Ssp1p is a lipid binding protein involved in shaping of the prospore membrane during meiosis in S. cerevisiae

Meiosis is a special form of cell division which results in the formation of haploid cells. At the end of meiosis in yeast four new cells, the so-called spores, are formed inside the boundaries of the mother cell. This morphogenetic process requires de novo formation of the cell membranes. Surprisingly it is the spindle pole bodies (SPBs) which organize the formation of these prospore membranes (PSMs). Membrane vesicles, probably redirected from the secretory pathway, accumulate at the cytoplasmic face of the SPB and fuse to form a continuous membrane system. In our lab we have identified a protein complex which localizes to the tip of this growing membrane, the leading edge protein coat (LEP coat). In this thesis I demonstrate that the S. cereviaiae protein Ssp1p is a novel component of the LEP coat. It is even the most important constituent of the LEP coat as it recruits all other components to this structure. I can show here that Ssp1p is a lipid binding protein and this affinity is probably required for anchoring the protein complex in the membrane. Ssp1p would then act like a hinge, connecting the PSM to Ady3p, another protein of the LEP coat. Deletion of SSP1 results in a block of sporulation. Here I show that this is most probably due to a defect in membrane shaping. In the deletion mutant the PSM sticks very tightly to the nuclear envelope and closes without incorporating cytoplasm. This later on leads to a defect in spore formation and to a loss of viability. One possible explanation for this phenotype would be that the LEP coat serves as a scaffold which provides some structural stability to the membrane while it grows. The protein ring at its tip might also keep the membrane open until all constituents required are enclosed. In addition to its lipid binding activity it is demonstrated that Ssp1p localizes to the plasma membrane of the bud when it is overexpressed in mitotic cells. This is a hint that Ssp1p might be involved in membrane vesicle targeting. Ssp1p could either be directed to target membranes by their lipid composition or by other interacting proteins. As overexpression of Ssp1p in mitotic cells is toxic some interference with the secretory pathway machinery is proposed.Meiose ist eine spezielle Form der Zellteilung, als Endprodukte entstehen haploide Zellen. In der Bäckerhefe S. cerevisiae werden am Ende der Meiose vier Tochterzellen, die sogenannten Sporen, innerhalb des alten Kompartiments der Mutterzelle gebildet. Dieser Differenzierungsprozess erfordert die komplette Neubildung der äußeren Membranen. Überraschenderweise wird diese Neubildung der sogenannten Prospormembranen von den Spindelpolkörpern organisiert. Membranvesikel, die vermutlich aus dem sekretorischen Pfad stammen, werden umgeleitet und akkumlieren am Spindelpolkörper, wo sie miteinander fusionieren und eine kontinuierliche Membran bilden. In unserem Labor haben wir haben einen Proteinkomplex identifiziert, der an der Spitze dieser wachsenden Membran lokalisiert und dort eine ringförmige Struktur ausbildet. In dieser Arbeit konnte ich zeigen, daß Ssp1p eine weitere Komponente dieses Proteinkomplexes ist. Ssp1p ist sogar die wichtigste der bisher identifizierten Komponenten, da die Lokalisierung aller anderen Proteine an diese Membranstruktur von Ssp1p abhängt. Die Entdeckung, daß Ssp1p ein Lipid-bindendes Protein ist, erklärt den Aufbau dieser Struktur. Ssp1p interagiert auf der einen Seite mit Ady3p, einem Bestandteil dieses membranständigen Proteinkomplexes, auf der anderen Seite verankert es mittels seiner Fähigkeit zur Lipidbindung den ganzen Komplex in der Membran. Wird SSP1 deletiert so verliert die Zelle die Fähigkeit zur Sporulation. Ich konnte zeigen, daß der Grund hierfür wahrscheinlich in einer Störung der Ausbildung der Prospormembran liegt. In der Deletionsmutante liegt die Prospormembran extrem eng auf der Kernmembran und der Abschluß erfolgt bereits, bevor Cytoplasma eingschlossen werden konnte. Dies führt dann später zu einem Defekt der Sporenbildung und einem Verlust der Lebensfähigkeit. Eine mögliche Erklärung für die Funktion dieses membranständigen Proteinkomplexes wäre, daß durch sein stabiles Gerüst der wachsenden Membran eine gewisse strukturelle Rigidität gegeben wird. Es ist auch denkbar, daß der Proteinring die Membran geöffnet hält bis alle notwendigen Bestandteile aufgenommen wurden. Zusätzlich zur Lipidbindungsaktivität von Ssp1p wurde entdeckt, daß Ssp1p, wenn es mitotisch überexprimiert wird, an der Plasmamembran der Tochterzelle (Knospe) lokalisiert. Dies könnte bedeuten, daß Ssp1p eine Rolle bei der Lenkung der sekretorischen Membranvesikel spielt. Durch die Bindung an spezielle Lipide könnte Ssp1p in Membranbereiche gelenkt werden, die Ziele für solche sekretorischen Vesikel darstellen. Diese spezielle Lokalisierung könnte aber auch durch Proteininteraktionen bewirkt werden. Da die Überexpression von Ssp1p für mitotische Zellen toxisch ist liegt es nahe anzunehmen, daß dieses Protein einen Einfluß auf die Funktion der Proteine des sekretorischen Pfades hat

