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Functional relevance of oligodendroglial CDC42 effector proteins CDC42EP1 and CDC42EP2 in myelin morphogenesis
No full textMyelin sheaths are composed of multiple compacted membrane layers that tightly encase the underlying axon. Structural abnormalities of myelin indicate pathological processes and are frequently associated with neurological disorders or age-related degeneration of the nervous system. The regular structure of healthy central nervous system (CNS) myelin relies on specialized structural proteins, including cytoskeletal filaments assembled from the septin subunits SEPTIN2, SEPTIN4, SEPTIN7, and SEPTIN8. This study addresses the vital question: How is septin filament assembly in CNS myelin regulated? It is hypothesized that a pathway downstream of the master regulator CDC42 influences septin assembly within myelin. This hypothesis was tested by genetically ablating the CDC42 effector proteins CDC42EP1 and CDC42EP2 specifically in oligodendrocytes. A multi-modal approach to characterize the resulting phenotypes was employed, including transmission electron microscopy (TEM) for ultrastructural analysis, immunohistochemical (IHC) imaging to assess myelin septin architecture and neuropathology, qRT-PCR to assess transcriptional changes in septin-associated genes, and quantitative myelin proteome analysis. The results indicate that recombination of the Cdc42ep1 and Cdc42ep2 genes in oligodendrocytes causes a marked reduction in septin protein levels within myelin, as demonstrated by proteomic profiling and IHC analysis. TEM imaging revealed that mutant mice developed myelin outfoldings as specific pathology, a phenotype that closely resembles the defects observed in Septin8-deficient mice, which lack functional myelin septin filaments. Together, the findings suggest that oligodendroglial CDC42 effector proteins regulate myelin septin assembly to facilitate structural integrity of healthy myelin sheaths. Mechanistically, it is demonstrated that CDC42EP1/EP2 directly interact with septin filaments and their loss results in fragmented, disorganized septin structure.2025-11-1
Ampicillin and cefotaxime in intensive care medicine: a retrospective plasma level analysis
No full textAmpicillin und Cefotaxim gehören zu den häufiger, unter anderem bei kritisch Kranken, eingesetzten Antibiotika. Ihr Einsatz in diesem Kontext wurde jedoch in der wissenschaftlichen Literatur bislang nur vereinzelt dargestellt und analysiert. Vor dem Hintergrund einer hohen sepsisassoziierten Mortalität und der komplexen Pharmakokinetik kritisch kranker Patienten war die retrospektive Erfolgskontrolle von Ampicillin- und Cefotaxim-Plasmaspiegeln sowie das Identifizieren von Risikofaktoren für das Unter- oder Überschreiten des Zielkorridors bei intensivmedizinischer Behandlung Ziel dieser Arbeit. Dazu erfolgte eine umfangreiche Datenbankabfrage der im Zeitraum 2015 bis 2022 bestimmten Ampicillin- und Cefotaxim-Plasmaspiegel gemeinsam mit zahlreichen möglicherweise relevanten klinischen, therapieassoziierten und laborchemischen Parametern. Die Auswertung erfolgte anhand deskriptiver Lagemaße, Korrelationsanalysen und einfacher sowie multipler Regressionsanalysen. Insgesamt wurden 466 Ampicillin- (225 Patienten) sowie 338 Cefotaxim-Plasmaspiegel (105 Patienten) berücksichtigt. Initial lagen lediglich 30% der 206 Ampicillin- bzw. 40% der 95 Cefotaxim-Plasmaspiegel im jeweiligen vordefinierten Zielbereich (Ampicillin 30–60 mg/l; Cefotaxim 32–80 mg/l). Basierend auf regelmäßigen Plasmaspiegelbestimmungen und anschließenden Dosisanpassungen konnte der Anteil der jeweils im Zielbereich liegenden Plasmaspiegel im Verlauf erhöht werden. Allgemein zeigte sich bei ähnlicher Dosis eine starke Streuung der Plasmaspiegel, wobei – bezogen auf die vorgegebenen Zielbereiche – der Anteil der Unterdosierungen mit etwa 50% bei beiden β-Laktamen überwog. Während sich der Zielbereich für Ampicillin seit 2015 kaum verändert hat, führte eine Neubewertung der wünschenswerten Cefotaxim-Plasmaspiegel zu einem aktuell gültigen erheblich restriktiveren Zielfenster von 8–16 mg/l. Dieser neuere Zielbereich verändert auch die Interpretation der Daten. Nun gewährleistet die gleiche Tagesdosis ein 100%iges Erreichen der Untergrenze des Zielspiegels, während die neue Obergrenze in fast 90% der Fälle überschritten wurde.
Die auf zahlreichen Korrelationsanalysen basierenden Regressionsanalysen zeigten, dass die Nierenfunktion den größten Einfluss auf die β-Laktam-Plasmaspiegel hat. Diese konnte allein ca. 60% der Varianz des Ampicillin- bzw. 45% der Varianz des Cefotaxim-Plasmaspiegels erklären. Verschiedene andere Parameter wie Geschlecht, Größe und Gewicht sowie Gesamt-Bilirubin (im Fall von Cefotaxim) zeigten ebenfalls signifikante Einflüsse, deren Effekte der eGFR jedoch deutlich untergeordnet waren. Unter Berücksichtigung dieser Größen konnte die Vorhersagekraft der linearen Regressionsmodelle dennoch verbessert werden, sodass bis zu 64% der Varianz des Ampicillin- bzw. 62% der Varianz des Cefotaxim-Plasmaspiegels erklärt werden konnten. Die Effekte korrelierender Größen wie Patientenalter, pH-Wert, PCT und SAPS II wurden auf jeweils enge Zusammenhänge mit der Nierenfunktion zurückgeführt. Es bleibt unklar, ob der in der Fachliteratur bisher nicht beschriebene Einfluss des Standardbikarbonats auf den Ampicillin-Plasmaspiegel bzw. des Laktates auf den Cefotaxim-Plasmaspiegel unabhängig von der eGFR zustande kommt. Weitere Untersuchungen werden benötigt. Plasmaspiegel im Rahmen einer RRT lagen durchschnittlich öfter im oder über dem Zielbereich, während für den Einsatz einer ECMO kein Effekt auf die Plasmaspiegel gezeigt werden konnte.
