| 1. |
- Katz Thor, Rebecka, 1982-
(författare)
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Beyond the Witness : Holocaust Representations and the Testimony of Images
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a time when the very last Holocaust witnesses will soon be gone, a possible route for commemoration is to ask what testimony images can give. This book seeks to answer the question of how images can bear witness by examining them as multifaceted entities produced, reproduced, and resituated in conflicting political and historical situations. In three archive-based films by Harun Farocki, Yael Hersonski, and Eyal Sivan, the moving image is reactivated and reinterpreted. Footage produced as internal Nazi propaganda and the video recordings of a politically charged trial in the aftermath of the Holocaust have accrued new meaning. The archival status, context, and conditions for production, and the means of representation, offer a framework for an analysis through which the testimony of images can be understood.
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| 2. |
- Bahrampour, Shahrzad
(författare)
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Genetic mechanisms regulating proliferation and cell specification in the Drosophila embryonic CNS
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The central nervous system (CNS) consists of an enormous number of cells, and large cellular variance, integrated into an elaborate network. The CNS is the most complex animal organ, and therefore its establishment must be controlled by many different genetic programs. Considering the high level of complexity in the human CNS, addressing issues related to human neurodevelopment represents a major challenge. Since comparative studies have revealed that neurodevelopmental programs are well conserved through evolution, on both the genetic and functional levels, studies on invertebrate neurodevelopmental programs are often translatable to vertebrates. Indeed, the basis of our current knowledge about vertebrate CNS development has been greatly aided by studies on invertebrates, and in particular on the Drosophila melanogaster (fruit fly) model system.This thesis attempted to identify novel genes regulating neural cell specification and proliferation in the CNS, using the Drosophila model system. Moreover, I aimed to address how those genes govern neural progenitor cells (neuroblasts; NBs) to obtain/maintain their stemness identity and proliferation capacity, and how they drive NBs through temporal windows and series of programmed asymmetric division, which gradually reduces their stemness identity in favor of neural differentiation, resulting in appropriate lineage progression. In the first project, we conducted a forward genetic screen in Drosophila embryos, aimed at isolating genes involved in regulation of neural proliferation and specification, at the single cell resolution. By taking advantage of the restricted expression of the neuropeptide FMRFa in the last-born cell of the NB lineage 5-6T, the Ap4 neuron, we could monitor the entire lineage progression. This screen succeeded in identifying 43 novel genes controlling different aspects of CNS development. One of the genes isolated, Ctr9, displayed extra Ap4/FMRFa neurons. Ctr9 encodes a component of the RNA polymerase II complex Paf1, which is involved in a number of transcriptional processes. The Paf1C, including Ctr9, is highly conserved from yeast to human, and in the past couple of years, its importance for transcription has become increasingly appreciated. However, studies in the Drosophila system have been limited. In the screen, we isolated the first mutant of Drosophila Ctr9 and conducted the first detailed phenotypic study on its function in the Drosophila embryonic CNS. Loss of function of Ctr9 leads to extra NB numbers, higher proliferation ratio and lower expression of neuropeptides. Gene expression analysis identified several other genes regulated by Ctr9, which may explain the Ctr9 mutant phenotypes. In summary, we identified Ctr9 as an essential gene for proper CNS development in Drosophila, and this provides a platform for future study on the Drosophila Paf1C. Another interesting gene isolated in the screen was worniou (wor), a member of the Snail family of transcription factors. In contrast to Ctr9, whichdisplayed additional Ap4/FMRFa neurons, wor mutants displayed a loss of these neurons. Previous studies in our group have identified many genes acting to stop NB lineage progression, but how NBs are pushed to proliferate and generate their lineages was not well known. Since wor may constitute a “driver” of proliferation, we decided to study it further. Also, we identified five other transcription factors acting together with Wor as pro-proliferative in both NBs and their daughter cells. These “drivers” are gradually replaced by the previously identified late-acting “stoppers.” Early and late factors regulate each other and the cell cycle, and thereby orchestrate proper neural lineage progression.
