A role for protein kinase C during rat egg activation

Area of Science:

• Reproductive Biology
• Cellular Biology
• Biochemistry

Background:

• Sperm-egg interaction elevates intracellular calcium ([Ca(2+)](i)), initiating the cortical reaction (CR).
• Protein Kinase C (PKC) activation also triggers CR, suggesting alternative signaling pathways.
• Conventional PKCs (cPKC) alpha and beta II are implicated as exocytosis mediators.

Purpose of the Study:

• To investigate cPKC activation in rat eggs during in vivo fertilization and parthenogenetic activation.
• To determine the role of cPKC in the CR and its relationship with [Ca(2+)](i) elevation.

Main Methods:

• Immunohistochemistry and confocal microscopy were used to visualize cPKC isozymes.
• Rat eggs were studied during in vivo fertilization and parthenogenetic activation.
• PKC activation was induced using phorbol ester (TPA), OAG, and ionomycin; inhibition was achieved with myrPKCPsi.

Main Results:

• cPKC alpha, beta I, and beta II translocated to the egg plasma membrane during in vivo fertilization.
• Translocation kinetics varied among isozymes, with all present by the sperm-binding stage.
• PKC alpha activation could be induced by TPA or OAG, but not ionomycin, suggesting calcium is not essential for PKC alpha activation.
• PKC alpha activation by OAG was accelerated by elevated [Ca(2+)](i).
• The CR was inhibited by a specific PKC inhibitor (myrPKCPsi).

Conclusions:

• Exocytosis, including the CR, can be triggered independently by either a [Ca(2+)](i) rise or PKC activation.
• cPKC alpha, beta I, and beta II are activated during rat egg fertilization.
• [Ca(2+)](i) elevation may modulate, but is not required for, PKC alpha activation during fertilization.