Cell Size Control in the Fission Yeast Schizosaccharomyces pombe: A Dissertation

The coordination between cell growth and division is a highly regulated process that is intimately linked to the cell cycle. Efforts to identify an independent mechanism that measures cell size have been unsuccessful. Instead, we propose that size control is an intrinsic function of the basic cell cycle machinery. My work shows that in the fission yeast Schizosaccharomyces pombe Cdc25 accumulates in a size dependent manner. This accumulation of Cdc25 occurs over a large range of cell sizes. Additionally, experiments with short pulses of cycloheximide have shown that Cdc25 is an inherently unstable protein that quickly returns to a size dependent equilibrium in the cell suggesting that Cdc25 concentration is dependent on size and not time. Thus, Cdc25 can act as a sizer for the cell. However, cells are still viable when Cdc25 is constitutively expressed suggesting that there is another sizer in the case that Cdc25 expression is compromised. Cdc13 is a likely candidate due to the similar characteristics to Cdc25 and the ability to activate Cdc2. Cdc13 accumulates during the cell cycle in a manner similar to Cdc25. I show that in the absence of Cdc2 tyrosine phosphorylation, the cell size is sensitive to Cdc13 activity showing that Cdc13 accumulation can determine when cells enter mitosis. These results suggest a two sizer model where Cdc25 is the main sizer with Cdc13 acting as a backup sizer in the event of Cdc25 expression is compromised. Additionally, in the absence of Cdc2 phosphorylation by the kinases Wee1 and Mik1, mitotic entry is regulated by the activity of Cdc2. In the absence of Cdc2 phosphorylation, this activity is regulated by binding of cyclins to Cdc2. Under these circumstances, the activity of Cdc13 can regulate mitotic entry provide further evidence that Cdc13 could be a sizer of the cell in the case where Cdc25 expression is compromised. The results I present in this dissertation provide the groundwork for understanding how cells regulate size and how this size regulation affects cell cycle control in S. pombe . The results show how the intrinsic cell cycle machinery can act as a sizer for the G2/M transition in S. pombe . Interestingly, this mitotic commitment pathway is well conserved suggesting a general solution for size control in eukaryotes at the G2/M transition. Understanding the mechanism of how protein concentration is regulated in a size dependent manner will give much needed insight into how cells control size. Elucidating the mechanism for size control will capitalize on decades of research and deepen our understanding of basic cell biology

A Study of the Hydrostatic and Hydrodynamic Properties of Aeoliscus Straigatus

Aeoliscus strigatus is a highly maneuverable fish found in the Indo-Pacific region. It boasts a unique head down posture and employs median paired fin propulsion to perform precise movements. The need for highly maneuverable underwater AUVs for exploration and testing drove the examination of the hydrostatics and hydrodynamics influencing Aeoliscus. To determine the stability of Aeoliscus the center of gravity and buoyancy were found. Center of gravity was experimentally located using the three plumb line method while center of buoyancy was located using two separate methods. The first method utilized the measured buoyant force, a rigidly mounted fish and a tank of water raised to displace ½ of the buoyant force. Method two utilized a microcomputed tomography (micro-CT) system to create a 3D model of the fish and allowed for computational location of the center of buoyancy. The average normalized approximation of the center of gravity was found to be 0.46 posterior to the mouth and 0.34 ventral to the leading dorsal edge of the fish. The average normalized approximation of the center of buoyancy was found to be 0.46 and 0.45 posterior to the mouth and 0.35 and 0.43 ventral to the leading dorsal edge of the fish by the micro-CT system and the experimental method respectively. Velocity, Reynold’s number and coefficient of drag were found to as a first step to understanding the hydrodynamics of Aeoliscus. The maximum observed velocity was 300 mm/s or about 22 body lengths per second, a Reynolds number of 4222, indicating laminar flow and a coefficient of drag of 0.029, which is similar to that of other fish