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| 3. |
- Gunnar, Erika, 1985-
(författare)
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Regulatory programs controlling profileration during Drosophila nervous system development
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The central nervous system (CNS) is the most complex organ in the body, responsible for complex functions, including thinking, reasoning and memory. The CNS contains cells of many different types, often generated in vast numbers. Hence, CNS development requires precise genetic control of both cell fate and of cell proliferation, to generate the right number of cells, with the proper identity, and in the proper location. The cells also need to make connections with each other for correct signaling and function. This complexity evokes the question of how this is regulated. How does the stem cells, responsible for building the CNS, know how many times to divide, and how does the daughters know which identity to acquire and in which location they shall end up? During Drosophila melanogaster development, the neuroblasts (NBs) are responsible for generating the CNS. In each hemisegment, every NB is unique in identity, and generates a predetermined number of daughters with specific identities. The lineages of different NBs vary in size, but are always the same for each specific NB, and the division modes of each NBs is hence stereotyped. Most NBs start dividing by renewing themselves while generating daughters that will in turn divide once to generate two neurons and/or glia (denoted type I mode). Many, maybe all, NBs later switch to generating daughters that will differentiate directly into a neuron or glia (denoted type 0 mode). This type I>0 switch occurs at different time-points during lineage progression, and influences the total numbers of cells generated from a single NB.The work presented in this thesis aimed at investigating the genetic regulation of proliferation, with particular focus on the type I>0 switch. In the first project, the implication of the Notch pathway on the type I>0 switch was studied. Mutants of the Notch pathway do not switch, and the results show that the Notch pathway regulates the switch by activation of several target genes, both regulators and cell cycle genes. One of the target genes, the E(spl)-C genes, have been difficult to study due to functional redundancy. This study reveals that even though they can functionally compensate for each other, they have individual functions in different lineages. Regarding cell cycle genes, both Notch and E(spl)-C regulate several key cell cycle genes, and molecular analysis indicated that this regulation is direct. In the second project we studied the seq gene, previously identified in a genetic screen. We found that seq controls the type I>0 switch by regulating the key cell cycle genes, but also through interplay with the Notch pathway. Notch and seq stop proliferation, and in the third project we wanted to identify genes that drive proliferation. We found that there is battery of early NB genes, socalled early factors, which activate the cell cycle, and drive NB and daughter proliferation. These are gradually replaced by late regulators, and the interplay between early and late factors acts to achieve precise control of lineage progression.The work presented here increases our understanding of how regulatory programs act to control the development of the CNS; to generate the right number of cells of different identities. These results demonstrate the importance of correct regulation of proliferation in both stem cells and daughters. Problems in this control can result in either an underdeveloped CNS or loss of control such as in cancer. Knowledge about these regulatory programs can contribute to the development of therapeutics against these diseases.
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| 4. |
- Jonson, Maria
(författare)
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Investigating Amyloid β toxicity in Drosophila melanogaster
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis Drosophila melanogaster (the fruit fly) has been used as a model organism to study the aggregation and toxic properties of the human amyloid β (Aβ) peptide involved in the onset of Alzheimer's disease (AD). AD is one of many misfolding diseases where the important event of a protein to adopt its’ specific three-dimensional structure has failed, leading to aggregation and formation of characteristic amyloid fibrils. AD has a complex pathology and probably reflects a variety of related molecular and cellular abnormalities, however, the most apparent common denominator so far is abnormal Amyloid-β precursor protein (APP) processing, resulting in a pool of various Aβ-peptides. In AD, the Aβ peptide misfolds, aggregates and forms amyloid plaques in the brain of patients, resulting in progressive neurodegeneration that eventually leads to death.By expressing the human Aβ protein in the fly, we have studied the mechanisms and toxicity of the aggregation in detail and how different cell types in the fly are affected. We have also used this model to investigate the effect of potential drugs that can have a positive impact on disease progression. In the first and second work in this thesis, we have, in a systematic way, proved that the length of the Aβ-peptide is essential for its toxicity and propensity to aggregate. If the peptide expressed ends at amino acid 42 it is extremely toxic to the fly nervous system. However, this toxicity can be completely abolished by expressing a variant that is shorter than 42 amino acids (1-37 to 1-41 aa), or be significantly reduced by expressing a longer variant (1-43 aa). Toxicity can be partly mitigated in trans by co-expressing the 1-42 variant with a 1-38 variant. This supports the theory that the disease progression could be inhibited if the formation of Aβ 1-42 is decreased. In the third work we demonstrate that amyloid aggregates can be found in various cell types of Drosophila, however, the toxicity seem to be selective to neurons. Our results indicate that the aggregates of glial expressing flies have a more mature structure, which appear to be less toxic. This also suggests that glial cells might spread Aβ aggregates without being harmed. The last work in this thesis investigates how curcumin (turmeric) can affect Aβ aggregation and toxicity. Curcumin appears to shift the equilibrium between the less stableaggregates and mature fibers toward the final stage resulting in an improved lifespan for treated flies.In summary, this thesis demonstrates that the toxicity of Aβ in Drosophila is highly dependent on the Aβ variant expressed, the structure of the protein aggregates and which cell type that expresses the protein. We have also shed light on the potential of using Drosophila when it comes to examining possible therapeutic substances as a tool for drug discovery.
