. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 366 C. H. SULLIVAN AND D. B. BONAR In these systems, sperm and embryos release divalent cation-requiring proteases, which is not surprising since envelopes are composed primarily of proteins (Katagiri, 1975; Bleil and Wassarman, 1980; Schools and Denuce, 1981; Urch and Hedrick, 198la). The emergence of sea urchin and amphibian embryos from the fertilization en- velope (a primary envelope produced by the oocyte) and fish embryos from a chorion (a secondary envelope derived from follicle cells) are the only systems in which th
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 366 C. H. SULLIVAN AND D. B. BONAR In these systems, sperm and embryos release divalent cation-requiring proteases, which is not surprising since envelopes are composed primarily of proteins (Katagiri, 1975; Bleil and Wassarman, 1980; Schools and Denuce, 1981; Urch and Hedrick, 198la). The emergence of sea urchin and amphibian embryos from the fertilization en- velope (a primary envelope produced by the oocyte) and fish embryos from a chorion (a secondary envelope derived from follicle cells) are the only systems in which the hatching process has been studied in detail. Considerable information is available on the hatching enzymes released by these embryos (see Sullivan and Bonar, 1984) yet the mechanism of action of these enzymes has been studied only during fish (Ya- mamoto and Yamagami, 1975; luchi and Yamagami, 1976; Yamagami, 1981) and frog(Yoshizaki, 1978; Urch and Hedrick, 1981b) hatching. Furthermore, similar data are not yet available on hatching from tertiary envelopes (secreted along the oviduct), so that it is impossible to draw any conclusions on the ubiquity of the hatching process for diverse animal groups. One example of an oviduct-derived tertiary envelope is the multi-layered gastropod egg capsule. Of the few species of snails for which chemical hatching has been described, Ilyanassa obsoleta was chosen for our studies because adults reproduce readily and females deposit an abundance of egg capsules (Fig. 1) in the laboratory and because hatching is an early developmental event (Scheltema, 1967). After about a week of development embryos hatch as swimming veligers by releasing a hatching substance that dissolves the capsule plug, which occupies a small region of the egg capsule apex (Pechenik, 1975). We have shown that the Ilyanassa hatching substance is a divalent cation-requiring protein that shares many of the biochemical characteristics of other well studied hatch- ing enzyme
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