Data Mining Based Analysis of Genomic Location Shifts of Conserved Annotated miRNA Genes gives Preliminary Insights on Molecular Network Evolution

Micro-RNAs (miRNAs) are key regulators of gene expression. Their post-transcriptional regulatory role was conserved in all eukaryotes during evolution. However, the genomic location of conserved miRNA genes has not been studied in the context of genetic network evolution. This study is based on the data mining of miRNA and genomic annotation databases. An individual retrieval of the genomic location of the 3,216 miRNA genes annotated in Danio rerio, Xenopus tropicalis, Rattus norvegicus, Mus musculus and Homo sapiens genome was performed. Despite a fairly constant proportion of protein coding sequences in vertebrates, approximately 60% of the conserved intergenic miRNA genes reported in zebra fish shift to an intragenic location in human genome. This phenomenon may be explained by duplication and/or transposition mechanisms. The increase of tight regulatory units in higher vertebrates, in which targets of intragenic miRNAs are within the host gene network, emphasized the importance of miRNAs and probably led to the appearance of oncogenic miRNAs (oncomiRs) that are mainly intragenic.