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Matrix recruitment and calcium sequestration for spatial specific otoconia development.

Yang H, Zhao X, Xu Y, Wang L, He Q, Lundberg YW - PLoS ONE (2011)

Bottom Line: In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+).Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins.Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

View Article: PubMed Central - PubMed

Affiliation: Vestibular Neurogenetics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska, United States of America.

ABSTRACT
Otoconia are bio-crystals anchored to the macular sensory epithelium of the utricle and saccule in the inner ear for motion sensing and bodily balance. Otoconia dislocation, degeneration and ectopic calcification can have detrimental effects on balance and vertigo/dizziness, yet the mechanism underlying otoconia formation is not fully understood. In this study, we show that selected matrix components are recruited to form the crystal matrix and sequester Ca(2+) for spatial specific formation of otoconia. Specifically, otoconin-90 (Oc90) binds otolin through both domains (TH and C1q) of otolin, but full-length otolin shows the strongest interaction. These proteins have much higher expression levels in the utricle and saccule than other inner ear epithelial tissues in mice. In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+). In vitro, either Oc90 or otolin can increase the propensity of extracellular matrix to calcify in cell culture, and co-expression has a synergistic effect on calcification. Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins. Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

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Oc90 (A, C) and otolin (B, D) expression levels in murine inner ear.Quantitative real-time RT-PCR (qRT-PCR) showed that both Oc90 and otolin had significantly higher expression levels in the utricle and saccule than the ampulla, canal or cochlea in wt mice. The mRNA levels were normalized to that of β-actin (relative mRNA level), and then different tissues were compared to the utricle and saccule whose relative mRNA level was set to 1 (A, B). In (C, D), the relative mRNA level in the E17.5 cochlea was set to 1. The vestibular samples in C and D mainly consisted of the utricle+saccule with a small part of the ampulla. ** and *** denote p<0.01 and 0.001, respectively, when the utricle+saccule are compared with other tissues (n = 3 for each type of tissue in each age group). ### and $$$ denote p<0.001 when P7 is compared with E17.5 and P0, respectively.
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pone-0020498-g003: Oc90 (A, C) and otolin (B, D) expression levels in murine inner ear.Quantitative real-time RT-PCR (qRT-PCR) showed that both Oc90 and otolin had significantly higher expression levels in the utricle and saccule than the ampulla, canal or cochlea in wt mice. The mRNA levels were normalized to that of β-actin (relative mRNA level), and then different tissues were compared to the utricle and saccule whose relative mRNA level was set to 1 (A, B). In (C, D), the relative mRNA level in the E17.5 cochlea was set to 1. The vestibular samples in C and D mainly consisted of the utricle+saccule with a small part of the ampulla. ** and *** denote p<0.01 and 0.001, respectively, when the utricle+saccule are compared with other tissues (n = 3 for each type of tissue in each age group). ### and $$$ denote p<0.001 when P7 is compared with E17.5 and P0, respectively.

Mentions: In order to examine whether Oc90 and otolin have higher expression levels in the utricle and saccule that may contribute to the spatial restriction of otoconia formation in these tissues, we performed qRT-PCR analysis of inner ear epithelial tissues dissected from E17.5 (embryonic day 17.5), P0 (postnatal day 0) and P7 wt mice. As shown in Figure 3, the expression levels of Oc90 and otolin were 10 to 20 times higher in the utricle and saccule than the cochlea at E17.5 (p<1.4 X10−6 and p<1.6X10−6, respectively, n = 3, indicated by *** in Figure 3). The Oc90 mRNA level in the utricle and saccule drastically reduced at around P7 as compared with that at E17.5 and neonatal (P0) stages (p<7.4X10−6 and p<2.0X10−6, respectively, n = 3, indicated by ### and $$$ in Figure 3C). The vestibular samples in Figure 3C and 3D mainly consisted of the utricle+saccule with a small part of the ampulla. The changes in Oc90 mRNA levels at these stages coincide with the growth and the arrest of growth thereafter of otoconia. In comparison, the otolin mRNA levels show smaller changes across ages. This, together with the relatively late onset of otolin expression in the utricle and saccule, likely reflects a possible role of otolin in crystal growth and maintenance. In contrast, the early onset of Oc90 expression [7]; [8] reflects its role in crystal seeding and growth [10]. The expression of either gene in adult tissues was extremely low (data not shown).


