smFISH of R genes were done on fresh-frozen liver cryosections (8μm) embedded in O.C.T Compound (Tissue-Tek; Sakura-Finetek USA), sampled every three hours (ZT0 to ZT21). RNAscope® probes for Bma1l mRNA (Mm-Arntl, catalog #: 438748-C3) and Per1 mRNA (Mm-Per1, catalog #: 438751) were used, according to the manufacturer’s instructions for the RNAscope Fluorescent Multiplex V1 Assay (Advanced Cell Diagnostics). To detect the central vein, an immunofluorescence of Glutamine Synthetase (ab49873, Abcam, diluted 1:2000 in PBS/BSA 0.5%/Triton-X0.01%) was done together with smFISH. Nuclei were counterstained with DAPI and sections were mounted with ProLong™ Gold Antifade Mountant. Liver sections were imaged with a Leica DM5500 widefield microscope and an oil-immersion x63 objective. Z-stacks were acquired (0.2μm between each Z position) and mRNA transcripts were quantified using ImageJ, as described previously in ref.50 (link). Pericentral (PC) and Periportal (PP) veins were manually detected based on Glutamine Synthetase IF or on bile ducts (DAPI staining). The Euclidean distance between two veins and the distance from the vein of each mRNA transcript were calculated. mRNA transcripts were assigned to a PP or PC zone if the distance from the corresponding vein was smaller than one-third of the distance between the PP and PC veins (ranging from 50 to 130μm).