Mouse TU tagging: A chemical/genetic intersectional method for purifying cell type-specific nascent RNA

Abstract

Transcriptional profiling is a powerful approach for understanding development and disease. Current celltype-specific RNA purification methods have limitations, including cell dissociation trauma or inability to identify all RNA species. Here, we describe "mouse thiouracil (TU) tagging" a genetic and chemical intersectional method for covalent labeling and purification of cell type-specific RNA in vivo. Cre-induced expression of uracil phosphoribosyltransferase (UPRT) provides spatial specificity; injection of 4-thiouracil (4TU) provides temporal specificity. Only UPRT+ cells exposed to 4TU produce thio-RNA, which is then purified for RNA sequencing (RNA-seq). This method can purify transcripts from spatially complex and rare (<5%) cells, such as Tie2:Cre+ brain endothelia/microglia (76% validated by expression pattern), or temporally dynamic transcripts, such as those acutely induced by lipopolysaccharide (LPS) injection. Moreover, generating chimeric mice via UPRT+ bone marrow transplants identifies immune versus niche spleen RNA. TU tagging provides a novel method for identifying actively transcribed genes in specific cells at specific times within intact mice. © 2013 by Cold Spring Harbor Laboratory Press.