Die Regulation der NANOG-Expression während der Keimzellreifung und in Keimzelltumoren sowie die Untersuchungen zu Differenzierungsprozessen von Seminomen <em>in vivo</em> und <em>in vitro</em>

Das Homeobox-Protein NANOG übernimmt Schlüsselfunktionen bei der Erhaltung der Selbsterneuerung und Pluripotenz von undifferenzierten Zellen. Die Mechanismen der NANOG-Expressionsregulation wurden während der humanen Keimzellreifung näher untersucht, dabei wurde gezeigt, dass die Herabregulation der NANOG-Expression während der Transition fetaler Keimzellen zu fetalen Spermatogonien durch fehlende OCT3/4-SOX2-Transaktivierung hervorgerufen wird. Eine Methylierung des NANOG-Promoters und somit eine epigenetische Repression wird erst bei der Differenzierung der Spermatogonien zu reifen Spermien etabliert. Interessant ist, dass die DNS während dieses Zeitraums global demethyliert wird. Die Methylierung des NANOG-Promoters wird also unabhängig von der globalen Methylierung reguliert. In testikulären Keimzelltumoren konnte der Differenzierungsgrad der Tumorentität an den DNS-Methylierungsstatus des NANOG-Promotors korreliert werden. Das bedeutet je differenzierter die Tumorentität desto höher die NANOG-Promotormethylierung und umso geringer die NANOG-Expression. Seminome sind undifferenzierte Tumoren der Keimzellen. Diese Tumoren sind durch die Expression von Pluripotenz- und Keimzellmarkern sowie uniformes Wachstum gekennzeichnet, d.h. die Zellen behalten ihren unipotenten Keimzellcharakter bei. Die humane Seminom-Zelllinie TCam-2 wurde als Modellsystem verwendet, um die Differenzierungsfähigkeiten von Seminomen in vitro und in vivo zu untersuchen. Es konnte gezeigt werden, dass die Wachstumsfaktoren TGF-β1, EGF und FGF4/Heparin synergistisch eine Differenzierung in ein gemischtes Nicht-Seminom induzieren. Sie bewirken einen Block des BMP-Signalwegs und eine Aktivierung des Hippo-Signalwegs sowie eine Inhibition des LIN28/BLIMP1-Signalwegs. Eine Injektion von TCam-2-Zellen in die Flanke von Nacktmäusen führte zum Wachstum embryonaler Karzinome (EK). Diese in vivo-Transition von einem Seminom zu einem EK wurde durch eine erneute in vitro-Kultivierung revertiert und deutete auf eine Plastizität der TCam-2-Zellen hin. Bis zu drei Monate nach Injektion von TCam-2-Zellen in die Testes von Nacktmäusen konnten Carcinoma-in-situ ähnliche Zellpopulationen in den Tubuli seminiferi nachgewiesen werden. Somit konnte ein KZT-Modell erzeugt werden, welches gezielte Untersuchungen zum Verhalten von CIS-Zellen in vivo erlaubt. Die Ergebnisse zeigen, dass die Zelllinie TCam-2 in der Lage ist in vitro und in vivo zu differenzieren. Die Richtung des Differenzierungsprozesses hängt dabei von dem zellulären Mikromilieu sowie den Kultivierungsbedingungen ab. Interessant ist die Tatsache, dass diesen Veränderungen in der Tumorklasse keine weiteren Gendefekte unterlagen

Sensitivity of a collisional single-atom spin probe

We study the sensitivity of a collisional single-atom probe for ultracold gases. Inelastic spin-exchange collisions map information about the gas temperature or external magnetic field onto the quantum spin-population of single-atom probes. We numerically investigate the steady-state sensitivity of such single-atom probes to various observables. We find that the probe has maximum sensitivity when sensing the energy ratio between thermal energy and Zeeman energy in an externally applied magnetic field, while the sensitivity to the absolute energy, i.e., the sum of kinetic and Zeeman energy, is low. We identify the parameters yielding maximum sensitivity for a given absolute energy, which we can relate to a direct comparison of the thermal Maxwell-Boltzmann distribution with the Zeeman-energy splitting. We compare our findings to experimental results from a single-atom quantum probe, showing the expected sensitivity behavior. Our work thereby yields a microscopic explanation for the properties and performance of this type of single-atom quantum probe and connecting thermodynamic properties to microscopic interaction mechanisms.Comment: 10 pages, 8 figure

