Syndecan-2 is differentially expressed by LT-HSCs. (A) Gating strategy used to isolate adult BM MPPs, ST-HSCs, 34^–KSL HSCs, and LT-HSCs. (B) qRT-PCR analysis of Sdc1, Sdc2, Sdc3, and Sdc4 in BM HSPCs (n = 7 mice, pooled per replicate per group). (C) Representative histograms of syndecan-2 expression on HSPCs. Quantification of syndecan-2 mean fluorescence intensity (MFI) (D) and percentages of syndecan-2⁺ cells (n = 7 mice per group) (E). Sequential gating of lineage-depleted mouse BM cells based on syndecan-2 expression (F) and quantification of the percent KSL of Lin^–, 34^–KSL of KSL, and LT-HSCs of 34^–KSL (n = 7 mice per group) (G). (H) Representative analysis of α-catulin^GFP+c-kit⁺ cells within lineage-depleted BM from adult α-catulin^GFP mice based on Syndecan-2 expression. (I) Quantification of percentage α-catulin^GFP+c-kit⁺ LT-HSCs within each population (n = 6 mice per group). (J) Quantification of colony-forming cells from BM syndecan-2^–Lin^– and syndecan-2⁺Lin^– cells and CD150⁺ Lin^– cells (n = 5 mice, pooled, n = 4 replicates per group). (K) Schematic representation of competitive repopulation assay of CD45.1⁺ BM syndecan-2^–Lin^– cells, syndecan-2⁺Lin^– cells, or CD150⁺ Lin^– cells transplanted into CD45.2⁺ mice. (L) Percentages of total donor CD45.1⁺ cells in the BM at 16 weeks after competitive transplantation of BM syndecan-2^–Lin^– cells, syndecan-2⁺Lin^– cells, and CD150⁺Lin^– cells from CD45.1⁺ mice into CD45.2⁺ recipients (n = 5 SJL mice, pooled for donor cells, n = 3-5 recipient mice per group). Error bars = standard error of the mean; statistics denote 1- or 2-way analysis of variance followed by Holm-Sidak’s corrected unpaired Student t test. *P < .05, *** P < .001, **** P < .0001, for competitive transplant. SSC-A, side scatter area.