The multitudinous role of microRNAs in various biological systems

MicroRNAs (miRNAs) belong to a large family of small, single-stranded 16-21 nucleotide long, highly conserved non-protein-coding duplex RNA molecules, which are crucial regulators of gene expression in animals, plants and protozoa. miRNAs have different expression patterns, to regulate various imperative developmental and physiological processes. Our aim in this review is to outline the current advancements to understand the role of miRNAs to influence in animals and plants, and we discuss some of the controversies regarding the diverse ways in which miRNA functions.