The involvement of arl-5b in the repair of hair cells in sea anemones

Proteomic identification of hair cell repair proteins in the model sea anemone Nematostella vectensis

Sea anemones have an extraordinary capability to repair damaged hair bundles, even after severe trauma. A group of secreted proteins, named repair proteins (RPs), found in mucus covering sea anemones significantly assists the repair of damaged hair bundle mechanoreceptors both in the sea anemone Haliplanella luciae and the blind cavefish Astyanax hubbsi. The polypeptide constituents of RPs must be identified in order to gain insight into the molecular mechanisms by which repair of hair bundles is accomplished. In this study, several polypeptides of RPs were isolated from mucus using blue native PAGE and then sequenced using LC-MS/MS. Thirty-seven known polypeptides were identified, including Hsp70s, as well as many polypeptide subunits of the 20S proteasome. Other identified polypeptides included those involved in cellular stress responses, protein folding, and protein degradation. Specific inhibitors of Hsp70s and the 20S proteasome were employed in experiments to test their involvement in hair bundle repair. The results of those experiments suggested that repair requires biologically active Hsp70s and 20S proteasomes. A model is proposed that considers the function of extracellular Hsp70s and 20S proteasomes in the repair of damaged hair cells.

Noise-induced hearing loss: new animal models

PURPOSE OF THE REVIEW

This article presents research findings from two invertebrate model systems with potential to advance both the understanding of noise-induced hearing loss mechanisms and the development of putative therapies to reduce human noise damage.

RECENT FINDINGS

Work on sea anemone hair bundles, which resemble auditory hair cells, has revealed secretions that exhibit astonishing healing properties not only for damaged hair bundles, but also for vertebrate lateral line neuromasts. We present progress on identifying functional components of the secretions, and their mechanisms of repair. The second model, the Johnston's organ in Drosophila, is also genetically homologous to hair cells and shows noise-induced hearing loss similar to vertebrates. Drosophila offers genetic and molecular insight into noise sensitivity and pathways that can be manipulated to reduce stress and damage from noise.

SUMMARY

Using the comparative approach is a productive avenue to understanding basic mechanisms, in this case cellular responses to noise trauma. Expanding study of these systems may accelerate identification of strategies to reduce or prevent noise damage in the human ear.

Repair of hair cells following mild trauma may involve extracellular chaperones

Sea anemones were subjected to mild trauma consisting of a 2 min immersion in calcium-depleted seawater. The trauma caused a loss of vibration sensitivity that spontaneously recovered within 50 min of returning the anemones to calcium containing seawater. Apparently, recovery is conferred by proteins contained in fraction gamma, a chromatographic fraction of homogenized mucus collected at the base of anemones allowed to recover from similar trauma. On silver stained SDS-PAGE gels, fraction gamma consists of a single band having an estimated mass of 55 kDa. Fraction gamma is alone sufficient to repair hair bundle mechanoreceptors in anemones. Its biological activity is enhanced in the presence of exogenously supplied ATP, but not GTP nor ADP-ribose. Biotinylated fraction gamma binds to hair bundles. The hypothesis that fraction gamma consists of Hsp60 proteins was tested. Commercial antibodies to Hsp60 label a band at 55 kDa in western blots. Hsp60 antibodies label hair bundles in traumatized anemones but not in untreated controls. Dilute Hsp60 antiserum (but not nonimmune serum) delays the spontaneous recovery of vibration sensitivity in anemones subjected to mild trauma. Thus, fraction gamma likely consists of Hsp60, or a Hsp60-like protein, that functions on the extracellular face of the plasma membrane to restore function to traumatized hair bundles.