150
“Developmental arrest is a critically important reproductive strategy in the large
range of egg-laying animals that provide no parental care after oviposition, because
it provides their eggs a mechanism to respond to changing environmental conditions
during embryonic development,” (Rafferty and Reina 2012 ).
Several researchers including Ewert ( 1985 ) and Miller ( 1982 , 1985 ) studied the
phenomenon of developmental arrest in chelonians in details.
In turtles, the oviduct seems to be the space where limited oxygen exchange might
occur as a result of shell mineralization and “the shell pores fi lling with oviducal
fl uid,” (Rafferty and Reina 2012 ; see also Andrews and Mathies 2000 ). Heulin et al.
( 2002 ) reported that pre-ovipositional calcifi cation of turtle eggs becomes complete
“when the embryos reach gastrulae and enter pre-ovipositional arrest approximately
7 days after ovulation,” (Rafferty and Reina 2012 ). Mineralization of the eggshell
may regulate the respiratory gas exchange needed for further development of the
embryo (Packard et al. 1977 ; Guillette 1982 ). After the availability of oxygen to the
embryo is enhanced, the reduction in eggshell thickness can be also associated with
extended egg retention (Ewert et al. 1984 ; Heulin et al. 2002 ). Additionally, the
“eggshell provides a source of calcium for developing turtle embryos, and reducing
the degree of eggshell calcifi cation in order to achieve greater O 2 exchange may
decrease embryo fi tness,” (Rafferty and Reina 2012 ; see also Andrews and Mathies
2000 ; Bilinski et al. 2001 ). After calcifi cation of turtle eggs, both the embryonic
vitelline membrane and inner shell membranes must adhere to one another. In this
way the embryonic growth and gas diffusion can proceed. The relationship between
membrane fusion and is discussed by Andrews and Mathies ( 2000 ). It was postulated
that “species that lay thinner-shelled pliable eggs typically do not use developmental
arrest after oviposition and as a result they have shorter incubation periods than
those laying thicker, more rigid, brittle-shelled eggs that do,” (Rafferty and Reina
2012 ; see also Ewert 1985 ).
In contrast to well-studied mineral components of marine reptilian egg shells, the
organic matrix proteins of this group of animals are poorly investigated. However,
especially proteins play an important role in the eggshells biomineralization.
Lakshminarayanan et al. ( 2005 ) reported about the isolation of a pelovaterin . This
glycine-rich peptide with 42 amino acid residues and three disulfi de bonds was
extracted from eggshells of a soft-shelled turtle Pelodiscus sinensis. It was shown
that pelovaterin induced the formation of a metastable vaterite phase in vitro . The
microarchitecture of vaterite crystals is dependent on concentrations of pelovaterin
added as follow: “the fl oret-shaped morphology formed at a lower concentration
(approximately 1 μM) was transformed into spherical particles at higher concentrations (>500 μM),” (Lakshminarayanan et al. 2008 ). Additionally it was shown the
entropy-driven dependence of the self-aggregation of this peptide in solution in the
form of micellar nanospheres. The development of these micelles is principally
possible because molecules of pelovaterin possess a large hydrophobic core and a
short hydrophilic N-terminal segment. Although pelovaterin show functional
similarity to human ß-defensins, structurally they are absolutely different. Probably,
the micellar state of pelovaterin determine the induction and stabilization of the
metastable mineral phase by altering the interfacial energy. Intriguingly, “pelovaterin
3 Biocomposites and Mineralized Tissues
“Developmental arrest is a critically important reproductive strategy in the large
range of egg-laying animals that provide no parental care after oviposition, because
it provides their eggs a mechanism to respond to changing environmental conditions
during embryonic development,” (Rafferty and Reina 2012 ).
Several researchers including Ewert ( 1985 ) and Miller ( 1982 , 1985 ) studied the
phenomenon of developmental arrest in chelonians in details.
In turtles, the oviduct seems to be the space where limited oxygen exchange might
occur as a result of shell mineralization and “the shell pores fi lling with oviducal
fl uid,” (Rafferty and Reina 2012 ; see also Andrews and Mathies 2000 ). Heulin et al.
( 2002 ) reported that pre-ovipositional calcifi cation of turtle eggs becomes complete
“when the embryos reach gastrulae and enter pre-ovipositional arrest approximately
7 days after ovulation,” (Rafferty and Reina 2012 ). Mineralization of the eggshell
may regulate the respiratory gas exchange needed for further development of the
embryo (Packard et al. 1977 ; Guillette 1982 ). After the availability of oxygen to the
embryo is enhanced, the reduction in eggshell thickness can be also associated with
extended egg retention (Ewert et al. 1984 ; Heulin et al. 2002 ). Additionally, the
“eggshell provides a source of calcium for developing turtle embryos, and reducing
the degree of eggshell calcifi cation in order to achieve greater O 2 exchange may
decrease embryo fi tness,” (Rafferty and Reina 2012 ; see also Andrews and Mathies
2000 ; Bilinski et al. 2001 ). After calcifi cation of turtle eggs, both the embryonic
vitelline membrane and inner shell membranes must adhere to one another. In this
way the embryonic growth and gas diffusion can proceed. The relationship between
membrane fusion and is discussed by Andrews and Mathies ( 2000 ). It was postulated
that “species that lay thinner-shelled pliable eggs typically do not use developmental
arrest after oviposition and as a result they have shorter incubation periods than
those laying thicker, more rigid, brittle-shelled eggs that do,” (Rafferty and Reina
2012 ; see also Ewert 1985 ).
In contrast to well-studied mineral components of marine reptilian egg shells, the
organic matrix proteins of this group of animals are poorly investigated. However,
especially proteins play an important role in the eggshells biomineralization.
Lakshminarayanan et al. ( 2005 ) reported about the isolation of a pelovaterin . This
glycine-rich peptide with 42 amino acid residues and three disulfi de bonds was
extracted from eggshells of a soft-shelled turtle Pelodiscus sinensis. It was shown
that pelovaterin induced the formation of a metastable vaterite phase in vitro . The
microarchitecture of vaterite crystals is dependent on concentrations of pelovaterin
added as follow: “the fl oret-shaped morphology formed at a lower concentration
(approximately 1 μM) was transformed into spherical particles at higher concentrations (>500 μM),” (Lakshminarayanan et al. 2008 ). Additionally it was shown the
entropy-driven dependence of the self-aggregation of this peptide in solution in the
form of micellar nanospheres. The development of these micelles is principally
possible because molecules of pelovaterin possess a large hydrophobic core and a
short hydrophilic N-terminal segment. Although pelovaterin show functional
similarity to human ß-defensins, structurally they are absolutely different. Probably,
the micellar state of pelovaterin determine the induction and stabilization of the
metastable mineral phase by altering the interfacial energy. Intriguingly, “pelovaterin
3 Biocomposites and Mineralized Tissues