Abstract
Fertilized eggs of Ilyanassa obsoleta form a protuberance which resembles a normal polar lobe when injected with Sr 2+ or Ca 2+ by microiontophoresis. Eggs also form a lobe-like protuberance when exposed to any of three drugs: compound 48 80 , ionophore X537A, and ionophore A23187. Protuberances form more quickly and at lower drug concentrations if additional exogenous Ca 2+ is added, whereas higher concentrations of Mg 2+ do not have such an effect. When eggs are exposed to these drugs in Ca 2+-, Mg 2+-“free” seawater, with or without 10 m M EDTA, the eggs are still able to undergo extensive shape changes and form protuberances. Drug-induced shape changes are prevented by cytochalasin B, but will still occur in the presence of colchicine. Approximately 75% of Ilyanassa eggs are capable of forming and resorbing their third polar lobe and undergoing cytokinesis in Ca 2+-, Mg 2+-“free” artificial seawater (even containing 10 m M EDTA), solutions which by atomic absorption spectroscopy are shown to contain low concentrations of Ca 2+ (3–5 μ M) and Mg 2+ (1.0–3.5 μ M). The data suggest that if Ca 2+ is required for normal polar lobe formation and cytokinesis, it is derived from intracellular sources or is required in only very low exogenous concentrations (i.e., less than 10 −2 μ M free Ca 2+, in the presence of 10 m M EDTA).
Published Version
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