Overexpression of Mir-197 und Mir-769 in human iPSCs

MicroRNAs (miRNAs) are post-transcriptional regulators that are involved in many essential biological processes. Recently, targeted searches for human miRNA orthologs revealed that 15 miRNA families are lost in the Eumuroidea lineage, including the model organisms mouse and rat, but not in other mammals. We here characterize this loss in more detail and investigate potential consequences for the Eumuroidean regulatory network. We confirm that the miRNA loss was not compensated by other miRNAs in rat or mouse, and we identify a significant overlap in the function of their target genes. We heterologously express two human miRNAs, Mir-197 and Mir-769, in mouse inducible pluripotent stem cells (iPSCs) and compare effects on the transcriptome to those of induced miRNA levels in human iPSCs. This reveals overlapping sets of down-regulated mRNAs in the two species, likely representing remnants of an ancient miRNA-dependent regulatory network that predates the diversification of the human and mouse lineages. The consequent elimination of established miRNA regulatory connections on the Eumuroidean lineage is accompanied by the lineage-specific loss of 37 transcription factors. Our results indicate that mouse and rat have modified their regulatory network of gene expression on transcriptional and post-transcriptional level compared to other vertebrate model organisms. This regulatory shift likely adds noise to studies of gene expression that, for example, use murine cells to study human diseases.