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- Baumgardt, Magnus, 1976-
(författare)
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Genetic mechanisms behind cell specification in the Drosophila CNS
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The human central nervous system (CNS) contains a daunting number of cells and tremendous cellular diversity. A fundamental challenge of developmental neurobiology is to address the questions of how so many different types of neurons and glia can be generated at the precise time and place, making precisely the right connections. Resolving this issue involves dissecting the elaborate genetic networks that act within neurons and glia, as well as in the neural progenitor cells that generates them, to specify their identities.My PhD project has involved addressing a number of unresolved issues pertaining to how neural progenitor cells are specified to generate different types of neurons and glial cells in different temporal and spatial domains, and also how these early temporal and spatial cues are integrated to activate late cell fate determinants, which act in post-mitotic neural cells to activate distinct batteries of terminal differentiation genes.Analyzing the development of a specific Drosophila melanogaster (Drosophila) CNS stem cell – the neuroblast 5-6 (NB5-6) – we have identified several novel mechanisms of cell fate specification in the Drosophila CNS. We find that, within this lineage, the differential specification of a group of sequentially generated neurons – the Ap cluster neurons – is critically dependent upon the simultaneous triggering of two opposing feed-forward loops (FFLs) within the neuroblast. The first FFL involves cell fate determinants and progresses within the post-mitotic neurons to establish a highly specific combinatorial code of regulators, which activates a distinct battery of terminal differentiation genes. The second loop, which progresses in the neuroblast, involves temporal and sub-temporal genes that together oppose the progression of the first FFL. This leads to the establishment of an alternative code of regulators in late-born Ap cluster neurons, whereby alternative cell fates are specified. Furthermore, we find that the generation and specification of the Ap cluster neurons is modulated along the neuraxis by two different mechanisms. In abdominal segments, Hox genes of the Bithorax cluster integrates with Pbx/Meis factors to instruct NB5-6 to leave the cell cycle before the Ap cluster neurons are generated. In brain segments, Ap cluster neuron equivalents are generated, but improperly specified due to the absence of the proper Hox and temporal code. Additionally, in thoracic segments we find that the specification of the Ap cluster neurons is critically dependent upon the integration of the Hox, Pbx/Meis, and the temporal genes, in the activation of the critical cell fate determinant FFL.We speculate that the developmental principles of (i) feed-forward combinatorial coding; (ii) simultaneously triggered yet opposing feed-forward loops; and (iii) integration of different Hox, Pbx/Meis, and temporal factors, at different axial levels to control inter-segmental differences in lineage progression and specification; might be used widely throughout the animal kingdom to generate cell type diversity in the CNS.
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| 2. |
- Dziedziech, Alexis, 1991-
(författare)
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Timing Matters : Wounding and entomopathogenic nematode infection kinetics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over time, insects have developed complex strategies to defend themselves against presenting threats. However, in the evolutionary arms race of survival, pathogens have adapted to quickly overcome the immune response mounted by the host. In this thesis, we assess how quickly entomopathogenic nematodes (EPNs) can overcome the host, Drosophila melanogaster. We then look at the clotting reaction at a hypothetical point of entry for the nematode and bring resolution to the order of protein interaction focusing on three proteins important in the anti-nematode defense. Finally, we look closer into detail at how crystal cells secrete one of those proteins, prophenoloxidase (PPOII) using a mode of programmed cell death. (Paper I) In the course of EPN infection, little was known about how quickly the worms can overcome the host immune system. Here we found that after penetrating the host, EPNs cause septicemia within 4 to 6 hours. (Paper II) Three proteins, Glutactin (Glt), Transglutaminase (Tg), and PPOII have been found to be important in the anti-nematode response. Here we created GFP-tagged fly constructs to follow their role in clot formation. In early clot formation, Tg was immediately secreted from hemocytes though it was localized around the cell membrane, Glt then entered clot fibers followed by PPOII which acted in late clot formation. (Paper III) Here we looked closer into Tg and PPOII secretion variability. PPOII from immature, but not mature crystal cells colocalized with a membrane marker. Tg, when driven with a pan tissue driver, was found located in clotting fibers, in contrast with paper II. (Paper IV) In an in vivo immune scenario, crystal cells were recruited to the wound site and burst rapidly in a caspase-dependent manner. We demonstrate that the mode of programmed cell death, pyroptosis, exists in Drosophila by way of convergent evolution.This thesis brings to light the variation found within the infection process for EPNs as well as the clotting response based on larval age, tissue type, and the maturity of a single cell type. Timing in each of these immune scenarios can give very different indications about the kind of immune response mounted and even the role of an individual cell.
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