Auf Grundlage des dominanten Einflusses der Nierenfunktion auf die Höhe der Plasmaspiegel wurden für die Risikogruppen mit gesteigerter Nierenfunktion (≥ 130 ml/min) bzw. stark eingeschränkter Nierenfunktion (< 30 ml/min) angepasste Dosisempfehlungen entwickelt. Das bestehende Standard-Dosis-Regime sollte für Cefotaxim bei eingeschränkter Nierenfunktion auf 2–4 g pro Tag reduziert werden. Konträr profitieren mit Ampicillin/Sulbactam (2:1) behandelte Patienten bei normaler bis gesteigerter Nierenfunktion voraussichtlich von einer Steigerung der Tagesdosis auf 12 g.
Aufbauend auf einem besseren Verständnis für das Verhalten von Ampicillin- und Cefotaxim-Plasmaspiegeln bei kritischer Krankheit kann diese Datenanalyse trotz ihrer retrospektiven Natur so zu einer effektiveren antiinfektiven Therapie beitragen.Ampicillin and cefotaxime are among the antibiotics most commonly used in critically ill patients. However, their use in this context has only been sporadically described and analyzed in the scientific literature to date. Against the backdrop of high sepsis-associated mortality and the complex pharmacokinetics of critically ill patients, the aim of this study was to retrospectively monitor the success of ampicillin and cefotaxime plasma levels and to identify risk factors for falling below or exceeding the target range in intensive care treatment. To this end, an extensive database query was performed on the ampicillin and cefotaxime plasma levels determined between 2015 and 2022, together with numerous potentially relevant clinical, therapy-associated, and laboratory chemical parameters. The evaluation was based on descriptive measures of central tendency, correlation analyses, and simple and multiple regression analyses. A total of 466 ampicillin (225 patients) and 338 cefotaxime plasma levels (105 patients) were included. Initially, only 30% of the 206 ampicillin and 40% of the 95 cefotaxime plasma levels were within the respective predefined target range (ampicillin 30–60 mg/L; cefotaxime 32–80 mg/L). Based on regular plasma level measurements and subsequent dose adjustments, the proportion of plasma levels within the target range could be increased over time. In general, there was a wide variation in plasma levels at similar doses, with underdosing predominating at around 50% for both β-lactams in relation to the specified target ranges. While the target range for ampicillin has hardly changed since 2015, a reassessment of the desirable cefotaxime plasma levels has led to a currently valid, significantly more restrictive target window of 8–16 mg/L. This newer target range also changes the interpretation of the data. Now, the same daily dose ensures 100% achievement of the lower limit of the target level, while the new upper limit was exceeded in almost 90% of cases.
Regression analyses based on numerous correlation analyses showed that renal function has the greatest influence on β-lactam plasma levels. This alone accounted for approximately 60% of the variance in ampicillin and 45% of the variance in cefotaxime plasma levels. Various other parameters such as gender, height, and weight, as well as total bilirubin (in the case of cefotaxime), also had significant influences, but their effects were clearly subordinate to those of eGFR. Taking these variables into account, the predictive power of the linear regression models could nevertheless be improved, so that up to 64% of the variance in ampicillin and 62% of the variance in cefotaxime plasma levels could be explained. The effects of correlating variables such as patient age, pH, PCT, and SAPS II were attributed to close correlations with renal function. It remains unclear whether the influence of standard bicarbonate on ampicillin plasma levels and lactate on cefotaxime plasma levels, which has not been described in the literature to date, is independent of eGFR. Further investigation is needed. Plasma levels during RRT were on average more often within or above the target range, while the use of ECMO had no demonstrable effect on plasma levels.
Based on the dominant influence of renal function on plasma levels, adjusted dose recommendations were developed for risk groups with increased renal function (≥ 130 mL/min) or severely impaired renal function (< 30 mL/min). The existing standard dose regimen for cefotaxime should be reduced to 2–4 g per day in patients with impaired renal function. Conversely, patients treated with ampicillin/sulbactam (2:1) with normal to increased renal function are likely to benefit from an increase in the daily dose to 12 g.
Based on a better understanding of the behavior of ampicillin and cefotaxime plasma levels in critical illness, this data analysis, despite its retrospective nature, can thus contribute to more effective anti-infective therapy.2025-12-2
Design Recommendations for Motivational Learning Systems to Promote Competencies in Software Testing
No full textSoftware testing is an integral part of the software development process and often determines the success or failure of software projects. Although testing can consume more than half of development time and costs, it is frequently underrepresented in both practice and education. This neglect leads not only to significant economic burdens due to increasing technical debt but also to persistent quality issues in software products. In higher education, there is a clear lack of solid competencies in software testing, for instance, through insufficient curricular integration or the abstract delivery of methodological knowledge. Furthermore, students often perceive testing as monotonous or even irrelevant compared to software development.
Against this backdrop, this dissertation investigates the challenges and potentials of software testing education in higher education, as well as the design of motivational learning systems. Following a Design Science Research approach, it develops and iteratively refines digital, game-based learning environments to foster testing competencies. Both fundamental and advanced knowledge in Black-Box, White-Box, and Grey-Box testing are addressed.
The dissertation is structured into three research complexes: Research Complex A explores central challenges, deficits, and potentials (Studies I–IV). Research Complex B focuses on the integration of fundamental testing knowledge in introductory courses. Here, an adaptive, narrative, mission-based learning environment was developed that intertwines programming and testing from the outset (Studies V–VI). Research Complex C addresses specialized testing techniques, resulting in practice-oriented learning systems that combine realistic test objects, feedback mechanisms, and motivational elements. Findings show that students not only write tests but also critically reflect on and systematically improve their quality.
