Insects are the most diverse group of animals on earth. They inhabit nearly all terrestrial habitats. One of the factors underlying this success is the ability of insect eggs to survive in adverse... Show moreInsects are the most diverse group of animals on earth. They inhabit nearly all terrestrial habitats. One of the factors underlying this success is the ability of insect eggs to survive in adverse conditions. For a long time the ability to survive these adverse conditions has been attributed to maternal investment in the form of a protective eggshell. In this thesis, I show that contrary to common belief, insect eggs are far from helpless. The insect egg itself develops a cellular layer around the egg called the serosa. This serosa protects the developing embryo from dehydration which enables it to survive in dry habitats. The serosa furthermore protects against infection, mounting an impressive immune response upon the entry of bacteria in the egg. The data presented in this thesis show the importance of the serosa in the survival of the insect egg. I propose that this multifunctional serosa contributed to the great success of insects. Show less
This thesis is focused on the innate immune defence mechanisms responsible for controlling mycobacterial growth after infection. To provide a detailed description of the host__s innate immune... Show moreThis thesis is focused on the innate immune defence mechanisms responsible for controlling mycobacterial growth after infection. To provide a detailed description of the host__s innate immune response to M. marinum infection, zebrafish gene expression levels were analysed by RNA sequencing at various time points during infection and correlated with imaging data of the process of pathogenesis. We demonstrate that the scavenger receptor Marco (macrophage receptor with collagenous structure) is a key player in the rapid phagocytosis of M. marinum and we use gene expression analysis in combination with gene knockdown studies to show that it is also essential in the establishment of an initial transient pro-inflammatory response to M. marinum infection. Once phagocytosed, M. marinum is capable of avoiding killing mechanisms of the host cell and can continue to grow within macrophages. This is the period when Membrane Attack Complex/Perforin proteins are involved in killing intracellular bacteria by their pore-forming activities. We reveal the regulatory mechanisms and function of two macrophage specific genes, mpeg1 and mpeg1.2 (macrophage expressed gene 1.2). The results from this thesis complement knowledge obtained from other model organisms by providing new insights into both counteracting and supporting mechanisms underlying the innate immune response. Show less
