The incorporation and turnover of radiolabelled amino acids in developing stereocilia of the chick cochlea

• Published in: Hearing research Vol. 101; no. 1; pp. 45 - 54
• Main Authors: Pickles, J.O., Billieux-Hawkins, D.A., Rouse, G.W.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.11.1996
• Subjects: Actin; Amino Acids - metabolism; Animals; Anti-Infective Agents, Local - chemistry; Autoradiography; Basilar Membrane - cytology; Basilar Membrane - metabolism; Chick; Chick Embryo; Ciliary Body - metabolism; Cochlea - cytology; Cochlea - metabolism; Development; Formaldehyde - chemistry; Glutaral - chemistry; Hair cell; Hair Cells, Auditory - cytology; Hair Cells, Auditory - metabolism; Image Processing, Computer-Assisted; Isotope Labeling; Polymers - chemistry; Protein; Stereocilia; Tissue Fixation; Turnover; Stereocilia; Actin; Turnover; Development; Hair cell; Chick; Protein
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/S0378-5955(96)00129-3

Hair cell stereocilia are composed of packed actin filaments, oriented such that the preferred end for the addition of actin monomers is at the tips of the stereocilia. It has therefore been suggested that when stereocilia grow, they do so from their tips (Tilney and DeRosier, 1986, Dev. Biol. 116, 119–129). In order to test the hypothesis, radiolabelled amino acids were applied to the air-sac of chicken eggs at day 17 of incubation, i.e., at the beginning of a phase in which the stereocilia have achieved their mature width, but are growing rapidly in length. Incorporation of radiolabel was studied autoradiographically, followed by image analysis and averaging grain counts over many hair cells. In contrast to the position expected from the above hypothesis, there was no sign of preferential incorporation of label in the upper part of the stereociliary bundle. The greatest density of labelling was found in the lower part of the bundle, while the upper part of the bundle was under-represented in the autoradiographic averages. The turnover time (to fall to 1/ e) was significantly greater in the bundle (16 days) than in the cuticular plate or in the rest of the cell (9 days). The results (i) give no support for the hypothesis that stereocilia grow from the tips, and (ii) suggest that during development at least some components of the stereocilia turn over with a relatively short time course.