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| 5. |
- Stratmann, Johannes
(författare)
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Genetic Mechanisms during Terminal Cell Fate Specification in the Drosophila CNS
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Specification of the many unique neuronal subtypes found in the nervous system depends on spatiotemporal cues and terminal selector cascades, mostly acting in sequential combinatorial codes of transcription factors (TFs) to dictate cell fate. Out of 10,000 cells in the Drosophila embryonic ventral nerve cord (VNC), only 28 cells selectively express Nplp1. The Nplp1 neurons in the Drosophila VNC can be subdivided into the thoracic ventro-lateral Tv1 and the dorsal-medial dAp neurons. Nplp1 expression in both cell subtypes is activated by the same terminal selector cascade: col > ap/eya > dimm > Nplp1. However Tv1 and dAp neurons are generated by different neuronal progenitors (neuroblasts, NB), and depend on different upstream cues to activate the cell specification cascade. The Tv1 cells are generated by NB5-6T, and in these cells the Nplp1 terminal selector cascade is triggered by spatio-temporal input provided by Antp/hth/exd/lbe/cas. Our studies identified that NB4-3 gives rise to the dAp cells and that the Nplp1 terminal selector cascade in dAp cells is activated by Kr/pdm>grn. I demonstrated how two different spatio-temporal combinations can funnel on a shared downstream terminal selector cascade to determine a highly related cell fate, in different regions of the VNC. I tested this scenario at the molecular level, by identification of cisregulatory modules (CRMs) for the main factors involved in the Nplp1 terminal selector cascade. Intriguingly, I found that col is under control of two separate CRMs, which are controlled by either Antp/hth/exd/lbe/cas in the NB5-6T lineage, and Kr/pdm/grn in the NB4-3 lineage. In addition, CRISPR deletion of the endogenous col CRMs did not result in loss of Col and Nplp1, indicating that col might be under control of more, yet unidentified CRMs. Nplp1 is expressed in one out of four cells in the thoracic Apterous cluster (Ap cluster); the Tv1 cell. The allocation of the right cell fate to each of the four Ap cluster cells, is regulated by the sub-temporal cascade including the factors Sqz/Nab/Svp, acting downstream of the temporal factor Cas. The sub-temporal factors have a repressive action on Col and Dimm, and thus on the terminal selector cascade regulating Nplp1 expression in the Tv1 cell. We demonstrated that the late and Tv1 specific expression of the early temporal factor Kr suppresses Svp in the Tv1 cell and allows for the progression of the Nplp1 cell fate specification cascade. Hence, early temporal factors involved in temporal progression of neuronal progenitors, can be re-utilized late and postmitotically to specify cell fate. It is tempting to speculate that similar mechanisms act to generate similar cell fate in different regions of the CNS, as well as the issue of sub-temporal multitasking, are common features both in Drosophila and higher organisms.
