HAIR-CELLS AND SUPPORTING CELLS SHARE A COMMON PROGENITOR IN THE AVIAN INNER-EAR

Sensory organs of the vertebrate inner ear contain two major cell type s: hair cells (HCs) and supporting cells (SCs). To study the lineage r elationships between these two populations, replication-defective retr oviral vectors encoding marker genes were delivered to the otic vesicl e of the chicken embryo. The resulting labeled clones were analyzed in the hearing organ of the chicken, called the basilar papilla (BP), af ter cellular differentiation. BPs were allowed to develop for 2 weeks after delivery of the retrovirus, were removed, and were processed his tochemically as whole mounts to identify clones of cells. Clusters of labeled cells were evident in the sensory epithelium, the nonsensory e pithelium, and in adjacent tissues. Labeled cell types included HCs, t wo morphologically distinct types of SCs, homogene cells, border cells , hyaline cells, ganglion cells, and connective tissue cells. Each clo ne was sectioned and cell-type identification was performed on sensory clones expressing retrovirally transduced beta-galactosidase. Cell co mposition was determined for 41 sensory clones, most of which containe d both HCs and SCs. Clones containing one HC and one SC were observed, suggesting that a common progenitor exists that can remain bipotentia l up to its final mitotic division. The possibility that these two cel l types may also arise from a mitotic precursor during HC regeneration in the mature basilar papilla is consistent with their developmental history.