Asymmetric inhibition of spicule formation in sea urchin embryos with low concentrations of gadolinium ion |
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Authors: | Saitoh Motoshi Kuroda Ritsu Muranaka Yoshinori Uto Norihiko Murai Junko Kuroda Hideyo |
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Institution: | Department of Environmental Biology and Chemistry, Faculty of Science, University of Toyama, Toyama, Toyama 930-8555, Japan. |
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Abstract: | As gastrulation proceeds during sea urchin embryogenesis, primary mesenchyme cells (PMCs) fuse to form syncytial cables, within which calcium is deposited as CaCO3, 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 (Gd3+), a Ca2+ channel blocker, on spicule formation. Gd3+ 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 Gd3+, of which levels are considered to be insufficient to block Ca2+ channels, a pair of triradiate spicules was formed asymmetrically. At 1–3 μmol/L Gd3+, 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 Gd3+ specifically during late blastula stage prior to spicule formation. An accumulation or adsorption of Gd3+ was not detected anywhere in the embryos by X‐ray microanalysis, which suggests that Ca2+ channels were not inhibited. These results suggest that Gd3+ exerts an inhibitory effect on spicule formation through a mechanism that does not involve inhibition of Ca2+ channels. |
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Keywords: | asymmetric spicule formation early development low concentration of Gd3+ sea urchin |
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