decapentaplegic protein (dpp) (Drosophila), and Vg-1 (Xenopus) (Stenzel et al.
1994; Lapraz et al. 2006). At the blastula stage, univin is expressed in a circumequatorial ring of ectodermal cells and during gastrulation is expressed in the
archenteron. Univin transcripts are confined to bilateral regions of the ectoderm
between the arms of the young pluteus larva (Stenzel et al. 1994; Range et al. 2007).
We have shown that embryos with skeletal defects caused by ECM–ectoderm cellbinding inhibition (see above, Fig. 8.6 proposed model), and expressing low levels
of univin and SM30, could be rescued by univin mRNA microinjection with the
contemporaneous partial resumption of SM30 mRNA levels (Zito et al. 2003). This
was the first evidence showing that a growth factor produced by ectoderm cells is
the inductive signal responsible for skeleton growth. Later, Duloquin et al. (2007)
demonstrated the guidance role of VEGF/VEGFR signaling for the positioning and
differentiation of PMCs during gastrulation. At the early gastrula stage, the VEGFR
is expressed only in the PMCs, while VEGF is expressed in two restricted areas of
the ventrolateral ectoderm overlying the PMCs clusters. At the pluteus stage, VEGF
transcripts are detected only in a few ectodermal cells, located at the tip of the arm
buds, which face VEGFR-expressing PMCs. The impairment of VEGF/VEGFR
expression, obtained by morpholinos injection, causes the inhibition of SM50
and SM30 and leads to skeleton-lacking embryos. MSP130 expression is not
significantly affected, suggesting that it is not under the control of the VEGF/
VEGFR signaling machinery. In the same way, R€ ottinger et al. (2008) have
identified and characterized the FGFA gene, and its putative receptor genes
FGFR1 and FGFR2. The co-localization of their transcripts during development,
observed by in situ hybridization, as well as loss-of-function experiments, involving morpholinos injection, have shown that they regulate PMCs migration and
dramatically affect skeleton elongation. Again, a block of SM30 and SM50 expression is demonstrated in the PMCs.
8.5 Ecotoxicological Approaches to the Study of Skeletogenesis
Toxicology is one of the oldest sciences. In the 1500s, Paracelsus found a way to
overcome the difficulties in defining which substances are toxic and which are not,
by his famous aphorism: “only dose makes the difference”. Modern ecotoxicology,
can be defined as the integration of toxicology and ecology, and aims to quantify the
toxic effects of stressors upon changes in the ecosystem composition (Truhaut
1977; Chapman 2002). The most relevant chemical/physical stressors for all
organisms, including the marine ones, are: (1) physical agents such as ionizing
radiation (UV-B and X-rays); (2) inorganic chemicals, such as heavy metals,
nitrates, and nitrites; (3) organic chemicals, such as pesticides, oil, haloorganics,
hydrocarbons, phenols, synthetic materials; and (4) emerging stressors, such as
metallic and engineered nanoparticles, CO 2 , pH, temperature. Here, we focused on
reports about the negative influences of chemical/physical stressors on biomineralization in echinoderms.
8 Echinoderms as Blueprints for Biocalcification
239
1994; Lapraz et al. 2006). At the blastula stage, univin is expressed in a circumequatorial ring of ectodermal cells and during gastrulation is expressed in the
archenteron. Univin transcripts are confined to bilateral regions of the ectoderm
between the arms of the young pluteus larva (Stenzel et al. 1994; Range et al. 2007).
We have shown that embryos with skeletal defects caused by ECM–ectoderm cellbinding inhibition (see above, Fig. 8.6 proposed model), and expressing low levels
of univin and SM30, could be rescued by univin mRNA microinjection with the
contemporaneous partial resumption of SM30 mRNA levels (Zito et al. 2003). This
was the first evidence showing that a growth factor produced by ectoderm cells is
the inductive signal responsible for skeleton growth. Later, Duloquin et al. (2007)
demonstrated the guidance role of VEGF/VEGFR signaling for the positioning and
differentiation of PMCs during gastrulation. At the early gastrula stage, the VEGFR
is expressed only in the PMCs, while VEGF is expressed in two restricted areas of
the ventrolateral ectoderm overlying the PMCs clusters. At the pluteus stage, VEGF
transcripts are detected only in a few ectodermal cells, located at the tip of the arm
buds, which face VEGFR-expressing PMCs. The impairment of VEGF/VEGFR
expression, obtained by morpholinos injection, causes the inhibition of SM50
and SM30 and leads to skeleton-lacking embryos. MSP130 expression is not
significantly affected, suggesting that it is not under the control of the VEGF/
VEGFR signaling machinery. In the same way, R€ ottinger et al. (2008) have
identified and characterized the FGFA gene, and its putative receptor genes
FGFR1 and FGFR2. The co-localization of their transcripts during development,
observed by in situ hybridization, as well as loss-of-function experiments, involving morpholinos injection, have shown that they regulate PMCs migration and
dramatically affect skeleton elongation. Again, a block of SM30 and SM50 expression is demonstrated in the PMCs.
8.5 Ecotoxicological Approaches to the Study of Skeletogenesis
Toxicology is one of the oldest sciences. In the 1500s, Paracelsus found a way to
overcome the difficulties in defining which substances are toxic and which are not,
by his famous aphorism: “only dose makes the difference”. Modern ecotoxicology,
can be defined as the integration of toxicology and ecology, and aims to quantify the
toxic effects of stressors upon changes in the ecosystem composition (Truhaut
1977; Chapman 2002). The most relevant chemical/physical stressors for all
organisms, including the marine ones, are: (1) physical agents such as ionizing
radiation (UV-B and X-rays); (2) inorganic chemicals, such as heavy metals,
nitrates, and nitrites; (3) organic chemicals, such as pesticides, oil, haloorganics,
hydrocarbons, phenols, synthetic materials; and (4) emerging stressors, such as
metallic and engineered nanoparticles, CO 2 , pH, temperature. Here, we focused on
reports about the negative influences of chemical/physical stressors on biomineralization in echinoderms.
8 Echinoderms as Blueprints for Biocalcification
239