Calcification processes in the chick otoconia and calcium binding proteins: patterns of tetracycline incorporation and calbindin-D28K distribution

In order to clarify the otoconia formation and turnover, tetracycline, an a ntibiotic that precipitates at calcifying fronts and serves as a fluorescen t marker, was injected into eggs at different stages of chick embryonic dev elopment, as well as into postnatal chicken and into adult animals. The cha nges in the intensity, location patterns and time course of fluorescent lab elling in each examined stage in the otolithic organs was studied. The pres ence and distribution of calbindin (CB)-D28K, one of the calcium-binding pr oteins constantly found in the mammalian and chicken cochlea and also in ot olithic membrane of some adult mammals, was studied. Results in embryonal s tages, postnatal and adult animals allow us to postulate that otoliths are mainly produced during the embryonal phase, but they may also be produced t hroughout the whole life span. Results also indicate that otoconia are dyna mic structures which undergo turnover. The correspondence between the patte rns of CB-D28K immunoreactivity and tetracycline fluorescence may indicate that CB-D28K participates in the formation of otoconia. (C) 2000 Elsevier S cience B.V. All rights reserved.