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Novel two‐step Ca 2+ increase and its mechanisms and functions at fertilization in oocytes of the annelidan worm Pseudopotamilla occelata
Author(s) -
Nakano Takeshi,
Kyozuka Keiichiro,
Deguchi Ryusaku
Publication year - 2008
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1111/j.1440-169x.2008.01022.x
Subject(s) - oocyte , human fertilization , oocyte activation , perivitelline space , phospholipase c , sperm , inositol , microinjection , biology , metaphase , microbiology and biotechnology , chemistry , biophysics , anatomy , biochemistry , zona pellucida , botany , embryo , receptor , signal transduction , chromosome , gene
Mature oocytes of the annelidan worm Pseudopotamilla occelata have a wide perivitelline space between the oocyte surface and the vitelline envelope and are arrested at the first metaphase (MI). We found a novel two‐step Ca 2+ increase in normally fertilized oocytes. The first Ca 2+ increase originated at a cortex situated underneath a fertilizing sperm on the vitelline envelope, but failed to propagate beyond the center of the oocyte. The first localized Ca 2+ increase was then followed by a larger Ca 2+ increase starting from the whole oocyte cortex and spreading inwardly to the center. The first localized Ca 2+ increase at fertilization was suppressed by the phospholipase C inhibitor U73122, and a similar Ca 2+ change was induced by inositol 1,4,5‐trisphosphate (IP 3 ). On the other hand, the second global Ca 2+ increase in fertilized oocytes was blocked by removal of external Ca 2+ or the voltage‐gated Ca 2+ channel blocker D‐600, and a similar Ca 2+ change could be mimicked by addition of excess K + only when external Ca 2+ was present. These results suggest that the first localized Ca 2+ increase and the second global Ca 2+ increase at fertilization are regulated by Ca 2+ release from IP 3 ‐sensitive stores and Ca 2+ influx via voltage‐gated Ca 2+ channels, respectively. Our data also demonstrated that the localized Ca 2+ increase induces the formation of large cytoplasmic protrusion, which helps the fertilizing sperm to enter the oocyte, whereas the following global Ca 2+ increase is a prerequisite for the retraction of the cytoplasmic protrusion and the resumption of meiosis from MI.