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MBC in Press, published online ahead of print January 5, 2005
Mol. Biol. Cell 10.1091/mbc.E04-07-0585

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Submitted on July 13, 2004
Revised on November 24, 2004
Accepted on December 22, 2004

XGef Mediates Early CPEB Phosphorylation during Xenopus Oocyte Meiotic Maturation

Susana E. Martínez,* Lei Yuan,* Charlemagne Lacza,* Heather Ransom,* Gwendolyn M. Mahon,{dagger} Ian P. Whitehead,{dagger} and Laura E. Hake*{ddagger}

*Biology Department, Boston College, Chestnut Hill, MA 02467; {dagger}Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, Newark, NJ 07103-2714

Monitoring Editor: Joseph Gall

Polyadenylation-induced translation is an important regulatory mechanism during metazoan development. During Xenopus oocyte meiotic progression, polyadenylation-induced translation is regulated by CPEB, which is activated by phosphorylation. XGef, a guanine exchange factor, is a CPEB-interacting protein involved in the early steps of progesterone-stimulated oocyte maturation. We find that XGef influences early oocyte maturation by directly influencing CPEB function. XGef and CPEB interact during oogenesis and oocyte maturation and are present in a c-mos mRNP. Both proteins also interact directly in vitro. XGef overexpression increases the level of CPEB phosphorylated early during oocyte maturation and this directly correlates with increased Mos protein accumulation and acceleration of meiotic resumption. To exert this effect XGef must retain guanine exchange activity and the interaction with CPEB. Overexpression of a guanine exchange deficient version of XGef, which interacts with CPEB, does not enhance early CPEB phosphorylation. Overexpression of a version of XGef that has significantly reduced interaction with CPEB, but retains guanine exchange activity, decreases early CPEB phosphorylation and delays oocyte maturation. Injection of XGef antibodies into oocytes blocks rogesterone-induced oocyte maturation and early CPEB phosphorylation. These findings indicate that XGef is involved in early CPEB activation and implicate GTPase signaling in this process.

{ddagger}Corresponding author. E-mail: hakel{at}bc.edu




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