Power of a quasi-spin quantum Otto engine at negative effective temperature

Heat engines usually operate by exchanging heat with thermal baths at different (positive) temperatures. Nonthermal baths may, however, lead to a significant performance boost. We here experimentally analyze the power output of a single-atom quantum Otto engine realized in the quasi-spin states of individual Cesium atoms interacting with an atomic Rubidium bath. From measured time-resolved populations of the quasi-spin state, we determine the dynamics during the cycle of both the effective spin temperature and of the quantum fluctuations of the engine, which we quantify with the help of the Shannon entropy. We find that power is enhanced in the negative temperature regime, and that it reaches its maximum value at half the maximum entropy. Quantitatively, operating our engine at negative effective temperatures increases the power by up to 30% compared to operation at positive temperatures, including even the case of infinite temperature. At the same time, entering the negative temperature regime allows for reducing the entropy to values close to zero, offering highly stable operation at high power output. We furthermore numerically investigate the influence of the size of the Hilbert space on the performance of the quantum engine by varying the number of levels of the working medium. Our work thereby paves the way to fluctuation control in the operation of high-power and efficient single-atom quantum engines.Comment: 9 pages, 6 figure

Single-Atom Quantum Probes for Ultracold Gases Boosted by Nonequilibrium Spin Dynamics

Quantum probes are atomic sized devices mapping information of their environment to quantum-mechanical states. By improving measurements and at the same time minimizing perturbation of the environment, they form a central asset for quantum technologies. We realize spin-based quantum probes by immersing individual Cs atoms into an ultracold Rb bath. Controlling inelastic spin-exchange processes between the probe and bath allows us to map motional and thermal information onto quantum-spin states. We show that the steady-state spin population is well suited for absolute thermometry, reducing temperature measurements to detection of quantum-spin distributions. Moreover, we find that the information gain per inelastic collision can be maximized by accessing the nonequilibrium spin dynamic. Keeping the motional degree of freedom thermalized, individual spin-exchange collisions yield information about the gas quantum by quantum. We find that the sensitivity of this nonequilibrium quantum probing effectively beats the steady-state Cramér-Rao limit by almost an order of magnitude, while reducing the perturbation of the bath to only three quanta of angular momentum. Our work paves the way for local probing of quantum systems at the Heisenberg limit, and moreover, for optimizing measurement strategies via control of nonequilibrium dynamics. © 2020 authors. Published by the American Physical Society

Indication of critical scaling in time during the relaxation of an open quantum system

Phase transitions correspond to the singular behavior of physical systems in response to continuous control parameters like temperature or external fields. Near continuous phase transitions, associated with the divergence of a correlation length, universal power-law scaling behavior with critical exponents independent of microscopic system details is found. Recently, dynamical quantum phase transitions and universal scaling have been predicted and also observed in the non-equilibrium dynamics of isolated quantum systems after a quench, with time playing the role of the control parameter. However, signatures of such critical phenomena in time in open systems, whose dynamics is driven by the dissipative contact to an environment, were so far elusive. Here, we present results indicating that critical scaling with respect to time can also occur during the relaxation dynamics of an open quantum system described by mixed states. We experimentally measure the relaxation dynamics of the large atomic spin of individual Caesium atoms induced by the dissipative coupling via spin-exchange processes to an ultracold Bose gas of Rubidium atoms. For initial states far from equilibrium, the entropy of the spin state is found to peak in time, transiently approaching its maximum possible value, before eventually relaxing to its lower equilibrium value. Moreover, a finite-size scaling analysis based on numerical simulations shows that it corresponds to a critical point with respect to time of the dissipative system in the limit of large system sizes. It is signalled by the divergence of a characteristic length at a critical time, characterized by critical exponents that are found to be independent of system details