Microwave ISM Emission Observed by WMAP

We investigate the nature of the diffuse Galactic emission in the Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy data. Substantial dust-correlated emission is observed at all WMAP frequencies, far exceeding the expected thermal dust emission in the lowest frequency channels (23, 33, 41 GHz). The WMAP team (Bennett et al.) interpret this emission as dust-correlated synchrotron radiation, attributing the correlation to the natural association of relativistic electrons produced by SNae with massive star formation in dusty clouds, and deriving an upper limit of 5% on the contribution of Draine & Lazarian spinning dust at K-band (23 GHz). We pursue an alternative interpretation that much, perhaps most, of the dust-correlated emission at these frequencies is indeed spinning dust, and explore the spectral dependence on environment by considering a few specific objects as well as the full sky average. Models similar to Draine & Lazarian spinning dust provide a good fit to the full-sky data. The full-sky fit also requires a significant component with free-free spectrum uncorrelated with \Halpha, possibly hot (~million K) gas within 30 degrees of the Galactic center.Comment: ApJ in press (accepted 5 Dec 2003), version 2: corrected typos and added references. 23 pages, 5 figures, 2 tables. Free-free haze map is available at http://skymaps.inf

Evidence Of Dark Matter Annihilations In The WMAP Haze

The WMAP experiment has revealed an excess of microwave emission from the region around the center of our Galaxy. It has been suggested that this signal, known as the ``WMAP Haze'', could be synchrotron emission from relativistic electrons and positrons generated in dark matter annihilations. In this letter, we revisit this possibility. We find that the angular distribution of the WMAP Haze matches the prediction for dark matter annihilations with a cusped density profile, $\rho(r) \propto r^{-1.2}$ in the inner kiloparsecs. Comparing the intensity in different WMAP frequency bands, we find that a wide range of possible WIMP annihilation modes are consistent with the spectrum of the haze for a WIMP with a mass in the 100 GeV to multi-TeV range. Most interestingly, we find that to generate the observed intensity of the haze, the dark matter annihilation cross section is required to be approximately equal to the value needed for a thermal relic, $\sigma v \sim 3 \times 10^{-26}$ cm$^3$/s. No boost factors are required. If dark matter annihilations are in fact responsible for the WMAP Haze, and the slope of the halo profile continues into the inner Galaxy, GLAST is expected to detect gamma rays from the dark matter annihilations in the Galactic Center if the WIMP mass is less than several hundred GeV.Comment: 4 pages, 3 figure

Detecting Dark Matter Annihilation with CMB Polarization : Signatures and Experimental Prospects

