Fig. 3: Meis1 expression in the AGM during EHT.

A Representative image of more than 50 Meis1-GFP embryos dissected at E10.5 (scale bar = 500 µm). B Immunostaining of cross-sections of the dorsal aorta at E10.5 showing the expression of CD31 (red) and Meis1-GFP (green). The dotted line in the lower panels demarcates the endothelial layer from the subaortic mesenchyme. (Ao: Aorta, V: Ventral, scale bar = 20 µm). N = 7 embryos over 4 independent experiments. C Percentage of cells expressing Meis1 in defined cell populations based on GFP fluorescence by flow cytomerty (n = 9 at E9.5 and n = 12 at E10.5) and (D) associated GFP MFI values (n = 4 at E9.5 and n = 3 at E10.5 from the same experiment). Viable cells were gated as follows: EC: CD31⁺CD41⁻CD45⁻, pre-HSPC I: CD31⁺CD41^lowCD45⁻, pre-HSPC II: CD31⁺CD41^lowCD45⁺, hematopoietic cells (HC): CD31⁻CD45⁺. Data are presented as mean ± SEM and each data point represents a different embryo. E Violin plot depicting Meis1 mRNA expression in various CITE-seq subpopulations. Meis1 expression was detected at low level in 9.9% of all EC. F Histograms showing Meis1-GFP expression by flow cytometry in CD44⁻ and CD44⁺ EC (n = 4 for each group). WT represents a wildtype (GFP⁻) embryo. G Representative histograms of GFP fluoresence by flow cytometry in AGM EC at various time points. H Total number of GFP⁺ EC per AGM at E9.5 (n = 9) and E10.5 (n = 7) and (I) EC numbers subdivided according to CD44 co-expression (n = 5 at E9.5, n = 3 at E10.5) based on counting beads by flow cytometry. For the absolute cell number, one E10.5 data point was removed based on the Grubb test to identify outliers. J Proportion of GFP⁺ EC co-expressing CD44 at E9.5 (n = 5) and E10.5 (n = 4). Data are presented as mean ± SEM and each data point represents a different embryo. All indicated p-values were calculated using a two-sided t-test comparing two groups. Source data are provided as a Source Data file.