Unraveling cellular and molecular mechanisms that coordinate pre- and postsynaptic maturation by intravital imaging in the Drosophila central nervous system

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We aim to understand the cellular and molecular mechanisms that underlie the development of neural networks in the central nervous system (CNS). Transient cell-cell interactions and the dynamic assembly of synaptic protein scaffolds are hallmarks of network formation. Appropriate regulation of these interactive processes is a prerequisite for network function to emerge during embryogenesis and to be maintained during postembryonic growth and maturation. We identified the receptor tyrosine kinase Anaplastic lymphoma kinase (Alk) in a genetic screen to regulate postsynaptic growth and synapse formation in the motor system of the fruit fly Drosophila melanogaster. Alk is expressed in the developing gut and nervous system; intriguingly, this expression pattern is conserved between vertebrates (mouse) and the fly. The role of Alk signalling in regulating neuronal growth and synaptogenesis is incompletely understood, particularly how it affects the development of postsynaptic cells and their connectivity. In this proposal we specifically address i) how the cellular interactions between pre- and postsynaptic terminals lead to the stabilisation of neuronal branches and the development of synapses in the CNS; ii) the molecular maturation of nascent synapses that form on these branches; and iii) the role of Alk signalling in regulating these interactions. To investigate the dynamic mechanisms of network formation with minimal disturbance, we developed 2 novel techniques: i) intravital imaging of cellular and molecular interactions between partner neurons (inter- and motorneurons) in the embryonic and larval CNS of fruit flies and ii) targeted activation of fluorescent tagging of endogenously expressed proteins in individual neurons. The programme of work will significantly advance our understanding of the cellular interactions between partner neurons in a developing central network, the molecular dynamics of pre- and postsynaptic scaffold formation and how these are regulated. Further, it will generate a rich genetic tool kit that is readily applicable to study synapse biology in other parts of the nervous system, to investigate for example memory formation or neurodegenerative diseases.