Possible role of calcium on oocyte development after intracytoplasmic sperm injection in quail (Coturnix japonica)

Although a rise in intracellular calcium concentration of vertebrate oocytes plays a pivotal role for the initiation of fertilization or oocyte activation, no study on this subject has been reported in birds. This study was conducted to study the role of intracellular calcium in relation to fertilization in avian oocytes. First, immediately after a quail oocyte was injected with a sperm, it was treated with strontium chloride as an inducer for intracellular calcium rise at doses of 0, 2.5, 5, 7.5, 10 mM for 4 hr in the culture medium and was followed by 20-hr culture. Treatment with 5 mM of strontium chloride induced blastodermal development in 24.2% of injected eggs, although no oocytes developed without strontium treatment. Second, quail oocytes were injected with a sperm and 0.1 M calcium chloride or a sperm and saline solution, cultured without calcium for 4 hr and was followed by 20-hr culture without strontium. The calcium solution induced blastodermal development in 20.5% of the oocytes, although no oocytes developed without calcium treatment. Third, quail oocytes were injected with 1,2-bis (o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA) as a calcium chelator, cultured with strontium (5 mM) for 4 hr followed by 20-hr culture without strontium. Only one oocyte developed after BAPTA and strontium treatment of 36 oocytes examined. Developmental stages of all the oocytes ranged from IV to VII. These results suggest that intracellular calcium rise may participate in quail oocyte activation and allow fertilization and blastodermal development.