928 research outputs found
Genetic Analysis of Germline Development in the Model Organism C. elegans
My research investigated the relationships among several transcriptional and/or post-transcriptional regulators in the C. elegans germ line. I examined the relationship between the rha-1 gene and three other regulatory genes, ego-1, glp-1 and csr-1. These genes function in germline proliferation and differentiation and are required for fertility. Because these genes regulate similar processes, we have investigated the relationships among them. The rha-1 gene encodes an RNA helicase that is required for germline development, chromatin regulation, and RNA interference (RNAi). The ego-1 gene encodes an RNA-directed RNA polymerase that is also required for these processes. Although many of the rha-1 and ego-1 defects are similar, the rha-1 null phenotype is temperature-sensitive (ts) whereas the ego-1 null phenotype is not. The glp-1 gene encodes a Notch-type receptor that receives an inductive signal from distal tip cell (DTC), which maintains germline proliferation. In the absence of GLP-1 signaling, germ cells that are normally mitotic instead enter meiosis and undergo gametogenesis. The csr-1 gene encodes an Argonaute-type RNA binding protein that is required for germline development and chromatin regulation. Mutations in ego-1 and csr-1 enhance the phenotype of a weak glp-1 mutation. We constructed double mutant strains carrying the rha-1 null allele and either a null allele of ego-1 or csr-1, or a ts allele of glp-1. Our data suggest that EGO-1 and RHA-1 proteins work together to regulate some aspects of development and in parallel to regulate others. Preliminary genetic data also suggest that CSR-1 and RHA-1 work together to regulate development, but act antagonistically to regulate oogenesis onset or a very early step in oogenesis. Additionally, our research suggests that RHA-1 does not regulate germline proliferation by promoting GLP-1 signaling. These findings have improved our understanding of how germline development is regulated in this model organism
Recommended from our members
Surface analysis of Mercury with a mass-spectrometer
Introduction: The European Space Agency BepiColombo mission to Mercury will include a lander, the Mercury Surface Element (MSE). Although the final configuration of instruments is still to be decided, we are developing a mass spectrometer suitable for use on this lander, or in other missions where low mass and low power consumption are a priority. Advantages of a mass-spectrometer over other analytical instruments include sensitivity to almost all elements, high dynamic range, spatially resolved measurements (with an appropriate sampling technique) and the potential to determine isotopic compositions
Surface charging of thick porous water ice layers relevant for ion sputtering experiments
We use a laboratory facility to study the sputtering properties of
centimeter-thick porous water ice subjected to the bombardment of ions and
electrons to better understand the formation of exospheres of the icy moons of
Jupiter. Our ice samples are as similar as possible to the expected moon
surfaces but surface charging of the samples during ion irradiation may distort
the experimental results. We therefore monitor the time scales for charging and
dis- charging of the samples when subjected to a beam of ions. These
experiments allow us to derive an electric conductivity of deep porous ice
layers. The results imply that electron irradiation and sputtering play a
non-negligible role for certain plasma conditions at the icy moons of Jupiter.
The observed ion sputtering yields from our ice samples are similar to previous
experiments where compact ice films were sputtered off a micro-balance.Comment: arXiv admin note: text overlap with arXiv:1509.0400
Assessment of detectability of neutral interstellar deuterium by IBEX observations
The abundance of deuterium in the interstellar gas in front of the Sun gives
insight into the processes of filtration of neutral interstellar species
through the heliospheric interface and potentially into the chemical evolution
of the Galactic gas. We investigate the possibility of detection of neutral
interstellar deuterium at 1 AU from the Sun by direct sampling by the
Interstellar Boundary Explorer (IBEX). We simulate the flux of neutral
interstellar D at IBEX for the actual measurement conditions. We assess the
number of interstellar D atom counts expected during the first three years of
IBEX operation. We also simulate observations expected during an epoch of high
solar activity. In addition, we calculate the expected counts of D atoms from
the thin terrestrial water layer, sputtered from the IBEX-Lo conversion surface
by neutral interstellar He atoms. Most D counts registered by IBEX-Lo are
expected to originate from the water layer, exceeding the interstellar signal
by 2 orders of magnitude. However, the sputtering should stop once the Earth
leaves the portion of orbit traversed by interstellar He atoms. We identify
seasons during the year when mostly the genuine interstellar D atoms are
expected in the signal. During the first 3 years of IBEX operations about 2
detectable interstellar D atoms are expected. This number is comparable with
the expected number of sputtered D atoms registered during the same time
