Kimberly Epley
(Ph.D., 2003, Bowling Green State University)

Research Assistant Professor, Whitney Laboratory

epleyk@ufl.edu

Synaptogenesis and Synapse Physiology

Our goal is to elucidate the basic principles of synapse function and development using zebrafish as a model system. We use mutant fish lines that show abnormal behavior. These fish have defects in the way neural excitation is translated into movement. Since zebrafish develop rapidly inside transparent eggs, we can analyze their neural function before they die. In addition, the transparency of the embryo itself enables optical studies, tracing individual proteins marked by genetic methods through development in vivo. We take advantage of these merits that the zebrafish system provides to pursue the following projects.

Current Projects

Projects in the lab center around two locomotory mutants we found to have defects in two key molecules of the neuromuscular synapse. One lacks acetylcholine receptors (AChR) in the muscle. As a result, the fish cannot mount a movement when the motor neuron releases ACh. The other mutant has a dysfunctional rapsyn. Rapsyn is a post-synaptic protein that brings AChRs together. In this fish, AChRs do not make clusters at the synapse and are diffusely distributed over the muscle cell surface.

From the AChR-less mutant, we found that AChRs, which were thought to be passive players in synapse formation, play an active role, directing rapsyn molecules to the synapse. In the rapsyn mutant fish, we found that AChRs not only fail to form clusters at the synapse, but their functions are also altered. That is, when motor neurons fire at a high frequency, the amplitude of AChR current remains constant in wild type, whereas in rapsyn-mutant fish the response shows a marked attenuation with repeated firing of motor neurons.

We aim to elucidate the mechanisms underlying these unexpected functions of AChR and rapsyn. Specific questions include:

• How do AChRs direct rapsyns to the synapse?
• Do AChRs and rapsyn come together before reaching the membrane, or do they form clusters after reaching the plasma membrane?
• What molecule allows the AChR to be localized to the synapse?
• How does the rapsyn molecule regulate the function of AChR?
• Is it a direct interaction or does it involve intermediate players?

We also study the functions of AChRs expressed in the central nervous system (CNS). In the neuromuscular synapse of the AChR-less mutant, we showed that the pre-synaptic machinery releasing ACh develops normally. This mutant therefore offers a unique opportunity to study the AChRs of the CNS in a simple synapse context, when these receptors are ectopically expressed in muscle cells of AChR-less mutant. We use this "model synapse" to study the functions of CNS AChRs, which prove difficult to study in the CNS.

We are continuing to screen new locomotory mutants, using physiological tools we have at hand. Though our primary focus is the neuromuscular synapse, we are ready to pursue mutants that have defects higher in the nervous system – in the spinal cord or brain.

Personnel

Kimberly Epley, Research Assistant Professor
Anna Mistretta-Bradley, Laboratory Technician
Karen Overstreet, Laboratory Technician

Selected Publications

Kraus-Epley, K.E. and Moore, P.A.  (2002)  Bilateral and unilateral antennal lesions alter orientation abilities of the crayfish, /Orconectes rusticus/. Chemical Senses, 27: 49-55.