hARNTL1 is critical in controlling circadian oscillations of circulating hCD45⁺leukocytes. (A) Blood samples were taken from 10-week-old NSG and humanized mice every 6 hours (ZT1-ZT25) (n = 6). Mouse and human CD45⁺ leukocytes from different points were separated by cell sorting and analyzed for ARNTL1 expression by RT-PCR. Shown are fold changes of ARNTL1 mRNA levels after normalizing data from each point in individual mice to the initial point, ZT1. (B) Blood samples were taken from 12-week-old humanized mice (control) and hARNTL1^−/− humanized mice (hARNTL1 KO) (n = 4). The cell counts of each time in individual mice were normalized to the initial cell numbers at time ZT1. Shown are fold changes of numbers of hCD45⁺ cells. (C) Representative flow cytometry plots of CXCR4 expression on hCD45⁺ cells from ZT7 and ZT19 points in control and hARNTL1 KO humanized mice. (D) Mean fluorescence intensity (MFI) quantifications of the expression of CXCR4 on hCD45⁺ cells from ZT7 and ZT19 (n = 4). Shown are the fold changes normalized to MFI of CXCR4 at ZT7 in control humanized mice. *P < .05; **P < .01.