Imaging TGFBETA-Signaling in Synapse Formation and Synaptic Growth

Brian McCabe, Ph.D.

Columbia University

Funded in December, 2006: $250000 for 3 years
LAY SUMMARY . HYPOTHESIS . SELECTED PUBLICATIONS .

LAY SUMMARY

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Imaging Cell Signaling May Reveal How Synapses are Formed and Can Go Awry in Disease

Researchers will use cellular imaging in the fruit fly and mice to gain a better understanding of the signaling processes that regulate nervous system wiring and how such signaling may go awry in brain diseases such as Amyotrophic Lateral Sclerosis (ALS).

Signaling pathways regulate the differentiation, growth, and function of all cells.  In the nervous system, there are several types of electrochemical signals (called neurotransmitters).  The signals pass from the cell body, along its axon (communication cable), through a synapse that connects to a neighboring cell’s dendrite, and from there the signal travels up to the neighboring cell’s body. Cells using the same type of neurotransmitter communicate with one another this way. Scientists do not yet know, however, how the correct formation, assembly and maturation of specific synapses occur to facilitate this communication, especially when the signals need to travel long distances along axons to move from one cell to another.  Moreover, how do the synaptic defects that occur in conditions, such as ALS, occur?

Recent research indicates that cytokines, proteins that affect the activities of other cells, play an important role in the normal development, and disease-related dysfunction, of synapses. Specifically, the researchers hypothesize, a family of cytokines, called Transforming Growth Factor Beta (TGF-β), regulates the development and functioning of neural cell synapses that use the transmitter glutamate to communicate. These glutamate-transmitting cells are destroyed in ALS. The investigators will use the fruit fly as a genetic screening tool to identify TGF-β genes involved in formation of synapses that use glutamate.  They will then study, in transgenic mice, the relevance of these genetic factors to the development of synapses that transmit glutamate signals from brain stem cells to cerebral cortex cells. 

Significance:  Information on how TGF-β signaling directs nervous system wiring of glutamate-transmitting cells may help to further our understanding of brain development and of how alterations in these signaling pathways may contribute to the death of glutamate-transmitting cells in ALS and other devastating brain diseases.

HYPOTHESIS

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Hypothesis:
Our hypothesis is that synaptic TGF-β secretion, trafficking, and signal transduction represents a key, evolutionary conserved, signaling mechanism that regulates the development and function of glutamatergic synapses.

Goals:
The Transforming Growth Factor Beta (TGF-β) family of cytokines, which play important roles in early development, are also specifically required in mature organisms for synaptic growth, function, and plasticity. The primary goal of this collaborative project is to utilize a combination of imaging approaches with genetic and biochemical labeling techniques to address crucial gaps in our knowledge of the synaptic signaling mechanism and neuronal function of TGF-β.  We will analyze how retrograde TGF-β signaling is propagated both at Drosophila neuromuscular junction synapses and in cultured vertebrate neurons.  We will also determine the role of TGF-β in axon-target interactions in the ponto-cerebellar system of mice and use Drosophila genetics to investigate the function of synaptic genes regulated by TGF-β signaling.

Methods:
We will employ two complementary model systems (1) The Drosophila neuromuscular junction—a glutamatergic synapse that is readily accessible to genetic, electrophysiological, and in vivo imaging analysis and (2) the ponto-cerebellar projection in mice, an afferent projection in the central nervous system that forms glutamatergic synapses. We will utilize both in vivo and in vitro imaging tools, including fluorescent fusion proteins and quantum dot technology, in combination with both mouse and Drosophila genetic techniques, to exploit the unique advantages of each model system.

SELECTED PUBLICATIONS

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McCabe B.D., Marqués G., Haghighi A.P., Fetter R.D., Crotty M.L., Haerry T.E., Goodman C.S., and O'Connor M.B. The BMP homolog Gbb provides a retrograde signal that regulates synapse growth at the Drosophila neuromuscular junction. Neuron. 2003 Jul 17;39(2):241-54.

Kalinovsky A. and Scheiffele P. Transcriptional control of synaptic differentiation by retrograde signals. Curr Opin Neurobiol. 2004 Jun;14(3):272-9.