Matrix recruitment and calcium sequestration for spatial specific otoconia development.

Yang H, Zhao X, Xu Y, Wang L, He Q, Lundberg YW - PLoS ONE (2011)

Oc90 (A, C) and otolin (B, D) expression levels in murine inner ear.Quantitative real-time RT-PCR (qRT-PCR) showed that both Oc90 and otolin had significantly higher expression levels in the utricle and saccule than the ampulla, canal or cochlea in wt mice. The mRNA levels were normalized to that of β-actin (relative mRNA level), and then different tissues were compared to the utricle and saccule whose relative mRNA level was set to 1 (A, B). In (C, D), the relative mRNA level in the E17.5 cochlea was set to 1. The vestibular samples in C and D mainly consisted of the utricle+saccule with a small part of the ampulla. ** and *** denote p<0.01 and 0.001, respectively, when the utricle+saccule are compared with other tissues (n = 3 for each type of tissue in each age group). ### and $$$ denote p<0.001 when P7 is compared with E17.5 and P0, respectively.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3105080&req=5

pone-0020498-g003: Oc90 (A, C) and otolin (B, D) expression levels in murine inner ear.Quantitative real-time RT-PCR (qRT-PCR) showed that both Oc90 and otolin had significantly higher expression levels in the utricle and saccule than the ampulla, canal or cochlea in wt mice. The mRNA levels were normalized to that of β-actin (relative mRNA level), and then different tissues were compared to the utricle and saccule whose relative mRNA level was set to 1 (A, B). In (C, D), the relative mRNA level in the E17.5 cochlea was set to 1. The vestibular samples in C and D mainly consisted of the utricle+saccule with a small part of the ampulla. ** and *** denote p<0.01 and 0.001, respectively, when the utricle+saccule are compared with other tissues (n = 3 for each type of tissue in each age group). ### and $$$ denote p<0.001 when P7 is compared with E17.5 and P0, respectively.
Mentions: In order to examine whether Oc90 and otolin have higher expression levels in the utricle and saccule that may contribute to the spatial restriction of otoconia formation in these tissues, we performed qRT-PCR analysis of inner ear epithelial tissues dissected from E17.5 (embryonic day 17.5), P0 (postnatal day 0) and P7 wt mice. As shown in Figure 3, the expression levels of Oc90 and otolin were 10 to 20 times higher in the utricle and saccule than the cochlea at E17.5 (p<1.4 X10−6 and p<1.6X10−6, respectively, n = 3, indicated by *** in Figure 3). The Oc90 mRNA level in the utricle and saccule drastically reduced at around P7 as compared with that at E17.5 and neonatal (P0) stages (p<7.4X10−6 and p<2.0X10−6, respectively, n = 3, indicated by ### and $$$ in Figure 3C). The vestibular samples in Figure 3C and 3D mainly consisted of the utricle+saccule with a small part of the ampulla. The changes in Oc90 mRNA levels at these stages coincide with the growth and the arrest of growth thereafter of otoconia. In comparison, the otolin mRNA levels show smaller changes across ages. This, together with the relatively late onset of otolin expression in the utricle and saccule, likely reflects a possible role of otolin in crystal growth and maintenance. In contrast, the early onset of Oc90 expression [7]; [8] reflects its role in crystal seeding and growth [10]. The expression of either gene in adult tissues was extremely low (data not shown).

Bottom Line: In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+).Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins.Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

View Article: PubMed Central - PubMed

Affiliation: Vestibular Neurogenetics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska, United States of America.

ABSTRACT
Otoconia are bio-crystals anchored to the macular sensory epithelium of the utricle and saccule in the inner ear for motion sensing and bodily balance. Otoconia dislocation, degeneration and ectopic calcification can have detrimental effects on balance and vertigo/dizziness, yet the mechanism underlying otoconia formation is not fully understood. In this study, we show that selected matrix components are recruited to form the crystal matrix and sequester Ca(2+) for spatial specific formation of otoconia. Specifically, otoconin-90 (Oc90) binds otolin through both domains (TH and C1q) of otolin, but full-length otolin shows the strongest interaction. These proteins have much higher expression levels in the utricle and saccule than other inner ear epithelial tissues in mice. In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+). In vitro, either Oc90 or otolin can increase the propensity of extracellular matrix to calcify in cell culture, and co-expression has a synergistic effect on calcification. Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins. Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

Show MeSH
Related in: MedlinePlus