PROJECT SUMMARY/ABSTRACT The placenta plays a crucial role during pregnancy ensuring fetal growth and development. Successful pregnancy hinges upon placental adaptations to the maternal environment. The human placenta is classified as hemochorial and is characterized by extensive intrauterine trophoblast cell invasion. During the course of the gestation, invasive trophoblast cells or extravillous trophoblast, as they are referred to in humans, migrate from the placenta into the uterine parenchyma where they act to anchor the placenta to the uterus and remodel uterine spiral arteries. Uterine NK (NK) cells are major immune cell population at the uterine-placental interface. Uterine NK cell numbers expand at the uterine-placental interface during early gestation. In addition to functioning as sentinels, they promote uterine vasculature development by secreting proangiogenic factors and initiating crosstalk with cellular constituents. Invasive trophoblast cells and uterine NK cells contribute to an effective partnership in modifying the uterine vasculature. Uterine vascular remodeling is central to providing adequate nutrient flow to the fetus and normal fetal development. Aberrant modification of the uterine vasculature is directly linked to preeclampsia, early pregnancy loss, intrauterine growth restriction, pre-term birth, and placental abruption. Placentation in the rat is characterized by contributions of uterine NK cells and invasive trophoblast cell to uterine spiral artery remodeling, resembling developmental processes evident in human placentation. Global genome-editing in the rat is an effective tool for investigating a sub-set of candidate genes implicated in regulating events at the uterine-placental interface. Some genes possess multiple roles in the biology of the maternal rat, precluding an evaluation of a specific role in uterine NK cells. The generation of a conditional allele circumvents this issue. In the proposed research, we will develop a rat model for uterine NK cell specific conditional alleles using Crispr/Cas9 genome editing. We will generate a transgenic rat model expressing Cre recombinase in uterine NK cells under control of Ncr1 regulatory sequences and validate the Ncr1-Cre driver rat strain. The proposed experiments will provide valuable new tools for the scientific community to discern roles for candidate genes in the regulation of the uterine-placental interface, including uterine spiral artery remodeling, and thus a novel experimental paradigm to explore the etiology of high-risk pregnancies.