188 EFFECTS OF IN VITRO MATURATION ON GENE EXPRESSION IN RHESUS MONKEY OOCYTES

Abstract

Assisted reproduction technologies (ARTs) are achieving increasing prominence in reproductive medicine. With the increasing application of ARTs comes increased interest in optimizing efficiency while minimizing potential risks to the offspring. One area of assisted reproduction in which improvements are being sought is in vitro oocyte maturation. In vitro oocyte maturation (IVM) holds great promise as a tool for enhancing clinical treatment of infertility, enhancing availability of non-human primates for development of disease models, and facilitating endangered species preservation. However, IVM outcomes have remained significantly below success rates obtained using in vivo-matured (VVM) oocytes from humans and non-human primates. There is thus considerable interest in improving IVM. Key objectives toward achieving more efficient IVM will be to establish the molecular determinants of oocyte quality, identify specific biological processes or mechanisms that may be disrupted by ARTs, and identify specific modifications to procedures to eliminate these deficiencies. This study provides the first global comparison of mRNA expression profiles between in vitro- and in vivo-matured metaphase II stage oocytes in a non-human primate species. RNAs isolated from oocytes of each kind (IVM and VVM) were subjected to a 2-cycle labeling assay, and the labeled cRNAs were hybridized to Affymetrix rhesus macaque genome arrays (Affymetrix Inc., Santa Clara, CA, USA). To minimize false positive signals, only genes called present in at least 3 out of 4 biological replicates were used for significance analysis of microarray. Genes with significant differences among samples were identified at the 5% false discovery rate and were further selected on the basis of t-test (P < 0.05). We observed a small set of just 59 mRNAs that are differentially expressed between the 2 types of oocytes. Independent confirmation of gene expression differences was performed for 19 candidate genes using the quantitative RT-PCR. Gene functional classification analysis revealed that genes differentially expressed between IVM and VVM oocytes are related to cellular homeostasis, cell-cell interactions including growth factor and hormone stimulation and cell adhesion, and other functions such as mRNA stability and translation. Additionally, we observed in IVM oocytes overexpression of PLAGL1 and MEST, 2 maternally imprinted genes, indicating a possible interruption or loss of correct epigenetic programming. These results provide novel insight into the nature of oocyte-follicle cell interactions, the potential molecular and cellular consequences of altering these interactions, and the basis for compromised developmental competence following IVM procedures in a non-human primate model. The results also raise concerns about applying IVM clinically without addressing such developmental defects but indicate that these deficiencies may be overcome by further improvement in IVM culture systems.

This study was supported by grants from the National Institutes of Health, National Centers for Research Resources (NCRR) RR15253 (KEL), RR000169 (CAV), and RR13439 (CAV).