Dark matter (DM) annihilation during hydrogen recombination (z ~ 1000) will alter the recombination history of the Universe, and affect the observed CMB temperature and polarization fluctuations. Unlike other astrophysical probes of DM, this is free of the significant uncertainties in modelling galactic physics, and provides a method to detect and constrain the cosmological abundances of these particles. We parametrize the effect of DM annihilation as an injection of ionizing energy at a rate e_{dm}, and argue that this simple "on the spot'' modification is a good approximation to the complicated interaction of the annihilation products with the photon-electron plasma. Generic models of DM do not change the redshift of recombination, but change the residual ionization after recombination. This broadens the surface of last scattering, suppressing the temperature fluctuations and enhancing the polarization fluctuations. We use the temperature and polarization angular power spectra to measure these deviations from the standard recombination history, and therefore, indirectly probe DM annihilation. (abridged)Comment: 13 pages, 8 figures, submitted to PR

Microwave ISM Emission in the Green Bank Galactic Plane Survey: Evidence for Spinning Dust

We observe significant dust-correlated emission outside of H II regions in the Green Bank Galactic Plane Survey (-4 < b < 4 degrees) at 8.35 and 14.35 GHz. The rising spectral slope rules out synchrotron and free-free emission as majority constituents at 14 GHz, and the amplitude is at least 500 times higher than expected thermal dust emission. When combined with the Rhodes (2.326 GHz), and WMAP (23-94 GHz) data it is possible to fit dust-correlated emission at 2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an additional dust-correlated component similar to Draine & Lazarian spinning dust. The rising component generally dominates free-free and synchrotron for \nu >~ 14 GHz and is overwhelmed by thermal dust at \nu > 60 GHz. The current data fulfill most of the criteria laid out by Finkbeiner et al. (2002) for detection of spinning dust.Comment: ApJ in press. 26 pages, 11 figures, figures jpeg compressed to save spac

Synthesizing Finite-state Protocols from Scenarios and Requirements

Scenarios, or Message Sequence Charts, offer an intuitive way of describing the desired behaviors of a distributed protocol. In this paper we propose a new way of specifying finite-state protocols using scenarios: we show that it is possible to automatically derive a distributed implementation from a set of scenarios augmented with a set of safety and liveness requirements, provided the given scenarios adequately \emph{cover} all the states of the desired implementation. We first derive incomplete state machines from the given scenarios, and then synthesis corresponds to completing the transition relation of individual processes so that the global product meets the specified requirements. This completion problem, in general, has the same complexity, PSPACE, as the verification problem, but unlike the verification problem, is NP-complete for a constant number of processes. We present two algorithms for solving the completion problem, one based on a heuristic search in the space of possible completions and one based on OBDD-based symbolic fixpoint computation. We evaluate the proposed methodology for protocol specification and the effectiveness of the synthesis algorithms using the classical alternating-bit protocol.Comment: This is the working draft of a paper currently in submission. (February 10, 2014

Pseudo-Dipole Signal Removal from WMAP Data

It is discovered in our previous work that different observational systematics, e.g., errors of antenna pointing directions, asynchronous between the attitude and science data, can generate pseudo-dipole signal in full-sky maps of the cosmic microwave background (CMB) anisotropy published by The Wilkinson Microwave Anisotropy Probe (WMAP) team. Now the antenna sidelobe response to the Doppler signal is found to be able to produce similar effect as well. In this work, independent to the sources, we uniformly model the pseudo-dipole signal and remove it from published WMAP7 CMB maps by model fitting. The result demonstrates that most of the released WMAP CMB quadrupole is artificial.Comment: V3: using WMAP7 dat

Constraining the Cosmic Background Light with four BL Lac TeV spectra

The intrinsic BL Lac spectra above few hundreds GeV can be very different from the observed ones due to the absorption effects by the diffuse Extragalactic Background Light (EBL), at present poorly known. With the recent results, there are now 4 sources with good spectral information: Mkn 421 (z=0.031), Mkn 501 (z=0.034), 1ES 1426+428 (z=0.129) and 1ES 1959+650 (z=0.047). Making simple assumptions on the shape of the intrinsic spectra (according to the present blazar knowledge), we have considered the effects of different EBL spectral energy distributions (SED) for the first time on all 4 objects together, deriving constraints for the EBL fluxes. These resulted significantly lower than many direct estimates.Comment: 4 pages, 8 figures; to appear in the proceedings of the 2nd Veritas Symposium: "TeV Astrophysics of extragalactic sources". April 2003, Chicag