The maternal pool of mRNA undergoes major changes during oocyte maturation and early embryonic development. Specific genes are activated or degraded in response to changes in poly-(A) tail length. However, little is known about how the oocyte targets specific transcripts for degradation or translation in a timely manner. The objective of this study was to determine how poly-(A) tail length of different transcripts is affected in bovine oocytes by time of in vitro maturation. Cyclin B1 and GDF-9 3' untranslated regions (UTRs) were cloned into modified p-GEM plasmids containing a poly-(A) tract of 60 or 0 adenosines (A60 or A0, respectively). Each 3' UTR was transcribed in vitro with (A60) or without (A0) a poly-(A) tail to generate UTP32 labeled RNA. Transcriptions producing at least 200,000 counts per min (cpm) per ?L were used for subsequent injections into denuded bovine oocytes. Cumulus-oocyte complexes (COC's) recovered from slaughterhouse-derived ovaries (n=216) were vortexed to remove cumulus cells immediately after aspiration, after 3 h of in vitro maturation, or after 19 h of maturation in a chemically defined medium supplemented with FSH, LH, EGF, and cysteamine. After vortexing, denuded oocytes were injected and snap frozen, or matured in vitro for 1 or 3 h. Eight oocytes were injected with ~0.5 nL (~100 cpm/oocyte) labeled RNA at each timepoint in three replicates. Total RNA was isolated from injected oocyte pools and loaded onto a 5% denaturing acrylamide gel for size separation. Radiolabeled A0 was used as a control point of reference for deadenylation. Gels were dried, and RNA was visualized on a phosphoimager after 24 h exposure to a phosphor screen. Changes in polyadenylation status (transcript size) were evaluated by comparing shifts in bands from gene-specific A60's size to A0. Cyclin B1 3' UTR A60 began shortening by 1 h and was mostly degraded by 3 h regardless of cell cycle stage (0, 3, or 19 h of maturation) before being degraded. GDF-9 3' UTR A60 remained stable in oocytes injected immediately or 3 h after aspiration. Oocytes matured 19 h maintained stable GDF-9 3'UTR A60 until 1 h after injection, after which GDF-9 3' UTR A60 degraded rapidly. Thus, the polyadenylated GDF-9 3' UTR is regulated differently than the Cyclin B1 polyadenylated 3' UTR during oocyte maturation. Interactions between proteins and 3' UTR sequence elements direct mRNA fate. Understanding 3' UTR regulation will facilitate development of methods for detecting and treating inappropriate RNA regulation. Furthermore, this research shows that RNA produced in vitro and injected into bovine oocytes can be recovered with sufficient sensitivity to test hypotheses in a physiologically relevant system. As few as 8 oocytes injected with ~0.5 nL of 200,000 cpm/uL radiolabeled diagnostic RNA can be used to determine how specific genes are regulated during oocyte development and early embryogenesis.