge whether a candidate meets the standards expected for board certification more properly. This special article describes the ABA's journey from initial conceptualization through first administration of the OSCE, including the format of the OSCE, the process for scenario development, the standardized patient program that supports OSCE administration, examiner training, scoring, and future assessment of reliability, validity, and impact of the OSCE. This information will be beneficial to both those involved in the initial certification process, such as residency graduate candidates and program directors, and others contemplating the use of high-stakes summative OSCE assessments
The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds
Motivated by the long-standing "luminosity problem" in low-mass star
formation whereby protostars are underluminous compared to theoretical
expectations, we identify 230 protostars in 18 molecular clouds observed by two
Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We
compile complete spectral energy distributions, calculate Lbol for each source,
and study the protostellar luminosity distribution. This distribution extends
over three orders of magnitude, from 0.01 Lsun - 69 Lsun, and has a mean and
median of 4.3 Lsun and 1.3 Lsun, respectively. The distributions are very
similar for Class 0 and Class I sources except for an excess of low luminosity
(Lbol < 0.5 Lsun) Class I sources compared to Class 0. 100 out of the 230
protostars (43%) lack any available data in the far-infrared and submillimeter
(70 um < wavelength < 850 um) and have Lbol underestimated by factors of 2.5 on
average, and up to factors of 8-10 in extreme cases. Correcting these
underestimates for each source individually once additional data becomes
available will likely increase both the mean and median of the sample by 35% -
40%. We discuss and compare our results to several recent theoretical studies
of protostellar luminosities and show that our new results do not invalidate
the conclusions of any of these studies. As these studies demonstrate that
there is more than one plausible accretion scenario that can match
observations, future attention is clearly needed. The better statistics
provided by our increased dataset should aid such future work.Comment: Accepted for publication in AJ. 21 pages, 10 figures, 4 table
Genome-Wide Assessment of Efficiency and Specificity in CRISPR/Cas9 Mediated Multiple Site Targeting in Arabidopsis
Simultaneous multiplex mutation of large gene families using Cas9 has the potential to revolutionize agriculture and plant sciences. The targeting of multiple genomic sites at once raises concerns about the efficiency and specificity in targeting. The model Arabidopsis thaliana is widely used in basic plant research. Previous work has suggested that the Cas9 off-target rate in Arabidopsis is undetectable. Here we use deep sequencing on pooled plants simultaneously targeting 14 distinct genomic loci to demonstrate that multiplex targeting in Arabidopsis is highly specific to on-target sites with no detectable off-target events. In addition, chromosomal translocations are extremely rare. The high specificity of Cas9 in Arabidopsis makes this a reliable method for clean mutant generation with no need to enhance specificity or adopt alternate Cas9 variants
Young Stellar Objects in the Gould Belt
We present the full catalog of Young Stellar Objects (YSOs) identified in the
18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks"
(c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed
by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of
which survive visual inspection and form our final catalog of YSOs in the Gould
Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and
tabulate the infrared spectral index, bolometric luminosity, and bolometric
temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and
1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III,
respectively, and show that the Class III sample suffers from an overall
contamination rate by background AGB stars between 25% and 90%. Adopting
standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs
and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass
uncertainties in the adopted assumptions. Including information from
(sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as
Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr
(Class I). We revisit infrared color-color diagrams used in the literature to
classify YSOs and propose minor revisions to classification boundaries in these
diagrams. Finally, we show that the bolometric temperature is a poor
discriminator between Class II and Class III YSOs.Comment: Accepted for publication in ApJS. 29 pages, 11 figures, 14 tables, 4
appendices. Full versions of data tables (to be published in machine-readable
format by ApJS) available at the end of the latex source cod
The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud observed with IRAC and MIPS
We present observations of the Auriga-California Molecular Cloud (AMC) at
3.6, 4.5, 5.8, 8.0, 24, 70 and 160 micron observed with the IRAC and MIPS
detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped
areas are 2.5 sq-deg with IRAC and 10.47 sq-deg with MIPS. This giant molecular
cloud is one of two in the nearby Gould Belt of star-forming regions, the other
being the Orion A Molecular Cloud (OMC). We compare source counts, colors and
magnitudes in our observed region to a subset of the SWIRE data that was
processed through our pipeline. Using color-magnitude and color-color diagrams,
we find evidence for a substantial population of 166 young stellar objects
(YSOs) in the cloud, many of which were previously unknown. Most of this
population is concentrated around the LkHalpha 101 cluster and the filament
extending from it. We present a quantitative description of the degree of
clustering and discuss the fraction of YSOs in the region with disks relative
to an estimate of the diskless YSO population. Although the AMC is similar in
mass, size and distance to the OMC, it is forming about 15 - 20 times fewer
stars.Comment: (30 pages, 17 figures (2 multipage figures), accepted for publication
in ApJ
RELICS: Strong Lens Models for Five Galaxy Clusters From the Reionization Lensing Cluster Survey
Strong gravitational lensing by galaxy clusters magnifies background
galaxies, enhancing our ability to discover statistically significant samples
of galaxies at z>6, in order to constrain the high-redshift galaxy luminosity
functions. Here, we present the first five lens models out of the Reionization
Lensing Cluster Survey (RELICS) Hubble Treasury Program, based on new HST
WFC3/IR and ACS imaging of the clusters RXC J0142.9+4438, Abell 2537, Abell
2163, RXC J2211.7-0349, and ACT-CLJ0102-49151. The derived lensing
magnification is essential for estimating the intrinsic properties of
high-redshift galaxy candidates, and properly accounting for the survey volume.