Appropriated Threads: The Unpicking and Reweaving Imported Textiles

The Silk Route has become synonymous with the movement of knowledge that accompanies the trade of objects. Many of the textiles discussed here were not traded along the Silk Route, but all are representative of the associations that are made with this artery of cultural exchange. The examples cited arrive from a range of cultures and geographies: Indonesia and Nigeria, the Southwest United States and New Zealand. From these vastly different regions, using a variety of materials, weavers painstakingly unpicked yarns from woven fabrics for use in other weavings. The term ‘raveled yarn’ refers to threads that have been unpicked from a piece of woven cloth and rewoven into another. This paper attempts to determine the reasons behind what seems in the twenty-first century to be such a laborious undertaking. Unpicking fabric to remove flaws, examine the structures involved or possibly recycle precious threads is common. But rarely does the contemporary designer work with materials of such inherent value that time is not considered more valuable. Historically, the reasons for unpicking yarn have been both aesthetic and economic. Penelope’s ruse to stall time by unpicking her daily weaving each night may be one of the earliest examples. Certain cities developed reputations for deconstructing fabrics for thread such as the ancient Syrian city of Palmyra along the Silk Road which was devoted to the unpicking and reweaving of silk to local fashions. On a more intimate level the instinct to recover threads from woven materials appears in an example from the other side of the world where slave women and girls in the southern United States are thought to have unwound threads from their owner’s discarded stockings and fabric remnants so that they could use the thread to stylishly wrap around their own hair. As early as 1730 a Danish envoy in Africa wrote, “Opoku bought silk taffeta and materials of all colours. The artists unravelled them so that they obtained large quantities of woolen and silk threads which they mixed with their cotton and got many colours.” In 1817 a British envoy wrote of chiefs “in a general blaze of splendor” who “wore Ashantee cloths, of extravagant price from the costly foreign silks which has been unravelled to weave them in all the varieties of colour, as well as pattern.” In Documents on the Portuguese in Mozambique and Central Africa it is written: Now, the Moors once more make in this land quantities of cotton, much of which is gathered here; they spin it and weave it into white cloth and, since they do not know how to dye, or because they do not have dyes, they take blue painted cloths from Cambay, unravel them and gather the thread into a ball and, with their white weave and with the other they make them painted, from which they obtain a great sum of gold

Suicide « à la kashinawa ». Le désir de l’au-delà ou la séduction olfactive et auditive par les esprits des morts

Suicide « à la kashinawa ». Le désir de l’au-delà ou la séduction olfactive et auditive par les esprits des morts. La conception kashinawa du suicide, selon laquelle la cause de la mort volontaire doit être recherchée dans un contact olfactif et auditif avec les esprits des morts, pose la question fondamentale du processus de médiation – spécifique à chaque culture – entre perception sensorielle et interprétation. Afin d’éclairer ce processus dans le contexte kashinawa, l’article présente quelques particularités de l’univers perceptif indigène.The Kashinawa’s concept of suicide. Longing for the other world or sensory seduction by the spirits of the deceased. The Kashinawa’s concept of suicide according to which the cause for a voluntary death must be searched for in the olfactory and auditory contact with the spirits of the deceased, raises fundamental questions concerning the process of mediation – specific to every culture – between sensory perception and interpretation. In order to clarify this process in the case of the Kashinawa, this article presents some particularities of the indigenous universe of perception.Suicidarse en el mundo kashinawa. El deseo del más allá o cómo los espíritus de los muertos seducen por los olores y los sonidos a los vivos. La concepción kashinawa del suicidio revela que la causa de toda muerte voluntaria se encuentra en un contacto olfativo u auditivo con los espíritus de los muertos. Esto nos remite al tema fundamental de los procesos de mediación – particulares a cada cultura – entre percepción sensorial e interpretación. Con el fin de dilucidar estos procesos en el contexto kashinawa, el presente trabajo examina algunas particularidades del universo indígena de la percepción

The Fission Yeast S-Phase Cyclin Cig2 Can Drive Mitosis [preprint]

Commitment to mitosis is regulated by cyclin-dependent kinase (CDK) activity. In the fission yeast Schizosaccharomyces pombe, the major B-type cyclin, Cdc13, is necessary and sufficient to drive mitotic entry. Furthermore, Cdc13 is also sufficient to drive S phase, demonstrating that a single cyclin can regulate alternating rounds of replication and mitosis and providing the foundation of the quantitative model of CDK function. It has been assumed that Cig2, a B-type cyclin expressed only during S-phase and incapable of driving mitosis in wild-type cells, was specialized for S-phase regulation. Here, we show that Cig2 is capable of driving mitosis. Cig2/CDK activity drives mitotic catastrophe -- lethal mitosis in inviably small cells -- in cells that lack CDK inhibition by tyrosine-phosphorylation. Moreover, Cig2/CDK can drive mitosis in the absence of Cdc13/CDK activity. These results demonstrate that in fission yeast, not only can the presumptive M-phase cyclin drive S phase, but the presumptive S-phase cyclin can drive M phase, further supporting the quantitative model of CDK function. Furthermore, these results provide an explanation, previously proposed on the basis of computation analyses, for the surprising observation that cells expressing a single-chain Cdc13-Cdc2 CDK do not require Y15 phosphorylation for viability. Their viability is due to the fact that in such cells, which lack Cig2/CDK complexes, Cdc13/CDK activity is unable to drive mitotic catastrophe

Cell cycle responses to Topoisomerase II inhibition: Molecular mechanisms and clinical implications.