In summary, this dissertation contributes by systematically identifying educational deficits in software testing and linking them to industry requirements. Moreover, it provides prescriptive design knowledge through the development and evaluation of gamified learning systems.2025-11-2
DEAR Drainage extraction after rinsing
No full textIn our clinic, several cases occurred in which the greater omentum herniated through the drain site during drain removal, requiring surgical repositioning under general anesthesia. To prevent this complication, we introduced a technique of flushing the drain with sterile saline before removal, assuming that omental tissue might be caught in the drain holes and could be released by flushing.
A prospective randomized study was conducted including pediatric surgical patients with intraoperatively placed drains. After informed consent, patients were randomized into two groups: Group A received conventional drain removal, while Group B had the drain shortened, flushed with 5 ml of saline, and then removed. Collected data included age, underlying condition, drain size, duration of drain placement, and the occurrence of omental herniation.
Herniation of the greater omentum through drain channels is known but extremely rare. Existing literature consists mainly of retrospective reports and case studies, comparable to trocar hernias in adult surgery. The observed findings resemble “special” trocar hernia categories, though technically they do not represent true hernias because no hernia sac is present—more similar to a small abdominal wall dehiscence.
Across 32 patients and 41 drains, no cases of omental herniation occurred in either study group. Although this suggests that the complication is exceedingly uncommon, the flushing technique did not produce any disadvantages.
Given the heterogeneous pediatric population—varying in age, size, and reactions to stress—the authors conclude that a standardized approach may not always be suitable. Flushing the drain before removal appears particularly useful in situations involving additional risk factors such as young patient age, significant anxiety, crying, or increased intra-abdominal pressure.2026-01-1
β-Hydrogen Eliminations from Organoaluminates and -Cuprates in the Gas Phase
No full textThe β-hydride elimination is a fundamental process in many organometallic reaction mechanisms and decomposition pathways. This thesis investigates the β-hydride elimination of alkyl organoaluminates and alkyl organocuprates in the gas phase using electrospray ionization mass spectrometry (ESI-MS). The formation of homoleptic and heteroleptic alkyl organoaluminates and alkyl organocuprates was observed in ESI-MS measurements of a solution of the corresponding metal salts and transmetalation reagents. Alkyl aluminates could be generated using both Grignard and organolithium reagents. As expected, only the latter yielded the corresponding alkyl cuprate species.
Using a single transmetalation reagent predominantly produced the homoleptic species [R4Al]−. These species, when mass-selected and subjected to CID, exclusively fragmented to [R3AlH]− with the loss of one alkene. This reaction was confirmed to be a β-hydride elimination by using a deuterium labeled (in the β position) ligand. The MSn functionality of the used mass spectrometer allowed for the investigation of the fragment ions (hydrides), revealing two possible reaction pathways: first, another β-hydride elimination to [R2AlH2]−, or second, the loss of H2, with the former being the major reaction pathway. This behavior was observed for all measured alkyl ligands (Et, nBu, Hex, C14H29, iPr, Cy), whereas unexpectedly the homoleptic complex [iPr4Al]− exhibited direct loss of H2. For systems containing a Al−H moiety, two possible reaction pathways are feasible: first the reductive elimination, if two hydrides are directly bound to the metal center, or second via the loss of one aluminum-bound hydride and a β-hydride from an alkyl ligand.
To directly compare the reactivity of different alkyl ligands, heteroleptic complexes of the form [RnAlBu4-n]− were generated using two different transmetalation reagents. In all cases, at least one ligand was Bu, serving as a reference for the comparison of the reactivity of the other ligand to that of Bu. These experiments revealed differences in the reactivity that could be rationalized through a combination of steric effects, differences in double bond strength, and the difference in hydridic character of the β-hydrogens. The observed reactivity of both homoleptic and heteroleptic complexes was further rationalized by supporting DFT calculations.
The same approach was applied for the investigation of alkyl cuprates, which were observed in two different oxidation states. The main species, homoleptic alkylcopper(III) complexes [R4Cu]− (R = nBu, sBu, tBu, Hex, Dec), exhibit a single reaction pathway: the reductive elimination of two alkyl ligands, forming the corresponding copper(I) species [R2Cu]−. These species, which were also observed in the MS1 spectra, react only via a β-hydride elimination forming [RCuH]−, which could further eliminate a second alkene yielding [CuH2]−. Unlike the aluminates, no loss of H2 was observed, neither from the homoleptic species nor from the hydride.
Next, the reactivity of homoleptic copper(I) complexes with different butyl ligands (nBu, sBu, tBu) was compared, enabled by the same molar mass and the same number of degrees of freedom of these systems. This revealed an at first unexpected trend of reactivity sBu > nBu > tBu, which could be rationalized by steric effects in the transition states. For the heteroleptic complex [HexCuBu]−, a strong preference for the elimination of butene was experimentally observed. This selectivity could not yet be rationalized and may be caused by a mass discrimination effect of the mass spectrometer. The observed reactivity of the homoleptic complexes was further rationalized by supporting DFT calculations, which revealed a significantly lower barrier for the β-hydride elimination of homoleptic copper(I) complexes (163 kJ mol−1) compared to the analogous organoaluminate species (241 kJ mol−1). This difference can be rationalized by the reduced steric hindrance and the more easily accessible vacant coordination site in the cuprate. In addition, agostic interactions between the copper center and the β-C−H bond may further contribute to the lower barrier observed for the cuprate species.2025-12-1
Resolving intermediate states of mitotic entry
No full textMitosis, the division of cells, is a fundamental biological process essential for growth, tissue repair, and the propagation of genetic material. Mitosis is tightly regulated and its dysregulation has severe consequences, underlying diseases such as cancer. A critical first step of mitosis is mitotic entry, the "point of no return", when a biochemical switch transitions the cell from an interphase to a mitotic state. This switch is mediated by mitotic kinases, which phosphorylate a large number of substrates, driving dramatic changes to cellular organization. These include the complete remodeling of the actin and microtubule cytoskeleton, the condensation of chromosomes, and the breakdown of the nuclear envelope (NEBD), mixing nuclear and cytoplasmic compartments.
