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 transported to the cytoplasm where they direct the synthesis of a protein product. 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 protein. Many of these noncoding RNAs are developmentally regulated or show highly restricted patterns of gene expression, and their functions are providing important insight into RNA-based mechanisms of gene expression, genomic 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 human disease.