Figure 1.

Opn ^−/− mice show increased hepatic hematopoietic progenitors compared to WT mice. (A,B) H&E staining reveals small aggregates of cells with intensely basophilic nuclei and clusters of cells in the liver of (top panels) young (14‐16 weeks;) and (bottom panels) old (>1.5 years; green arrows in panels and zoomed views) Opn ^−/− mice. (C) Spleen‐to‐body weight and liver‐to‐body weight ratios in young males and females show hepatosplenomegaly in Opn ^−/− compared to WT mice. (D) Pathology scores from old Opn ^−/− and WT mice. (E) Kitl mRNA in liver of young and old Opn ^−/− and WT male mice. (F) Opn deletion increases CD34⁺ and CD127⁺ cell hepatic population in old and young mice. (G) Old and young Opn ^−/− mice displayed increased Lin^– Sca‐1⁺ c‐kit⁺ CD34⁺ CD135⁺ short‐term HPSCs and Lin^– Sca‐1⁺ c‐kit⁺ CD127⁺ CD135⁺ CLPs compared to WT littermates. Bar graphs and representative flow plots are shown. Liver leukocytes were isolated and gated using SSC/FSC, viability dye (to exclude dead cells), single‐cell population (to exclude doublets), and Lin^– Sca‐1⁺ c‐kit⁺ (to identify hematopoietic cells). Results are expressed as mean ± SD; n = 6/group, ^• P < 0.05, ^•• P < 0.01, and ^••• P < 0.001 for Opn ^−/− versus WT mice (both genders). Abbreviations: APC, antigen‐presenting cell; CV, central vein; FSC, forward scatter; H&E, hematoxylin and eosin; Lin^– Sca‐1⁺ c‐kit⁺, lineage‐negative, stem cell antigen‐1‐positive, and c‐kit receptor‐positive; PE, phycoerythrin; PV, portal vein; SSC, side scatter.