MicroRNAs as post-transcriptional machines and their interplay with cellular networks.

Gene expression is a highly controlled process which is known to occur at several levels in eukaryotic organisms. Although RNAs have been traditionally viewed as passive molecules in the pathway from transcription to translation, there is increasing evidence that their metabolism is controlled by a class of small noncoding RNAs called MicroRNAs (miRNAs). MicroRNAs (miRNAs) control essential gene regulatory pathways in both plants and animals however our understanding about their function, evolution and interplay with other cellular components is only beginning to be elucidated. In this chapter, we provide an overview of the recent developments in our understanding of this class of RNAs from diverse perspectives including biogenesis, mechanism of their function, evolution of their clusters, and discuss the approaches currently available for the construction of post-transcriptional networks governed by them. We also present our current understanding on these post-transcriptional networks in the context other cellular networks. We finally argue that such developments would not only allow us to gain a deeper understanding of regulation at a level that has been under-appreciated over the past decades, but would also allow us to use the newly developed high-throughput approaches to interrogate the prevalence of these phenomena in different states, and thereby exploit the functions of these RNA molecules for therapeutic advantage in higher eukaryotes.