Fig. 7: Blood precursors emerge from intra-embryonic LYVE1⁺ cells at the onset of the heartbeat.

a Experimental schematic. YS and embryos dissected from CD45.2⁺ E8.5 (5–7sp) Lyve1^+/CreRosa26^+/mTmG concepti were either analyzed by flow cytometry for Lyve1-Cre-dependent labeling (GFP⁺ cells), cultured as explants for 10 days to examine Lyve1-Cre-dependent labeling in emerging hematopoietic populations or transplanted. b–g Flow cytometry analysis and confocal microscopy of freshly isolated E8.5 (5–7sp) Lyve1^+/CreRosa26^mTmG YS and embryos. Non-recombined Rosa26^+/mTmG cells are tdTomato⁺ and recombined Rosa26^+/mTmG cells are GFP⁺. b Representative flow cytometry plots. c Average % recombination (i.e., GFP⁺) of total YS or embryo cells. (n = 14) from three independent litters. d % of total GFP⁺ cells expressing CD41. e %CD41⁺ in total cells. f % recombination (i.e., GFP⁺) in CD41⁺ cells. g Representative confocal microscopy images. GFP (green), tdTomato (red). Endothelial cells (blue, labeled by anti-CD31-BV421). An inset of a paired-aorta is shown. Scale bars: 50 µm and 10 µm. Schematics: A: paired-aorta; NT: Neural tube. h–i Flow cytometry analysis of E8.5 (5–7sp) Lyve1^+/CreRosa26^mT/mG YS-Ex and Em-Ex after 10 days of culture. h Representative flow cytometry analysis of tdTomato and GFP labeling in YS-Ex and Em-Ex-derived CD31⁺CD45⁺c-Kit⁺CD41⁻ cells. I Quantification of Lyve1-Cre dependent GFP labeling in CD31⁺CD45⁺c-Kit⁺CD41⁻ cells. Each dot represents an independent conceptus. Bars represent average %recombination (n = 12) from three independent litters. j–l PB of recipients transplanted with cultured E8.5 (5–7sp) or E9.5 (19–22sp) Lyve1^+/CreRosa26^mT/mG Em-Ex or YS-Ex. j Representative flow cytometry plots of recipient PB. tdTomato and GFP labeling is shown. k % Explant-derived PB, estimated as the sum of the % of tdTomato⁺ and % of GFP⁺ cells in the PB. Each circle represents an independent recipient. l %Lyve1-Cre dependent GFP labeling estimated as %GFP⁺ amongst % of Explant-derived PB cells is shown. Each circle represents an independent mouse transplanted with four ee of E8.5 CD45.2⁺ Lyve1^+/CreRosa26^mTmG cultured Em-Ex (n = 4) in three independent experiments or one ee of E9.5 CD45.2⁺ Lyve1^+/CreRosa26^mTmG cultured Em-Ex (n = 10) or YS-Ex (n = 6) in other three independent experiments. (*p < 0.05; ***p < 0.001; eWrs-test). Means and standard deviations are shown. Source data are provided as a Source Data file