Nuclear astrophysics: the unfinished quest for the origin of the elements

Half a century has passed since the foundation of nuclear astrophysics. Since then, this discipline has reached its maturity. Today, nuclear astrophysics constitutes a multidisciplinary crucible of knowledge that combines the achievements in theoretical astrophysics, observational astronomy, cosmochemistry and nuclear physics. New tools and developments have revolutionized our understanding of the origin of the elements: supercomputers have provided astrophysicists with the required computational capabilities to study the evolution of stars in a multidimensional framework; the emergence of high-energy astrophysics with space-borne observatories has opened new windows to observe the Universe, from a novel panchromatic perspective; cosmochemists have isolated tiny pieces of stardust embedded in primitive meteorites, giving clues on the processes operating in stars as well as on the way matter condenses to form solids; and nuclear physicists have measured reactions near stellar energies, through the combined efforts using stable and radioactive ion beam facilities. This review provides comprehensive insight into the nuclear history of the Universe and related topics: starting from the Big Bang, when the ashes from the primordial explosion were transformed to hydrogen, helium, and few trace elements, to the rich variety of nucleosynthesis mechanisms and sites in the Universe. Particular attention is paid to the hydrostatic processes governing the evolution of low-mass stars, red giants and asymptotic giant-branch stars, as well as to the explosive nucleosynthesis occurring in core-collapse and thermonuclear supernovae, gamma-ray bursts, classical novae, X-ray bursts, superbursts, and stellar mergers.Comment: Invited Review. Accepted for publication in "Reports on Progress in Physics" (version with low-resolution figures

Lysosomal Signaling Licenses Embryonic Stem Cell Differentiation via Inactivation of Tfe3

Self-renewal and differentiation of pluripotent murine embryonic stem cells (ESCs) is regulated by extrinsic signaling pathways. It is less clear whether cellular metabolism instructs developmental progression. In an unbiased genome-wide CRISPR/Cas9 screen, we identified components of a conserved amino-acid-sensing pathway as critical drivers of ESC differentiation. Functional analysis revealed that lysosome activity, the Ragulator protein complex, and the tumor-suppressor protein Folliculin enable the Rag GTPases C and D to bind and seclude the bHLH transcription factor Tfe3 in the cytoplasm. In contrast, ectopic nuclear Tfe3 represses specific developmental and metabolic transcriptional programs that are associated with peri-implantation development. We show differentiation-specific and non-canonical regulation of Rag GTPase in ESCs and, importantly, identify point mutations in a Tfe3 domain required for cytoplasmic inactivation as potentially causal for a human developmental disorder. Our work reveals an instructive and biomedically relevant role of metabolic signaling in licensing embryonic cell fate transitions

The histone chaperone CAF-1 safeguards somatic cell identity

Cellular differentiation involves profound remodeling of chromatic landscapes, yet the mechanisms by which somatic cell identity is subsequently maintained remain incompletely understood. To further elucidate regulatory pathways that safeguard the somatic state, we performed two comprehensive RNAi screens targeting chromatin factors during transcription factor-mediated reprogramming of mouse fibroblasts to induced pluripotent stem cells (iPSCs). Remarkably, subunits of the chromatin assembly factor-1 (CAF-1) complex emerged as the most prominent hits from both screens, followed by modulators of lysine sumoylation and heterochromatin maintenance. Optimal modulation of both CAF-1 and transcription factor levels increased reprogramming efficiency by several orders of magnitude and facilitated iPSC formation in as little as 4 days. Mechanistically, CAF-1 suppression led to a more accessible chromatin structure at enhancer elements early during reprogramming. These changes were accompanied by a decrease in somatic heterochromatin domains, increased binding of Sox2 to pluripotency-specific targets and activation of associated genes. Notably, suppression of CAF-1 also enhanced the direct conversion of B cells into macrophages and fibroblasts into neurons. Together, our findings reveal the histone chaperone CAF-1 as a novel regulator of somatic cell identity during transcription factor-induced cell fate transitions and provide a potential strategy to modulate cellular plasticity in a regenerative setting

Cometary Matter Analyser (COMA/CRAF) Schlussbericht

This prospect was part of an international program under which the chemical composition of cometary dust particles was to be measured 'in situ' during a rendezvous and flyby mission of a Mariner Mark II space probe and a comet (depending on the time of launch). Two necessary tasks, preliminary hardware development and interface definition, have been completed within the projects submitted for approval. As a result a model close to the flight configuration has been created, which was to be made available to the flight hardware contractor and his purposes. The Comet Redezvous and Asteroid Flyby (CRAF) mission was abondoned after joint resolution adopted by NASA and the Federal Ministry for Research and Technology in 1992. Since an instrument like CoMa is an important contribution both to future cometary redezvous missions, such as ROSETTA, as well as for accompanying laboratory activities, this project was terminated in a 'qualified conclusion'. In the process, components suitable for the laboratory developed from the preliminary units were produced and put into operation. (orig./HM)Das Vorhaben war Teil eines internationalen Programms, bei dem die chemische Zusammensetzung kometarer Staubteilchen waehrend eines Mitfluges einer Raumsonde vom Typ Mariner Mark II mit einem Kometen (abhaengig vom Startzeitpunkt) 'in situ' gemessen werden sollte. Diese beiden notwendigen Aufgaben, Vorentwicklung der Hardware und Interfacedefinition sind innerhalb des beantragten Vorhabens erledigt worden. Als Ergebnis ist ein der Flugkonfiguration nahes Modell entstanden, das dem Auftragnehmer fuer die Flug-Hardware fuer seine Zwecke zur Verfuegung gestellt werden sollte. Die Mission CRAF ist im Januar 1992 von NASA und BMFT nach einem gemeinsamen Beschluss aufgegeben worden. Da ein Geraet wie CoMA sowohl fuer zukuenftige Kometen-Rendezvous-Missionen wie ROSETTA, wie auch fuer begleitende Laboraktivitaeten ein wichtiger Beitrag ist, wurde noch ein 'qualifizierter Abschluss' der Arbeiten durchgefuehrt. Dabei wurden dem aus den vorentwickelten Einheiten labortaugliche Komponenten hergestellt und in Betrieb genommen. (orig./HM)Available from TIB Hannover: F94B0615 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Prinicpal investigator instrument proposal. Type 1 procedure Commentary Matter Analyser. Pt. 2

Available from TIB Hannover: F94B0543 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman