Chromatin Structure and Regulation of Gene Expression at the Histidine/Adenine Branch Point in Yeast and Aspergillus

Das Enzym Imidazol-glyzerol-phosphat (IGP) Synthase (E.C.2.4.2.14 & E.C.4.3.2.4) katalysiert den fünften und sechsten Reaktionsschritt der Histidinbiosynthese. Das bei diesen Reaktionen entstehende Nebenprodukt AICAR ist gleichzeitig ein Intermediat der de novo Biosynthese von Purinen und fließt in diese mit ein. Diese metabolische Verknüpfung beider Biosynthesen spiegelt sich in der Hefe Saccharomyces cerevisiae auch auf der Ebene der Regulation des für die IGP-Synthase codierenden HIS7 -Gens durch Aminosäure- und Purinverfügbarkeit wider. In der vorliegenden Arbeit wurde zunächst das homologe Gen eines filamentösen Pilzes isoliert und seine Regulation durch Aminosäure-und Purinverfügbarkeit nachgewiesen. Eine starke Überexpression dieses hisHF-Gens aus Aspergillus nidulans führt zu einer Blockierung der sexuellen Fruchtkörperbildung in einem frühen Stadium der Entwicklung. Eine genaue Regulation der hisHF-Expression ist daher Voraussetzung für das Durchlaufen des komplexen Entwicklungsprogrammes der Cleistothecien-Bildung. Eukaryotische Gene liegen im Chromatinverbund vor, welches per se repressiv auf die Genexpression wirkt. Die Zelle benötigt chromatinmodifizierende Aktivitäten, die diese Repression überwinden können. Die transkriptionelle Aktivierung des HIS7-Gens durch Aminosäuremangel benötigt dafür die Anwesenheit des Swi/Snf-Komplexes und der Transkriptionsaktivatoren Gcn4p und Abf1p, die gemeinsam eine Veränderung der Nukleosomenverteilung an dem HIS7-Promotor bewirken. Im Vergleich dazu benötigt die HIS7-Aktivierung bei Purinmangel durch den Transkriptionsaktivator Bas1p/Bas2p eine chromatinmodifizierende Aktivität, die Nukleosomen GCN5-abhängig azetyliert. Darüberhinaus stellt ein Nukleosom, das sich direkt stromaufwärts des HIS7-Promotors befindet, eine Grenze zum vorhergehenden ARO4-Gen dar. Möglicherweise dient es dem Schutz vor transkriptioneller Interferenz zwischen beiden gleichgerichteten Genen, die nur durch eine kurze intergenische Region getrennt sind

The Nma1 protein promotes long distance transport mediated by early endosomes in Ustilago maydis

Early endosomes (EEs) are part of the endocytic transport pathway and resemble the earliest class of transport vesicles between the internalization of extracellular material, their cellular distribution or vacuolar degradation. In filamentous fungi, EEs fulfill important functions in long distance transport of cargoes as mRNAs, ribosomes, and peroxisomes. Formation and maturation of early endosomes is controlled by the specific membrane-bound Rab-GTPase Rab5 and tethering complexes as CORVET (class C core vacuole/endosome tethering). In the basidiomycete Ustilago maydis, Rab5a is the prominent GTPase to recruit CORVET to EEs; in rab5a deletion strains, this function is maintained by the second EE-associated GTPase Rab5b. The tethering- and core-subunits of CORVET are essential, buttressing a central role for EE transport in U. maydis. The function of EEs in long distance transport is supported by the Nma1 protein that interacts with the Vps3 subunit of CORVET. The interaction stabilizes the binding of Vps3 to the CORVET core complex that is recruited to Rab5a via Vps8. Deletion of nma1 leads to a significantly reduced number of EEs, and an increased conversion rate of EEs to late endosomes. Thus, Nma1 modulates the lifespan of EEs to ensure their availability for the various long distance transport processes

A seed-like proteome in oil-rich tubers

There are numerous examples of plant organs or developmental stages that are desiccation-tolerant and can withstand extended periods of severe water loss. One prime example are seeds and pollen of many spermatophytes. However, in some plants, also vegetative organs can be desiccation-tolerant. One example are the tubers of yellow nutsedge (Cyperus esculentus), which also store large amounts of lipids similar to seeds. Interestingly, the closest known relative, purple nutsedge (Cyperus rotundus), generates tubers that do not accumulate oil and are not desiccation-tolerant. We generated nanoLC-MS/MS-based proteomes of yellow nutsedge in five replicates of four stages of tuber development and compared them to the proteomes of roots and leaves, yielding 2257 distinct protein groups. Our data reveal a striking upregulation of hallmark proteins of seeds in the tubers. A deeper comparison to the tuber proteome of the close relative purple nutsedge (C. rotundus) and a previously published proteome of Arabidopsis seeds and seedlings indicates that indeed a seed-like proteome was found in yellow but not purple nutsedge. This was further supported by an analysis of the proteome of a lipid droplet-enriched fraction of yellow nutsedge, which also displayed seed-like characteristics. One reason for the differences between the two nutsedge species might be the expression of certain transcription factors homologous to ABSCISIC ACID INSENSITIVE3, WRINKLED1, and LEAFY COTYLEDON1 that drive gene expression in Arabidopsis seed embryos

