![pclp scholar pclp scholar](https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs10570-020-03675-9/MediaObjects/10570_2020_3675_Fig4_HTML.png)
Furthermore, the inner ear in fish is also easily accessible for further manipulations such as injection of pharmacological substances, which have been shown to directly influence otolith biomineralization (Faucher et al., 2009). These ear stones are an appropriate system in which to investigate the process of biomineralization, because their mineralization takes place in the closed environment of the inner ear and the otoliths are easy to remove without any other tissue residues. The otoliths of fish assist with balance, spatial orientation and hearing, whereas mammalian otoconia only function in balance and spatial orientation. In contrast to bone, which is cellular and consists of calcium phosphate, the acellular otoliths (ear stones of fish) and otoconia (ear crystals of mammals) of the inner ear are composed of calcium carbonate. The underlying biomineralization process is based on proteins that control the incorporation and aggregation of inorganic substances.
![pclp scholar pclp scholar](https://pbs.twimg.com/media/DBQYJtgUQAA2mp_.jpg)
Vertebrates have a variety of calcified structures that include bones, teeth, scales and otoliths. secreted protein acidic and rich in cysteine.Further functional studies of the novel proteins we identified during otolith development are required. mossambicus does not have all of the known otolith proteins indicating that the matrix proteins in the inner ear of fish are not the same across species. In further analyses, we show that the absence of the OMP starmaker corresponds to calcitic otoliths and that pre-cerebellin-like protein is not present at any stage during the development of the otoliths of the inner ear. Moreover, we were able to exclude the occurrence of two matrix proteins (starmaker and pre-cerebellin-like protein) known from other fish species. These include the common otolith matrix proteins (OMP-1, otolin-1, neuroserpin, SPARC and otoconin), and three proteins (alpha tectorin, otogelin and transferrin) not previously localized to the otoliths. Using this method we identified eight proteins in the inner ear of Oreochromis mossambicus. For this purpose, an enhanced protein purification technique was developed that excludes any potential contamination of proteins from body fluids. We analyzed the composition of this proteinous matrix by mass spectrometry in a shotgun approach. This matrix consists of macromolecules, which directly control the biomineralization process. The fish ear stones (otoliths) consist mainly of calcium carbonate and have lower amounts of a proteinous matrix.