Research Interests

Our goal is to understand the mechanisms that underlie the development of neural circuits and the emergence of coordinated function. We use the embryonic nervous system of Drosophila as a model, focussing on the development of the motor network that generates the simple crawling movements of the Drosophila larva.

Drosophila has been extremely influential for our understanding of mechanisms of neurogenesis and axon guidance, which have been highly conserved from flies to humans. Drosophila brings three crucial strengths to this kind of analysis. The first is that we can work with identified neurons to which we can return again and again, as they develop and in experiments. The second is that by using targeted genetic constructs we can access specific cells in the developing network for experimentation and analysis (Diegelmann 2008). This is particularly important in the context of emerging function because it gives us an unparalleled ability to manipulate the excitability and synaptic connections of individual cells or cell classes. The third point is that we can use genetic methods to identify the molecular mechanisms that regulate structure, excitability and connectivity in the final stages of circuit assembly.

More recently, in collaboration with Sean Sweeney at the University of York, we have begun exploring how oxidative stress, a hallmark of a ageing and neurodegenerative conditions, affects synaptic terminal growth.

Ongoing projects

Organised growth of axons and dendrites We study the mechanisms that regulate the growth, branching and targeting of postsynaptic dendritic arbors (Ou 2008). We have shown that the terminal phases of growth in both axons and dendrites depend on the responses of individual neurons to positioning cues in the mediolateral (Zlatic 2003; Mauss 2009) and dorsoventral axes of the developing nervous system (Zlatic 2009). We have identified these cues and shown that axons and dendrites respond to them by growing to specific locations within the network in an autonomous, target independent fashion. The implication of these findings is that the terminals of connecting pre and postsynaptic partners are delivered autonomously to common localised volumes of the neuropile within which connections will subsequently form.

The regulation of scaling growth As the Drosophila larva grows, motorneurons, which constitute the output of the locomotor network, need to adjust in order to maintain their ability to efficiently induce contractions of the growing postsynaptic body wall muscles. One possible mechanism is scaling of synapses, which is well studied in the context of the neuromuscular junction. Within the central nervous system, we find that the size of motoneuron dendrites increases during larval development, accommodating a greater number of synapses. Moreover, this dendritic growth is proportional to increases in animal body size and it requires the integration of multiple environmental and internal cues. We are currently investigating the role of systemic signals by combining imaging, electrophysiology, and transcriptional profiling techniques.

Activity dependent maturation of network properties By imaging function in the motor system we have precisely identified the point at which the motor network first becomes active. During this early phase network activity is episodic, recurring at regular intervals separated by extended periods of quiescence. Early episodes are unpatterned, but as the episodes continue, elements of coordinated output begin to appear, culminating finally in episodes of well-patterned crawling-like activity (Crisp 2008). We find that early activity is instructive and required for the normal maturation of motor circuitry (Crisp 2011), suggesting that the requirement for tuning and adjustment in developing circuitry is far more widespread than previously supposed.

Oxidative stress Reactive Oxygen Species (ROS) are a natural byproduct of mitochondrial respiration and lysosomal function. ROS are able to damage cellular macro-molecules including protein, lipid and DNA and are therefore tightly regulated, both within the mitochondria and cytoplasm by the action of superoxide dismutase (SOD) and catalase. Oxidative Stress can occur if the balance between ROS production and clearance is disrupted, an effect observed in multiple neurodegenerative disorders including Alzheimer's and Parkinson's diseases. Building upon work conducted in and in close collaboration with the Sweeney lab (University of York), we are investigating how either genetically (e.g., spinster mutant) or chemically (e.g., paraquat treatment) induced oxidative stress produces an overgrowth of the Drosophila neuromuscular junction (see bouton analysis data above). We are using the Drosophila larval motor system to dissect the mechanisms by which cytoplasmic and mitochondrially derived ROS impinge on neuronal growth. Specifically, working with identified motorneurons we analyse the effects of ROS on both their presynaptic axonal and postsynaptic dendritic terminal arbors. Scale 20µm.