Nrxn3 is required for early synapse maturation in lateral-line hair cells. (A-F) Confocal images of developing hair cells (3 dpf) from wild-type controls (A-C) and nrxn3a; nrxn3b mutants (D-F). CTBP labels presynapses (A,D) and MAGUK labels postsynapses (B,E). Merged images are shown in C and F. The boxed areas (magnified on right) in C and F show three examples of individual synapses. Dashed lines in C and F outline the hair-cell region [via a MYO7A co-label (not shown)]. (G-J) Quantification shows a similar number of hair cells per neuromast (G), but significantly fewer complete synapses per hair cell in nrxn3a; nrxn3b mutants (H). There are significantly more unpaired presynapses (I) and postsynapses (J) per hair cell in nrxn3a; nrxn3b mutants. In developing hair cells, there is no change in the total number of presynapses (I) or postsynapses (J) per hair cell in nrxn3a; nrxn3b mutants. n=17 wild-type and 13 nrxn3a; nrxn3b mutant neuromasts. An unpaired two-tailed t-test was used in G and H, and a two-way ANOVA was used in I and J. ns, P>0.05; **P<0.01; ****P<0.0001. Data are mean±s.e.m. Scale bars: 5 µm (C,F); 0.5 µm (C,F, insets).
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