Otolith matrix proteins OMP-1 and Otolin-1 are necessary for normal otolith growth and their correct anchoring onto the sensory maculae

• Published in: Mechanisms of development Vol. 122; no. 6; pp. 791 - 803
• Main Authors: Murayama, Emi, Herbomel, Philippe, Kawakami, Atsushi, Takeda, Hiroyuki, Nagasawa, Hiromichi
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 01.06.2005
• Subjects: Amino Acid Sequence; Animals; Biomineralization; Calcium Carbonate - metabolism; Cloning, Molecular; DNA, Complementary - metabolism; Ear, Inner - embryology; Extracellular Matrix Proteins - physiology; Gene Expression Regulation, Developmental; In Situ Hybridization; Matrix protein; Microscopy, Video; Molecular Sequence Data; Morpholino; Nerve Tissue Proteins - physiology; Olfactory Marker Protein; Oligonucleotides, Antisense - pharmacology; Otolith; Otolithic Membrane - embryology; Otolithic Membrane - physiology; Phalloidine - pharmacology; Phenotype; Protein Structure, Tertiary; RNA, Messenger - metabolism; Time Factors; Zebrafish; Zebrafish Proteins; Biomineralization; Zebrafish; Matrix protein; Morpholino; Otolith
• ISSN: 0925-4773; 1872-6356
• DOI: 10.1016/j.mod.2005.03.002

Fish otoliths are highly calcified concretions deposited in the inner ear and serve as a part of the hearing and balance systems. They consist mainly of calcium carbonate and a small amount of organic matrix. The latter component is considered to play important roles in otolith formation. Previously, we identified two major otolith matrix proteins, OMP-1 ( otolith matrix protein-1) and Otolin-1, from salmonid species. To assess the function of these proteins in otolith formation, we performed antisense morpholino oligonucleotide (MO)-mediated knockdown of omp-1 and otolin-1 in zebrafish embryos. We first identified zebrafish cDNA homologs of omp-1 ( zomp-1) and otolin-1 ( zotolin-1). Whole-mount in situ hybridization then revealed that the expression of both zomp-1 and zotolin-1 mRNAs is restricted to the otic vesicles. zomp-1 mRNA was expressed from the 14-somite stage in the otic placode, but the zOMP-1 protein was detected only from 26-somite stage onwards. In contrast, zotolin-1 mRNA expression became clear around 72 hpf. MOs designed to inhibit zomp-1 and zotolin-1 mRNA translation, respectively, were injected into 1–2 cell stage embryos. zomp-1 MO caused a reduction in otolith size and an absence of zOtolin-1 deposition, while zotolin-1 MO caused a fusion of the two otoliths, and an increased instability of otoliths after fixation. We conclude that zOMP-1 is required for normal otolith growth and deposition of zOtolin-1 in the otolith, while zOtolin-1, a collagenous protein, is involved in the correct arrangement of the otoliths onto the sensory epithelium of the inner ear and probably in stabilization of the otolith matrix.