Fussing About Fission: Defining Variety Among Mainstream and Exotic Apicomplexan Cell Division Modes

Cellular reproduction defines life, yet our textbook-level understanding of cell division is limited to a small number of model organisms centered around humans. The horizon on cell division variants is expanded here by advancing insights on the fascinating cell division modes found in the Apicomplexa, a key group of protozoan parasites. The Apicomplexa display remarkable variation in offspring number, whether karyokinesis follows each S/M-phase or not, and whether daughter cells bud in the cytoplasm or bud from the cortex. We find that the terminology used to describe the various manifestations of asexual apicomplexan cell division emphasizes either the number of offspring or site of budding, which are not directly comparable features and has led to confusion in the literature. Division modes have been primarily studied in two human pathogenic Apicomplexa, malaria-causing Plasmodium spp. and Toxoplasma gondii, a major cause of opportunistic infections. Plasmodium spp. divide asexually by schizogony, producing multiple daughters per division round through a cortical budding process, though at several life-cycle nuclear amplifications stages, are not followed by karyokinesis. T. gondii divides by endodyogeny producing two internally budding daughters per division round. Here we add to this diversity in replication mechanisms by considering the cattle parasite Babesia bigemina and the pig parasite Cystoisospora suis. B. bigemina produces two daughters per division round by a “binary fission” mechanism whereas C. suis produces daughters through both endodyogeny and multiple internal budding known as endopolygeny. In addition, we provide new data from the causative agent of equine protozoal myeloencephalitis (EPM), Sarcocystis neurona, which also undergoes endopolygeny but differs from C. suis by maintaining a single multiploid nucleus. Overall, we operationally define two principally different division modes: internal budding found in cyst-forming Coccidia (comprising endodyogeny and two forms of endopolygeny) and external budding found in the other parasites studied (comprising the two forms of schizogony, binary fission and multiple fission). Progressive insights into the principles defining the molecular and cellular requirements for internal vs. external budding, as well as variations encountered in sexual stages are discussed. The evolutionary pressures and mechanisms underlying apicomplexan cell division diversification carries relevance across Eukaryota

Necessary conditions for variational regularization schemes

We study variational regularization methods in a general framework, more precisely those methods that use a discrepancy and a regularization functional. While several sets of sufficient conditions are known to obtain a regularization method, we start with an investigation of the converse question: How could necessary conditions for a variational method to provide a regularization method look like? To this end, we formalize the notion of a variational scheme and start with comparison of three different instances of variational methods. Then we focus on the data space model and investigate the role and interplay of the topological structure, the convergence notion and the discrepancy functional. Especially, we deduce necessary conditions for the discrepancy functional to fulfill usual continuity assumptions. The results are applied to discrepancy functionals given by Bregman distances and especially to the Kullback-Leibler divergence.Comment: To appear in Inverse Problem

Pacific island regional preparedness for El Niño

The El Niño Southern Oscillation (ENSO) cycle is often blamed for disasters in Pacific island communities. From a disaster risk reduction (DRR) perspective, the challenges with the El Niño part of the ENSO cycle, in particular, are more related to inadequate vulnerability reduction within development than to ENSO-induced hazard influences. This paper analyses this situation, filling in a conceptual and geographic gap in El Niño-related research, by reviewing El Niño-related preparedness (the conceptual gap) for Pacific islands (the geographic gap). Through exploring El Niño impacts on Pacific island communities alongside their vulnerabilities, resiliences, and preparedness with respect to El Niño, El Niño is seen as a constructed discourse rather than as a damaging phenomenon, leading to suggestions for El Niño preparedness as DRR as part of development. Yet the attention which El Niño garners might bring resources to the Pacific region and its development needs, albeit in the short term while El Niño lasts. Conversely, the attention given to El Niño could shift blame from underlying causes of vulnerability to a hazard-centric viewpoint. Instead of focusing on one hazard-influencing phenomenon, opportunities should be created for the Pacific region to tackle wider DRR and development concerns

Molecularizing microscopic imaging : a history of immunofluorescence microscopy as a visual epistemic tool of modern cell biology (1959-1980)

