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Title: Investigating the role of Wnt/PCP proteins in axon growth and neuronal cytoskeleton regulation
Author: Kaltenecker, Péter
ISNI:       0000 0004 9358 4139
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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The Wnt/Planar Cell Polarity (PCP) signalling is responsible for the establishment of planar polarity in epithelial tissues. Besides this function, it is also known to play multiple roles in neuronal development, however, the mechanism by which PCP signalling acts in these processes remained largely unclear. Neurons are highly polarised cells with extended neuronal protrusions in order to connect to target cells. The growth and maintenance of these protrusions crucially depend on the cytoskeleton. In recent years, many direct regulators of the neuronal cytoskeleton have been described, however it is still not completely understood how external or internal signals are conveyed to the neuronal cytoskeleton. The aim of this project was to study how core members of the PCP signalling module regulate the neuronal cytoskeleton, and to understand how they contribute to axon growth in Drosophila melanogaster. To this end, we used primary embryonic cell cultures which provide powerful subcellular readouts to determine the state of the neuronal cytoskeleton; and we studied the embryonic and the adult nervous system in order to assess the in vivo relevance of our findings. Our results showed that most PCP proteins are present both in the embryonic central and peripheral nervous system, and the loss of some of these components causes an early stall of the intersegmental nerve b (ISNb) in embryos. In addition, we found that the PCP proteins regulate axon growth and guidance in the ventral lateral neurons (LNv), a group of neurons in the adult brain that are responsible for controlling the locomotor activity and sleeping behaviour of the flies, as the LNv axons project ectopically in most of the PCP mutants. Accordingly, these pathfinding defects result in a strongly reduced LNv function and lead to severe alterations, particularly in the sleep/wake transition, since the morning activity of the PCP mutant flies is disrupted and becomes associated with an increased amount of daytime sleep. In accordance with these, we found that some PCP proteins affect axon growth in primary neuronal cell cultures as well. In addition, the lack of some of the PCP components alters the state of the actin and microtubule (MT) cytoskeleton in cultured neurons. In order to investigate the mechanism by which these PCP proteins can control the neuronal cytoskeleton and contribute to axon growth, we also studied DAAM (Dishevelled Associated Activator of Morphogenesis), a formin type of protein which has previously been linked to PCP signalling. Besides its known actinregulatory function, we found that DAAM strongly affects the MT cytoskeleton as well, in ways similar to the PCP proteins. Moreover, the loss of DAAM causes a similar ISNb stalling phenotype than that of the PCP proteins in the embryo. Together these findings suggest that the PCP proteins are necessary to properly regulate the neuronal cytoskeleton, presumably by controlling DAAM, and contribute to axon growth in vivo in the embryonic nervous system and in the adult brain. Beyond that, our studies also revealed a new physiological function of the Wnt/PCP pathway in controlling the sleeping behaviour of the adult flies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral