Figure 5.

Gustatory innervation of fungiform papillae is reduced in EphB1^−/−/EphB2^−/− mice. Geniculate afferents were labeled by applying DiI at the geniculate ganglion in fixed embryos (see Methods). A. In E13.5 wild type (WT) mice (A) we observed extensive nerve labeling, presumably just below the dorsal epithelium. EphB1^−/−/EphB2^−/− mice exhibited the same pattern of innervation, but labeling was somewhat less intense. B. At E15.5, after the afferents have entered the fungiform papilla epithelium, EphB1^−/−/EphB2^−/− mice again exhibit a slight decrease in the amount of innervation. C. At E17.5 there was qualitatively much less innervation by geniculate axons in EphB1^−/−/EphB2^−/− mice than in wild type mice. To quantify this phenomenon we prepared parasagittal vibratome sections of the E17.5 tongues and measured the width of the nerve bundle just below the point of arborization within the pre-taste bud (arrowheads in insets). The average thickness of DiI labeled geniculate nerve bundles was significantly less in mutant tongues than wild type tongues (see Results). Calibration bar in A = 500 μm and applies to A–C, except the insets in C, in which the calibration bar = 25 μm.