Altered localization of the stem/progenitor cells (cKit^pos) within the architecture of the marrow of Gata1^low mice. (A) Genomic organization of the murine Gata1 locus indicating the position of the proximal (IE) and distal (IT) promoter and of the HS1 (also known as HS-3.5 and G1HE), the HS2, and the HS4/5 (also known as HS+3.5) enhancer. The shaded box indicates the sequences deleted by the hypomorphic Gata1^low mutation. The sequences −2.7 Kb upstream and 1.5 Kb downstream of IE driving the expression of the GFP reporter (^{−2.7Kb Gata1}GFP) are indicated at the bottom (see also Skoda¹⁵  and Onodera et al²⁵ ). (B-C) Double cKit and GFP immunofluorescence analysis of marrow and spleen sections of ^{−2.7KbGata1}GPFGata1^+/0 (B) and ^{−2.7KbGata1}GPFGata1^low/0 (C) mice, as indicated. The panels on the top present the merged pictures of representative areas of the bone marrow and spleen at ×20 magnification. The rectangles indicate the areas of the sections shown at higher (×40) magnification on the panels in the bottom. These bottom panels present the fluorescent signal of cKit and GFP captured individually and merged. The arrows track the position of individual cKit^pos cells in the different panels. The red arrowhead in panel E indicates a GFP^neg MK in proximity to the bone endosteum of the Gata1^low mouse. Legend: ^{−2.7KbGata1}GPFGata1^+/0 mouse: (i) 3 cKit^posGFP^neg cells, one of which is close to the endosteum; (ii) a cluster of cKit^posGFP^neg cells in the medulla; (iii) a cluster of cKit^posGFP^pos cells in the medulla; (iv) a cluster of cKit^posGFP^pos cells in the spleen. ^{−2.7Kbgata1}GPFGata1^low/0 mouse: (v) a cluster of cKit^posGFP^pos cells close to the bone endosteum; (vi) a cluster of cKit^posGFP^neg cells in the medulla; (vii) a cluster of cKit^posGFP^pos cells in the spleen.