Abstract PR04: Analyses of Pax2 and Pax8 in maintaining oviduct epithelial homeostasis and fertility
Authors: Soofi Abdulsalam , Zahi Yali , Cho Kathleen , Dressler Greg 
Published: September 2020

Introduction: The female urogenital tract develops through a multistep process from the intermediate mesoderm (IM). Among several transcriptional regulators, Pax2 and Pax8 expression in the IM distinguishes all of the cells fated to become epithelia in the urogenital tract and are necessary to establish and maintain this phenotype. Fallopian tube epithelium mainly consists of two cell types, secretory and ciliated cells. In mice, Pax2 and Pax8 positive secretory cells are the oviduct epithelial progenitors and have the potential to self-renew as well as differentiate to ciliated cell progeny. Serous ovarian cancer (SOC) is the most common and the most lethal, and secretory cells are believed to be the progenitors of SOC. Patients with a predisposition for developing SOC were found to have tubal epithelial dysplastic lesions, such as serous tubal intraepithelial carcinoma (STIC). By generating double and single KO mouse modules of Pax2 and Pax8, we investigate their roles in maintaining the integrity of the oviductal cells and whether these proteins will provide new insight into epithelial homeostasis.

Procedures: We used the Cre-loxP system to generate conditional KO of Pax2 and Pax8, using standard genetic and biochemical techniques to study the deletion of both proteins specifically in epithelium secretory cells. We used the OVGP1-Cre tamoxifen-inducible; also, some mice carried the combination with reporter mT/mG. Histology, immunohistochemistry, Western blot, and RNA meta-analysis data were collected and analyzed.

Results: Mice carrying the single conditional KO of Pax2 f/f and Pax8f/f;OVGP1-CRE-ER or the double conditional KO of Pax2.flox-Pax8flox;OVGP1-CRE-ER appeared normal with no evidence of loss of function or other abnormalities. After tamoxifen administration and specific oviductal deletion of these proteins, the double Pax2 and Pax8 mutants showed oviduct phenotypes as early as 16 weeks. Such mice also failed to conceive even 8 weeks after tamoxifen administration. We observed progressive phenotypes at later times in the three combinations of protein deletion for up to one year after tamoxifen administration. Strikingly, cell lineage tracing revealed that surviving mutant cells could break through and migrate without losing their epithelial markers. These data demonstrate that Pax2 and Pax8 are needed for regenerating and maintaining the integrity of the fallopian tubes.

Conclusions: Human ovarian cancer precursor lesions primarily consist of secretory cells. In mouse oviduct, secretory cells are the most frequently dividing cells of the oviductal epithelium. The mechanisms underlying epithelial homeostasis are still unknown. This in vivo genetic cell lineage tracing study showed that secretory cells give rise to ciliated cells that are altered upon Pax2 and Pax8 deletion. Using a conditional KO mouse model of Pax2 and Pax8 will allow us to identify future novel therapeutic targets and step further in the right direction to develop a novel of biomarkers for diagnostics and treatments.

This abstract is also being presented as Poster B44.

Citation Format: Abdulsalam Soofi, Yali Zahi, Kathleen Cho, Greg Dressler. Analyses of Pax2 and Pax8 in maintaining oviduct epithelial homeostasis and fertility [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr PR04.