During mammalian oocyte maturation, protein synthesis is mainly controlled 
through cytoplasmic polyadenylation of stored maternal mRNAs. In this study, the 
role of polyadenylation modification of maternal transcripts in pig oocytes was 
investigated by adding cordycepin (3'-dA), a potent polyadenylation inhibitor, 
to the culture medium of porcine oocytes maturing in vitro. 3'-dA significantly 
prevented cumulus expansion regardless of the concentration used, and inhibited 
pig oocyte maturation in a dose-dependent manner. Further, 3'-dA 1 
microg/ml-treated MII oocytes experienced significantly lower rates of cleavage 
(29%) and blastocyst formation (15.35%) compared to control MII oocytes (58.6% 
and 35.3%, respectively). Western blotting revealed that the activity of 
mitogen-activated protein kinase (MAPK) and p34(cdc2) was significantly 
decreased in oocytes and cumulus cells treated with 3'-dA at a concentration of 
1 microg/ml or greater. To further explore the underlying molecular mechanisms, 
expression patterns and polyadenylation states of four important genes, C-mos, 
cyclin B, GDF9 and BMP15, were studied as representative maternal transcripts by 
real-time PCR and the PAT assay. 3'-dA at concentrations above 1 microg/ml 
significantly prevented polyadenylation and caused aberrant expression of C-mos 
and GDF9 during oocyte maturation. These results suggest that polyadenylation 
inhibitor blocked pig oocyte maturation in vitro by one or more of the following 
actions: (1) inactivation of MAPK and MPF in oocytes, especially at the late 
stages (MI and MII); (2) prevention of cumulus cell expansion through 
inactivation of cellular MAPK; and (3) inhibition of the maternal mRNA 
polyadenylation process, which in reverse, disrupted the maternal mRNA patterns 
in pig oocytes' maturation in vitro.