Spatiotemporal characteristics and mechanisms of intracellular Ca(2+) increases at fertilization in eggs of jellyfish (Phylum Cnidaria, Class Hydrozoa).
We have clarified, for the first time, the spatiotemporal patterns of intracellular Ca(2+) increases at fertilization and the Ca(2+)-mobilizing mechanisms in eggs of hydrozoan jellyfish, which belong to the evolutionarily old diploblastic phylum, Cnidaria. An initial Ca(2+) increase just after fertilization took the form of a Ca(2+) wave starting from one cortical region of the egg and propagating to its antipode in all of four hydrozoan species tested: Cytaeis uchidae, Cladonema pacificum, Clytia sp., and Gonionema vertens. The initiation site of the Ca(2+) wave was restricted to the animal pole, which is known to be the only area of sperm-egg fusion in hydrozoan eggs, and the wave propagating velocity was estimated to be 4.2-5.9 mum/s. After a Ca(2+) peak had been attained by the initial Ca(2+) wave, the elevated Ca(2+) gradually declined and returned nearly to the resting value at 7-10 min following fertilization. Injection of inositol 1,4,5-trisphosphate (IP(3)), an agonist of IP(3) receptors (IP(3)R), was highly effective in inducing a Ca(2+) increase in unfertilized eggs; IP(3) at a final intracellular concentration of 12-60 nM produced a fully propagating Ca(2+) wave equivalent to that observed at fertilization. In contrast, a higher concentration of cyclic ADP-ribose (cADPR), an agonist of ryanodine receptors (RyR), only generated a localized Ca(2+) increase that did not propagate in the egg. In addition, caffeine, another stimulator of RyR, was completely without effect. Sperm-induced Ca(2+) increases in Gonionema eggs were severely affected by preinjection of heparin, an inhibitor of Ca(2+) release from IP(3)R. These results strongly suggest that there is a well-developed IP(3)R-, but not RyR-mediated Ca(2+) release mechanism in hydrozoan eggs and that the former system primarily functions at fertilization. Our present data also demonstrate that the spatial characteristics and mechanisms of Ca(2+) increases at fertilization in hydrozoan eggs resemble those reported in higher triploblastic animals.
Deguchi
Ryusaku
R
Department of Biology, Miyagi University of Education, Aoba-ku, Sendai, Miyagi 980-0845, Japan. deguchi@staff.miyakyo-u.ac.jp
Kondoh
Eri
E
Itoh
Junko
J
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D016764:Cell Polarity; D036563:Cyclic ADP-Ribose / Q000494:pharmacology; D005306:Fertilization; D006493:Heparin / Q000494:pharmacology; D037402:Hydrozoa / Q000166:cytology / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008856:Microscopy, Fluorescence; D010063:Ovum / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D013997:Time Factors
D010726:Phosphodiesterase Inhibitors; D036563:Cyclic ADP-Ribose; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D002118:Calcium