296 Recombination efficiency and expression of fibroblast-specific Cre drivers in mouse skin

Abstract

Cell-type specific genetic recombination is a powerful strategy for advancing understanding of cellular function in genetically-modified mouse models. This approach relies on cell-type specific gene promoters to drive genetic recombination in target cells. Although the utility of many cell-type specific promoters has been well characterized, thorough characterization of fibroblast-specific promoters is lacking. Therefore, we employed the mTmG two-color fluorescent reporter system to examine the genetic recombination efficiency and expression patterns of three fibroblast-specific promoters in mouse skin. mTmG mice express the red fluorescent protein tdTomato (mT) constitutively and ubiquitously. Genetic recombination catalyzed by Cre recombinase silences mT expression and induces expression of enhanced green fluorescent protein (mG). Thus, cells that express Cre recombinase appear green, while all other cells appear red. We generated mTmG mice that express Cre recombinase under the control of promoter elements in three fibroblast-specific genes 1) fibroblast specific protein-1 (FSP-1), 2) type Iα2 collagen (COL1A2), or 3) platelet-derived growth factor receptor-α (PDGFRα). Dorsal skin from mTmG/Cre positive and control mice were analyzed by immunofluorescence microscopy. Surprisingly, mTmG/FSP-1 Cre mice exhibited recombination largely in keratinocytes throughout all the layers of the epidermis and follicular epithelium. Recombination was also observed in scattered fibroblast-like cells in the dermis. mTmG/COL1A2 Cre mice displayed recombination that was specific for dermal cells with fibroblast-like morphology throughout the interstitial dermis and in dermal papillae. mTmG/PDGFRα Cre mice displayed recombination that was similar to that of COL1A2-driven recombination, although the number of positive dermal cells and the intensity of mG expression was approximately five-fold greater. These data provide a foundation for the use of Cre drivers to study fibroblast gene expression in genetically-modified mouse models.