New insights into the function of noncoding RNA and its potential role in disease pathogenesis

All polyadenylated RNAs expressed in mammalian tissues are assumed to be tr ansported to the cytoplasm where they direct the synthesis of a protein pro duct. This mainstream view of the function of polyadenylated transcripts is currently being challenged by the identification of a novel class of genes which, although they encode polyadenylated RNA, do not make a translated p rotein. Many of these noncoding RNAs are developmentally regulated or show highly restricted patterns of gene expression, and their functions are prov iding important insight into RNA-based mechanisms of gene expression, genom ic imprinting, cell cycle progression, and differentiation. The purpose of this review is to discuss the current understanding of mammalian noncoding RNAs, and to highlight their potential for identifying new pathways of huma n disease.