analysis of neuromuscular development in Drosophila
	Haig Keshishian, Ph.D. Professor of Molecular, Cellular & Developmental Biology; Co-Director of Interdepartmental Neuroscience Program Email: haig.keshishian@yale.edu Room: KBT 640Phone: (203) 432-3478/ (203) 432-8925 Fax: (203) 432-26161 Ph.D. University of California, Berkeley 1982

A major challenge of developmental neurobiology is to understand how synapses are established. The problems faced by a developing neuron include the guidance of the axon to the vicinity of its targets, the recognition of appropriate synaptic partners, and the refinement and plasticity of the developing synapses. For the past several years my laboratory has been examining this problem in Drosophila, focusing on the synapses made by motoneurons onto bodywall muscle fibers. This system is particularly well-suited for analyzing how a nervous system gets wired together. Both the neurons and target muscle cells are singly identifiable, and can be directly manipulated at both the cellular and molecular level. Furthermore, the Drosophila nervous system exhibits a high degree of synaptic sophistication, so that complex problems involving experience-dependent plasticity of connections can be examined.

When the embryonic growth cones first contact their targets they make stereotypic projections, probably in response to specific recognition cues expressed by the muscles. Work in the lab has established that growth cones are capable of distinguishing between the different muscles, and molecular studies have pointed to candidate recognition molecules. In about three hours the growth cones establish their basic synaptic connectivity, branch anatomy, projection trajectories and transmitter expression. We are now using both cellular micromanipulation and molecular genetic methods to examine the cellular and molecular mechanisms governing this remarkably precise form of synaptogenesis.

In addition, the synapses are capable of altering their cellular connectivity, anatomy, and molecular expression patterns as a function of prior synaptic activity. The molecular mechanisms that govern these changes are fascinating, as they resemble the plasticity events seen in higher nervous systems, and may be related to the structural changes associated with learning and memory in the CNS. Drosophila is an excellent system to examine these events, as the powerful techniques of molecular genetics can be used to understand the underlying cellular mechanisms.

One recent approach the lab has taken taken is to reengineer ion channels, so that they can be used as experimental tools for controlling neuronal activity. The modified ion channels are targeted to specific compartments of the synapse during development. Through this approach one can either reduce or enhance membrane electrical excitability. Using these tools we have examined how synaptic activity regulates events such as early synaptic refinement, growth, and plasticity.  We have also use the constructs to characterize how retrograde transsynaptic signals regulate the development of the synapse.

Work in the lab involves intracellular physiology of embryonic neurons, micromanipulation, embryo and tissue culture, molecular genetics, and digital optical microscopy.

Selected Publications

Keshishian, H., Broadie, K., Chiba, A., Bate, M. (1996). The Drosophila neuromuscular junction: a model system for studying synaptic development and function. Annu Rev Neurosci 19, 545-75.

White, B. H., Osterwalder, T.P., Yoon, K.S., Joiner, W.J., Whim, M.D.,Kaczmarek, L.K., Keshishian, H. (2001). Targeted attenuation of electrical activity in Drosophila using a genetically modified K(+) channel. Neuron 31,699-711.

Osterwalder, T. Kuhnen, A. Leiserson, W.M., Kim, Y.S., Keshishian, H. (2004). Drosophila Serpin 4 functions as a neuroserpin-like inhibitor of subtilisin-like proprotein convertases. J. Neurosci 24, 5482-5491.

Fernandes, J., Keshishian, H. (2005). Motoneurons regulate myoblast proliferation during adult myogenesis in Drosophila, Dev Biol 277, 493-505.

Mosca, T.J., B.H. White, Keshishian, H (2005). Dissection of synaptic excitability phenotypes using a dominant-negative Shaker K+ channel subunit. PNAS 102, 3477-3482.

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