BMP Inhibition in Seminomas Initiates Acquisition of Pluripotency via NODAL Signaling Resulting in Reprogramming to an Embryonal Carcinoma

Type II germ cell cancers (GCC) can be subdivided into seminomas and non-seminomas. Seminomas are similar to carcinoma in situ (CIS) cells, the common precursor of type II GCCs, with regard to epigenetics and expression, while embryonal carcinomas (EC) are totipotent and differentiate into teratomas, yolk-sac tumors and choriocarcinomas. GCCs can present as seminomas with a non-seminoma component, raising the question if a CIS gives rise to seminomas and ECs at the same time or whether seminomas can be repro- grammed to ECs. In this study, we utilized the seminoma cell line TCam-2 that acquires an EC-like status after xenografting into the murine flank as a model for a seminoma to EC tran- sition and screened for factors initiating and driving this process. Analysis of expression and DNA methylation dynamics during transition of TCam-2 revealed that many pluripotency- and reprogramming-associated genes were upregulated while seminoma-markers were downregulated. Changes in expression level of 53 genes inversely correlated to changes in DNA methylation. Interestingly, after xenotransplantation 6 genes ( GDF3 , NODAL , DNMT3B , DPPA3 , GAL , AK3L1 ) were rapidly induced, followed by demethylation of their genomic loci, suggesting that these 6 genes are poised for expression driving the repro- gramming. We demonstrate that inhibition of BMP signaling is the initial event in reprogram- ming, resulting in activation of the pluripotency-associated genes and NODAL signaling. We propose that reprogramming of seminomas to ECs is a multi-step process. Initially, the microenvironment causes inhibition of BMP signaling, leading to induction of NODAL sig- naling. During a maturation phase, a fast acting NODAL loop stimulates its own activity and temporarily inhibits BMP signaling. During the stabilization phase, a slow acting NODAL loop, involving WNTs re-establishes BMP signaling and the pluripotency circuitry. In parallel, DNMT3B-driven de novo methylation silences seminoma-associated genes and epigenetically fixes the EC state

A signaling cascade including ARID1A, GADD45B and DUSP1 induces apoptosis and affects the cell cycle of germ cell cancers after romidepsin treatment

In Western countries, the incidence of testicular germ cell cancers (GCC) is steadily rising over the last decades. Mostly, men between 20 and 40 years of age are affected. In general, patients suffering from GCCs are treated by orchiectomy and radio- or chemotherapy. Due to resistance mechanisms, intolerance to the therapy or denial of chemo- / radiotherapy by the patients, GCCs are still a lethal threat, highlighting the need for alternative treatment strategies. In this study, we revealed that germ cell cancer cell lines are highly sensitive to the histone deacetylase inhibitor romidepsin in vitro and in vivo, highlighting romidepsin as a potential therapeutic option for GCC patients. Romidepsin-mediated inhibition of histone deacetylases led to disturbances of the chromatin landscape. This resulted in locus-specific histone-hyper- or hypoacetylation. We found that hypoacetylation at the ARID1A promotor caused repression of the SWI/SNF-complex member ARID1A. In consequence, this resulted in upregulation of the stress-sensors and apoptosis-regulators GADD45B, DUSP1 and CDKN1A. RNAi-driven knock down of ARID1A mimicked in parts the effects of romidepsin, while CRISPR/Cas9-mediated deletion of GADD45B attenuated the romidepsin-provoked induction of apoptosis and cell cycle alterations. We propose a signaling cascade involving ARID1A, GADD45B and DUSP1 as mediators of the romidepsin effects in GCC cells