MicroRNA regulation of immune events at conception.

The reproductive tract environment at conception programs the developmental trajectory of the embryo, sets the course of pregnancy, and impacts offspring phenotype and health. Despite the fundamental importance of this stage of reproduction, the rate-limiting regulatory mechanisms operating locally to control fertility and fecundity are incompletely understood. Emerging studies highlight roles for microRNAs (miRNAs) in regulating reproductive and developmental processes and in modulating the quality and strength of the female immune response. Since endometrial receptivity and robust placentation require specific adaptation of the immune response, we hypothesize that miRNAs participate in establishing pregnancy through effects on key gene networks in immune cells. Our recent studies investigated miRNAs that are induced in the peri-conception environment, focusing on miRNAs that have immune-regulatory roles-particularly miR-223, miR-155, and miR-146a. Genetic mouse models deficient in individual miRNAs are proving informative in defining roles for these miRNAs in the generation and stabilization of regulatory T cells (Treg cells) that confer adaptive immune tolerance. Overlapping and redundant functions between miRNAs that target multiple genes, combined with multiple miRNAs targeting individual genes, indicate complex and sensitive regulatory networks. Although to date most data on miRNA regulation of reproductive events are from mice, conserved functions of miRNAs across species imply similar biological pathways operate in all mammals. Understanding the regulation and roles of miRNAs in the peri-conception immune response will advance our knowledge of how environmental determinants act at conception, and could have practical applications for animal breeding as well as human fertility.