RORalpha and Hepatic Zonal Regulation

We have had a long-standing interest in the zonal control of gene expression in the adult liver. This phenomenon, whereby specific genes are expressed in pericentral hepatocytes and other genes are expressed in periportal hepatocytes, allows the liver to compartmentalize different metabolic functions in distinct regions. Using mouse models, we previously characterized defined enhancer elements that confer zonal expression to linked transgenes. We also demonstrated that the beta-catenin signaling pathway is important for activity of pericentral enhancers. During the last funding period of this grant, we made the novel observation that the retinoic acid related orphan receptor alpha (RORA) is important for pericentral gene regulation. The goal of this competitive renewal is to use mouse models and high throughput sequencing to explore further the role of RORA in zonal gene regulation in the mouse liver. This will be accomplished by the following aims: Aim 1: Analysis of direct and indirect targets of RORA in pericentral gene expression. Pericentral and periportal hepatocytes will be purified from our unique transgenic mouse line and performing RNA-Seq and ChIP-Seq with antibodies against RORA and related factors as well as modified chromatin marks. Aim 2. Identify additional enhancers that exhibit pericentral or periportal activity using a novel Adenoassociated virus (AAV) system developed in our lab. Aim 3: Determine whether RORA is important for the homeostatic stem cell properties of pericentral hepatocytes by Cre-recombinase mediated cell lineage tracing. Aim 4: Determine whether RORA is important for liver regeneration using the well established carbon tetrachloride model of liver injury.