Abstract 2395: Effect of Brca1 knockout on gene expression in mouse ovarian granulosa cells
Authors: Liu Ying , Punj Vasu , Hong Hao , Enbom Elena , Maxson Robert , Dubeau Louis 
Published: June 2012

We previously reported that conditional inactivation of Brca1 in ovarian granulosa cells leads to the development of benign epithelial tumors in two thirds of the mutant mice. The tumors were localized either in the ovarian hilum, oviducts, or on the external surface of the uterine horns. They resembled human ovarian serous cystadenomas, which are the benign counterparts of the tumors seen in human BRCA1 mutation carriers. The tumors did not harbor mutant Brca1 alleles, implying that the mechanism of tumor predisposition in this model is driven by a cell non-autonomous mechanism. We recently showed that mutant mice had increased estrogen stimulation unopposed by progesterone due to higher circulating levels of estradiol and to a prolongation of pro-estrus phase of the estrus cycle, the equivalent of the estrogen-dominating follicular phase in the human menstrual cycle, providing evidence that such stimulation was instrumental in mediating tumor predisposition in this mouse model.

We sought to get further insights into the consequences of Brca1 inactivation on gene expression in ovarian granulosa cells. We used laser capture microdissection to isolate granulosa cells from mutant and wild type mice at the age of 8 months when the mutant mice displayed most significant elongation in pro-estrus phase. All mice were synchronized in pro-estrus phase, with 5IU of Pregnant Mare Serum Gonadotropin inoculated 48 hours before they were harvested. Granulosa cell mRNA from each group was pooled and analyzed using mouse all-exon arrays. The expression of 2,972 genes was changed more than 2-fold in mutant versus wild type animals.

Selected differentially expressed genes were further analysed by quantitative RT-PCR to verify the authenticity of the differential expression. Linear regression analysis showed excellent correlation between the qRT-PCR and microarray data, with a coefficient of variation R2 of 0.8088. Here we report that the gene family that was most frequently influenced by Brca1 inactivation in ovarian granulosa cells was that of olfactory receptors. The second most significant difference based on magnitude of changes in expression level between the 2 groups of mice involved an olfactory receptor. Ten of the thirty genes that showed the highest fold increase in expression in mutant animals were olfactory receptors. These data are interesting in light of Kallmann syndrome, characterized by hypogonadism and loss of ability to smell. Our data suggest that olfactory receptors may play an important role in signal transduction in granulosa cells. Assuming that the decrease in gene dosage present in BRCA1 mutation carriers is sufficient to induce changes in gene expression similar to those seen in homozygous Brca1 knockouts, the results also suggest that such signaling is altered in human BRCA1 mutation carriers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2395. doi:10.1158/1538-7445.AM2011-2395