Starfish oocyte maturation: evidence for a cyclic AMP-dependent inhibitory pathway

Area of Science:

• Reproductive Biology
• Cell Signaling
• Molecular Endocrinology

Background:

• Oocyte maturation in starfish is triggered by 1-methyladenine (1-MeAde).
• Cyclic AMP (cAMP) appears to inhibit maturation, as 1-MeAde decreases oocyte cAMP levels and cAMP microinjections delay maturation.
• Other nucleotides like cCMP, cIMP, and cUMP do not affect maturation.

Purpose of the Study:

• To investigate the role of cAMP and cyclic GMP (cGMP) in controlling starfish oocyte maturation.
• To elucidate the signaling pathways involved in 1-MeAde-induced meiosis reinitiation.
• To determine if specific kinase activities mediate the inhibitory effects of cAMP and cGMP.

Main Methods:

• Utilized phosphodiesterase-stable stereoisomers of adenosine and guanosine 3',5'-phosphorothioates (cAMPS and cGMPS).
• Microinjected Sp (kinase-activating) and Rp (kinase-inhibiting) isomers into starfish oocytes.
• Assessed the effects of microinjections on 1-MeAde-induced maturation and utilized analogs and inhibitors of cAMP-dependent protein kinase.

Main Results:

• Microinjection of kinase-activating (Sp)-cAMPS and (Sp)-cGMPS inhibited maturation in a dose-dependent manner.
• (Rp)-cAMPS and (Rp)-cGMPS isomers had no inhibitory effects.
• The inhibitory effect was specific to compounds activating cAMP-dependent kinase; inhibition was reversible by a protein kinase inhibitor, the antagonist (Rp)-cAMPS, or increased 1-MeAde concentration.

Conclusions:

• A cAMP-dependent inhibitory pathway maintains prophase arrest in starfish oocytes.
• 1-Methyladenine (1-MeAde) induces maturation by inhibiting this negative pathway and activating a parallel positive pathway.
• This mechanism highlights a dual role for cAMP signaling in regulating oocyte meiotic progression.