Animals’ blood samples were first collected by cardiac puncture after anesthesia, and then immediately sacrificed. Serum samples were isolated from the blood samples after centrifugation (1000 g, 10 min, 4℃) and stored at −80℃ for later analysis. One thyroid gland lobe was stored at −80℃ having been frozen for 10 min in liquid nitrogen. Another thyroid gland lobe was placed in 4% PFA for 12 h, and underwent gradient dehydration in 15%, 30% sucrose for 2 days. Tissue sections were cut to 2 μm thickness. Primary antibodies against BMAL1 (NB100-2288, dilution 1:500; Novus, USA) and PER2 (NB100-125, dilution 1:250; Novus) and HRP-conjugated secondary antibodies (1:2000) supplied in a DAB kit (CW2069S, CWBIO, Beijing, China) were used for immunostaining of thyroid sections. To validate the specificity of the antibodies used for immunocytochemistry, we performed primary controls (+primary antibody/−secondary antibody) and secondary controls (−primary antibody/+secondary antibody), both of which showed no positive labeling. Immunohistochemistry images were taken with Leica Aperrio Versa 8 microscope (Leica), details of quantification by IHC Profiler (20 (link)) were listed as Supplementary Data 1.