Despite its critical importance, many questions remain open regarding the precise mechanisms governing mitotic entry. To a large part, this is due to the fact that this dramatic transition occurs in a very short time and therefore its intermediate states are nearly impossible to access experimentally. In my thesis work, I developed novel protocols, whereby using a combination of small-molecule kinase inhibitors, I was able to drive cells into such intermediate states for the first time. By combining cellular assays and phosphoproteomics, I could resolve and characterize in detail intermediates of mitotic entry, providing critical new insights into mitotic regulation.
In the first part of my thesis study, I explored the role of PLK1 in mitotic prophase. My results demonstrate that PLK1 inhibition in synchronized G2 cell populations of multiple mammalian cell lines delays mitotic entry, with significant variability observed between individual cells. To explain this variability, we used a mathematical model that recapitulates the observed phenotypic differences. Our results show that PLK1-inhibited cells are delayed in a prophase-like state characterized by low CDK1 activity, which increases gradually over hours. During this state, cells exhibit progressively condensing chromosomes, increased microtubule dynamics, and reorganization of the actin cortex, while the nuclear envelope remains intact. To further characterize this state, we employed phosphoproteomics, revealing phosphorylation of key regulators of chromatin organization and the cytoskeleton, consistent with the observed cellular phenotypes. These findings, presented in the first manuscript published in the EMBO Journal earlier this year, demonstrate that PLK1 inhibition stabilizes cells in a prophase-like state with low CDK1 activity, revealing a distinct set of early mitotic phosphorylation events.
In the second part of my thesis, I investigated the role of CDK1 in mitotic progression. CDK1 is the central regulator of mitosis, and its activity is controlled by a series of feedback loops that ensure proper timing and execution of mitotic events. Our results show that when the feedback loops are disabled, CDK1 activity can be titrated to a sub-threshold level, leading to a novel state termed "low CDK mitosis". In this state, while cells apparently progress through mitosis, the nuclear envelope does not break down. Cells enter mitosis, condense their chromosomes, accumulate nuclear Cyclin B1, progress through mitosis within the same duration as in control cells, and then exit mitosis, decondense their chromosomes and completely degrade Cyclin B1. Proteomic analysis confirms that these cells return to a G1-like proteomic state after low CDK mitosis. Strikingly different from normal mitosis, the nuclear pore complex (NPC) scaffold and the nuclear lamina remain intact throughout low CDK mitosis. However, I was able to show that the nuclear-cytoplasmic transport is compromised due to partial disassembly of NPCs. I show that this partial loss of nuclear integrity releases spindle assembly factors from the nucleus and therefore the mitotic spindle assembles in the cytoplasm. However, the intact nuclear envelope prevents spindle microtubules from accessing the chromosomes, ultimately leading to mitotic exit without chromosome segregation. To further characterize this state, we performed phosphoproteomics on a pure population of cells in low CDK mitosis. Our analysis reveals that most phosphorylation events responsible for the observed mitotic changes are mediated by kinases other than CDK1. There are, however, phosphosite sequences containing the CDK1 minimal consensus motif. In these, I identified a basic amino acid-rich motif that follows CDK1 phosphorylation sites, providing new insights into CDK1 temporal regulation and substrate specificity.
Together, my findings substantially advance our understanding of mitotic regulation. They highlight the critical role of PLK1 in catalyzing mitotic entry and the dynamic activation of CDK1 in ordering mitotic events. Additionally, the discovery of "low CDK mitosis" challenges the traditional view of mitosis as an all-or-none process and provides new insights into the molecular mechanisms underlying mitotic regulation in mammalian cells. This work not only contributes to our fundamental understanding of cell division but also has implications for the development of therapeutic strategies targeting mitotic kinases in cancer and other diseases.2025-12-1
Spatial Predictions of Evapotranspiration from Tropical Landscapes Using Remote Sensing Data
No full textTropische Wälder spielen eine zentrale Rolle bei der globalen terrestrischen Evapotranspiration (ET).
Durch die fortschreitende Umwandlung dieser Wälder in andere Landnutzungsformen könnten sich
Veränderungen der ET mit weitreichenden Folgen für regionale und globale Klimasysteme ergeben.
Dennoch bestehen weiterhin erhebliche Wissenslücken bezüglich der ET tropischer Wälder,
insbesondere in Trockengebieten mit variierender Aridität, in Gebirgsregionen sowie in
Waldfragmenten, die zu räumlich heterogenen Bedingungen führen. Jüngste Fortschritte in der
Fernerkundung eröffnen neue Möglichkeiten zur Untersuchung der ET in den Tropen. Zu den
wichtigsten Entwicklungen zählen verbesserte satellitengestützten Thermalinfrarotbildgebung,
LiDAR-basierte Analysen der Vegetationsstruktur sowie die Verfügbarkeit von
Open-Source-Datensätzen. In Kombination mit fortschrittlichen Methoden der räumlichen Analyse,
eröffnen diese Innovationen bislang unerreichte Möglichkeiten zur Erforschung der ET in tropischen
Regionen.
Aufbauend auf diesen Entwicklungen verfolgt diese Arbeit das Ziel, ein besseres Verständnis darüber
zu erlangen, wie Vegetationsstruktur, topografische Merkmale, meteorologische Bedingungen und die
räumliche Konfiguration der Landschaft die räumlichen Muster der ET in tropischen Waldlandschaften
Ecuadors und Madagaskars beeinflussen.
