Post-transcriptional regulations of gene expression (control of mRNA stability and translation) play a central role in achieving cellular functions. In a large number of cases, post-transcriptional regulations are dependent on mRNA poly(A) tails, as mRNAs with a long poly(A) tail are generally much more stable and actively translated than deadenylated mRNAs. In this review, we will discuss the activities that modify poly(A) tail lengths in Xenopus oocytes and embryos. We will particularly focus on one activity, the "EDEN" mechanism, that provokes specific poly(A) tail shortening rapidly after fertilization. EDEN-dependent deadenylation is mediated by the specific binding of a protein, EDEN-BP. The EDEN mechanism will be compared with several other mechanisms that provoke deadenylation in a large variety of species. The proposal that the EDEN mechanism is probably a mechanism of widespread importance in the metazoan world will be discussed.