In the last decade it has become clear that a number of the molecular mechanisms that are required for proper navigation of axons in complex nervous systems are also employed to guide muscles to... Show moreIn the last decade it has become clear that a number of the molecular mechanisms that are required for proper navigation of axons in complex nervous systems are also employed to guide muscles to their appropriate attachment sites. Among the gene families that mediate these diverse processes is the Ryk family, the topic of this thesis. In different chapters we improve the understanding of the basic biological roles and operating mechanisms of Drosophila Ryks in the ventral nerve cord, a specific brain structure and musculature. Hopefully, this work will also contribute to future therapies for diseases in which these proteins are likely implicated such as cancer and poor regeneration after nervous system trauma. Show less
Wnt genes encode highly conserved glycoproteins that play a variety of roles at different stages of development. Their functions include the regulation of cell proliferation, cell fate... Show moreWnt genes encode highly conserved glycoproteins that play a variety of roles at different stages of development. Their functions include the regulation of cell proliferation, cell fate specification, cell polarity, apoptosis, stem cell self-renewal, cell migration and tissue homeostasis. In the nervous system, Wnts act in neuronal migration, axon path finding, dendritic morphogenesis and synapse differentiation. Wnts serve as both attractive and repulsive cues during axon guidance, mediated through distinct mechanisms. The attractive responses to axonal growth are guided, at least in part, by the Frizzled receptors. Repulsive cues, on the other hand, can be mediated by the tyrosine kinase receptor Ryk. The aim of this thesis is the dissection of the basic biological and likely evolutionary conserved, functions of Wnt signaling through two different receptor families, the Ryks and Rors. We have employed genetic, biochemical, and electrophysiological approaches in order to understand the functions of these receptors and the pathways that they mediate. The studies in this thesis present novel insights into the biochemical mechanisms and the biological relevance of Wnt/Ror and Wnt/Ryk signaling for the development of a complex nervous system. Our findings can provide a starting point for the design of future therapeutic approaches for modulating the Wnt-Ryk and or Wnt-Ror pathways to treat post-injury nervous system lesions and aid neuronal regeneration. Show less
Duchenne muscular dystrophy (DMD) is a disease, characterized by progressive muscle wasting, caused by the lack of Dystrophin. A subset of DMD patients also have cognitive deficits likely due to... Show moreDuchenne muscular dystrophy (DMD) is a disease, characterized by progressive muscle wasting, caused by the lack of Dystrophin. A subset of DMD patients also have cognitive deficits likely due to the absence of Dystrophin from brain synapses where it is usually localized. Dystrophin and a number of other conserved proteins form the so-called Dystrophin Glycoprotein Complex (DGC). Here, I explored how the absence of DGC proteins might cause cognitive impairment by examining the roles of DGC members at peripheral and central synapses in the Drosophila model system. We found that the Rho-GAP crossveinless-c (cv-c) gene, which encodes a negative regulator of Rho-GTPase pathways, genetically interacts with Dystrophin. Both the cv-c1 and Dystrophin DLP2 mutants display increased presynaptic neurotransmitter release. We showed that the Rho-GTPase CDC42 is an important substrate of CV-C in this pathway. Furthermore, we de monstrated that it is the delocalization of the DGC protein Dystrobrevin in the absence of Dystrophin which causes the phenotype. We conclude that postsynaptic Dystrophin and this Rho-GTPase signaling pathway interact to regulate the synaptic homeostatic endpoint of neurotransmitter release. We hope that our findings may provide insights for the development of novel approaches to treat the cognitive deficits in DMD patients Show less
mRNA transport and targeting are essential to gene expression regulation. Specific mRNA sequences can bind several proteins and together form RiboNucleoProtein particles (RNP). The various proteins... Show moremRNA transport and targeting are essential to gene expression regulation. Specific mRNA sequences can bind several proteins and together form RiboNucleoProtein particles (RNP). The various proteins within the RNP determine mRNA fate: translation, transport or decay. RNP composition varies with localization, cell cycle and environmental cues. RNPs can move freely throughout the cytoplasm or bind subcellular cell structures depending on the contained mRNA. RNPs are associated with ribosomes when the mRNAs need to be translated, with transport granules if the mRNAs are targeted to a specific cellular location or with Processing Bodies (PB) or Stress Granules (SG) if translation needs to be turned down or the mRNAs are to be degraded. Insight into the mechanisms dictating RNP transition from one state to the other will lead to improved understanding of gene regulation itself. Therefore, this thesis aimed at investigating mRNA dynamics. Most experiments were performed in Drosophila embryonic muscles as they can be visualized in the whole living organism placed on a microscope stage, thus approaching endogenous conditions. Besides, several strategies involving gene or cell therapies to treat myopathies are being developed, implying that therapeutic mRNAs have the ability to move throughout the entire myoplasm. This was another reason for using muscle cells in most of our experiments. Show less
