Expression of EphA4 in developing inner ears of the mouse and guinea pig

The expression of EphA4, an Eph-class receptor tyrosine kinase, was determi ned by immunohistochemistry in developing inner ears of the mouse and the g uinea pig. In the mouse, EphA4 expression was visible in the fibroblasts of the spiral ligament and in the structures that were to become the osseous spiral lamina. Cochlear nerve ganglion cells expressed ephrin-B2, and the m odiolus expressed mRNA coding for ephrin-B3, both transmembrane ligands for EphA4. In contrast, in the guinea pig, cells of the cochlear nerve ganglio n expressed EphA4, as did supporting cells of the organ of Corti (Wensen's cells and inner pillar cells). There was also some expression in fibroblast s of the spiral ligament but none in the structures that were to become the osseous spiral lamina. It is suggested that in the mouse, EphA4 may help d irect the cochlear innervation towards the organ of Corti by a repulsive in teraction, but that this is highly species dependent. (C) 2000 Elsevier Sci ence B.V. All rights reserved.