812 research outputs found
The Hox Gene egl-5 Acts as a Terminal Selector for VD13 Development via Wnt Signaling
This work is licensed under a Creative Commons Attribution 4.0 International License.Nervous systems are comprised of diverse cell types that differ functionally and morphologically. During development, extrinsic signals, e.g., growth factors, can activate intrinsic programs, usually orchestrated by networks of transcription factors. Within that network, transcription factors that drive the specification of features specific to a limited number of cells are often referred to as terminal selectors. While we still have an incomplete view of how individual neurons within organisms become specified, reporters limited to a subset of neurons in a nervous system can facilitate the discovery of cell specification programs. We have identified a fluorescent reporter that labels VD13, the most posterior of the 19 inhibitory GABA (Îł-amino butyric acid)-ergic motorneurons, and two additional neurons, LUAL and LUAR. Loss of function in multiple Wnt signaling genes resulted in an incompletely penetrant loss of the marker, selectively in VD13, but not the LUAs, even though other aspects of GABAergic specification in VD13 were normal. The posterior Hox gene, egl-5, was necessary for expression of our marker in VD13, and ectopic expression of egl-5 in more anterior GABAergic neurons induced expression of the marker. These results suggest egl-5 is a terminal selector of VD13, subsequent to GABAergic specification
Prevalence, heterogeneity of asymptomatic malaria infections and associated factors in a high transmission region
Background: Although current reports have shown a reduction in malaria cases, the disease still remains a major public health problem in Kenya. In most endemic regions, the majority of infections are asymptomatic which means those infected may not even know and yet they remain infectious to the mosquitoes. Asymptomatic infections are a major threat to malaria control programs since they act as silent reservoirs for the malaria parasites.Objective: The study sought to determine the prevalence of asymptomatic malaria infections, whether they show heterogeneity spatially, across age groups and across time as well as their determinants in a high transmission region.Study Design: This was part of a larger prospective cohort study on malaria indices in the HDSS.Study Setting: The study was conducted in the Webuye Health and Demographic Surveillance Site in Bungoma East Sub-County.Study Subjects: Quarterly parasitological surveys were conducted for a cohort of 400 participants from randomly selected households located in known fever âhotspotsâ and âcoldspotsâ. Follow-up of all the participants continued for a period of one year. Generalized estimating equations were used to model risk factors associated with asymptomatic parasitemia.Results: Of the total 321 malaria infections detected during the five cross-sectional surveys conducted over the period of one year, almost half (46.3%) of these were asymptomatic. Overall, most of the asymptomatic cases (67%) were in households within known fever âhotspotsâ. The proportion of infections that were asymptomatic in the coldspots were 73.1%, 31.8%, 13.3%, 55.6% and 48.2% during the first, second, third, fourth and fifth visits respectively. In the known fever âhotspotsâ, the proportion of infections without symptoms was 47.7%, 48.5%, 35%, 41.3% and 47.5% during the first, second, third, fourth and fifth visits respectively. Factors associated with asymptomatic malaria include; the village one lives: people living in village M were twice likely to be asymptomatic (A.O.R: 2.141, C.I: 0.03 - 1.488), age: children aged between 6 to 15 years were more than twice likely to be asymptomatic (A.O.R: 2.67, C.I. 0.434 - 1.533) and the season: infections during the dry season (January) were less likely to be asymptomatic (A.O.R: 0.26, C.I: -2.289 - 0.400).Conclusion: The prevalence of asymptomatic infections in this region is still very high. The highest proportion of asymptomatic infections was registered in a fever coldpspot village which may explain why the village is a fever coldspot in the first place. There is a need for active surveillance to detect the asymptomatic cases as well as treat them in-order to reduce the reservoir. Targeting interventions to the asymptomatic individuals will further reduce the transmission within this region
Malaria âhotspotsâ within a larger hotspot; whatâs the role of behavioural factors in fine scale heterogeneity in western Kenya?
