Fig. 6.

NRXN3 is required at 6 weeks for proper synapse number in mouse auditory inner hair cells. (A,B) Confocal images of mouse inner hair cells (IHCs) at 6 weeks (P42) from control (A) and Nrxn3 mutant animals (Atoh1-Cre; Nrxn3^flox/flox) (B). CTBP2 labels the presynapses and GluR2 labels the postsynapses. Merged images show four IHCs from three different regions of the cochlea (apex, middle and basal thirds) for each genotype. Dashed lines outline hair-cell bodies [via a MYO7A co-label (not shown)]. White boxes in the top panels are magnified below to highlight synapses more clearly. (C-E) Quantification reveals that, compared with controls, Nrxn3 mutants have significantly fewer complete synapses per IHC at the apex (C), mid (D) and base (E). These findings were compiled from four animals from each genotype and from two independent litters and immunostains. Each dot represents the average synapse number from one imaging region (6-9 IHCs). Two imaging regions were examined per animal for each tonotopic region. An unpaired two-tailed t-test was used in C-E. *P<0.05; **P<0.01. Data are mean±s.e.m. Scale bar: 5 µm (A,B); 1 µm (A,B, insets).