MicroRNAs are a class of small, evolutionarily conserved, endogenous RNAs, capable of controlling gene expression. MicroRNAs are transcribed by RNA polymerases II and III, generating precursors that undergo a series of cleavage events to form mature microRNA. They play an important regulatory role in animals at the posttranscriptional levels by targeting mRNAs for direct cleavage of mRNAs or repression of mRNA translation. The main biological function of miRNA is the post-translation regulation of cells, like: proliferation and differentiation, cell death, fat metabolism, neuronal patterning and angiogenesis. These molecules are the main regulators of biological features of economic