Fig. 3.

Grafted inner ear progenitor cells integrate into the developing inner ear and differentiate into hair cells. (A) Cross section of the developing chicken inner ear at embryonic day 3.5, 16 h postinjection of ROSA26-derived progenitor cells. β-gal-expressing murine cells invade the epithelium that surrounds the lumen of the otic vesicle (arrow). The arrowhead labels β-gal-positive murine cells that remain in the lumen of the otic vesicle. F-actin labeling reveals disruptions of the epithelium, caused by injury during the grafting procedure. (B-C) Longitudinal section of a developing cochlear sensory epithelium at embryonic day 6, 3 days postinjection, immunolabeled with antibodies for β-gal (B) and myosin VIIA (C). F-actin labeling is shown for orientation. (B) β-gal-positive cells occur in the developing sensory patch. (C) Myosin VIIA-positive early hair cells can be detected in the cochlea at embryonic day 6. Merging the confocal images reveals a patch of myosin VIIA-positive hair cells that express β-gal. β-gal-positive cells observed in the developing supporting cell layer, located below the apical cell layer of early hair cells, do not express myosin VIIA (arrow). (D) At day 14 of embryonic development, 11 days postinjection, we found patches of β-gal-positive cells in inner ear sections. The patch of β-gal-positive cells in a utricular section, here revealed with X-gal histochemistry, is surrounded by cells that did not display blue X-gal staining, which served as negative control for the staining method. (E) Enlargement of an area with β-gal-positive cells exposes espin-positive cells with cylindrical hair cell morphology that display espin-positive hair bundles. (F) Espin-positive hair bundles are rich in F-actin, here apparent as yellow staining in the merged confocal images.