The segregation of Calb1, Calb2, and Prph neurons reveals distinct and mixed neuronal populations and projections to hair cells in the inner ear and central nuclei.

BACKGROUND

Knockin mouse models expressing calbindin (Calb1), calretinin (Calb2), and peripherin (Prph) exhibit changes in hair cells (HCs), spiral ganglion neurons (SGN), vestibular ganglion neurons (VGNs), and their central projections.

RESULTS

Developing cristae HCs show strong Calb1-positive expression, but adult HCs are mainly Calb2-positive. Utricle and saccule initially have Calb2-positive HCs and later develop Calb1-positive HCs in the striola region. Inner hair cells (IHCs) and outer hair cells (OHCs) in the cochlea express Calb2 early on. Calb1 expression in OHCs overlaps with Calb2; the expression of Myo7a, Calb1, and Calb2 reaches the apex later. SGNs and VGNs exhibit distinct Calb1 and Calb2 patterns but include a subpopulation with mixed expression. Central fibers are Calb1- and Calb2-positive early in the developing cochlear nuclei (CN) and vestibular nuclei (VN) but remain highly Prph-positive. VGNs innervate the lateral and VN, which are positive for Calb2 and Prph. Distinct Calb1-positive neurons overlap with the anterior (A) and ventral (V) cochlear nuclei (AVCN, PVCN) with Calb2, while the dorsal cochlear nucleus (DCN) shows segregation of Calb2 and Calb1.

CONCLUSION

We offer insights into the timing of how neuronal identity and connectivity are regulated in the auditory and vestibular systems, as shown by the expression of Calb1, Calb2, and Prph.