Studie 1 untersucht die ET entlang eines Trockenökotonos in West-Ecuador, wo die räumliche
Verteilung der Vegetationsmerkmale maßgeblich durch Umweltfaktoren, insbesondere durch Aridität
geprägt ist. Wir stellten die Hypothese auf, dass strukturelle Vegetationsmerkmale maßgeblich zur
räumlichen Variation der ET in der Trocken- als auch Regenzeiten beitragen. Die dreidimensionale
Vegetationsstruktur wurde mittels eines mobilen, bodengestützten Laserscanner auf 75 Probeflächen
verschiedener Waldtypen erfasst. Die ET-Daten stammten aus MODIS-Satellitenprodukten. In der
Regenzeit erklärten Modelle, die räumliche Autokorrelation über Moran’s Eigenvector Maps
berücksichtigten, 35% bzw. 36 % der räumlichen ET-Variabilität anhand des Pflanzenflächenindex bzw.
der strukturellen Komplexität (Db). In der Trockenzeit erklärten dieselben Prädiktoren über 70% der
räumlichen Variation. Unsere Ergebnisse belegen, dass Unterschiede in der Vegetationsstruktur -
insbesondere der strukturellen Komplexität (Db) - die räumliche Variation der ET signifikant
beeinflussen, wobei dieser Zusammenhang in der Trockenzeit besonders ausgeprägt ist. Wir schlagen
vor, dass aride Bedingungen in der Trockenzeit strukturelle Anpassungen der Vegetation fördern,
welche die ET-Raten im Ökosystem reduzieren. Die Ergebnisse unterstreichen die Bedeutung des
Erhalts der strukturellen Vielfalt von Trockengebieten zur Sicherung ihrer ökologischen Funktionen.
Studie 2 analysierte ET-Muster in einer großflächigen, geschützten tropischen Waldregion an der
Westflanke der Anden. Ziel war es, diejenige Kombination von Variablen zu identifizieren, die für die
räumliche ET-Vorhersage am relevantesten ist, sowie die spezifische Rolle der Vegetationsstruktur im
Modellierungsprozess zu bestimmen. Hierfür wurde ein Random-Forest-Ansatz unter
Berücksichtigung räumlicher Autokorrelation gemäß bewährter Verfahren für räumliche Vorhersagen
eingesetzt. Die Analyse umfasste topografische, meteorologische und vegetationsstrukturelle
Variablen, die aus Open-Source-Produkten wie GEDI, PROBA-V und ERA5 abgeleitet wurden; Variablen, die im ECOSTRESS-L3-Daten Algorithmus verwendet werden, wurden ausgeschlossen, um
die Unabhängigkeit der Modelle zu gewährleisten. Die Modelle erzielten eine hohe Genauigkeit bei der
räumlichen ET-Vorhersage mit R2-Werten zwischen 0.61 und 0.74. Keine einzelne Variabel dominierte
die Modelle; fünf Schlüsselvariablen erklärten gemeinsam 60% der Modellleistung. Der
Blattflächenindex zählte neben topographischen Variablen wie Höhe und Exposition zu den drei
wichtigsten Prädiktoren. Wir schließen daraus, dass der Random-Forest-Ansatz robuste
ET-Schätzungen liefert, die dazu beitragen können Beobachtungslücken in tropischen Regionen zu
schließen. Die Ergebnisse unterstreichen die Bedeutung, Gelände- und Vegetationsmerkmale
gemeinsam zu berücksichtigen, um die Wasserkreisläufe tropischer Wälder zu verstehen.
Studie 3 untersuchte Waldfragmente in anthropogen geprägten Landschaften der Tiefland- und
Andenregionen West-Ecuadors. Die räumlichen Muster der ET von 83 Waldfragmenten wurden
mithilfe von ECOSTRESS-Satellitendaten analysiert. Ziel war es, das Ausmaß und die Richtung von
Randeffekten auf die ET im Vergleich zu den Bedingungen im Waldinneren zu untersuchen und dabei
die Wechselwirkungen zwischen abiotischen und biotischen Faktoren zu berücksichtigen. Die
Anwendung einer Changepoint-Analyse zeigte, dass die Häufigkeit von ET-Änderungen vom Inneren
zum Rand hin zunahm, wobei in 61% der Fälle erhöhte ET-Werte am Rand beobachtet wurden. Ein
Random-Forest-Modell mit zielgerichteter Kreuzvalidierung erreichte eine Vorhersagegenauigkeit von
64 %; Höhe, Aridität und Entfernung zum Rand waren die wichtigsten Prädiktoren. Die SHAP-Analyse
unterstrich die Bedeutung von Randeffekten und zeigte eine erhöhte ET insbesondere in mittleren
Höhenlagen und in Gebieten mit hoher Kronendichte. Diese Muster sind vermutlich auf das
Zusammenspiel klimatischer Bedingungen, Vegetationsstruktur, Randausrichtung und angrenzender
Landnutzungen zurückzuführen. Unsere Ergebnisse deuten darauf hin, dass Waldfragmente durch
Randeffekte die ET erhöhen, wobei die hohe Variabilität an den Rändern weiteren Forschungsbedarf
aufzeigt. Während der Schutz großflächiger Primärwälder weiterhin zentral für die Klimaregulation
tropischer Landschaften ist, legen unsere Ergebnisse nahe, dass auch kleinere Waldfragmente eine
bedeutsame Rolle in regionalen Wasserkreisläufen spielen.
