Pulse treatment of sea urchin embryos with A23187 blocks their hatching out

Pulse treatment of sea urchin embryos with 3 µM A23187 for 2 h at 20° C, starting from 3 to 6 h of development, prevented the embryos from hatching. Many embryos thus treated with A23187 produced mesenchyme cells and underwent gastrulation while still enclosed within the fertilization membrane. The pulse treatment in this pre-hatching period exerts markedly stronger inhibitory effects on hatching than on other events in early development. Treatment beginning at times earlier than 2 h and later than 8 h of development caused only a slight delay of hatching. The activity of hatching enzyme, known to increase between 6 and 8 h after fertilization, was quite low, if present at all, in embryos in which hatching was blocked by A23187. Hatching enzyme synthesis is probably blocked by the preceding pulse treatment. However, overall protein synthesis, estimated with methionine S 35 incorporation, was somewhat augmented in embryos by the pulse treatment. The blockage of hatching and the augmentation of overall protein synthesis by A23187 were appreciably reversed by procaine, tetracaine, ruthenium red or verapamil. Probably, an artificial Ca²⁺ signal induced by A23187 activates protein synthesis but blocks the induction of hatching enzyme synthesis.