216
“The fi ne structural features of collar enamel in Polypterus are similar to those
of tooth enamel in Lepisosteus (gars), coelacanths, lungfi sh and amphibians. The
enamel matrix shows intense immunoreactivity to the antibody and antiserum
against mammalian amelogenins, and to the middle region- and C-terminalspecifi c anti-amelogenin antibodies. These fi ndings suggest that the proteins in
the enamel of Polypterus contain domains that closely resemble those of bovine
and porcine amelogenins. The enamel matrix, which exhibits positive immunoreactivity to mammalian amelogenins, extends to the cap enameloid surface.
This implies that amelogenin-like proteins are secreted by ameloblasts as a thin
matrix layer that covers the cap enameloid after enameloid maturation,”
(Sasagawa et al. 2012 ).
Enameloid is an example of hypermineralized enamel-like tissue with unique
pattern of mineralization (Sasagawa 2002 ; Sasagawa et al. 2009 ) that contains ectomesenchymal and ectodermal proteins. Scales of many fossil fi sh are the best location of the enameloid. It is assumed that the enameloid is an analogue of mammalian
enamel, because the origin of enameloid is somewhat different from that of enamel
(Sasagawa et al. 2006 ). According to Meinke ( 1986 ): “Enameloid is distinct from
enamel in that enameloid develops prior to dentine and consists primarily of collagenous matrix that is deposited by odontoblasts,” (Meinke 1986 ). While amelogenesis in mammals is a major subject of basic dental sciences, enameloid formation
in bony fi shes is paid little attention, so there are still many unclear aspects of
enameloid formation.
The origin and evolution of both enamel and enameloid mineralization are well
debated subjects from chemical, biochemical and genetic points of view. Enamel
and enameloid were identifi ed in early jawless vertebrates, about 500 million years
ago. This suggests that enamel matrix proteins (EMPs) have at least the same age
(Sire et al. 2007 ).
Three EMPs are secreted by ameloblasts during enamel formation: amelogenin
(AMEL), ameloblastin (AMBN) and enamelin (ENAM). It was hypothesized, that
“the full-length amelogenin uniquely regulates proper enamel formation through a
process of cooperative mineralization, and not as a pre-formed matrix,” (Margolis
et al. 2006 ). Recently, two new genes, amelotin (AMTN) and odontogenic ameloblast associated (ODAM), were found to be expressed by ameloblasts during maturation, increasing the group of ameloblast-secreted proteins to fi ve members (Sire
et al. 2007 ). The evolutionary analysis of these fi ve genes indicates that they are
related: AMEL is derived from AMBN, AMTN and ODAM are sister genes, and all
are derived from ENAM. Kawasaki et al. ( 2004 ) reported that they found genes for
three major enamel ECM proteins (AMEL, AMBN, and ENAM) and fi ve dentin
bone ECM proteins:
– “dentine sialophosphoprotein (DSPP),
– dentine matrix acidic phosphoprotein 1 (DMP1),
– integrin-binding sialoprotein (IBSP),
– matrix extracellular, phosphoglycoprotein (MEPE),
– Osteopontin, or secreted phosphoprotein 1 (SPP1),” (Kawasaki et al. 2004 ).
4 Fish Scales as Mineral-Based Composites
“The fi ne structural features of collar enamel in Polypterus are similar to those
of tooth enamel in Lepisosteus (gars), coelacanths, lungfi sh and amphibians. The
enamel matrix shows intense immunoreactivity to the antibody and antiserum
against mammalian amelogenins, and to the middle region- and C-terminalspecifi c anti-amelogenin antibodies. These fi ndings suggest that the proteins in
the enamel of Polypterus contain domains that closely resemble those of bovine
and porcine amelogenins. The enamel matrix, which exhibits positive immunoreactivity to mammalian amelogenins, extends to the cap enameloid surface.
This implies that amelogenin-like proteins are secreted by ameloblasts as a thin
matrix layer that covers the cap enameloid after enameloid maturation,”
(Sasagawa et al. 2012 ).
Enameloid is an example of hypermineralized enamel-like tissue with unique
pattern of mineralization (Sasagawa 2002 ; Sasagawa et al. 2009 ) that contains ectomesenchymal and ectodermal proteins. Scales of many fossil fi sh are the best location of the enameloid. It is assumed that the enameloid is an analogue of mammalian
enamel, because the origin of enameloid is somewhat different from that of enamel
(Sasagawa et al. 2006 ). According to Meinke ( 1986 ): “Enameloid is distinct from
enamel in that enameloid develops prior to dentine and consists primarily of collagenous matrix that is deposited by odontoblasts,” (Meinke 1986 ). While amelogenesis in mammals is a major subject of basic dental sciences, enameloid formation
in bony fi shes is paid little attention, so there are still many unclear aspects of
enameloid formation.
The origin and evolution of both enamel and enameloid mineralization are well
debated subjects from chemical, biochemical and genetic points of view. Enamel
and enameloid were identifi ed in early jawless vertebrates, about 500 million years
ago. This suggests that enamel matrix proteins (EMPs) have at least the same age
(Sire et al. 2007 ).
Three EMPs are secreted by ameloblasts during enamel formation: amelogenin
(AMEL), ameloblastin (AMBN) and enamelin (ENAM). It was hypothesized, that
“the full-length amelogenin uniquely regulates proper enamel formation through a
process of cooperative mineralization, and not as a pre-formed matrix,” (Margolis
et al. 2006 ). Recently, two new genes, amelotin (AMTN) and odontogenic ameloblast associated (ODAM), were found to be expressed by ameloblasts during maturation, increasing the group of ameloblast-secreted proteins to fi ve members (Sire
et al. 2007 ). The evolutionary analysis of these fi ve genes indicates that they are
related: AMEL is derived from AMBN, AMTN and ODAM are sister genes, and all
are derived from ENAM. Kawasaki et al. ( 2004 ) reported that they found genes for
three major enamel ECM proteins (AMEL, AMBN, and ENAM) and fi ve dentin
bone ECM proteins:
– “dentine sialophosphoprotein (DSPP),
– dentine matrix acidic phosphoprotein 1 (DMP1),
– integrin-binding sialoprotein (IBSP),
– matrix extracellular, phosphoglycoprotein (MEPE),
– Osteopontin, or secreted phosphoprotein 1 (SPP1),” (Kawasaki et al. 2004 ).
4 Fish Scales as Mineral-Based Composites