Dye tracing reveals Type II fiber outgrowth problems in the organ of Corti of Prox1^flox/flox; Tg(Nes-Cre) conditional mutant embryos.

<p>NV Maroon (green) was inserted into the cochlear nucleus and NV Orange (red) was inserted into the olivocochlear bundle to label a small population of afferents (green) and all efferents (red). Efferents show a similarly organized intraganglionic spiral bundles in wildtype (A–C) and <i>Prox1^flox/flox</i>; <i>Nes-Cre</i> conditional mutant mice (D–J) and grow toether with afferents in radial fiber bundles (RF) to the organ of Corti. Note that at this stage only occasional efferents extent to outer hair cells. In contrast, type II afferents grow to the second or third row of outer hair cells (OHC) where they invariably turn toward the base (B,C). At this stage, none of the multiple type II afferents of <i>Prox1^flox/flox</i>; <i>Nes-Cre</i> conditional mutant mice show this coordinated growth pattern. Instead, fibers grow randomly toward the base or apex but mostly seem to stall with multiple branches extending toward the base and the apex (F,G). IGSB, intraganglionic spiral bundle; OHC, outer hair cells; RF, radial fibers; SPG, spiral ganglion. Bar, 100 µm (A–D), 50 µm (E–H; inserts in A,A′, A″).