The development of connectivity...

We study how the nervous system of the adult fruit fly is ‘wired together’. By exploiting the extreme biology of metamorphosis, we have been able to uncover novel cellular and molecular mechanisms of neurodevelopment.

At present two topics occupy most of our waking hours; firstly, the role that dendritic guidance plays in establishing the specificity of synaptic connections and secondly, how neurons remove branches during pruning.

Large-scale pruning

Pruning is the selective elimination of synapses, axons or dendrites and is essential for the refinement of circuits. Large-scale pruning involves the removal of relatively long neuronal processes and is deployed in many parts of the nervous system during development. At present we know little about the cellular and molecular mechanisms that underlie this phenomenon. To study this type of pruning we take advantage of the metamorphic biology of the fly, using a subset of larval sensory neurons that undergo a dramatic remodeling during metamorphosis (see below).

We have developed live imaging techniques that have given us unprecedented access to the cellular mechanisms of pruning in intact animals. These large-scale pruning events take place by a local degeneration that is reminiscent of Wallerian degeneration.

We, and others, have shown that the apoptotic machinery, that a cell normally uses to kill itself, is deployed within these neurons during pruning. Using a genetically encoded reporter CD8::PARP::Venus, we found that caspases are activated locally within the dendritic compartment of these pruning sensory neurons and not in the soma or axon .

Our goal is to learn more about the molecular machinery that orchestrates this program of neurite autodestruction. Our hope is that insights from these studies will tell us more about the sequence of events that take place when neuronal processes degenerate during disease or following injury.

Dendritic guidance

To establish ordered patterns of connectivity appropriate pre and postsynaptic elements must come together during development. Most work on this topic has been 'axonocentric', focusing on the guidance of presynaptic elements.

We would like to know more about the role dendritic growth and guidance plays in the development of connectivity. To explore this topic we are using the 'leg network', the local network that controls the movement of the fly's leg. This system is complex enough to be interesting but contains a small enough number of components to be experimentally tractable.

Our recent work has revealed that the dendrites of leg motoneurons have distinct organizations that relate to the muscles they innervate and that this topography is built by dendritic targeting. The targeting within the mediolateral axis is controlled by the midline guidance cues Slit and Netrin. We have collaborated on this work with Eric Blanc and K.VijayRaghavan.

Previously others have shown that presynaptic terminals are positioned independent of their postsynaptic partners using Robo/Slit signaling. We believe such global third-party cues could be important for generating the specificity of synaptic connections.

Lineage-Based Analysis of the Adult CNS of Drosophila

The scientific objective is to generate a light microscope-level neuro-anatomical atlas of the adult ventral nerve cord (VNC) of Drosophila using a lineage-based approach. This is funded by the visitor program at Janelia Farm.