Necdin maintains adult HSC quiescence. (A) Cell-cycle analysis of Lin⁻Sca-1⁺c-Kit⁺CD48⁻CD150⁺ cells (left panels) isolated from mice reconstituted with wild-type (WT) or necdin-null (Ndn null) fetal liver cells was performed by staining with Hoechst 33 342 and Ki67. Data shown are the mean values of G₀ cells (± SD; P = .0025, n = 7). (B) The proliferation of Lin⁻Sca-1⁺c-Kit⁺CD48⁻CD150⁺ cells isolated from mice reconstituted with wild-type or necdin-null fetal liver cells was measured by in vivo BrdU incorporation over 48 hours. Greater proliferation of necdin-null Lin⁻Sca-1⁺c-Kit⁺CD48⁻CD150⁺ cells was observed (38.9% vs 14.8% for wild-type cells; P = .0007, n = 7). (C) Cell-cycle analysis of Lin⁻Sca-1⁺c-Kit⁺CD48⁻CD150⁺ cells isolated from the BM of mice reconstituted with wild-type, necdin-null, p53-null, or necdin/p53 double-null fetal liver cells was performed by staining with Hoechst 33342 and Ki67. Data shown are the mean values of G₀ cells (± SD; P < .0001 by 1-way ANOVA, n = 4). Significant differences were observed between wild-type and necdin-null, wild-type and p53-null, wild-type and necdin/p53 double-null, necdin-null and p53-null, and p53-null and necdin/p53 double-null recipients.