Sperm-egg fusion in the sea urchin is blocked in Mg(2+)-free seawater.
Magnesium ions as well as calcium ions are required for successful fertilisation in sea urchins. In the absence of Mg2+ spermatozoa attached to the egg plasma membrane, their acrosomal processes passing through the vitelline envelope, but could not enter the egg cytoplasm (Sano et al., Dev. Growth Differ. 22, 531-41, 1980). Such an individual spermatozoon was observed microscopically to resume entry into the egg immediately after the addition of a sufficient amount of Mg2+ to the surrounding medium. Neither any change in membrane potential nor an increase in intracellular Ca2+ concentration of the egg was observed after insemination in the absence of Mg2+, although both could be observed after the addition of Mg2+. The sperm heads did not show fluorescence when attached to the surface of an egg previously microinjected with mithramycin A in Mg-free seawater, indicating that there was no connection between the sperm and the egg. Therefore, occurrence of fertilisation potential must be a post-fusional event. These results suggest that Mg2+ are indispensable for fusion between the sperm acrosomal membrane and the egg plasma membrane.
Mohri
H
H
University of the Air, Tokyo Institute of Technology, Hokkaido University, Japan.
Hamaguchi
Y
Y
Hamaguchi
M S
MS
Sano
K
K
Shirakawa
H
H
Nakada
K
K
Miyazaki
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002459:Cell Fusion / Q000187:drug effects / Q000502:physiology; D005260:Female; D007424:Intracellular Fluid / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials; D012617:Sea Urchins / Q000187:drug effects / Q000502:physiology*; D012623:Seawater; D013084:Sperm-Ovum Interactions / Q000187:drug effects* / Q000502:physiology*
D008274:Magnesium; D002118:Calcium