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| 6. |
- Bivik Stadler, Caroline, 1986-
(författare)
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Genetic pathways controlling CNS development : The role of Notch signaling in regulating daughter cell proliferation in Drosophila
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The human central nervous system (CNS) displays the greatest cellular diversity of any organ system, consisting of billions of neurons, of numerous cell sub-types, interconnected in a vast network. Given this enormous complexity, decoding the genetic programs controlling the multistep process of CNS development remains a major challenge. While great progress has been made with respect to understanding sub-type specification, considerably less is known regarding how the generation of the precise number of each sub-type is controlled.The aim of this thesis was to gain deeper knowledge into the regulatory programs controlling cell specification and proliferation. To address these questions I have studied the Drosophila embryonic CNS as a model system, to thereby be able to investigate the genetic mechanisms at high resolution. Despite the different size and morphology between the Drosophila and the mammalian CNS, the lineages of their progenitors share similarity. Importantly for this thesis, both species progenitors show elaborate variations in their proliferation modes, either giving rise to daughters that can directly differentiate into neurons or glia (type 0), divide once (type I), or multiple times (type II).The studies launched off with a comprehensive chemical forward genetic screen, for the very last born cell in the well-studied lineage of progenitor NB5-6T: the Ap4 neuron, which expresses the neuropeptide FMRFa. NB5-6T is a powerful model to use, because it undergoes a programmed type I>0 daughter cell proliferation switch. An FMRF-eGFP transgenic reporter was utilized as readout for successful terminal differentiation of Ap4/FMRFa and thereby proper lineage progression of the ∼20 cells generated. The strongest mutants were mapped to genes with both known and novel essential functions e.g., spatial and temporal patterning, cell cycle control, cell specification and chromatin modification. Subsequently, we focused on some of the genes that showed a loss of function phenotype with an excess of lineage cells. We found that Notch is critical for the type I>0 daughter cell proliferation switch in the NB5-6T lineage and globally as well. When addressing the broader relevance of these findings, and to further decipher the Notch pathway, we discovered that selective groups of E(spl) genes is controlling the switch in a close interplay with four key cell cycle factors: Cyclin E, String, E2F and Dacapo, in most if not all embryonic progenitors. The Notch mediation of the switch is likely to be by direct transcriptional regulation. Furthermore, another gene identified in the screen, sequoia, was investigated. The analysis revealed that sequoia is also controlling the daughter cell switch in the CNS, and this partly through context dependent interactions with the Notch pathway.Taken together, the findings presented in this thesis demonstrate that daughter cell proliferation switches in Drosophila neural lineages are genetically programmed, and that Notch contributes to the triggering of these events. Given that early embryonic processes is frequently shown to be evolutionary conserved, you can speculate that changeable daughter proliferation programs could be applied to mammals, and contribute to a broader understanding of proliferation processes in humans as well.
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| 7. |
- Jafari, Shadi
(författare)
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Mechanisms of Olfactory sensory neuron class maintenance in Drosophila : It is all about design and equilibrium
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- How the cellular diversity of our body is generated and maintained is still a great mystery regardless of the wealth of research that has been done on this issue. The greatest complexity is found in the nervous system that contains a vast number of neurons and displays a great diversity in cell types and classes. For example the Drosophila olfactory system is a complex but defined set of neurons with extremely high specificity and sensitivity. The 34 OSN classes are each defined by their expression of a specific odorant receptor (OR). During development each OSN chooses one OR from 60 different OR genes in the genome to express. Furthermore, a cell is subject to immense challenges during its life cycle. Confronting each challenge the cell needs to perform its function and maintain its fate. OSNs continue to express the same OR during their whole life regardless of fluctuations in the environment.Although the olfactory system is remarkably conserved across the phyla, it is still unclear how an OSN chooses to express a particular OR from a large genomic repertoire. In this thesis the final steps of the specification and diversification for establishing an OSN identity is addressed. We find seven transcription factors that are continuously required in different combinations for the expression of the Drosophila ORs. The TFs can in different background context both activate and repress OR expression, making the regulation more economical. We also imply that repression is crucial for correct OR gene expression. We further show that short DNA sequences from OR gene promoters are sufficient to drive OSN class specific expression. These regions contain clusters of TF binding motifs, which we show to be sensitive to any change in their composition or to changes of the internal or external environment. We demonstrate that the chromatin state is responsible for the clusters response to environmental challenges. We reveal that Su(var)3-9 controls the OSN response to environmental stresses. We address the epigenetic mechanisms that initiate and pertain the single OR expression to a single OSN class. Our results show that OSNs have an epigenetic switch marking the end of development and the transition to mature OSNs. This switch supplies the expression of a single OR gene.
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| 8. |
- Pennells, Lisa, et al.
