Otolith matrix proteins OMP-1 and Otolin-1 are necessary for normal otolith growth and their correct anchoring onto the sensory maculae.
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.
Murayama
Emi
E
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, 113-8657 Tokyo, Japan. emur@pasteur.fr
Herbomel
Philippe
P
Kawakami
Atsushi
A
Takeda
Hiroyuki
H
Nagasawa
Hiromichi
H
D000595:Amino Acid Sequence; D000818:Animals; D002119:Calcium Carbonate / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D007758:Ear, Inner / Q000196:embryology; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D018715:Microscopy, Video; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000502:physiology*; D051842:Olfactory Marker Protein; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010037:Otolithic Membrane / Q000196:embryology* / Q000502:physiology; D010590:Phalloidine / Q000494:pharmacology; D010641:Phenotype; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D015027:Zebrafish; D029961:Zebrafish Proteins
D018076:DNA, Complementary; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; D051842:Olfactory Marker Protein; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D029961:Zebrafish Proteins; C497600:ompb protein, zebrafish; C449659:otolin-1; D010590:Phalloidine; D002119:Calcium Carbonate