Changes in poly(A) tail length of maternal transcripts during in vitro maturation of bovine oocytes and their relation with developmental competence

Molecules of mRNA are stored in the oocyte cytoplasm in order to be used du ring the initial phases of embryonic development. The storage takes place d uring oocyte growth and the extent of poly(A) tail at the 3' end of the tra nscripts has emerged as an important regulatory element for determining the ir stability. The objective of the present study was to analyse changes in polyadenylation levels of mRNA transcripts, stored in bovine oocytes, durin g in vitro maturation and their possible relation with developmental compet ence. Oocyte developmental competence was predicted on the basis of the mor phological appearance of their originating ovary as previously established (Gandolfi et al. 1997a. Theriogenology 48:1153-1160) and were divided into groups H (high competence) and L (low competence). The length of the poly(A ) tail of the following genes, beta-actin (beta-Act), connexin 43, glucose transporter type 1, heat shock protein 70, oct-4, plakophilin, pyruvate deh ydrogenase phosphatase (PDP), and RNA poly(A) polymerase, was determined at the germinal vesicle (GV) and metaphase II (MII) stage. The results indica ted that the poly(A) tail of all genes except for p-Act and PDP, is shorter after in vitro maturation (IVM) in both groups. Moreover, group L oocytes showed a shorter poly(A) tail than group H oocytes in all genes except for p-Act and PDP, both at GV and MII stage. We conclude that most of the exami ned transcripts follow the default deadenylation pattern described during o ocyte maturation in other species and that a shorter poly(A) tail is correl ated with low developmental competence. (C) 1999 Wiley-Liss, Inc.