An increase in intracellular Ca2+ concentration ([Ca2+]i) at a focal plane was recorded simultaneously with sperm-egg binding and membrane current upon insemination of sea urchin Hemicentrotus pulcherrimus eggs. No change in current and [Ca2+]i occurred in the presence of jaspisin, a novel substance that inhibits metallo-endoproteinase and sperm-egg membrane fusion (S. Ikegami, H. Kobayashi, Y. Myotoishi, S. Ohta and K. H. Kato (1994) J. Biol. Chem. 269, 23262–23267). With low doses of jaspisin, a spermatozoon first produced a step inward current (I(on)) as an indication of gamete membrane fusion and then induced a local [Ca2+]i rise at the site of sperm attachment 6–10 seconds after I(on). The sperm, however, soon detached from the egg. Increasing inward current was abruptly cut off (I(off)) within 9–15 seconds and the local [Ca2+]i rise began to decline 1–3 seconds after I(off). In most cases, no further responses or an elevation of fertilization envelope (FE) occurred. In some cases, [Ca2+]i at the sperm attachment site increased again even after the sperm detached and triggered a Ca2+ wave which caused an activation current and FE formation. This recording of a gamete membrane-fusion-induced local [Ca2+]i rise, separated from the Ca2+ wave, is a key phenomenon for elucidating the initial sperm stimulation of the egg at fertilization.
Involvement of Huntingtin in Development and Ciliary Beating Regulation of Larvae of the Sea Urchin, Hemicentrotus pulcherrimus
