Comparative gene expression profiling of mouse ovaries upon stimulation with native equine chorionic gonadotropin (eCG) and tethered recombinant-eCG

Abstract

Background: Equine chorionic gonadotropin (eCG) induces super-ovulation in laboratory animals. Notwithstanding its extensive usage, limited information is available regarding the differences between the in vivo effects of native eCG and recombinant eCG (rec-eCG). This study aimed to investigate the gene expression profiles of mouse ovaries upon stimulation with native eCG and rec-eCG produced from CHO-suspension (CHO-S) cells. eCG and rec-eCG were cloned and transfected into CHO-S cells and quantified. Thereafter, we determined the metabolic clearance rate (MCR) of native eCG and rec-eCG up to 24 h after intravenous administration through the tail vein and identified differentially expressed genes in both ovarian tissues, via quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC).Results: Rec-eCG was markedly up-regulated initially after transfection and maintained until recovery on day 9. Oligosaccharide chains were substantially modified in rec-eCG protein produced from CHO-S cells and eliminated through PNGase F treatment. The MCR was slightly lower for rec-eCG than for eCG, and no significant difference was observed after 60 min. Notwithstanding their low concentration, rec-eCG and native eCG were detected in the blood at 24h post-injection. Microarray analysis of ovarian tissue revealed that 20 of 12,816 genes assessed therein were significantly up-regulated and 43 genes were down-regulated by >2-fold in the group receiving rec-eCG (63 [0.49%] differentially regulated genes in total). The microarray results were concurrent with and hence validated by those of RT-PCR, qRT-PCR, and IHC analyses.Conclusions: The present results indicate that rec-eCG can be adequately produced through a cell-based expression system through post-translational modification of eCG and can induce ovulation in vivo. These results provide novel insights into the molecular mechanisms underlying the up- or down-regulation of specific ovarian genes and the production of rec-eCG with enhanced biological activity in vivo.