Neuronal Morphology in the Drosophila Embryo: Visualisation, Digital Reconstruction and Quantification

Studying the formation of neural networks requires a thorough understanding of their constituent neurons, their development, connectivity and electrical properties. Neuronal morphology is a key element, encompassing parameters important for neuronal function: projection patterns and synaptic termination zones inform on connectivity, while ontogeny is reflected by cell body locations. Drosophila is one of the most successful genetic model organisms for studying nervous system development and function. It presents a unique combination of neural networks of intermediate complexity, which are composed of identified neurons that can be genetically manipulated and interrogated throughout their development by imaging and electrophysiology. Here, we present approaches for studying neuronal morphology in the Drosophila embryo. The methods are applicable to any cell, though by way of example we focus on motor neurons in the ventral nerve cord. Specifically, we outline and discuss genetic approaches for visualising individual neurons, their detailed neuritic arborisations and putative synaptic sites. We present a method for analysing quantitatively the topology of complex branched neuronal structures through digital reconstruction. This combination of genetic single-cell labelling methods and semi-automated, highly accurate digital 3D reconstructions of complex cell morphologies has already opened up to investigation new areas of nervous system development and it will be central to future progress in our understanding of neural network development.