Dual checkpoint blockade of CD47 and LILRB1 enhances CD20 antibody-dependent phagocytosis of lymphoma cells by macrophages

Antibody-dependent cellular phagocytosis (ADCP) by macrophages, an important effector function of tumor targeting antibodies, is hampered by ‘Don´t Eat Me!’ signals such as CD47 expressed by cancer cells. Yet, human leukocyte antigen (HLA) class I expression may also impair ADCP by engaging leukocyte immunoglobulin-like receptor subfamily B (LILRB) member 1 (LILRB1) or LILRB2. Analysis of different lymphoma cell lines revealed that the ratio of CD20 to HLA class I cell surface molecules determined the sensitivity to ADCP by the combination of rituximab and an Fc-silent variant of the CD47 antibody magrolimab (CD47-IgGσ). To boost ADCP, Fc-silent antibodies against LILRB1 and LILRB2 were generated (LILRB1-IgGσ and LILRB2-IgGσ, respectively). While LILRB2-IgGσ was not effective, LILRB1-IgGσ significantly enhanced ADCP of lymphoma cell lines when combined with both rituximab and CD47-IgGσ. LILRB1-IgGσ promoted serial engulfment of lymphoma cells and potentiated ADCP by non-polarized M0 as well as polarized M1 and M2 macrophages, but required CD47 co-blockade and the presence of the CD20 antibody. Importantly, complementing rituximab and CD47-IgGσ, LILRB1-IgGσ increased ADCP of chronic lymphocytic leukemia (CLL) or lymphoma cells isolated from patients. Thus, dual checkpoint blockade of CD47 and LILRB1 may be promising to improve antibody therapy of CLL and lymphomas through enhancing ADCP by macrophages

Microtubules control cellular shape and coherence in amoeboid migrating cells

Cells navigating through complex tissues face a fundamental challenge: while multiple protrusions explore different paths, the cell needs to avoid entanglement. How a cell surveys and then corrects its own shape is poorly understood. Here, we demonstrate that spatially distinct microtubule dynamics regulate amoeboid cell migration by locally promoting the retraction of protrusions. In migrating dendritic cells, local microtubule depolymerization within protrusions remote from the microtubule organizing center triggers actomyosin contractility controlled by RhoA and its exchange factor Lfc. Depletion of Lfc leads to aberrant myosin localization, thereby causing two effects that rate-limit locomotion: (1) impaired cell edge coordination during path finding and (2) defective adhesion resolution. Compromised shape control is particularly hindering in geometrically complex microenvironments, where it leads to entanglement and ultimately fragmentation of the cell body. We thus demonstrate that microtubules can act as a proprioceptive device: they sense cell shape and control actomyosin retraction to sustain cellular coherence

A Next-Generation Liquid Xenon Observatory for Dark Matter and Neutrino Physics

The nature of dark matter and properties of neutrinos are among the mostpressing issues in contemporary particle physics. The dual-phase xenontime-projection chamber is the leading technology to cover the availableparameter space for Weakly Interacting Massive Particles (WIMPs), whilefeaturing extensive sensitivity to many alternative dark matter candidates.These detectors can also study neutrinos through neutrinoless double-beta decayand through a variety of astrophysical sources. A next-generation xenon-baseddetector will therefore be a true multi-purpose observatory to significantlyadvance particle physics, nuclear physics, astrophysics, solar physics, andcosmology. This review article presents the science cases for such a detector.<br

A next-generation liquid xenon observatory for dark matter and neutrino physics

The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector

yRACK1/Asc1 proxiOMICs—Towards Illuminating Ships Passing in the Night

Diverse signals and stress factors regulate the activity and homeostasis of ribosomes in all cells. The Saccharomyces cerevisiae protein Asc1/yRACK1 occupies an exposed site at the head region of the 40S ribosomal subunit (hr40S) and represents a central hub for signaling pathways. Asc1 strongly affects protein phosphorylation and is involved in quality control pathways induced by translation elongation arrest. Therefore, it is important to understand the dynamics of protein formations in the Asc1 microenvironment at the hr40S. We made use of the in vivo protein-proximity labeling technique Biotin IDentification (BioID). Unbiased proxiOMICs from two adjacent perspectives identified nucleocytoplasmic shuttling mRNA-binding proteins, the deubiquitinase complex Ubp3-Bre5, as well as the ubiquitin E3 ligase Hel2 as neighbors of Asc1. We observed Asc1-dependency of hr40S localization of mRNA-binding proteins and the Ubp3 co-factor Bre5. Hel2 and Ubp3-Bre5 are described to balance the mono-ubiquitination of Rps3 (uS3) during ribosome quality control. Here, we show that the absence of Asc1 resulted in massive exposure and accessibility of the C-terminal tail of its ribosomal neighbor Rps3 (uS3). Asc1 and some of its direct neighbors together might form a ribosomal decision tree that is tightly connected to close-by signaling modules