Background: Malaria remains a major public health problem in Kenya accounting for the highest morbidity and mortality especially among children. Previous reports indicate that infectious agents display heterogeneity in both space and time and malaria is no exception. Heterogeneity has been shown to reduce the effectiveness of interventions. Previous studies have implicated genetic (both human and parasite) and environmental factors as mainly responsible for variation in malaria risk. Human behaviour and its potential risk for contributing to variation in malaria risk has not been extensively explored.Objective: To determine if there were behavioural differences between the people living in hotspots (high malaria burden) and cold spots (low malaria burden) within a geographically homogeneous and high malaria transmission region.Design: A prospective closed cohort study.Setting: The study was conducted in the Health and Demographic Surveillance Site in Bungoma East sub-County.Subjects: A total of 400 people in randomly selected households in both the fever hotspots and cold spots were tested for malaria at quarterly intervals using malaria rapid diagnostic tests (RDTs).Results: Significant heterogeneity in malaria incidence and prevalence was observed between villages. Incidence of malaria was significantly higher in the hotspots (high malaria burden areas) compared to the cold spots (low malaria burden) (49 episodes per 1000 person months compared to 26/1000, t test p < 0.001). The incidence also varied significantly among the individual villages by season (P: 0.0071). Knowledge on malaria therapy was significantly associated with whether one was in the cold spot or hotspot (P: 0.033). Behavioural practices relating to ITN use were significantly associated with region during particular seasons (P: 0.0001 and P: 0.0001 respectively).Conclusion: There is marked and significant variation in the incidence of malaria among the villages creating actual hotspots of malaria within the larger hotspot. There is a significant difference in malaria infections between the hotspots and cold spots. Knowledge on malaria therapy and behavioural factors such as ITN use may contribute to the observed differences during some seasons
Constraining the variation of the coupling constants with big bang nucleosynthesis
We consider the possibility of the coupling constants of the gauge interactions at the time of big bang nucleosynthesis
having taken different values from what we measure at present, and investigate
the allowed difference requiring the shift in the coupling constants not
violate the successful calculation of the primordial abundances of the light
elements. We vary gauge couplings and Yukawa couplings (fermion masses) using a
model in which their relative variations are governed by a single scalar field,
dilaton, as found in string theory. The results include a limit on the fine
structure constant
, which is
two orders stricter than the limit obtained by considering the variation of
alone.Comment: 7 page
Andromeda's Parachute: A Bright Quadruply Lensed Quasar at z = 2.377
We present Keck Cosmic Web Imager spectroscopy of the four putative images of the lensed quasar candidate J014710+463040 recently discovered by Berghea et al. The data verify the source as a quadruply lensed, broad absorption-line quasar having . We detect intervening absorption in the Fe ii λλ2586, 2600, Mg ii λλ2796, 2803, and/or C iv λλ1548, 1550 transitions in eight foreground systems, three of which have redshifts consistent with the photometric-redshift estimate reported for the lensing galaxy (z L â 0.57). The source images probe these absorbers over transverse physical scales of â0.3â22 kpc, permitting assessment of the variation in metal-line equivalent width as a function of sight-line separation. We measure differences in of 50% over the same scales across the majority of sight-line pairs, while C iv absorption exhibits a wide range in differences of â5%â80% within transverse distances of lesssim3 kpc. These spatial variations are consistent with those measured in intervening absorbers detected toward lensed quasars drawn from the literature, in which and vary by â€20% in 35 ± 7% and 47 ± 6% of sight lines separated by 2 quadruply lensed systems for which all four source images are very bright (r = 15.4â17.7 mag) and are easily separated in ground-based seeing conditions. As such, it is an ideal candidate for higher-resolution spectroscopy probing the spatial variation in the kinematic structure and physical state of intervening absorbers
The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium
