The role of microRNAs in the expression of DNA methyltransferase 3B during the differentiation of embryonic stem cells

Abstract

The early embryonic development in mammals is marked by the reprogramming of epigenetic marks over the genome, consisting of a global demethylation followed by the establishment of a new DNA methylation pattern. The repression of pluripotency-related genes and the cell commitment towards its differentiation pathway, fundamental phenomena to the phenotypic stability of all cell types to be formed, are under the influence of the epigenetic regulation of gene expression. Among the enzymes that catalyze DNA methylation during this epigenetic reprogramming Dnmt3b is a methyltransferase traditionally associated with de novo methylation, mainly of CpG-rich regions. Although the expression of this enzyme is reduced after the cell differentiation period, and occurs concurrently with germ layers differentiation at the early embryonic development, little is known about Dnmt3b regulation along the process. However, small regulatory molecules involved with inhibition of gene transcription, the microRNAs (miRNAs), seem to be good candidates to the regulation of this DNMT, and some of them were already associated with its control under other physiological and even pathological contexts. So, it is a matter of interest to verify if miRNAs exert a direct post-transcriptional control over DNMT3B in human embryonic stem cells submitted to differentiation, as well as to verify possible alterations in global DNA methylation in this cell system and, lastly, to verify the cells capacity to maintain their undifferentiated status and their global methylation pattern after the introduction of a chosen miRNA. To answer to those questions, the human embryonic stem cells are going to be transfected with the hsa-miR-203 and/or other candidates (hsa-miR-26a and has-miR-26b). Besides these miRNAs have been pointed by more than one miRNA target prediction software, they were also chosen because they are involved with the control of other genes related to epigenetic modifications, and they show a significant increased expression in differentiated cells when compared with pluripotent stem cells. (AU)