Both the structure and the function of the hair cell's synaptic ribbon have been enigmatic since its discovery in the early days of electron microscopy. It is assumed that it plays a key role in determining the amazing temporal and dynamic characteristics of afferent neurotransmission between the hair cell and the auditory nerve fiber, but whether it has other functions is not known. In the half-century since its discovery, we have learned relatively little about its molecular anatomy or its function. Though many proteins known to be important in conventional synapses are present at the ribbon, we know little about the dominant components of the structure itself. The recent development of mass-spectrometric-based proteomics approaches for protein identification, coupled to a relatively complete proteome for the mouse, allows identification of hundreds of proteins in very small samples. Thus revisiting protein identification in purified samples of synaptic ribbon should yield most if not all of the proteins in and associated with the synaptic ribbon. The work is straightforward, the procedures are in place, the mouse proteome is highly developed, and the proteomic analysis of mass spec data is routine.
The specific aims are to (1) Identify protein components in purified synaptic ribbon complexes, and in the electron dense core of the ribbon. (2) Immunochemically verify presence of candidates in synaptic ribbons of the mouse inner ear and in ribbon complexes purified from bovine retina. It seems evident that a prerequisite to understanding function of a structure as complex as the ribbon is to define the structure of the ribbon at the proteomics level. For many proteins identified, function will be implicit, based on analysis of the protein in other systems. Others may need some thought or experimentation to determine what they do. There seems no question that this straightforward quest to identify proteins in the synaptic ribbon should generate many hypotheses for what the ribbon is doing that could keep investigators busy for some time to come. Identification of the molecular components of the synaptic ribbon will be a fundamental step towards understanding its specific function at the afferent synapse.
The synaptic ribbon's role in transmission at the hair cell synapse has been enigmatic since its discovery over a half century ago. Recent advances in proteomics will allow identification of the molecular structure of this unusual subcellular structure that is essential for normal hearing. Because most proteins have specific molecular functions, knowing the panel of players in this structure should engender specific, testable hypotheses as to its function that may provide insights into a range of auditory disorders, including tinnitus and noise-induced hearing loss. ? ?
| Kantardzhieva, Albena; Liberman, M Charles; Sewell, William F (2013) Quantitative analysis of ribbons, vesicles, and cisterns at the cat inner hair cell synapse: correlations with spontaneous rate. J Comp Neurol 521:3260-71 |
| Kantardzhieva, A; Peppi, M; Lane, W S et al. (2012) Protein composition of immunoprecipitated synaptic ribbons. J Proteome Res 11:1163-74 |
