Chapter 7
Molecular Aspects of Biomineralization
of the Echinoderm Endoskeleton
P.U.P.A. Gilbert and Fred H. Wilt
Contents
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
7.2 Formation of the Endoskeleton in the Embryo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
7.2.1 Spicule Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
7.2.2 Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
7.2.3 Occluded Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
7.2.4 Formation of Postembryonic Skeletal Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
7.2.5 Recent Work on the Structure and Composition
of the Embryonic Spicule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
7.3 ACC: Discovery, Importance, and Implications in Other Systems . . . . . . . . . . . . . . . . . . . . . 208
7.4 Recent Work on the Adult Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
7.5 Recent Work on the Adult Tooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.5.1 The Mineral Structure of the Sea Urchin Tooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.5.2 Matrix Proteins of the Tooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
7.6 Generalizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Abstract Echinoderms possess a rigid endoskeleton composed of calcite and small
amounts of occluded organic matrix proteins. The test (i.e., the shell-like structure
of adults), spines, pedicellariae, tube feet, and teeth of adults, as well as delicate
endoskeletal spicules found in larvae of some classes, are the main skeletal
structures. They have been intensively studied for insight into the mechanisms of
biomineralization. Recent work on characterization of the mineral phase and
occluded proteins in embryonic skeletal spicules shows that these simple-looking
structures contain scores of different proteins, and that the mineral phase is composed of amorphous calcium carbonate (ACC), which then transforms to an
P.U.P.A. Gilbert (*)
Department of Physics, University of Wisconsin-Madison, 1150 University Ave, Madison,
WI 53706, USA
e-mail: pupa@physics.wisc.edu
W.E.G. M€ uller (ed.), Molecular Biomineralization, Progress in Molecular
and Subcellular Biology 52, DOI 10.1007/978-3-642-21230-7_7,
# Springer-Verlag Berlin Heidelberg 2011
199
Molecular Aspects of Biomineralization
of the Echinoderm Endoskeleton
P.U.P.A. Gilbert and Fred H. Wilt
Contents
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
7.2 Formation of the Endoskeleton in the Embryo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
7.2.1 Spicule Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
7.2.2 Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
7.2.3 Occluded Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
7.2.4 Formation of Postembryonic Skeletal Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
7.2.5 Recent Work on the Structure and Composition
of the Embryonic Spicule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
7.3 ACC: Discovery, Importance, and Implications in Other Systems . . . . . . . . . . . . . . . . . . . . . 208
7.4 Recent Work on the Adult Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
7.5 Recent Work on the Adult Tooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.5.1 The Mineral Structure of the Sea Urchin Tooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.5.2 Matrix Proteins of the Tooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
7.6 Generalizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Abstract Echinoderms possess a rigid endoskeleton composed of calcite and small
amounts of occluded organic matrix proteins. The test (i.e., the shell-like structure
of adults), spines, pedicellariae, tube feet, and teeth of adults, as well as delicate
endoskeletal spicules found in larvae of some classes, are the main skeletal
structures. They have been intensively studied for insight into the mechanisms of
biomineralization. Recent work on characterization of the mineral phase and
occluded proteins in embryonic skeletal spicules shows that these simple-looking
structures contain scores of different proteins, and that the mineral phase is composed of amorphous calcium carbonate (ACC), which then transforms to an
P.U.P.A. Gilbert (*)
Department of Physics, University of Wisconsin-Madison, 1150 University Ave, Madison,
WI 53706, USA
e-mail: pupa@physics.wisc.edu
W.E.G. M€ uller (ed.), Molecular Biomineralization, Progress in Molecular
and Subcellular Biology 52, DOI 10.1007/978-3-642-21230-7_7,
# Springer-Verlag Berlin Heidelberg 2011
199