A significant portion of the mammalian genome encodes numerous transcripts that 
are not translated into proteins, termed long non-coding RNAs. Initial studies 
identifying long non-coding RNAs inferred these RNA sequences were a consequence 
of transcriptional noise or promiscuous RNA polymerase II activity. However, the 
last decade has seen a revolution in the understanding of regulation and 
function of long non-coding RNAs. Now it has become apparent that long 
non-coding RNAs play critical roles in a wide variety of biological processes. 
In this review, we describe the current understanding of long non-coding 
RNA-mediated regulation of cellular processes: differentiation, development, and 
disease.