Studie 4 untersuchte eine heterogene tropische Landschaft im Nordosten Madagaskars, die aus
zusammenhängendem Primärwald, Fragmenten, landwirtschaftlichen Flächen, Agroforsten und sich
regenerierenden Wäldern besteht. Die drei Hauptziele waren: (1) die relevanten Kombinationen
meteorologischer, topografischer, bodenbezogener und vegetationsstruktureller Variablen für die
räumliche ET-Vorhersage zu identifizieren, (2) Beobachtungslücken in den ET-Daten zu adressieren
und (3) die relativen Beiträge und Interaktionen der Vegetationsstruktur in den Vorhersagemodellen zu
quantifizieren. Tägliche ET-Werte wurden aus ECOSTRESS-Daten gewonnen; die Prädiktorvariabeln
stammten aus verschiedenen offenen Datensätzen. Um räumliche Autokorrelation zu berücksichtigen,
kombinierten wir Forward Feature Selection mit zielgerichteter Kreuzvalidierung. Die
Random-Forest-Modelle erzielten hohe Genauigkeiten mit R²-Werten zwischen 0.7 und 0.9. Die
SHAP-Analyse zeigte, dass meteorologische Variablen den größten Beitrag zu den Vorhersagen
leisteten (51 - 62%), gefolgt von Vegetationsstruktur (15 - 18%), Topografie (6 - 24%) und
Bodeneigenschaften (8 - 13%). Die Analyse offenbarte zudem wichtige Interaktionen, insbesondere
wie Vegetationsstruktur ET-Reaktionen bei unterschiedlichen Niederschlags- und Windverhältnissen
beeinflusst.
Zusammenfassend zeigen die vier Studien, dass räumliche Variationen der Evapotranspiration in
tropischen Landschaften durch das Zusammenspiel von Vegetationsstruktur, Topografie,
meteorologischen Bedingungen und der räumlichen Konfiguration der Landschaft erklärt werden
können. Strukturelle Merkmale der Vegetation zählen durchgängig zu den wichtigsten Prädiktoren und
zeigen Wechselwirkungen mit topografischen und klimatischen Variablen. Zudem modulieren
Waldränder die ET-Muster, was die potenzielle Bedeutung von Waldfragmenten für den
Wasserkreislauf tropischer Ökosysteme unterstreicht. Darüber hinaus modulieren Waldränder die ET-Muster, was die Bedeutung von Waldfragmenten im Wasserkreislauf tropischer Ökosysteme
unterstreicht.Tropical forests play a crucial role in global terrestrial evapotranspiration (ET). As these forests continue
to be converted to other land uses, the resulting changes in ET could have significant implications
for both regional and global climate systems. However, many questions about forest ET remain open,
particularly in drylands with varying aridity, mountainous areas, and forest fragments that create
variable conditions across the space. Recent advances in remote sensing have opened new possibilities
for studying ET in the tropics. Key developments include improvements in spaceborne thermal imaging
capabilities, LiDAR for vegetation structure assessments, and the availability of open-source datasets.
These, combined with advanced spatial analysis methods, provide unprecedented opportunities for
studying ET in the tropics. Building on these developments, the overall objective of this dissertation is to
advance understanding of how critical biophysical factors, including vegetation structure, topographic
features, climatic conditions, and landscape configuration, influence spatial ET variation across tropical
forest landscapes.
Study 1 addressed ET across a dryland ecotone in western Ecuador, where the spatial distribution of
vegetation characteristics is shaped by environmental conditions, with aridity being a key factor. We
hypothesized that vegetation structural features significantly contribute to the spatial variation in ET
during both wet and dry seasons. We assessed three-dimensional vegetation structure using a
ground-based mobile laser scanner on 75 plots representing different forest types. ET data were
retrieved from MODIS satellite observations. During the wet season, models incorporating spatial
autocorrelation through Moran’s Eigenvector Maps explained 35% and 36% of spatial ET variability
using plant area index and structural complexity (Db), respectively. In the dry season, same predictors
explained over 70% of the spatial variation in ET. Our results demonstrate that differences in vegetation
structure, particularly Db, significantly contribute to explaining spatial ET variation, with this
relationship being especially pronounced during the dry season. We propose that dry-season aridity
drives structural adaptations in vegetation that reduce ecosystem ET rates. Our findings emphasize the
importance of preserving the complex structural diversity of dryland ecosystems to ensure their
continued functionality.
Study 2 investigated ET patterns across a large, protected tropical forest region on the western slope
of the Andes. Our objectives were to identify the combination of variables most relevant for spatial
ET prediction across the region and to determine the specific role of forest structure in spatial ET
modelling. We employed a random forest (RF) approach following established best practices for spatial
predictions to address spatial autocorrelation. The analysis utilized topographic, meteorological, and
forest structure variables derived from open-source products including GEDI, PROBA-V, and ERA5,
excluding any variables incorporated in the ECOSTRESS-L3 algorithm to ensure model independence.
The models demonstrated high accuracy for spatially explicit ET prediction across different locations,
achieving R2 values ranging from 0.61 to 0.74. Notably, no single predictor dominated the models, with
five key variables collectively explaining 60% of model performance. Leaf area index emerged as one of
the three most influential variables for ET prediction across all study days, alongside the topographic
variables of elevation and aspect. We conclude that the random forest approach provides robust ET predictions that could help address observation gaps in tropical regions. Our findings highlight the
importance of considering both terrain characteristics and vegetation properties in understanding
tropical forest water cycles.
Study 3 examined forest fragments within human-dominated landscapes across the lowlands and
Andes of western Ecuador. We analysed the spatial pattern of ET from 83 forest fragments using
spaceborne ECOSTRESS data. Our objective was to investigate the extent and direction of edge effects
on ET, focusing on changes relative to interior forest conditions, while considering how abiotic and
biotic factors interact to contribute to these observed variations at forest edges. We applied changepoint
analysis and found that the frequency of ET shifts increased progressively from the interior of fragments
toward the edge, where ET was enhanced in most cases (61%). A RF model with target-oriented crossvalidation achieved a spatial prediction accuracy of 64%, identifying elevation, aridity, and distance to
edge as the most important predictors. SHAP analysis also highlighted the importance of edge effects
and indicated greater enhancement of ET, particularly at mid-elevations and in areas with high canopy
cover. These patterns likely resulted from a combination of factors, including climatic conditions, forest
structure, edge orientation, and surrounding land-use types. Our findings suggest that forest fragments
may enhance ET through edge effects, though the high variability observed at edges indicates need
for further investigation. While conserving large old-growth forests remains the primary strategy for
maintaining climate regulation functions in tropical landscapes, our study indicates that the numerous
small forest fragments—which have been disappearing rapidly in recent decades—may also play an
important role in regional water cycles.
