Figure 1.
SGNs undergo a stereotyped refinement processes while Sema5b and Plxnas are expressed in differentiating hair cells and SGNs, respectively. A, A whole-mount view of hair cells from a P1 cochlea, shown by MyoVI labeling, organized into one row of inner hair cells (IHCs) and three rows of outer hair cells (OHCs). B, Sample from A with NF200 labeling of type I and II SGNs. C, A cross-sectional view of the same structures and labeling from the orientation of the dotted line in B. D, At E15.5, immature SGN peripheral axons have many terminal branches (red arrowheads), which explore the differentiating cochlear sensory domain. A few days before birth, SGNs begin to retract and remove excess branches, as type-I SGNs prepare to ultimately form a single connection with a single IHC. E–G, In situ hybridizations showing that Sema5b mRNA is specifically expressed in hair cells, identified by arrows, in late embryonic (E) and early postnatal (F) development, but is largely eliminated by P5 (G). H–K, Plxna mRNA expression in E17.5 cochlear cross-sections using Plxna1 (H, I) and Plxna3 (J, K) antisense probes along with sense controls. Plxna1 transcripts are visible in the spiral ganglion (SG) and in lateral region of the cochlear sensory domain (arrowhead) in H. Plxna3 transcripts are visible in the SG in J. Sense controls show no reactivity. Scale bar (in G): A, B, ∼100 μm; C, 20 μm; E–G, 60 μm; H–K, 200 μm.