We report on new spectroscopic redshifts of multiply imaged lensed galaxies
behind these clusters, which are used as constraints, and detail our strategy
to reduce systematic uncertainties due to lack of spectroscopic information. In
addition, we quantify the uncertainty on the lensing magnification due to
statistical and systematic errors related to the lens modeling process, and
find that in all but one cluster, the magnification is constrained to better
than 20% in at least 80% of the field of view, including statistical and
systematic uncertainties. The five clusters presented in this paper span the
range of masses and redshifts of the clusters in the RELICS program. We find
that they exhibit similar strong lensing efficiencies to the clusters targeted
by the Hubble Frontier Fields within the WFC3/IR field of view. Outputs of the
lens models are made available to the community through the Mikulski Archive
for Space TelescopesComment: Accepted to Ap
Associations of sedentary behaviour, physical activity, blood pressure and anthropometric measures with cardiorespiratory fitness in children with cerebral palsy
Background - Children with cerebral palsy (CP) have poor cardiorespiratory fitness in comparison to their peers with typical development, which may be due to low levels of physical activity. Poor cardiorespiratory fitness may contribute to increased cardiometabolic risk. Purpose - The aim of this study was to determine the association between sedentary behaviour, physical activity and cardiorespiratory fitness in children with CP. An objective was to determine the association between cardiorespiratory fitness, anthropometric measures and blood pressure in children with CP. Methods- This study included 55 ambulatory children with CP [mean (SD) age 11.3 (0.2) yr, range 6-17 yr; Gross Motor Function Classification System (GMFCS) levels I and II]. Anthropometric measures (BMI, waist circumference and waist-height ratio) and blood pressure were taken. Cardiorespiratory fitness was measured using a 10 m shuttle run test. Children were classified as low, middle and high fitness according to level achieved on the test using reference curves. Physical activity was measured by accelerometry over 7 days. In addition to total activity, time in sedentary behaviour and light, moderate, vigorous, and sustained moderate-to-vigorous activity (≥10 min bouts) were calculated. Results - Multiple regression analyses revealed that vigorous activity (β = 0.339, p<0.01), sustained moderate-to-vigorous activity (β = 0.250, p<0.05) and total activity (β = 0.238, p<0.05) were associated with level achieved on the shuttle run test after adjustment for age, sex and GMFCS level. Children with high fitness spent more time in vigorous activity than children with middle fitness (p<0.05). Shuttle run test level was negatively associated with BMI (r2 = -0.451, p<0.01), waist circumference (r2 = -0.560, p<0.001), waist-height ratio (r2 = -0.560, p<0.001) and systolic blood pressure (r2 = -0.306, p<0.05) after adjustment for age, sex and GMFCS level. Conclusions - Participation in physical activity, particularly at a vigorous intensity, is associated with high cardiorespiratory fitness in children with CP. Low cardiorespiratory fitness is associated with increased cardiometabolic risk
RELICS: High-Resolution Constraints on the Inner Mass Distribution of the z=0.83 Merging Cluster RXJ0152.7-1357 from strong lensing
Strong gravitational lensing (SL) is a powerful means to map the distribution
of dark matter. In this work, we perform a SL analysis of the prominent X-ray
cluster RXJ0152.7-1357 (z=0.83, also known as CL 0152.7-1357) in \textit{Hubble
Space Telescope} images, taken in the framework of the Reionization Lensing
Cluster Survey (RELICS). On top of a previously known galaxy multiply
imaged by RXJ0152.7-1357, for which we identify an additional multiple image,
guided by a light-traces-mass approach we identify seven new sets of multiply
imaged background sources lensed by this cluster, spanning the redshift range
[1.79-3.93]. A total of 25 multiple images are seen over a small area of ~0.4
, allowing us to put relatively high-resolution constraints on the
inner matter distribution. Although modestly massive, the high degree of
substructure together with its very elongated shape make RXJ0152.7-1357 a very
efficient lens for its size. This cluster also comprises the third-largest
sample of z~6-7 candidates in the RELICS survey. Finally, we present a
comparison of our resulting mass distribution and magnification estimates with
those from a Lenstool model. These models are made publicly available through
the MAST archive.Comment: 15 Pages, 7 Figures, 4 Tables Accepted for publication in Ap
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