There is evidence showing that the sperm-induced Ca2+ oscillations in mamma
lian eggs at fertilization are triggered by a sperm-derived protein factor.
It was established recently that the activity of the putative sperm protei
n in causing Ca2+ oscillations in mammalian eggs is not species-specific in
vertebrates (1, 16). Here we report that cytosolic soluble extracts derive
d from flowering plant sperms in Brassica campestris can also induce fertil
ization-like Ca2+ oscillations when microinjected into mouse eggs. The fact
or responsible for inducing Ca2+ oscillations in the plant sperm was sperm-
specific and heat- or trypsin-labile. Eight to ten sperm equivalents of the
plant sperm extracts had enough activity to trigger Ca2+ oscillations in m
ouse eggs. Our study suggests that, although plant and mammal are evolution
ary divergent species, the activity of the putative sperm protein factor in
triggering Ca2+ signaling in mammalian eggs is not specific to the animal
kingdom. (C) 2001 Academic Press.