Postdoctoral Profiles

Current Research: 
Mapping the Functional Heterogeneity of Tomosyn Isoforms in Neurotransmission

Tomosyn has been previously identified as a syntaxin-binding protein that inhibits SNARE-mediated regulation of neurotransmitter release from presynaptic nerve terminals. In the mammalian brain two paralogous genes, designated tomosyn-1 and -2, are alternately spliced to express 7 different isoforms. Interestingly, tomosyn 1- and -2 genes and their isoforms are differentially expressed in the brain from development to postnatal stages. All structural differences between these isoforms occur within a hypervariable region (HVR) of tomosyn positioned just upstream from the SNARE domain. The molecular complexity at the HVR has been reported to modulate the inhibitory function of tomosyn in neurosecretion. To date, all mammalian studies have focused on only one tomosyn isoform, m-tomosyn-1.  In addition, it has been recently reported that a predominant inhibitory mechanism of tomosyn resides beyond its ability to interact with syntaxin1A, although other interacting proteins have not yet been identified.  Based on these considerations our proposed experiments are placed into two specific aims.  In specific aim 1 we will determine the functional differences between mammalian tomosyn 1 and 2 genes and their isoforms in inhibiting secretion and then define those regions critical to regulation within the HVR.  The experiments will use a combination of fluorescence microscopy and electrophysiological analysis on intact chromaffin cells, as well as biochemical secretion assays in intact PC-12 cells.  In specific aim 2 we will use proteomic analysis to identify and characterize novel binding partners of tomosyn and to map tomosyn domains important to these interactions. These experiments will employ mammalian expressed tomosyn constructs and proteomic analysis based on a tandem affinity tag purification scheme.  In summary, the results of the proposed investigations will identify functional differences between tomosyn isoforms, provide novel insight into tomosyn?s HVR domain and identify novel protein interactions that are critical mediators of tomosyn?s action to fine-tune neurotransmitter release. A molecular and biochemical understanding of the process of neurotransmitter release is essential to appreciate the normal function of the nervous system and fundamental towards the development of therapeutic treatments in many neurologic disorders typified by an imbalance of particular neurotransmitters such as depression, dementia, schizophrenia, Parkinson's disease, epilepsy, Huntington's disease, and autism, to name a few.

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