70
secretion is “primarily the ancestral mode of making pharyngeal cartilage in
deuterostoes,” (Hecht et al. 2008 ).
Cartilage forms the major supporting structure in very primitive marine vertebrates, like jawless lamprey and hagfi sh. Both are representatives of cyclostomes
and diverged from the mammalian lineage about 500 million years ago (Forey and
Janvier 1993 ). Lamprey and hagfi sh are well known key species for understanding
of numerous developmental mechanisms in vertebrates, including evolution of the
neural crest, cartilage, mineralized cartilage, and bones. Interestingly, a large
amount of diversity in the highly viscoelastic cartilage forms has been observed
within each individuum of these animals. According to Fernandesa and Eyre ( 1999 ),
in lamprey, “the head and gill regions are cartilaginous in texture and histological
appearance. For example, annular cartilage supports the mouth, while branchial
cartilages support the gills. Trabecular, piston and pericardial cartilages have also
been described,” (Fernandesa and Eyre 1999 ). Experiments using transmission
electron microscopy showed that the extracellular matrix of all these fi brillarlybased structures is collagen-free (Fernandesa and Eyre 1999 ).
In spite of the presence of special structural proteins and differences in extracellular
matrix organization, mechanical properties of the lamprey’s cartilages are largely similar to those of mammalian cartilages. The dense network of randomly arranged,
branched, noncollagenous matrix fi brils constitutes the basis of the extracellular matrix
(ECM) of lamprey cartilages (Wright and Youson 1983 ; Wright et al. 1988 ). Special
attention was paid to lamprin , the unique insoluble matrix protein. This was found to
constitute 44–51 % of the dry mass of the annular cartilage (Wright et al. 1983 ; Robson
et al. 1993 ). However, the major matrix protein(s) of pericardial cartilage possess rather
noncollagenous, elastin-like proteins than lamprin (Wright et al. 2001 ).
The branchial basket that supports the lamprey pharynx represents the viscerocranial skeleton. Its development was recently described in the sea lamprey,
Petromyzon marinus by Martin et al. ( 2009 ). The authors reported about the skeletal
rods within the branchial basket, which are comprised of chondrocyte stacks.
Meanwhile, “the subchordal, parachordal, and trabecular cartilages form as aggregate condensations of polygonal cells. The subchordal and parachordal cartilage
condensations form anchor points that tether the skeletal rods to the notochord,”
(Lakiza et al. 2011 ). This rod-like midline structure is of mesodermal origin and
serves as a primitive axial skeleton.
The body axis of vertebrates, established during gastrulation, is characterized by
the formation of the notochord (Stemple 2005 ). Both structural and compositional
features of notochord are similar to that of cartilage. Thus, the composition of the
sheath of the lamprey notochord, where the major collagen is type II, resembling
that of cartilage of higher animals (see for review Eikenberry et al. 1984 ). “The collagen fi brils in the notochord sheath are of small, uniform diameter but, in contrast
to cartilage, are highly oriented and crystalline” (Eikenberry et al. 1984 ). It cannot
exclude that chondrogenesis in the ancestral vertebrate was determined by the SoxE
genes and regulation of cartilage effector proteins. Some authors proposed that
“type II collagen arose early in vertebrate evolution as an extracellular matrix
protein in cartilage formation” (see for review Lakiza et al. 2011 ).
2 Cartilage of Marine Vertebrates
secretion is “primarily the ancestral mode of making pharyngeal cartilage in
deuterostoes,” (Hecht et al. 2008 ).
Cartilage forms the major supporting structure in very primitive marine vertebrates, like jawless lamprey and hagfi sh. Both are representatives of cyclostomes
and diverged from the mammalian lineage about 500 million years ago (Forey and
Janvier 1993 ). Lamprey and hagfi sh are well known key species for understanding
of numerous developmental mechanisms in vertebrates, including evolution of the
neural crest, cartilage, mineralized cartilage, and bones. Interestingly, a large
amount of diversity in the highly viscoelastic cartilage forms has been observed
within each individuum of these animals. According to Fernandesa and Eyre ( 1999 ),
in lamprey, “the head and gill regions are cartilaginous in texture and histological
appearance. For example, annular cartilage supports the mouth, while branchial
cartilages support the gills. Trabecular, piston and pericardial cartilages have also
been described,” (Fernandesa and Eyre 1999 ). Experiments using transmission
electron microscopy showed that the extracellular matrix of all these fi brillarlybased structures is collagen-free (Fernandesa and Eyre 1999 ).
In spite of the presence of special structural proteins and differences in extracellular
matrix organization, mechanical properties of the lamprey’s cartilages are largely similar to those of mammalian cartilages. The dense network of randomly arranged,
branched, noncollagenous matrix fi brils constitutes the basis of the extracellular matrix
(ECM) of lamprey cartilages (Wright and Youson 1983 ; Wright et al. 1988 ). Special
attention was paid to lamprin , the unique insoluble matrix protein. This was found to
constitute 44–51 % of the dry mass of the annular cartilage (Wright et al. 1983 ; Robson
et al. 1993 ). However, the major matrix protein(s) of pericardial cartilage possess rather
noncollagenous, elastin-like proteins than lamprin (Wright et al. 2001 ).
The branchial basket that supports the lamprey pharynx represents the viscerocranial skeleton. Its development was recently described in the sea lamprey,
Petromyzon marinus by Martin et al. ( 2009 ). The authors reported about the skeletal
rods within the branchial basket, which are comprised of chondrocyte stacks.
Meanwhile, “the subchordal, parachordal, and trabecular cartilages form as aggregate condensations of polygonal cells. The subchordal and parachordal cartilage
condensations form anchor points that tether the skeletal rods to the notochord,”
(Lakiza et al. 2011 ). This rod-like midline structure is of mesodermal origin and
serves as a primitive axial skeleton.
The body axis of vertebrates, established during gastrulation, is characterized by
the formation of the notochord (Stemple 2005 ). Both structural and compositional
features of notochord are similar to that of cartilage. Thus, the composition of the
sheath of the lamprey notochord, where the major collagen is type II, resembling
that of cartilage of higher animals (see for review Eikenberry et al. 1984 ). “The collagen fi brils in the notochord sheath are of small, uniform diameter but, in contrast
to cartilage, are highly oriented and crystalline” (Eikenberry et al. 1984 ). It cannot
exclude that chondrogenesis in the ancestral vertebrate was determined by the SoxE
genes and regulation of cartilage effector proteins. Some authors proposed that
“type II collagen arose early in vertebrate evolution as an extracellular matrix
protein in cartilage formation” (see for review Lakiza et al. 2011 ).
2 Cartilage of Marine Vertebrates