SPLTRAK Abstract Submission
Neurexin isoforms may coordinate innervation of mouse taste bud cells
Gennady Dvoryanchikov1, Damian Hernandez1, Nirupa Chaudhari1,2,3
1Department of Physiology & Biophysics, University of Miami Miller School of Medicine, MIAMI, FL, United States
2Program in Neurosciences, University of Miami Miller School of Medicine, MIAMI, FL, United States
3Department of Otolaryngology, University of Miami Miller School of Medicine, MIAMI, FL, United States

Taste buds are innervated by fibers of primary gustatory neurons. We asked if taste bud cells express synaptic recognition molecules that could promote interactions with afferent fibers. Neurexins (Nrxn1, 2, 3) are presynaptic proteins with numerous isoforms, permitting selective recognition between pre- and post-synaptic membranes in the CNS. Using RT-qPCR, we found that Nrxn1 is expressed only as the longer α-isoform, while Nrxn3 is expressed only as the truncated β-isoform. Nrxnα can exist as many splice variants, to confer synaptic specificity. Hence, we used primers flanking all 6 splice sites (SS1-SS6) for single-cell RT-qPCR. Taste bud cells were identified by GFP fluorescence (from PLCb2-GFP or Gad1-GFP mice for cell types 2 and 3 respectively). At SS1, SS3 and SS5 sites, both alternative forms of Nrxn1 could be detected in both type 2 and 3 cells. However, at the SS2 site, type 2 and type 3 cells express different splice variants. Another difference between the taste bud cell types was that we detected Nrxn3 only in type 2 cells and only as Nrxn3β. The difference between type 2 and type 3 cells was also reflected in markedly different patterns of staining with anti-Nrxn antibody. We also looked for Neuroligins (Nlgn1, 2, 3), known postsynaptic partners for Nrxns. Geniculate ganglion gustatory neurons express RNA for all three Nlgns; and immunohistochemistry revealed a punctate pattern of staining over taste buds, which was lacking over adjacent non-taste epithelium. Finally, we found that Neurexophilin, which can regulate the Nrxn-Nlgn interaction, is only expressed in type 2 cells. Thus, neurexins, with differentially expressed splice variants, may be good candidates for coordinating selective innervation of taste bud cells.