This first chapter of the book aims to provide readers the basic information necessary for better
understanding the contents of other chapters. The chapter begins with the stories or history of discovery of
miRNAs. From this section, readers can get a sense on how some groundbreaking scientific findings could be
achieved from small but mysterious things. In the second section, the whole pathway of biogenesis of miRNAs is
described in detail, from transcription to maturation. This is followed by the section on action of miRNAs
describing how mature miRNAs are hooked up to the protein complex and guide the complex to target genes to
execute repression of gene expression at the post-transcriptional level. Finally, some important issues related to
miRNA function are introduced in the section entitled “Some conceptual notes about miRNA function.”
