Enhancement of direct reprogramming from fibroblasts to epithelial lineages by OVOL2-induced mesenchymal-to-epithelial transition [ATAC-seq]

Mesenchymal-to-epithelial transition (MET) is an important step in cell reprogramming from fibroblast, a most frequently used cell type for this purpose, to various epithelial cell types. However, how MET can be induced in fibroblast has not been fully studied. In this study, we sought for transcription factors (TFs) that can efficiently induce MET in dermal fibroblasts and identified OVOL2 as a potent inducer of key epithelial genes. In addition, OVOL2 cooperatively enhanced MET induced by HNF1A, TP63 and KLF4, known reprogramming TFs to epithelial lineages. In TP63/KLF4-induced fibroblast-keratinocyte cell reprogramming, OVOL2 greatly facilitated activation of epithelial genes as well as keratinocyte-specific genes. This enhancement of epithelial gene expression program was accompanied by enhanced changes in chromatin accessibility across the genome. Mechanistically, motif enrichment analysis revealed that target loci of KLF4 and TP63 become accessible upon reprogramming while OVOL2 target loci become inaccessible, indicating that KLF4 and TP63 positively regulate their targets while OVOL2 primarily induces closed chromatin state at its target loci.  Thus, OVOL2 and tissue-specific reprogramming factors cooperatively facilitate cell reprogramming of fibroblast into epithelial lineages through distinct mechanisms. Overall design: Primary fibroblasts are infected with doxycycline (DOX)-inducible Control vector (MCS), TK (TP63+KLF4), TK+ OVOL2 (Group5), or OVOL2 (Group6). After selection with Puromycin, DOX treatment (500ng/mL) was started at day0 for 5 days (until day5). At day2, medium was changed to KGM medium. RNA samples were collected at day7.