Abstract
Microinjection through the tough vitelline coats of oocytes from three molluscan species (Haliotis rufescens, Norrisia norrisi, and Astrea undosa) was facilitated by the local application of sperm vitelline coat lysin with a micropipet. Extracts containing lysin were the 12,000__g__ supernates of frozen‐thawed sperm. In H. rufescens and N. norrisi, lysin extracts dissolved a small hole through the vitelline coat, whereas in A. undosa, the lysin created a pathway for microinjection by softening the vitelline coat without dissolving it. Similar effects were observed when oocytes were suspended in lysin extracts: Vitelline coats dissolved completely in H. rufescens (previously reported by Lewis et al. [1982], Dev. Biol. 92:227–239) and N. norrisi, but only softened and swelled in A. undosa (although they could then be removed by mechanical agitation). The lysin extracts were highly species specific and had no visible effects on heterologous vitelline coats even at concentrations higher than those required to dissolve/soften homologous coats. Evidence that N. norrisi lysin acts by a non‐enzymatic mechanism was provided by the observation that mobilities of radioactive bands in sodium dodecyl sulfate polyacrylamide gels were unchanged following dissolution of ^125^I‐labeled vitelline coats. Electron micrographs of the previously undescribed sperm from N. norrisi and A. undosa are also presented. © 1995 Wiley‐Liss, Inc.