MicroRNA expression in mouse oligodendrocytes and regulation of proteolipid protein gene expression

Overexpression of the major myelin proteolipid protein (PLP) is detrimental to brain development and function and is the most common cause of Pelizaeus-Merzbacher disease. microRNA (miRNA), small, noncoding RNAs, have been shown to play critical roles in oligodendrocyte lineage. In this study, we sought to investigate whether miRNAs control PLP abundance. To identify candidate miRNAs involved in this regulation, we have examined differentiation-induced changes in the expression of miRNAs in the oligodendroglial cell line Oli-neu and in enhanced green fluorescent protein positive oligodendrocytes ex vivo. We have identified 145 miRNAs that are expressed in oligodendrocyte cell lineage progression. Dicer1 expression decreases in differentiated oligodendrocytes, and knock down of Dicer1 results in changes in miRNAs similar to those associated with differentiation. To identify miRNAs that control the PLP expression, we have selected miRNAs whose expression is lower in differentiated vs. undifferentiated Oli-neu cells and that have one or more binding site(s) in the PLP 3'-untranslated region (3'UTR). The PLP 3'UTR fused to the luciferase gene reduces the activity of the reporter, suggesting that it negatively regulates message stability or translation. Such suppression is relieved by knock down of miR-20a. Overexpression of miR-20a decreases expression of the endogenous PLP in primary oligodendrocytes and of the reporter gene. Deletion or mutation of the putative binding site for miR-20a in the PLP 3'UTR abrogated such effects. Our data indicate that miRNA expression is regulated by Dicer1 levels in differentiated oligodendrocytes and that miR-20a, a component of the cluster that controls oligodendrocyte cell number, regulates PLP gene expression through its 3'UTR.