SM30 D is dominant, with only low levels of some of the other forms. This is
unusual since SM30 D is completely missing in the embryo and is a very minor
component in test, teeth, and tube feet. Mann et al. (2008a) have recently published
a very thorough proteomic study of the proteins occluded in the spine; there is a
very large number, including many of those found in embryonic spicules. SM50,
C-lectin-containing proteins, carbonic anhydrase, MSP 130, and proteases were
also well represented.
Most of the characterization of spine growth and maturation has been carried out
by studying the process of spine regeneration, a process known at least since the
mid-nineteenth century. Figure 7.6 depicts the stereom of the tip of a regenerating
spine. Elongation of the spine occurs first in the center of existing truncated
material by deposition of thin trabeculae; subsequently, lateral “branches” of
mineral are laid down and girth is increased. Newly deposited spine is gradually
filled in with additional mineral so that the spongy nature of the stereom decreases
and prominent columns of calcite dominate. A review of studies of spine regeneration by Dubois and Ameye (2001) provides a good overview of the subject.
The nature of the newly deposited mineral at the tip of a regenerating spine has
been studied by Politi et al. (2004). They provided evidence using etching, FTIR,
and electron microscopy that the newly deposited mineral is ACC, initially probably in a hydrated form, which is later gradually transformed into anhydrous ACC
state, and finally into calcite. This is reminiscent of the findings on the growing tip
of the sea urchin embryo spicule, and corroborates the idea that deposition of ACC
as a precursor is a general mode of biomineralization of calcite in echinoderms.
7.5 Recent Work on the Adult Tooth
7.5.1 The Mineral Structure of the Sea Urchin Tooth
Sea urchins use their teeth to bite food, but also to burrow into rocks and shelter
their bodies from predators (Moore 1966; Nelson and Vance 1979) and from
pounding waves (Otter 1932), as seen in Fig. 7.7. In all sea urchins, five teeth are
continuously forming at their proximal end (the plumula) and are worn by grinding
at their distal end (the tooth tip). They are arranged and supported in a jaw-like
apparatus called Aristotle’s lantern (Fig. 7.7), as it was first described by Aristotle
in his Historia Animalium, in 343 BCE.
The tooth structures in several sea urchin species are remarkably similar: the
tooth is elongated, slightly curved, approximately 2-cm long, and it has a T-shape
cross section (Kniprath 1974; Ma et al. 2008; M€ arkel and Titschack 1969; Wang
Fig. 7.5 (continued) are EBSD crystallographic orientation maps according to the same color key
These maps also indicate that the c-axis is parallel to spine long axis. Data from Moureaux et al.
(2010). Reprinted by permission from Elsevier Publishers
212
P.U.P.A Gilbert and F.H. Wilt
unusual since SM30 D is completely missing in the embryo and is a very minor
component in test, teeth, and tube feet. Mann et al. (2008a) have recently published
a very thorough proteomic study of the proteins occluded in the spine; there is a
very large number, including many of those found in embryonic spicules. SM50,
C-lectin-containing proteins, carbonic anhydrase, MSP 130, and proteases were
also well represented.
Most of the characterization of spine growth and maturation has been carried out
by studying the process of spine regeneration, a process known at least since the
mid-nineteenth century. Figure 7.6 depicts the stereom of the tip of a regenerating
spine. Elongation of the spine occurs first in the center of existing truncated
material by deposition of thin trabeculae; subsequently, lateral “branches” of
mineral are laid down and girth is increased. Newly deposited spine is gradually
filled in with additional mineral so that the spongy nature of the stereom decreases
and prominent columns of calcite dominate. A review of studies of spine regeneration by Dubois and Ameye (2001) provides a good overview of the subject.
The nature of the newly deposited mineral at the tip of a regenerating spine has
been studied by Politi et al. (2004). They provided evidence using etching, FTIR,
and electron microscopy that the newly deposited mineral is ACC, initially probably in a hydrated form, which is later gradually transformed into anhydrous ACC
state, and finally into calcite. This is reminiscent of the findings on the growing tip
of the sea urchin embryo spicule, and corroborates the idea that deposition of ACC
as a precursor is a general mode of biomineralization of calcite in echinoderms.
7.5 Recent Work on the Adult Tooth
7.5.1 The Mineral Structure of the Sea Urchin Tooth
Sea urchins use their teeth to bite food, but also to burrow into rocks and shelter
their bodies from predators (Moore 1966; Nelson and Vance 1979) and from
pounding waves (Otter 1932), as seen in Fig. 7.7. In all sea urchins, five teeth are
continuously forming at their proximal end (the plumula) and are worn by grinding
at their distal end (the tooth tip). They are arranged and supported in a jaw-like
apparatus called Aristotle’s lantern (Fig. 7.7), as it was first described by Aristotle
in his Historia Animalium, in 343 BCE.
The tooth structures in several sea urchin species are remarkably similar: the
tooth is elongated, slightly curved, approximately 2-cm long, and it has a T-shape
cross section (Kniprath 1974; Ma et al. 2008; M€ arkel and Titschack 1969; Wang
Fig. 7.5 (continued) are EBSD crystallographic orientation maps according to the same color key
These maps also indicate that the c-axis is parallel to spine long axis. Data from Moureaux et al.
(2010). Reprinted by permission from Elsevier Publishers
212
P.U.P.A Gilbert and F.H. Wilt