By comparing the widths of absorption lines from OI, SiII and FeII in the
redshift z=2.076 single-component damped Lyman alpha absorption system in the
spectrum of Q2206-199 we establish that these absorption lines arise in Warm
Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal
equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies,
but not with the presence of a significant cold component. It is also
consistent with, but not required by, the absence of CII* fine structure
absorption in this system. Some possible implications concerning abundance
estimates in narrow-line WNM absorbers are discussed.Comment: 9 pages, 3 figures. MNRAS accepte
High-Redshift Metals. II. Probing Reionization Galaxies with Low-Ionization Absorption Lines at Redshift Six
We present a survey for low-ionization metal absorption line systems towards
17 QSOs at redshifts z_em=5.8-6.4. Nine of our objects were observed at high
resolution with either Keck/HIRES or Magellan/MIKE, and the remainder at
moderate resolution with Keck/ESI. The survey spans 5.3 < z_abs < 6.4 and has a
pathlength interval \Delta X=39.5, or \Delta z=8.0. In total we detect ten
systems, five of which are new discoveries. The line-of-sight number density is
consistent with the combined number density at z~3 of DLAs and sub-DLAs, which
comprise the main population of low-ionization systems at lower redshifts. This
apparent lack of evolution may occur because low ionization systems are hosted
by lower-mass halos at higher redshifts, or because the mean cross section of
low-ionization gas at a given halo mass increases with redshift due to the
higher densities and lower ionizing background. The roughly constant number
density notably contrasts with the sharp decline at z > 5.3 in the number
density of highly-ionized systems traced by C IV. The low-ionization systems at
z~6 span a similar range of velocity widths as lower-redshift sub-DLAs but have
significantly weaker lines at a given width. This implies that the
mass-metallicity relation of the host galaxies evolves towards lower
metallicities at higher redshifts. These systems lack strong Si IV and C IV,
which are common among lower-redshift DLAs and sub-DLAs. This is consistent,
however, with a similar decrease in the metallicity of the low- and
high-ionization phases, and does not necessarily indicate a lack of nearby,
highly-ionized gas. The high number density of low-ionization systems at z~6
suggests that we may be detecting galaxies below the current limits of
i-dropout and Ly-alpha emission galaxy surveys. These systems may therefore be
the first direct probes of the `typical' galaxies responsible for hydrogen
reionization.Comment: 15 pages, 15 figures, submitted to Ap
The primordial Helium-4 abundance determination: systematic effects
By extrapolating to O/H = N/H = 0 the empirical correlations Y-O/H and Y-N/H
defined by a relatively large sample of ~ 45 Blue Compact Dwarfs (BCDs), we
have obtained a primordial 4Helium mass fraction Yp= 0.2443+/-0.0015 with dY/dZ
= 2.4+/-1.0. This result is in excellent agreement with the average Yp=
0.2452+/-0.0015 determined in the two most metal-deficient BCDs known, I Zw 18
(Zsun/50) and SBS 0335-052 (Zsun/41), where the correction for He production is
smallest. The quoted error (1sigma) of < 1% is statistical and does not include
systematic effects. We examine various systematic effects including collisional
excitation of Hydrogen lines, ionization structure and temperature fluctuation
effects, and underlying stellar HeI absorption, and conclude that combining all
systematic effects, our Yp may be underestimated by ~ 2-4%. Taken at face
value, our Yp implies a baryon-to-photon number ratio eta = 4.7x10^-10 and a
baryon mass fraction Omega_b h^2_{100} = 0.017+/-0.005 (2sigma), consistent
with the values obtained from deuterium and Cosmic Microwave Background
measurements. Correcting Yp upward by 2-4% would make the agreement even
better.Comment: 12 pages, 5 PS figures, to appear in "Matter in the Universe", ed P.
Jetzer, K. Pretzl and R. von Steiger, Kluwer, Dordrecht (2002
Precision Primordial He Measurement with CMB Experiments
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances (He, D, He and Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find and
(fraction of baryon mass as He) using CMB data alone, in agreement with
He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find
and . We also find that the inclusion of deuterium
abundance observations reduces the and ranges by a factor
of 2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.Comment: 7 pages, 3 color figures made minor changes to bring inline with
journal versio
- âŠ