The PNS regulates nocturnal HSC BM adhesion and homing. (A) Scheme showing the protocol used for the HSPC BM homing assay with irradiation (12 Gy). (B) Frequencies of HSPCs (homing efficiency) at ZT2 that homed during the night to the BM after IV transplantation into lethally irradiated mice (12 Gy) (to promote homing) at ZT10. Gfra2^−/− mice and control Gfra2^+/− mice were used as donor (lower genotypes) or recipients (upper genotypes) in all combinations. Homing efficiency is determined as the percentage of CFU-Cs obtained from BM harvested from irradiated mice in comparison with CFU-Cs obtained from a nonirradiated mouse. (C) Scheme showing the protocol used for the HSPC BM homing assay without irradiation. (D) Frequencies of donor-derived Gfra2^+/+ or Gfra2^−/− lin⁻sca-1⁺c-kit⁺ HSPCs (identified by flow cytometry) at ZT2 that homed during the night to the BM after IV transplantation in nonirradiated congenic mice at ZT10. Vcam1 (E), Sele (F), and Selp (G) mRNA expression in the unfractionated BM of Gfra2^−/− and Gfra2^+/− control mice at the specified ZT. ZT21 has been duplicated to facilitate viewing. (B,D-G) Data are mean ± standard error of the mean; n (inside bars) and P values (multivariate analysis for >2 groups) are indicated. *P < .05, 1-way analysis of variance and Bonferroni comparisons (B,D), multiple 2-tailed test (E-G). ns, not significant.