Our lab has several interests related to the mechanisms involved with membrane fusion, synaptic transmission, and synaptic plasticity: 

  1.   Nanomechanics of Ca2+-triggered membrane fusion.  These studies involve the analysis of a number of Ca2+-binding proteins (synaptotagmin, Doc2, Otoferlin, Rabphilin, etc.), as well as a number of other accessory proteins (nSec1, complexin, munc13, etc.) that regulate the core of the fusion apparatus - the SNARE complex - to control fusion reactions. We employ a diverse range of research tools to study membrane fusion including biophysical (electrophysiology, imaging etc.) and time-resolved biochemical (reconstituted fusion, stopped-flow kinetics, SPR, ITC etc.) techniques.  Using these methods we are able to relate the function of individual proteins in in vitro systems with their function(s) in living neurons and in neuronal circuits. Of particular interest to the lab are the mechanisms underlying the asynchronous phase of neurotransmitter release, and engineering the release machinery to tune the kinetics of synaptic transmission.

  1.   Probing the structure and dynamics of fusion pores.   During exocytosis, fusion pores form the first aqueous connection that allows escape of neurotransmitters and hormones from secretory vesicles. The structure of of the pore is the subject of debate, with some evidence that the pore might be composed of the membrane anchors of SNARE proteins while others argue the pore is purely lipidic.  We employ the rigid framework and defined size of nanodiscs to interrogate the properties of reconstituted fusion pores, using the neurotransmitter glutamate as a content mixing marker.  Fusion pore dynamics in cells are monitored with carbon fiber amperometry.  In addition, we are developing single molecule fusion assays to monitor the opening and closing of fusion pores optically.  In our view, synaptic vesicle exocytosis often involves a kiss-and-run in which open fusion pores close without dilating to give rise to full fusion and bilayer merger.

  1.   Relating basic synaptic properties to aspects of network-level function and plasticity.   We are interested in how elementary processes in synapses (multivesicular release kinetics, synaptic vesicle replenishment, endocytosis, etc.) underlie higher-level properties in neurons and networks of neurons. We have characterized synaptotagmin isoforms that underlie elements of short-term plasticity (synaptotagmin-7) and long-term plasticity (synaptotagmin-4), and have several ongoing projects studying the diverse roles of synaptotagmins at the molecular, systems, and behavioral levels. Additional projects include characterizing the function of asynchronous neurotransmitter release, and studying the effects of network topology on population-level oscillations in artificially-patterned networks of neurons.

  1.    Elucidation of the receptors, entry pathways, and the molecular basis for translocation across membranes, of Botulinum (BoNT) and Tetanus neurotoxins (TeNT).  These toxins are the most deadly substances known to humankind, and are also used to treat myriad medical maladies. They are highly specific proteases that target to nerve terminals and cleave SNARE proteins to block exocytosis.  We are in the process of identifying the cell surface receptors, entry pathways, and mechanisms of translocation of these toxins.  We are also using quantum dots to track their movement and putative transcytosis in simple neuronal circuits.

  1. Molecular mechanisms regulating organelle distribution and homeostasis in mammalian neurons. Neurons are hyperpolarized eukaryotic cells which transmit chemical and electrical information and whose collective functions give rise to the nervous system. Neuronal cell bodies are tens of microns in diameter. These polarized cells send our dendritic processes tens to hundreds of micrometers in length and axonal processes millimeters to centimeters in length. Maintenance of organelle distribution in such a polarized network of extensions presents a unique challenge for viability of neurons. Namely, we’ve chosen to focus on the distribution and homeostatic mechanisms of signaling endosomes, mitochondria, and lysosomes. We are using microfluidic devices to spatially separate axonal and somatodendritic compartments, while pioneering novel cell disruption and organelle isolation techniques from these fluidics. These methods will allow us to visually and physically interrogate organelle dynamics in mature neurons.

  1. Role of synaptotagmins in hormone secretion in the pituitary. The anterior pituitary regulates virtually all aspects of vertebrate physiology, including growth, metabolism, and reproduction, through the secretion of six different hormones. These hormone are packaged into large dense core vesicles (LDCVs) and the release of these hormones from LDCVs is triggered by Ca2+. The molecular mechanism underlying this Ca2+ triggered hormone release release are not known. Therefore, we are also investigating the regulation of pituitary hormone secretion by the synaptotagmins (syt). There are 17 isoforms of syt in mammals, and they have different intrinsic calcium affinities and membrane binding properties, which suggests that have different functions. Through our studies of syt regulation of pituitary hormone secretion, we also aim to elucidate the functional significance of large syt mulit-gene family.

Contact info:                                    

Chapman Lab       

University of Wisconsin

Department of Neuroscience

Wisconsin Institute for Medical Research (WIMR)

1111 Highland Ave, rm 9555

Madison, WI 53705


Research Focus: