Invited Reviews

MiRNAs are a widespread class of small non-coding RNAs that have the ability to silence gene expression through sequence complementarity to their targets. We describe their initial discovery in the nematode C.elegans and review what is currently known about their biogenesis. The regulation of expression and processing of miRNAs, and the mechanisms through which miRNAs locate their correct targets are not yet fully understood. MiRNAs are involved in a multitude of developmental and pathological processes leading to an explosion of research in disparate subject areas. In this review we draw attention to placentally expressed miRNAs that can be detected in the maternal plasma; and we discuss their potential use as biomarkers in non-invasive prenatal diagnostics.