Study 4 investigated a heterogeneous tropical landscape in northeastern Madagascar, encompassing
continuous old-growth forest, forest fragments, agricultural land, agroforests, and recovering forests.
Our research had three primary objectives: to identify combinations of meteorological, topographical,
soil, and vegetation structure variables most relevant for spatially predicting ET in the region; to
address observation gaps in ET data; and to quantify the relative contributions and interactions
of vegetation structure variables in spatial prediction models. Daily ET data were obtained from
ECOSTRESS, while predictor variables were sourced from multiple open datasets. To address potential
spatial autocorrelation, we implemented forward feature selection combined with target-oriented
cross-validation. RF models demonstrated high predictive accuracy for spatial ET estimation, achieving
R2 values ranging from 0.7 to 0.9 across different days. Using SHAP for model interpretation, we found
that meteorological variables contributed most substantially to predictions (51 - 62%), followed by
vegetation structure (15 - 18%), topographical features (6 - 24%), and soil properties (8 - 13%). The
SHAP analysis further revealed critical interactions between variables, particularly demonstrating how
vegetation structure influences ET responses under varying rainfall and wind speed conditions.
In conclusion, the four studies show that the spatial variations of ET in tropical landscapes can be
explained from the interplay between vegetation structure, topography, meteorology, and spatial
configuration. Forest structural characteristics repeatedly ranked among the strongest predictors,
and showed interactions with topography and climate. Forest edges further modulated ET patterns,
highlighting the potential role of forest fragments in the water cycle.2025-12-1
Fresnel Propagation and Photon Counting: New Methods for Coded Aperture and Phase Contrast Imaging with X-Rays
No full textX-rays offer unique opportunities for imaging, enabled by properties such as penetration power for tomography and elemental contrast in characteristic fluorescence emission. However, their weak interaction with matter makes guiding them challenging. Lens-less techniques address this by shifting image retrieval from the physical domain, where lenses or mirrors are used, to the computational domain. Meanwhile, decreasing pixel sizes in single-photon counting cameras offer growing potential for high-resolution imaging.
This dissertation revisits Fresnel zone plate coded apertures for x-ray fluorescence imaging and demonstrates the technique for material-sensitive, single-shot microscopy using a laboratory x-ray source and an energy-resolving camera. By combining this approach with computational ghost imaging and variable-energy excitation, the technique is modified to eliminate the requirement for energy resolution in the camera, achieving several-micrometer resolution at a synchrotron source. Finally, the dissertation presents further development of super-resolution holography, a propagation-based phase contrast imaging technique, toward tomographic applications.2026-01-3
Visualizing mitochondrial proteostasis using cryo-electron tomography
No full textMitochondria are the primary site of energy generation in many organisms, including
humans, underscoring their fundamental role in numerous cellular processes. Proper
mitochondrial function is safeguarded by an extensive quality control (QC) network that
responds to diverse stress conditions. Impairment of this QC system can have severe
consequences, as mutations in key components are associated with devastating
diseases, often affecting highly energy-dependent tissues such as the brain and
muscle.
Mitochondrial QC operates on multiple levels and is deeply intertwined with other
cellular stress responses, forming a highly complex regulatory system. While
significant progress has been made in uncovering individual aspects of mitochondrial
QC, the precise orchestration of its components and their spatiotemporal dynamics
remain only partially understood. In this thesis, we investigated mechanisms and
structural alterations associated with mitochondrial stress to better understand distinct
elements of mitochondrial QC.
In our first study, we focused on the PINK1-TOM complex, which is stabilized during
mitochondrial import arrest and marks damaged mitochondria for autophagic
degradation. The impairment of this mechanism is linked to familial forms of
Parkinson’s disease. Using a combined approach of in silico structural prediction with
AlphaFold and biochemical validation through site-directed mutagenesis, we
demonstrated that the import receptors TOM20 and TOM70 are essential for PINK1–
TOM complex formation. Moreover, we mapped possible interaction sites between
PINK1 and TOM20/TOM70, leading to a model in which PINK1 is shuttled to the TOM
complex through either simultaneous or sequential receptor engagement.
Our second study investigated the effects of intramitochondrial protein aggregation
following inhibition of the mitochondrial chaperone TRAP1, using in situ cryo-electron
tomography (cryo-ET). We observed local distortions of cristae architecture near
aggregates and localized mitochondrial ribosomes as well as mtHsp60:mtHsp10
chaperone complexes through subtomogram averaging (STA). Under aggregate-
inducing conditions, fully assembled mitochondrial ribosomes were drastically
V
reduced, while mtHsp60:mtHsp10 complexes underwent a dramatic remodeling of
their conformational landscape. By combining focused STA classification with single-
particle analysis of purified complexes, we identified distinct conformations and
proposed a functional folding cycle for mtHsp60:mtHsp10, providing mechanistic
insight into its mode of action.
In our third study, we analyzed intramitochondrial aggregation induced by importing
aggregation-prone proteins into mitochondria. Super-resolution microscopy and
cryo-ET showed alterations in cristae morphology and aggregate formation. Functional
assays and biochemical experiments revealed sequestration of key factors leading to
reduced translation. Importantly, we showed that components of the mitochondrial
ribosome rely on mtHsp60:mtHsp10-assisted folding to achieve their functional three-
dimensional structure; otherwise, they are degraded by the mitochondrial protease
LonP1. This finding highlights an intricate interplay between mitochondrial QC
components and complements the observations from our second study.
