486 Molecular Mechanisms of Type II Spiral Ganglion Neuron Development

OBJECTIVES/GOALS: 30,000,000 people in the U.S. have hearing loss, negatively impacting quality of life and work. Understanding auditory axon guidance for spiral ganglia neurons (SGNs) will aid development of new therapies. I study role of Eph/Ephrin signaling in mediating type II SGN turning events, and how planar cell polarity (PCP) signaling modulates this process. METHODS/STUDY POPULATION: This quantitative study was conducted on Efna3 and Vangl2 null mice possessing Neurog1CreERT2 and R26RtdTomato mutations. Spontaneous Cre activity within the Neurogenin 1 CreERT2 line causes recombination and expression of fluorescent Rosa26 Reporter (R26R)tdTomato in a restricted number of SGNs, including type IIs. Together these lines permit SGN sparse labeling. Bulk-labeling was used for Efna3;Vangl2 double knockout (DKO) mutants. Immunostaining and confocal imaging was used to analyze dsRed in Efna3; Vangl2 and NF-200 in DKOs to quantify type II SGN turning. In combination, 3D rendering in Imaris software was used to quantify type II SGN turning, branching and other growth and navigation characteristics. 5-6 cochleae per genotype were analyzed and compared by t-test to wildtype controls. RESULTS/ANTICIPATED RESULTS: EPHRIN-A3 is expressed on the membranes of outer pillar and Deiters’cells of the cochlear epithelium. Efna3 nulls showed a small rise in type II SGNs incorrectly turning toward the apex at an error frequency of 16.9% compared to controls (n=6; p=0.05). Efna3 nulls had reduced branch number/fiber compared to controls, 4.14 and 7.22, respectively (n=129; p DISCUSSION/SIGNIFICANCE: Our results suggest that Eph/Ephrin signaling acts parallel of PCP signaling to mediate type II SGN guidance during development. The clinical implications of these findings are that therapeutics targeting EPHRIN-A3 and/or VANGL2 in this pathway could stimulate new outer hair cell innervation by type II SGNs following auditory damage.