261 IDENTIFICATION OF OOCYTE- AND CUMULUS-DERIVED CO-REGULATED AND DIFFERENTIALLY REGULATED TRANSCRIPTS ASSOCIATED WITH BOVINE MEIOTIC MATURATION
Authors: Patel O. V. , Bettegowda A. , Ireland J. J. , Smith G. W. 
Published: December 2006

Understanding the process of oocyte maturation is critical for efficient application of biotechnologies such as in vitro embryo production and nuclear transfer/cloning. Intercellular communication between the oocyte and the encompassing somatic (cumulus) cells is pivotal for successful growth of ovarian follicles and oocyte maturation. Therefore, we utilized global gene expression profiling to determine changes in the transcriptome of oocytes and their adjacent cumulus cells during meiotic maturation in vitro to identify both co-regulated and differentially regulated transcripts within the two cell compartments of the cumulus oocyte complex (COC). Germinal vesicle (GV) and in vitro matured metaphase II (MII) COC (n = 5 pools of 5 COC per group) were denuded and separated into oocytes and cumulus cells. RNA was extracted from the oocytes and cumulus cells and subjected separately to microarray analysis using a bovine cDNA array containing expressed sequence tags (ESTs) representing 15 500 unique genes. A combined total of 1045 genes displaying greater mRNA abundance in GV oocytes and associated cumulus cells compared to MII samples were detected (P < 0.05; false discovery rate (FDR) = 5%). A combined total of 711 genes displaying greater mRNA abundance in MII oocytes and enclosing cumulus cells compared to GV samples were detected (P < 0.05; FDR = 5%). Fourteen transcripts were identified that were co-regulated and of greater abundance in GV or MII oocytes and in their matching cumulus cells (P < 0.05; FDR = 5%). The co-regulated transcripts identified are implicated in metabolism (e.g. heme oxygenase-2, leukotriene B4 12-hydroxydehydrogenase), signal transduction (e.g. caveolin 1, ring finger protein 31), and cell growth (e.g. BTG family member 2, myosin regulatory light chain 2). In contrast, thirteen transcripts differentially regulated in the GV oocyte versus MII cumulus cells were identified (P < 0.05; FDR = 5%). Similarly, nine transcripts differentially regulated in the MII oocyte versus GV cumulus cells were identified (P < 0.05; FDR = 5%). Some of the identified differentially regulated transcripts encode for genes associated with the cytoskeleton (e.g. tropomyosin 1), apoptotic activity (e.g. death effector domain containing protein 2) and DNA replication (e.g. epsilon polymerase). The results provide novel insights into the identity of transcripts whose abundance is co-regulated or differentially regulated between the oocyte and cumulus cells during the transition of a COC from the GV to the MII stage. Characterization of the signaling pathways driving changes in transcript abundance for co-regulated and differentially regulated genes in oocytes versus associated cumulus cells may lead to a better understanding of regulation of meiotic maturation and potential cross-talk between germ cells and somatic cells during the oocyte maturation cascade.
This work was supported by the Rackham Foundation and the MI Agriculture Experiment Station.