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Proc Natl Acad Sci U S A. 2014 Jan 7;111(1):39-44. doi: 10.1073/pnas.1312833110. Epub 2013 Dec 16.

Initial stages of calcium uptake and mineral deposition in sea urchin embryos.

Author information

1
Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel.

Abstract

Sea urchin larvae have an endoskeleton consisting of two calcitic spicules. We reconstructed various stages of the formation pathway of calcium carbonate from calcium ions in sea water to mineral deposition and integration into the forming spicules. Monitoring calcium uptake with the fluorescent dye calcein shows that calcium ions first penetrate the embryo and later are deposited intracellularly. Surprisingly, calcium carbonate deposits are distributed widely all over the embryo, including in the primary mesenchyme cells and in the surface epithelial cells. Using cryo-SEM, we show that the intracellular calcium carbonate deposits are contained in vesicles of diameter 0.5-1.5 μm. Using the newly developed airSEM, which allows direct correlation between fluorescence and energy dispersive spectroscopy, we confirmed the presence of solid calcium carbonate in the vesicles. This mineral phase appears as aggregates of 20-30-nm nanospheres, consistent with amorphous calcium carbonate. The aggregates finally are introduced into the spicule compartment, where they integrate into the growing spicule.

KEYWORDS:

biomineralization; intracellular mineral deposition; mineralization pathway; sea urchin embryonic spicule; transient precursor mineral phase

PMID:
24344263
PMCID:
PMC3890786
DOI:
10.1073/pnas.1312833110
[Indexed for MEDLINE]
Free PMC Article

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