intervals. The most favorable conditions for the detection occur during low
solar activity, in an interval including March and April each year. The
detection chances could be improved by extending the instrument duty cycle,
e.g., by making observations in the special deuterium mode of IBEX-Lo.Comment: Accepted for Astronomy & Astrophysic
Space Weathering on Near-Earth Objects investigated by neutral-particle detection
The ion-sputtering (IS) process is active in many planetary environments in
the Solar System where plasma precipitates directly on the surface (for
instance, Mercury, Moon, Europa). In particular, solar-wind sputtering is one
of the most important agents for the surface erosion of a Near-Earth Object
(NEO), acting together with other surface release processes, such as Photon
Stimulated Desorption (PSD), Thermal Desorption (TD) and Micrometeoroid Impact
Vaporization (MIV). The energy distribution of the IS-released neutrals peaks
at a few eVs and extends up to hundreds of eVs. Since all other release
processes produce particles of lower energies, the presence of neutral atoms in
the energy range above 10 eV and below a few keVs (Sputtered High-Energy Atoms
- SHEA) identifies the IS process. SHEA easily escape from the NEO, due to
NEO's extremely weak gravity. Detection and analysis of SHEA will give
important information on surface-loss processes as well as on surface elemental
composition. The investigation of the active release processes, as a function
of the external conditions and the NEO surface properties, is crucial for
obtaining a clear view of the body's present loss rate as well as for getting
clues on its evolution, which depends significantly on space weather. In this
work, an attempt to analyze the processes that take place on the surface of
these small airless bodies, as a result of their exposure to the space
environment, has been realized. For this reason a new space weathering model
(Space Weathering on NEO - SPAWN), is presented. Moreover, an instrument
concept of a neutral-particle analyzer specifically designed for the
measurement of neutral density and the detection of SHEA from a NEO is proposedComment: 36 page
Advances in Mass Spectrometers for Flyby Space Missions for the Analysis of Biosignatures and Other Complex Molecules
Spacecraft flybys provide access to the chemical composition of the gaseous envelope of the planetary object. Typical relative encounter velocities range from km/s to tens of km/s in flybys. For speeds exceeding about 5 km/s, modern mass spectrometers analyzing the rapidly encountering gas suffer from intrinsic hypervelocity impact-induced fragmentation processes causing ambiguous results when analyzing complex molecules. In this case, instruments use an antechamber, inside which the incoming species collide many times with the chamber wall. These collisions cause the desired deceleration and thermalization of the gas molecules. However, these collisions also dissociate molecular bonds, thus fragmenting the molecules, and possibly forming new ones precluding scientists from inferring the actual chemical composition of the sampled gas. We developed a novel time-of-flight mass spectrometer that handles relative encounter velocities of up to 20 km/s omitting an antechamber and its related fragmentation. It analyzes the complete mass range of m/z 1 to 1000 at an instance. This innovation leads to unambiguous analysis of complex (organic) molecules. Applied to Enceladus, Europa or Io, it will provide reliable chemical composition datasets for exploration of the Solar System to determine its status, origin and evolution
The downwind hemisphere of the heliosphere: Eight years of IBEX-Lo observations
We present a comprehensive study of energetic neutral atoms (ENAs) of 10 eV
to 2.5 keV from the downwind hemisphere of the heliosphere. These ENAs are
believed to originate mostly from pickup protons and solar wind protons in the
inner heliosheath. This study includes all low-energy observations made with
the Interstellar Boundary Explorer over the first 8 years. Since the protons
around 0.1 keV dominate the plasma pressure in the inner heliosheath in
downwind direction, these ENA observations offer the unique opportunity to
constrain the plasma properties and dimensions of the heliosheath where no
in-situ observations are available.
We first derive energy spectra of ENA intensities averaged over time for 49
macropixels covering the entire downwind hemisphere. The results confirm
previous studies regarding integral intensities and the roll-over around 0.1
keV energy. With the expanded dataset we now find that ENA intensities at 0.2
and 0.1 keV seem to anti-correlate with solar activity. We then derive the
product of total plasma pressure and emission thickness of protons in the
heliosheath to estimate lower limits on the thickness of the inner heliosheath.
The temporally averaged ENA intensities support a rather spherical shape of the
termination shock and a heliosheath thickness between 150 and 210 au for most
regions of the downwind hemisphere. Around the nominal downwind direction of
76{\deg} ecliptic longitude, the heliosheath is at least 280 au thick. There,
the neutral hydrogen density seems to be depleted compared to upwind directions
by roughly a factor of 2.Comment: Preprint of article in The Astrophysical Journa
- …