Materials Science

Factoring the Growth

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Science  09 Nov 2012:
Vol. 338, Issue 6108, pp. 723
DOI: 10.1126/science.338.6108.723-a
CREDIT: KIRT L. ONTHANK/WIKIMEDIA COMMONS

Many organisms, including diatoms, create very complex single-crystal mineral structures, whose shaping and patterning are regulated by a small number of proteins. It has been a challenge to decipher which proteins are fundamental to the process, and conversely, how close to the biological shapes one can get by growing the crystals in vitro using only a limited set of proteins. For sea urchins, the construction of the magnesian calcite endoskeleton is controlled by a single cell type—the primary mesenchyme cells (PMCs). Knapp et al. exploited this well-defined system to explore the role of recombinant vascular endothelial growth factor (rVEGF), which acts as a signaling molecule, on the shape and crystallography of the spicules that form when the PMCs are cultured in vitro. At low concentrations of rVEGF, linear spicules formed with growth parallel to the calcite c axis, but at much higher concentrations a triple branch point formed, with elongated arms growing parallel to the a-axis. Close to the branch point, the three arms were 120° apart, but these angles changed once the arms grew past 7 µm, which may explain why in sea urchins they are limited to 3 to 5 µm in size.

J. Am. Chem. Soc. 10.1021/ja309024b (2012).

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