(författare)
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Equalization of four cardiovascular risk algorithms after systematic recalibration : individual-participant meta-analysis of 86 prospective studies
- 2019
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Ingår i: European Heart Journal. - : Oxford University Press (OUP). - 0195-668X .- 1522-9645. ; 40:7, s. 621-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: There is debate about the optimum algorithm for cardiovascular disease (CVD) risk estimation. We conducted head-to-head comparisons of four algorithms recommended by primary prevention guidelines, before and after ‘recalibration’, a method that adapts risk algorithms to take account of differences in the risk characteristics of the populations being studied.Methods and results: Using individual-participant data on 360 737 participants without CVD at baseline in 86 prospective studies from 22 countries, we compared the Framingham risk score (FRS), Systematic COronary Risk Evaluation (SCORE), pooled cohort equations (PCE), and Reynolds risk score (RRS). We calculated measures of risk discrimination and calibration, and modelled clinical implications of initiating statin therapy in people judged to be at ‘high’ 10 year CVD risk. Original risk algorithms were recalibrated using the risk factor profile and CVD incidence of target populations. The four algorithms had similar risk discrimination. Before recalibration, FRS, SCORE, and PCE over-predicted CVD risk on average by 10%, 52%, and 41%, respectively, whereas RRS under-predicted by 10%. Original versions of algorithms classified 29–39% of individuals aged ≥40 years as high risk. By contrast, recalibration reduced this proportion to 22–24% for every algorithm. We estimated that to prevent one CVD event, it would be necessary to initiate statin therapy in 44–51 such individuals using original algorithms, in contrast to 37–39 individuals with recalibrated algorithms.Conclusion: Before recalibration, the clinical performance of four widely used CVD risk algorithms varied substantially. By contrast, simple recalibration nearly equalized their performance and improved modelled targeting of preventive action to clinical need.
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| 9. |
- Yaghmaeian Salmani, Behzad, 1978-
(författare)
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Genetic Mechanisms Regulating the Spatiotemporal Modulation of Proliferation Rate and Mode in Neural Progenitors and Daughter Cells during Embryonic CNS Development
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The central nervous system (CNS) is a hallmark feature of animals with a bilateral symmetry: bilateria and can be sub-divided into the brain and nerve cord. One of the prominent properties of the CNS across bilateria is the discernible expansion of its anterior part (brain) compared with the posterior one (nerve cord). This evolutionarily conserved feature could be attributed to four major developmental agencies: First, the existence of more anterior progenitors. Second, anterior progenitors are more proliferative. Third, anterior daughter cells, generated by the progenitors, are more proliferative. Forth, fewer cells are removed by programmed cell death (PCD) anteriorly. My thesis has addressed these issues, and uncovered both biological principles and genetic regulatory networks that promote these A-P differences. I have used the Drosophila and mouse embryonic CNSs as model systems. Regarding the 1st issue, while the brain indeed contains more progenitors, my studies demonstrate that this only partly explains the anterior expansion. Indeed, with regard to the 2nd issue, my studies, on both the Drosophila and mouse CNS, demonstrate that anterior progenitors divide more extensively. Concerning the 3rd issue, in Drosophila we identified a gradient of daughter proliferation along the AP axis of the developing CNS with brain daughter cells being more proliferative. Specifically, in the brain, progenitors divide to generate a series of daughter cells that divide once (Type I), to generate two neurons or glia. In contrast, in the nerve cord, progenitors switch during later stages, from first generating dividing daughters to subsequently generating daughters that directly differentiate (Type 0). Hence, nerve cord progenitors undergo a programmed Type I->0 proliferation switch. In the Drosophila posterior CNS, this switch occurs earlier and is more prevalent, contributing to the generation of smaller lineages in the posterior regions. Similar to Drosophila, in the mouse brain we also found that progenitor and daughter cell proliferation was elevated and extended into later developmental stages, when compared to the spinal cord. DNA-labeling experiments revealed faster cycling cells in the brain when compared to the nerve cord, in both Drosophila and mouse. In both Drosophila and mouse, we found that the suppression of progenitor and daughter proliferation in the nerve cord is controlled by the Hox homeotic gene family. Hence, the absence of Hox gene expression in the brain provides a logical explanation for the extended progenitor proliferation and lack of Type I->0 switch. The repression of Hox genes in the brain is mediated by the histonemodifying Polycomb Group complex (PcG), which thereby is responsible for the anterior expansion. With respect to the 4th issue, we found no effect of PCD on anterior expansion in Drosophila, while this cannot be asserted for the mouse embryonic neurodevelopment as there are no genetic tools to abolish PCD effectively in mammals. Taken together, the studies presented in this thesis identified global and evolutionarily-conserved genetic programs that promote anterior CNS expansion, and pave the way for understanding the evolution of size along the anterior-posterior CNS axis.
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