Transient increases of intracellular calcium ion concentration ([Ca 2+ ] i ) have been observed during fertilization of eggs, from invertebrates to mammals. Caenorhabditis elegans seems to be a hopeful model organism to study the signaling pathway from a sperm-egg fusion to a transient increase in [Ca 2+ ] i . Since we have not succeeded to bring about the fertilization in vitro , we measured the [Ca 2+ ] i changes of oocytes during fertilization in vivo . A Ca 2+ indicator, Calcium-Green 1 dextran (10,000 MW) was injected into the distal portion of the ovary of adult worms. Two hrs after injection, the oocytescontaining the indicator lined up at the proximal portion of the ovary. Even in the worm anesthetized with tricaine and tetramisole, the oocytes moved against the proximal end of the ovary and entered into spermatheca in order. We collected the [Ca 2+ ] i images of oocytes in the ovary or spermatheca with a cooled CCD camera. We observed the fluorescent change of hermaphrodite oocytes during self-fertilization. Several seconds after passing through the valve between the ovary and spermatheca, an oocyte showed a transient increase in [Ca 2+ ] i . These results suggest that sperm of C. elegans fertilizes oocytes in the spermatheca and bring about a transient change in [Ca 2+ ] i of oocytes. In mammal eggs, the inositol 1,4,5-trisphosphate receptor/channels (IP 3 R) of endoplasmic reticulum membrane are responsible for these Ca 2+ -changes. The Ca 2+ -transients of sea urchin eggs seems to depend on the synergistical release via both of IP 3 R and ryanodine receptor/channel (RyR). To examine the contribution of IP 3 R or RyR to the Ca 2+ -transient of C. elegans , we examined the changes in [Ca 2+ ] i during self-fertilization of mutant strains of two genes,
unc-68 encoding RyR and
itr-1 encoding IP 3 R. Both in oocytes of
unc-68 and
itr-1 , similar changes to the Ca 2+ -transient in N2 oocytes were recorded. These results suggest two possibility, the Ca 2+ -transient during fertilization depend on (1) the synergistical release of Ca 2+ via RyR and IP 3 R from endoplasmic reticulum, or (2) the Ca 2+ -influx through a Ca 2+ channel of the plasmamembrane. To examine these possibilities, we are trying the RNAi of
itr-1 and
unc-68 .