Regenerated hair cells can originate from supporting cell progeny: evidence from phototoxicity and laser ablation experiments in the lateral line system

Abstract

The mechanisms that lead to the production of sensory hair cells during regeneration have been investigated by using 2 different procedures to ablate preexisting hair cells in individual neuromast sensory epithelia of the lateral line in the tails of salamanders, then monitoring the responses of surviving cells. In one series of experiments, fluorescent excitation was used to cause the phototoxic death of hair cells that selectively take up the pyridinium dye DASPEI. In the other experiments, the ultraviolet output of a pulsed neodymium-YAG laser was focused to a microbeam through a quartz objective lens in epi-illumination mode and used to selectively kill individual unlabeled hair cells while the cells were simultaneously imaged by transmitted light DIC microscopy. Through observation of the treated neuromasts in vivo, these experiments demonstrated that mature sensory epithelia that have been completely depleted of hair cells can still generate new hair cells. Preexisting hair cells are not necessary for regeneration. Immediately after the ablations the only resident cells in the sensory epithelia were supporting cells. These cells were observed to divide at rates that were increased over control values, and eventually those cell divisions gave rise to progeny that differentiated as hair cells, replacing those that had been killed. Macrophages were active in these epithelia, and their phagocytic activity had a significant influence on the standing population of cells. The first new hair cells appeared 3-5 d after the treatments, and additional hair cells usually appeared every 1-2 d for at least 2 weeks. We conclude that the fate of the progeny produced by supporting cell divisions is plastic to a degree, in that these progeny can differentiate either as supporting cells or as hair cells in epithelia where hair cells are missing or depleted.

Neuroanatomical evidence for segregation of nerve fibers conveying light touch and pain sensation in Eimer’s organ of the mole

“…Styryl pyridinium dyes have been shown to label mechanosensory cells (10)(11)(12)(13)(14)(15)(16)(17)(18). In this study we used AM1-43, the fixable analog of the styryl pyridinium dye FM1-43 (19), to identify and examine the presumptive mechanosensory receptors in the rhinarium of the mole.…”

Hair Cell Differentiation in Chick Cochlear Epithelium after Aminoglycoside Toxicity:In VivoandIn VitroObservations

“…Some animals demonstrate the capacity to generate hair cells throughout their lifetime (Popper and Hoxter, 1984;Corwin, 1985;Jörgenson and Mathiessen, 1989;Roberson et al, 1992) or to initiate hair cell regeneration in the event of their loss (Corwin and Cotanche, 1988;Ryals and Rubel, 1988). The progenitors of hair cells seem to be a subset of support cells that reside adjacent to hair cells in the sensory epithelia (Girod et al, 1989;Balak et al, 1990;Raphael, 1992;Hashino and Salvi, 1993;Weisleder and Rubel, 1993;Stone and Cotanche, 1994;Tsue et al, 1994a;Roberson et al, 1996). Although mature mammals normally do not generate new hair cells, recent in vivo and in vitro studies have documented mitotic activity and immature-looking hair cells in mammalian vestibular epithelia after exposure to ototoxic drugs Warchol et al, 1993;Rubel et al, 1995), suggesting that hair cell regeneration in mammals may be inducible.…”

“…Second, support cells undergo significant morphological changes by 2 d in vitro, including attachment to a laminin substratum, and flattening and spreading, which may also stimulate support cell division. Third, dying hair cells in vitro may release factors that are mitogenic for support cells (Balak et al, 1990;Hashino and Salvi, 1993;Stone and Cotanche, 1994;Bhave et al, 1995).…”

A two-step mechanism underlies the planar polarization of regenerating sensory hair cells

“…Furthermore, the long periods needed by some animals to regenerate hair cells pose severe limitations to analyzing the process continuously. Attempts to monitor cellular behavior in neuromasts after hair-cell ablation in salamanders suffered from the absence of cellular and molecular markers (13), which prevented the unambiguous identification of cellular types and the analysis of the recovery of epithelial architecture upon regeneration. In this study, we used the lateral-line system of the zebrafish to circumvent these limitations and to acquire time-lapse sequences of hair-cell formation and regeneration.…”