Sheep oocyte activation after intracytoplasmic sperm injection (ICSI)

Area of Science:

• Reproductive Biology
• Cellular Biology
• Developmental Biology

Background:

• Oocyte activation is a critical step following fertilization.
• The role of calcium in initiating oocyte activation after sperm injection is not fully understood.

Purpose of the Study:

• To investigate the effect of calcium concentration on oocyte fertilization and activation after sperm injection.
• To determine if sperm itself or the injection process is the primary trigger for early oocyte activation events.

Main Methods:

• Oocytes were subjected to sperm injection (ICSI), sham injection, or left uninjected.
• Oocytes were cultured in calcium-free media, media with calcium chloride, or media with calcium ionophore.
• Fertilization and activation rates were assessed after 19 hours of in vitro culture.

Main Results:

• Fertilization rates were similar with calcium chloride or calcium ionophore but lower in calcium-free media.
• In vitro fertilization rates mirrored in vivo rates when calcium was present.
• Oocyte activation was induced by mechanical injection with calcium chloride or by ionophore, but not by calcium alone in uninjected oocytes.
• No difference in activation was observed between ICSI and sham injection.

Conclusions:

• Calcium is necessary for proper oocyte activation, even when initiated by mechanical injection.
• The injection process itself can induce some activation, but it is insufficient without calcium.
• Sperm may not play a role in the initial events of oocyte activation; the injection process and calcium are key.