Mature oligodendrocytes are critical for myelin maintenance. To understand the molecular basis for this, genetic manipulation of mature oligodendrocytes is needed. Here we generated a mature oligodendrocyte tTA (tetracycline-controlled transcriptional activator) mouse line which, in combination with a tTA-dependent promoter line driving the expression of the desired transgene, can be used for gain-of-function studies. We used an oligodendrocyte promoter, the mouse proteolipid protein (PLP) promoter, to express mammalianized tTA, and generated a PLP-mtTA mouse line. In adults, mtTA mRNA was predominantly detected in brain white matter where it co-localized with PLP mRNA. mtTA-mediated gene induction was confirmed by crossing to mice with a tTA-dependent promoter driving expression of yellow fluorescent protein (tetO-YFP mice). YFP induction in PLP-mtTA::tetO-YFP mice was consistent with PLP expression in adult mature oligodendrocytes and premyelinating-stage myelinating oligodendrocytes. This PLP-mtTA mouse line is the first to enable gain-of-function studies in mature oligodendrocytes with the tet system. genesis 50:424428, 2012. (C) 2011 Wiley Periodicals, Inc.