Heutige Zellbiologinnen und Zellbiologen schreiben der Immunfluoreszenzmikroskopie (IFM) einen besonderen historischen Wert zu: das grundlegende Wissen über Form und molekulare Zusammensetzung des Cytoskeletts sei überwiegend der Anwendung dieses bildgebenden Verfahrens geschuldet. Trotzdem stellt die Geschichte der IFM in der Zellbiologie eine wissenschaftshistorische Lücke dar, die mit der vorliegenden Dissertation bearbeitet wird. Unter Berücksichtigung der maßgeblichen biologiehistorischen Kontexte untersuche ich die IFM in ihrer Bedeutung für die zellbiologische visuelle Kultur und frage nach den Prozessen, die zu ihrer Adoption und Stabilisierung als visuelle Domäne geführt haben. Dabei wird auch danach gefragt, wie die IFM von Zellbiolog_innen kritisch verhandelt wurde, inwiefern ihre Adoption die zellbiologische Erkenntnispraxis beeinflusste, und welche Schnittflächen mit anderen Disziplinen zum Tragen kamen. Ausgehend von einer kritischen Bearbeitung relevanter wissenschaftshistorischer Literatur wird zunächst die Molekularisierung der Zellbiologie als zentraler Kontext herausgearbeitet. Dabei gewann ab den späten 1950er-Jahren eine Forderung zunehmend an Bedeutung: zelluläre Strukturen seien in ihrer molekularen Identität sichtbar zu machen. An dieser Forderung war die Elektronenmikroskopie als dominante visuelle Domäne gescheitert. Erst die Aneignung der IFM als visuelles Erkenntnisinstrument sollte Zellbiolog_innen eine allgemein anwendbare molekularisierte Bildgebung erlauben. Mittels einer Mikrogeschichte zur ersten Publikation, in der die molekulare Architektur des Cytoskeletts 1974 erstmals überzeugend visualisiert worden war, untersuche ich die zellbiologische Aneignung der IFM am Cold Spring Harbor Laboratory. Diese Institution war von der Molekularbiologie und ihrer Finanzierung durch öffentliche Mittel aus Richard Nixons 1971 ausgerufenen „War on Cancer“ geprägt. Die zentralen Akteur_innen dieser Aneignung verfügten zwar über eine fundierte molekularbiologische Expertise, verstanden sich selbst aber (noch) nicht als Angehörige der Zellbiologie; damit waren sie frei von visuellen wie epistemischen Zwängen dieser Disziplin und offen für unkonventionelle Forschungszugänge. Parallel zur Stabilisierung der IFM als visuelle Domäne begannen sie, die „biochemische Anatomie“ des Cytoskeletts mittels IFM zu entschlüsseln. Die dazu eingesetzte epistemische Praxis bezeichne ich als „molekularisierte Morphologie der Zelle“: die Visualisierung und Beschreibung der molekularen Architektur subzellulärer Strukturen. Diese Praxis wird abschließend untersucht, um zu verstehen, wie es für Forscher_innen möglich wurde, einen breit rezipierten Wissensbestand hervorzubringen, der vor allem molekular-morphologische Beschreibungen, aber keine mechanistischen Erklärungen zellulärer Funktionen bereitstellte – und damit dem epistemischen Ideal der Zellbiologie zuwiderlief.Today’s cell biologists ascribe a significant historical value to immunofluorescence microscopy (IFM): almost all fundamental knowledge on form and molecular composition of the cytoskeleton is owed to the application of this imaging technique. Despite its relevance, the history of IFM in cell biology represents a historiographical lacuna that is addressed in this thesis. Drawing from Klaus Hentschel’s concept of visual cultures of science and technology, I ask how IFM was adopted and stabilized as a visual domain of cell biology. I investigate the context of this adoption in the history of biology, how the visual culture and the epistemic practices of cell biology were influenced by it, and how IFM was received by representatives of already established visual domains. Moreover, I address intersections with other disciplines in these dynamics. The first part of this thesis scrutinizes the relevant historiographic literature to carve out the central context: the molecularization of cell biology. Between the late 1950s and the mid-1960s this process brought about demands for visualizing the molecular identity of cellular structures. Electron microscopy as the dominant visual domain of cell biology failed to fulfill these demands. Only the adoption of IFM as a visual epistemic tool made it possible for cell biologists to implement a generally applicable mode of molecularized imaging. The second part of the thesis represents a microhistory of the first scientific paper that convincingly fulfilled these demands in 1974 by using IFM to visualize the molecular composition of the cytoskeleton. I unfold the context of its effective adoption by investigating a development from first attempts to utilize IFM in cell biology in the late 1950s until its successful application in the mid-1970s at the Cold Spring Harbor Laboratory. This institution was epistemically and socially shaped by molecular biology and by its public funding from the “War on Cancer”, announced in 1971 by Richard Nixon. The major scientific actors who adopted IFM for cell biology had a substantial expertise in molecular biology but did not understand themselves (yet) as members of the cell biological scientific community. They retrospectively described themselves as exempt from epistemic and visual constraints of this discipline and consequently as free to apply unconventional research strategies. In parallel to the stabilization of IFM as a visual domain of cell biology, the protagonists of its initial adoption started to map the “biochemical anatomy” of the cytoskeleton by using this imaging technique. I conceptualize their epistemic practice as “molecularized morphology of the cell”: visualizing and describing the molecular architecture of subcellular structures. This practice is analyzed in the last part of this thesis to understand how researchers succeeded in publishing an essential body of knowledge that was nevertheless at odds with the epistemic ideal of cell biology. Practitioners of “molecularized morphology” provided detailed molecular-morphological descriptions but not mechanistic explanations of cellular functions, with the latter becoming a designator for research worth publishing in major cell biology journals during the 1970s