Depleting circulating galectin-3 with therapeutic apheresis: a noveltreatment for sepsis/AKI - otoliths ("ear stones") of RAY-finned fish and the homologous otoconia ("ear dust") of tetrapods are…

Depleting circulating galectin-3 with therapeutic apheresis: a noveltreatment for sepsis/AKI - otoliths ("ear stones") of RAY-finned fish and the homologous otoconia ("ear dust") of tetrapods are acellular accretions of protein and more than 95% calcium carbonate that often display strikingly elaborate shapes. They convey linear accelerations to sensory hair cells in the utricle, saccule, and lagena and are, therefore, essential components of the vestibular apparatus. They also are involved in one of the most common human balance disorders, benign paroxysmal positional vertigo, in which otoconia are displaced into the semicircular canals. The growth and accumulation of otoliths and otoconia precisely matches their underlying sensory maculae; however, we know very little about the mechanism that regulate this process. Studies of other biominerals suggest that the constituent proteins play critical roles. One class of proteins, the large and insoluble framework proteins, form a matrix for the biomineral to grow in; their local secretion determines the site of morphogenesis. A second class, the highly charged control proteins, interact with the ions and promote or inhibit nucleation or the growth of specific crystallographic faces, thus determining the biomineral's shape. Unfortunately, one cannot test this model because the identities of most of the proteins in otoliths and otoconia are unknown. We intend to remedy this situtation by taking advantage of the unique combination of experimental approaches possible with the zebrafish, danio rerio. We will identify its otolith proteins by sequencing peptides and mining its genome assembly; we will examine if the proteins' expression patterns correlate with the sites of otolith formation; and we will probe the proteins' function by manipulating their expression and analyzing mutants with otolith defects. We will learn from these experiments whether the formation of otoliths and otoconia is governed by the same fundamental principles as that of other biominerals. For future studies of the physiology and pathology of their morphogenesis, we will have developed molecular probes and learned the targets of regulation.