Taken together, our studies provide new insights into mitochondrial QC, with a
particular emphasis on the impact of intramitochondrial aggregation. We uncovered
the vulnerability of mitochondrial ribosomes to aggregation and highlighted the
dynamic interdependence of protein homeostasis factors such as mtHsp60:mtHsp10
and LonP1. These findings expand our understanding of the mechanisms
safeguarding mitochondrial function and their relevance to cellular health.2026-02-1
Neodymium:YAG-laser therapy of mucoid dorsal cysts: clinical efficacy and effects in a 3D tissue model
No full textDiese Arbeit evaluiert die Nd:YAG-Laserbehandlung als neue Methode zur Behandlung von mukoiden Dorsalzysten, für die bislang kein einheitliches Behandlungsverfahren existiert. Dafür werden zum einen die klinische Wirksamkeit und das Potential dieser neuen Therapieoption untersucht. Zum anderen werden die zellulären und molekularen Veränderungen in dermalen Fibroblasten sowie der zugrunde liegende Wirkmechanismus, der durch die Nd:YAG-Laserbehandlung ausgelöst wird, analysiert.
Zur Bewertung der klinischen Wirksamkeit sowie zur Erfassung von Langzeitergebnissen und der Patientenzufriedenheit wurde ein Fragebogen eingesetzt, der an einem Kollektiv von 39 Patienten angewendet wurde. Von den befragten Patienten waren 64 % weiblich und das Durchschnittsalter aller Befragten lag bei 62,9 Jahren. Die vorgestellte Behandlungsmethode kombiniert Punktion, Expression und Nd:YAG-Lasertherapie und zeigte in der Patientenbefragung eine hohe Rezidivfreiheit (86,7 %), eine sehr gute Verträglichkeit und eine entsprechend hohe Patientenzufriedenheit.
Um den Einfluss der Nd:YAG-Laserbehandlung auf dermale Fibroblasten zu untersuchen, wurden zugrundeliegenden zellulären und molekularen Wirkmechanismen mit besonderem Fokus auf Fibrose-assoziierte Prozesse analysiert. Dazu wurden BJ-Fibroblasten in eine 3D-Kollagenmatrix (dermale Äquivalente) eingebettet und hinsichtlich Morphologie, Zellvitalität und Genexpression analysiert. Mittels Phasenkontrast- und Konfokalmikroskopie konnte gezeigt werden, dass die Nd:YAG-Lasertherapie keinen erkennbaren Einfluss auf die Zellvitalität und Morphologie der Fibroblasten hat. Sowohl behandelte als auch unbehandelte Zellen wiesen eine elongierte Zellform sowie die charakteristische Schwarmstruktur, ohne Anzeichen einer Zellschädigung auf. Die mit dem Nd:YAG-Laser behandelten Fibroblasten zeigten neben einer verstärkten Expression von pro-fibrotischen Markern wie PAI-1 und VIM auch eine signifikant erhöhte Genexpression der Hyaluronsäuresynthase HAS2, die für die Bildung von Hyaluronsäure verantwortlich ist. Zudem konnte eine Reduktion der Hyaluronsäurekonzentration im Zellkulturüberstand nach der Laserbehandlung nachgewiesen werden. Insgesamt deuten die Ergebnisse auf ein durch die Nd:YAG-Laserbehandlung ausgelöstes dermales Remodeling und eine damit assoziierte Wundheilung hin, welche potenziell die Pathogenese der mukoiden Dorsalzyste beeinflussen könnte.
Diese Arbeit zeigt somit die Effektivität, die zugrunde liegenden molekularen Prozesse und das maßgebliche Potenzial der Nd:YAG-Laserbehandlung als innovative und minimalinvasive Behandlung von mukoiden Dorsalzysten, die zukünftig als standardisiertes Verfahren in Betracht gezogen werden sollte.This study evaluates Nd:YAG-laser treatment as a novel therapeutic option for mucoid dorsal cysts, for which no standard procedure currently exists. In the first part, the clinical efficacy and potential of this new treatment are analyzed using a patient survey. In the second part, the cellular and molecular changes in dermal fibroblasts, as well as the underlying mechanism induced by the Nd:YAG-laser treatment will be investigated.
To evaluate the clinical efficacy, long-term results, and patient satisfaction, a questionnaire was used. The study cohort consisted of 39 patients, of whom 64 % were female. The mean age of all participants was 62.9 years. The treatment method evaluated in this study combines puncture, expression, and Nd:YAG-laser therapy, demonstrating a high recurrence-free rate (86.7 %), excellent tolerability, and a correspondingly high level of patient satisfaction in the patient survey.
To investigate the influence of Nd:YAG-laser treatment on dermal fibroblasts, the underlying cellular and molecular mechanisms were analyzed, with a particular focus on fibrosis-associated processes. To this end, BJ fibroblasts were embedded in a 3D collagen matrix (dermal equivalents) and assessed for morphology, cell viability, and gene expression. Phase contrast imaging and confocal microscopy confirmed that Nd:YAG-laser therapy had no discernible effect on fibroblast viability or morphology. Both treated and untreated cells exhibited an elongated cell shape and the characteristic swarm structure, with no evidence of cell damage. However, laser-treated fibroblasts showed increased expression of pro-fibrotic markers such as PAI-1 and VIM, along with a significantly increased expression of the hyaluronic acid synthase HAS2, which is responsible for the synthesis of hyaluronic acid. In addition, the hyaluronic acid concentration in the cell culture medium was reduced after laser treatment. Collectively, these observations suggest that Nd:YAG-laser treatment induces dermal remodeling and promotes wound healing, which may influence the pathogenesis of mucoid dorsal cyst.
In summary, this work demonstrates the efficacy, underlying molecular processes, and significant potential of Nd:YAG-laser treatment as an innovative, minimally invasive approach to the treatment of mucoid dorsal cysts, which should be considered as a standarized procedure in the future.2025-03-2