(A) EdU staining of runx1+23:mCherry embryos injected with either the calr3a, calr3b, or irf8 morpholinos identifies a significant reduction in proliferating HSPCs at 3 dpf. Data are means ± SD. Data were analyzed by one-way ANOVA with Dunnett?s multiple comparisons test; **P < 0.01 and ****P < 0.0001. (B and C) scRNA-seq analysis of runx1+23+ FACS-purified cells from irf8 or control morphants reveals a population of stressed HSPCs that persist in the absence of macrophages and a population of cycling cells enriched in the control sample. (D) Embryonic HSPCs marked by surface Calreticulin exhibit higher levels of ROS. Data are means ± SD. Data were analyzed by unpaired Student?s t test; **P < 0.01. MFI, median fluorescence intensity. (E) ROS inhibition with diphenylene iodonium significantly reduces macrophage-HSPC interactions. Data are means ± SD. Data were analyzed by unpaired Student?s t test; *P < 0.05. DMSO, dimethyl sulfoxide. (F) Expression of il1b by heat shock rescues the effect of macrophage depletion on HSPC proliferation. Data are means ± SD. Data were analyzed by one-way ANOVA with Sidak?s multiple comparisons test; *P < 0.05 and ****P < 0.001.