Asymmetric inhibition of spicule formation in sea urchin embryos with low concentrations of gadolinium ion

Abstract

As gastrulation proceeds during sea urchin embryogenesis, primary mesenchyme cells (PMCs) fuse to form syncytial cables, within which calcium is deposited as CaCO 3 , and a pair of spicules is formed. Earlier studies suggested that calcium, previously sequestered by primary mesenchyme cells, is secreted and incorporated into growing spicules. We examined the effects of gadolinium ion (Gd 3+ ), a Ca 2+ channel blocker, on spicule formation. Gd 3+ did not lead to a retardation of embryogenesis prior to the initiation of gastrulation and did not inhibit the ingression of PMCs from the blastula wall or their migration along the inner blastocoel surface. However, when embryos were raised in seawater containing submicromolar to a few micromolar Gd 3+ , of which levels are considered to be insufficient to block Ca 2+ channels, a pair of triradiate spicules was formed asymmetrically. At 1-3 lmol ⁄ L Gd 3+ , many embryos formed only one spicule on either the left or right side, or embryos formed a very small second spicule. Induction of the spicule abnormality required the presence of Gd 3+ specifically during late blastula stage prior to spicule formation. An accumulation or adsorption of Gd 3+was not detected anywhere in the embryos by X-ray microanalysis, which suggests that Ca 2+ channels were not inhibited. These results suggest that Gd 3+ exerts an inhibitory effect on spicule formation through a mechanism that does not involve inhibition of Ca 2+ channels.

Effects of exposure to gadolinium on the development of geographically and phylogenetically distant sea urchins species

“…As expected, the phenotypic response to Gd of impaired skeleton formation was similar across the four species, indicating a similar response mechanism, albeit with different levels of sensitivity with respect to the concentrations used. The response seen for the four species investigated here is similar to that reported for three Japanese species, Hemicentrotus pulcherrimus, Heliocidaris crassispina and Pseudocentrotus depressus (Saitoh et al, 2010), providing further evidence of a conserved mechanism of toxicity of Gd to sea urchin embryos.…”

“…It followed S. granularis, with an effective Ag-NP concentration range of 10e50 mg/L, and last P. lividus (50e100 mg/L). Thus, sympatric species living in the same environment can have different sensitivities to toxicants, as also shown here for the two Australian species and for Japanese species in response to Gd (Saitoh et al, 2010). This indicates that species, despite having a similar environmental history and potential exposure to pollution, might have similar sensitivities to some toxicants and different sensitivities to others.…”

“…To minimize the volumes to be used for the assessments of Gd toxicity, exposures were carried out in 24-multiwell plates (Cellstar, Greiner Bio-One), with 2000 embryos per well in 2 ml. P. lividus was used in preliminary experiments to assess the Gd concentration range causing developmental abnormalities and with respect to results with Hemicentrotus pulcherrimus, Pseudocentrotus depressus and Heliocidaris crassispina (Saitoh et al, 2010). Specifically, we used doses increasing by a factor of 5 (from 1 to 125 mM) and found about 50% of abnormal embryos at the lowest dose, and 100% lethality at the highest dose tested.…”

Gadolinium at Low Concentration Suppresses both Osteoclastic and Osteoblastic Activities in the Scales of Goldfish

“…Even Gd of 10 -13 M suppressed TRAP activity at 6 hours of incubation. In the case of the sea urchin, Gd in a range of 10 7 to 10 5 M influenced skeletogenesis (Saitoh et al, 2010;Martino et al, 2017;. We found that the detection limit of Gd in our bioassay was 10 13 M. Therefore, our assay system is quite effective as a biosensor for Gd.…”

“…Gd appears toxic in animals because Gd functions as a blocker of Ca channels, causing its ionic radius to be nearly equal to that of Ca (Sherry et al, 2009). Actually, Gd influences calcified tissue such as sea urchin spicules (Saitoh et al, 2010;Martino et al, 2017;. As Gd affects the skeletal formation of sea urchins, we presumed that Gd affects bone metabolism in fish.…”