DNA Topoisomerase IIA (Topo IIA) is an enzyme that alters the topological state of DNA and is essential for the separation of replicated sister chromatids and the integrity of cell division. Topo IIA dysfunction activates cell cycle checkpoints, resulting in arrest in either the G2-phase or metaphase of mitosis, ultimately triggering the abscission checkpoint if non-disjunction persists. These events, which directly or indirectly monitor the activity of Topo IIA, have become of major interest as many cancers have deficiencies in Topoisomerase checkpoints, leading to genome instability. Recent studies into how cells sense Topo IIA dysfunction and respond by regulating cell cycle progression demonstrate that the Topo IIA G2 checkpoint is distinct from the G2-DNA damage checkpoint. Likewise, in mitosis, the metaphase Topo IIA checkpoint is separate from the spindle assembly checkpoint. Here, we integrate mechanistic knowledge of Topo IIA checkpoints with the current understanding of how cells regulate progression through the cell cycle to accomplish faithful genome transmission and discuss the opportunities this offers for therapy

Land use inventory through merging of LANDSAT (satellite), aerial photography and map sources

There are no author-identified significant results in this report

Politikwissenschaftsstudierende und der 1. Mai 2004:Eine empirische Untersuchung zu Informiertheit, Wissen und Meinung von Hochschülern der Westfälischen Wilhelms-Universität Münster zur Osterweiterung der Europäischen Union

Seminar: Am Anfang steht das Problem: Einführung in die Durchführung empirischer Studien. Sommersemester 2004Dozentin: Susanne in der Smitten Forschungsprojekt im Rahmen der empirischen Sozialforschung Erstellungszeitraum: 19. April 2004 - 04. August 2004 Durchgeführt von: Martin Biederstedt, Dominik Bulla, Johanna Keifenheim, Maria Schröder, David Schulke</div

Size-Dependent Expression of the Mitotic Activator Cdc25 as a Mechanism of Size Control in Fission Yeast [preprint]

Proper cell size is essential for cellular function (Hall et al., 2004). Nonetheless, despite more than 100 years of work on the subject, the mechanisms that maintain cell size homeostasis are largely mysterious (Marshall et al., 2012). Cells in growing populations maintain cell size within a narrow range by coordinating growth and division. Bacterial and eukaryotic cells both demonstrate homeostatic size control, which maintains population-level variation in cell size within a certain range, and returns the population average to that range if it is perturbed (Marshall et al., 2012; Turner et al., 2012; Amodeo and Skotheim, 2015). Recent work has proposed two different strategies for size control: budding yeast has been proposed to use an inhibitor-dilution strategy to regulate size at the G1/S transition (Schmoller et al., 2015), while bacteria appear to use an adder strategy, in which a fixed amount of growth each generation causes cell size to converge on a stable average, a mechanism also suggested for budding yeast (Campos et al., 2014; Jun and Taheri-Araghi, 2015; Taheri-Araghi et al., 2015; Tanouchi et al., 2015; Soifer et al., 2016). Here we present evidence that cell size in the fission yeast Schizosaccharomyces pombe is regulated by a third strategy: the size dependent expression of the mitotic activator Cdc25. The cdc25 transcript levels are regulated such that smaller cells express less Cdc25 and larger cells express more Cdc25, creating an increasing concentration of Cdc25 as cell grow and providing a mechanism for cell to trigger cell division when they reach a threshold concentration of Cdc25. Since regulation of mitotic entry by Cdc25 is well conserved, this mechanism may provide a wide spread solution to the problem of size control in eukaryotes

Size-Dependent Expression of the Mitotic Activator Cdc25 Suggests a Mechanism of Size Control in Fission Yeast

Proper cell size is essential for cellular function. Nonetheless, despite more than 100 years of work on the subject, the mechanisms that maintain cell-size homeostasis are largely mysterious [ 1 ]. Cells in growing populations maintain cell size within a narrow range by coordinating growth and division. Bacterial and eukaryotic cells both demonstrate homeostatic size control, which maintains population-level variation in cell size within a certain range and returns the population average to that range if it is perturbed [ 1, 2 ]. Recent work has proposed two different strategies for size control: budding yeast has been proposed to use an inhibitor-dilution strategy to regulate size at the G1/S transition [ 3 ], whereas bacteria appear to use an adder strategy, in which a fixed amount of growth each generation causes cell size to converge on a stable average [ 4–6 ]. Here we present evidence that cell size in the fission yeast Schizosaccharomyces pombe is regulated by a third strategy: the size-dependent expression of the mitotic activator Cdc25. cdc25 transcript levels are regulated such that smaller cells express less Cdc25 and larger cells express more Cdc25, creating an increasing concentration of Cdc25 as cells grow and providing a mechanism for cells to trigger cell division when they reach a threshold concentration of Cdc25. Because regulation of mitotic entry by Cdc25 is well conserved, this mechanism may provide a widespread solution to the problem of size control in eukaryotes