Characterization of PRAP1 During Murine Gestation

Abstract

The development of Assisted Reproductive Technologies, such as in vitro fertilization (IVF), has allowed many couples struggling with fertility to conceive. However, IVF has a 60% failure rate. The leading cause of IVF failure is understood to be unsuccessful implantation. Improper or defective implantation leads to improper placentation which can affect fetal growth and development. While it is known that implantation is a complex reproductive process dependent on both competent embryos and a receptive uterus, many aspects of implantation remain unclear. Proline Rich Acidic Protein 1 (PRAP1), a 17 kDa protein, is expressed and secreted by the uterine endometrium. In the absence of PRAP1, female mice show defective implantation suggesting that PRAP1 has a role in this process. Nonetheless, PRAP1 remains largely uncharacterized. The objectives of this study are to characterize the role of PRAP1 during gestation and implantation. We hypothesize PRAP1 plays a role in implantation/placentation and overall pregnancy maintenance. Using timed pregnancies of wildtype C47BL/6J mice, uterine tissue was collected for each day of gestation and four days post‐partum, then analyzed by RT‐qPCR, immunofluorescence with a‐PRAP1 antibodies, and H&E staining. We found that Prap1 transcript is highly expressed during gestation compared to non‐ovulating females. Additionally, PRAP1 is downregulated during the window of implantation beginning at day 3.5 and increases on day 5.5. This increase continues and peaks just prior to parturition, and PRAP1 expression decreases 1000x within 4 days post‐partum. Immunofluorescence analysis demonstrated PRAP1 is localized to the endometrial epithelia during early gestation, but localized specifically to the anti‐mesometrial epithelia that interfaces with the amnion during mid‐ and late‐gestation. We have also found that our PRAP1−/− female mice have a slightly reduced fecundability (the ability to achieve a live birth from one cycle’s exposure to the risk of pregnancy) attributable to a reduced rate of implantation. We conclude PRAP1 plays a role in implantation/placentation and overall pregnancy maintenance.