Ethylenediamine-N,N,N',N'-tetraacetic acid induces parthenogenetic activation of porcine oocytes at the germinal vesicle stage, leading to formation of blastocysts.
The present study showed that treatment with a cell membrane-impermeable metal ion chelator, EDTA, of porcine oocytes at the germinal vesicle (GV) stage collected from follicles 2-6 mm in diameter induced artificial activation followed by formation of a pronucleus (PN). When the oocytes were cultured for 48 h in medium containing 0.1 to 2 mM EDTA disodium salt (Na-EDTA), they were activated to form PN, and the maximum PN formation rate (63%, n = 68) was achieved in oocytes cultured with 1 mM Na-EDTA. More than 90% of oocytes activated by 1 mM Na-EDTA treatment formed 1 PN without emission of the first and the second polar bodies (PB). This result suggests that EDTA at 1 mM may force the maturing (meiosis I) oocytes to form a PN without chromosome segregation. When oocytes at the GV stage that had been cultured with 1 mM Na-EDTA for 48 h were further cultured in 0.4% BSA-containing NCSU23 medium for 144 h, blastocysts that appeared to be morphologically normal were formed at the rate of 10%, whereas no blastocysts were formed from oocytes that had not been cultured with Na-EDTA. Next we examined the effects of Ca2+, Zn2+, Fe3+, or Cu2+-saturated EDTA (Ca-EDTA, Zn-EDTA, Fe-EDTA, and Cu-EDTA, respectively), and a Ca2+-specific chelator, EGTA, at a concentration of 1 mM. The Ca-EDTA, Fe-EDTA, and Cu-EDTA, but not Zn-EDTA or EGTA, had the ability to activate the oocytes. From these results, it is suggested that extracellular chelation of Zn2+ with EDTA of maturing (meiosis I) porcine oocytes results in parthenogenetic activation of the oocytes, which induces PN formation followed by development to blastocysts.
Azuma
T
T
Laboratory of Reproductive Physiology, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Ikeda
S
S
Kondo
T
T
Imai
H
H
Yamada
M
M
D000818:Animals; D001755:Blastocyst / Q000187:drug effects*; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D002614:Chelating Agents / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology*; D005260:Female; D018858:Germinal Center / Q000187:drug effects*; D008670:Metals / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects*; D010312:Parthenogenesis / Q000187:drug effects*; D011247:Pregnancy; D013552:Swine
D002614:Chelating Agents; D008670:Metals; D004492:Edetic Acid