Untitled

Abstract

We investigated nucleotide-labeling patterns during ongoing hair cell regeneration in the avian vestibular epithelium and during drug-induced regeneration in the avian auditory epithelium. For utricle experiments, post-hatch chicks received an injection of bromodeoxyuridine (BrdU) and were allowed to survive from 2 hours to 110 days after the injection. Utricles were fixed and immunoreacted to detect BrdU. The number of BrdU-labeled nuclei in the hair cell and support cell layers of the utricular sensory epithelium changes significantly between 2 hours and 110 days post-BrdU. At 2 hours, most labeled cells are isolated, while by 5-10 days, the majority of labeled cells are organized in pairs that are most frequently composed of a hair cell and a support cell. Pairs of labeled cells are seen as late as 110 days. Clusters of more than 3 labeled cells are uncommon at all time-points. The total number of labeled cells increases approximately 1.5-fold between 5 and 60 days post-BrdU. This increase is due primarily to a rise in the number of labeled support cells, and it is likely that it represents additional rounds of division by a subset of cells that were labeled at the time of the BrdU injection. There is a significant decrease in labeled nuclei in the hair cell layer between 60 and 110 days post-BrdU, suggesting that hair cells die during this period. To investigate support cell recycling in the drug-damaged auditory epithelium, we examined nucleotide double labeling after separate injections of BrdU and tritiated thymidine. A small number of support cells that incorporate BrdU administered at 3 days post-gentamicin treatment also label with tritiated thymidine administered between 17 and 38 hours later. We conclude that a small population of support cells recycles during regeneration in both the normal utricle and the drug-damaged basilar papilla.

Cellular studies of auditory hair cell regeneration in birds

“…We detected only very limited incorporation of two nucleotide analogs into the same progenitor cells when each nucleotide was administered separately at intervals estimated to mimic the average cycling time of mature eukaryotic cells. In contrast, recycling of progenitor cells occurs to a very high degree (70%) in the saccules of normal oscars (36) and to a more limited extent in the utricles of control chicks (30,36).…”

“…The total number of BrdUrd-labeled cells increased significantly, and clusters of labeled cells appeared to grow in size, suggesting growth of a colony of cells from one progenitor. However, a second study (30) suggests that progenitor cell recycling is in fact rare in the drug-damaged basilar papilla. We detected only very limited incorporation of two nucleotide analogs into the same progenitor cells when each nucleotide was administered separately at intervals estimated to mimic the average cycling time of mature eukaryotic cells.…”

“…Supporting cell entry into the cell cycle is detected by 18-24 h after the onset of the damaging stimulus to the basilar papilla (15,23,24,27,29,30). This delay reflects the latency of the triggering stimulus for cell proliferation plus the time required for supporting cells to progress from the growth-arrested state to S phase.…”

“…This delay reflects the latency of the triggering stimulus for cell proliferation plus the time required for supporting cells to progress from the growth-arrested state to S phase. The level of supporting cell proliferation peaks within 2-3 days after the onset of the stimulus, and it returns to normal levels by 7-9 days (19,23,24,30). Patterns of cell proliferation spatially and temporally mirror the progression of hair cell loss (31).…”

“…Fekete et al (112) used retroviral lineage analysis in the chick otocyst to show that hair cells and supporting cells in the basilar papilla often arise from a single progenitor cell division. Additional studies have shown that similar asymmetric differentiation predominates as the mode of cell production in the normal chick utricle (7,30,79) and the salamander lateral line organ (67). Asymmetric cell production is used during the ontogeny of many tissue types in a wide variety of species (reviewed in ref.…”