PSF1 expression in proliferating HSC population. (A,B) Immunostaining of several BM (A) or FL-derived (B) HC population with anti-PSF1 antibody. (A) CD34⁻KSL (CD34⁻c-kit⁺Sca-1⁺Lin⁻ cells), 34⁺KSL (CD34⁺c-kit⁺Sca-1⁺Lin⁻ cells), KL (c-kit⁺Sca-1⁻Lin⁻ cells), Lin⁺ (Lin⁺ cells), and 5-FU KSL (5-FU-treated mouse derived CD34⁺KSL cells). (B) KSL (c-kit⁺Sca-1⁺Lin⁻ cells), KL (c-kit⁺Sca-1⁻Lin⁻ cells), and Lin⁺ (Lin⁺ cells). Green color shows PSF1 staining. Nuclei were counterstained with PI (red). Bar represents 10 μm. (C) Sections of E12.5 FL from wild-type (WT) or Runx1^−/− mice were stained with anti-PSF1 polyclonal antibody. Sections were counterstained with hematoxylin (original magnification ×400). Arrows indicate PSF1⁺ cells. Bars represent 50 μm. (D) PSF1 mRNA expression in various HC fractions of BM or FL cells as indicated in panel A. 5-FU KSL indicates KSL cells were sorted from BM of mice 4 days after treatment with 5-FU. The values were normalized to the amount of mRNA in Lin⁺ cells from BM.