Hormonal Responsiveness by Immature Rabbit Uterine Epithelial Cells Polarizedin Vitro*

Abstract

This paper reports the development of an in vitro cell culture system of polarized uterine epithelial (UE) cells from the immature rabbit. UE cells from immature rabbit were cultured on EHS (Engelbreth-Holm-Swarm) matrix-coated semipermeable filter inserts in a serum-free, phenol red-free defined medium. The cells in primary culture attached, proliferated, formed monolayers, and exhibited structural and functional polarity. Structural differentiation was validated by ultrastructural features, such as apical microvilli, intercellular junctions, desmosomes, and polar organization of apical vs. basal membrane domains. Trans-monolayer epithelial resistance, a reflection of functional tight junctions, preferential basal uptake of [35S]methionine, polarized distribution of labeled secretory proteins, and increased secretory activity marked by preferential apical secretion (greater than 90%) of proteins were indices of functional polarity. With the development and maintenance of polarized state by the UE cells, some of the newly synthesized proteins were sorted and vectorially secreted into their distinct compartments. De novo synthesis and exclusive apical secretion of uteroglobin (a progesterone-induced protein in vivo) by the polarized UE cells occurred in response to progesterone treatment in vitro. The hormone responsiveness was maintained for a prolonged period under these conditions. A culture system in which the UE cells maintain functional and morphological polarity and sustain their hormonal responsiveness facilitates the study of regulation of specialized functions by the UE cells that are regulated by steroid hormones and their interactions with the other uterine cell types.