Molecular cloning of otoconin-22 complementary deoxyribonucleic acid in the bullfrog endolymphatic sac: effect of calcitonin on otoconin-22 messenger ribonucleic acid levels.
Anuran amphibians have a special organ called the endolymphatic sac (ELS), containing many calcium carbonate crystals, which is believed to have a calcium storage function. The major protein of aragonitic otoconia, otoconin-22, which is considered to be involved in the formation of calcium carbonate crystals, has been purified from the saccule of the Xenopus inner ear. In this study, we cloned a cDNA encoding otoconin-22 from the cDNA library constructed for the paravertebral lime sac (PVLS) of the bullfrog, Rana catesbeiana, and sequenced it. The bullfrog otoconin-22 encoded a protein consisting of 147 amino acids, including a signal peptide of 20 amino acids. The protein had cysteine residues identical in a number and position to those conserved among the secretory phospholipase A(2) family. The mRNA of bullfrog otoconin-22 was expressed in the ELS, including the PVLS and inner ear. This study also revealed the presence of calcitonin receptor-like protein in the ELS, with the putative seven-transmembrane domains of the G protein-coupled receptors. The ultimobranchialectomy induced a prominent decrease in the otoconin-22 mRNA levels of the bullfrog PVLS. Supplementation of the ultimobranchialectomized bullfrogs with synthetic salmon calcitonin elicited a significant increase in the mRNA levels of the sac. These findings suggest that calcitonin secreted from the ultimobranchial gland, regulates expression of bullfrog otoconin-22 mRNA via calcitonin receptor-like protein on the ELS, thereby stimulating the formation of calcium carbonate crystals in the lumen of the ELS.
Yaoi
Yuichi
Y
Department of Biology, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan.
Suzuki
Masakazu
M
Tomura
Hideaki
H
Sasayama
Yuichi
Y
Kikuyama
Sakae
S
Tanaka
Shigeyasu
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002116:Calcitonin / Q000494:pharmacology*; D002119:Calcium Carbonate / Q000032:analysis; D002135:Calcium-Binding Proteins; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D004712:Endolymphatic Sac / Q000737:chemistry*; D015870:Gene Expression / Q000187:drug effects; D015723:Gene Library; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009928:Organ Specificity; D012333:RNA, Messenger / Q000032:analysis*; D011892:Rana catesbeiana; D018003:Receptors, Calcitonin / Q000032:analysis / Q000235:genetics; D016415:Sequence Alignment; D014460:Ultimobranchial Body / Q000502:physiology; D029867:Xenopus Proteins
D002135:Calcium-Binding Proteins; D018076:DNA, Complementary; D006023:Glycoproteins; D012333:RNA, Messenger; D018003:Receptors, Calcitonin; D029867:Xenopus Proteins; C081347:otocinin-22 protein, Xenopus; D002116:Calcitonin; D002119:Calcium Carbonate