In vivo PAR-CLIP (viP-CLIP) of liver Tial1 unveils targets regulating cholesterol synthesis and secretion. Mus musculus

System-wide cross-linking and immunoprecipitation (CLIP) approaches have unveiled regulatory mechanisms of RNA-binding proteins (RBPs) mainly in cultured cells due to limitations in the cross-linking efficiency of tissues. Here, we describe viP-CLIP (in vivo PAR-CLIP), a method capable of identifying RBP targets in mammalian tissues, thereby facilitating the functional analysis of RBP-regulatory networks in vivo. We applied viP-CLIP to mouse livers and identified Insig2 and ApoB as prominent TIAL1 target transcripts, indicating an important role of TIAL1 in cholesterol synthesis and secretion. The functional relevance of these targets was confirmed by showing that the subcellular localization of TIAL1 in hepatocytes is regulated by cholesterol abundance and that mutant Tial1 mice exhibit altered cholesterol synthesis, APOB secretion and plasma cholesterol levels. Our results demonstrate that viP-CLIP is capable of identifying physiologically relevant RBP targets by identifying a novel factor implicated in the negative feedback regulation of cholesterol biosynthesis.