[Frontiers in Bioscience 16, 2540-2560, June 1, 2011]

Organic Matrix-related mineralization of sea urchin spicules, spines, test and teeth

Arthur Veis

Feinberg School of Medicine, Northwestern University, Department of Cell and Molecular Biology, 303 E. Chicago Avenue, Chicago Illinois, USA


1. Abstract
2. Introduction
3. Body plan and skeletal elements of the mature echinoid, Lytechinus variegatus (Lv)
3.1. Teeth and masticatory structure
3.2. Spines and body wall
3.3. Pluteus and embryonic spicule formation
4. Protein components of the sea urchin skeletal elements and biomineralization
5. Biochemical and immunological identification of mineralization related proteins
6. Categorizing the mineralization-related genomic sequences
7. The potential role of phosphopeptides in calcite mineralization processes
8. Prospects for the future
9. Acknowledgements
10. References


The camarodont echinoderms have five distinct mineralized skeletal elements: embryonic spicules, mature test, spines, lantern stereom and teeth. The spicules are transient structural elements whereas the spines, and test plates are permanent. The teeth grow continuously. The mineral is a high magnesium calcite, but the magnesium content is different in each type of skeletal element, varying from 5 to 40 mole% Mg. The organic matrix creates the spaces and environments for crystal initiation and growth. The detailed mechanisms of crystal regulation are not known, but acidic and phosphorylated matrix proteins may be of special importance. Biochemical studies, sequencing of the complete genome, and high-throughput proteomic analysis have not yet provided insight into the mechanisms of crystallization, calcite composition, and orientation applicable to all skeletal elements. The embryonic spicules are not representative of the mature skeletal elements. The next phase of research will have to focus on the specific localization of the proteins and individual biochemistries of each system with regard to mineral content and placement.