Lineage tracing studies suggest that the placenta is not a de novo source of hematopoietic stem cells
Fig 4
Measurement of placental hemogenic endothelium using ex vivo HEC assays.
(A) Schematic of the OP-9 co-culture procedure used to analyze HECs capable of differentiating into blood cells ex vivo. (B) Placental labyrinth, umbilical cord (UC) and AGM were dissected from Hoxa13Cre; Ai14 E10.5 embryos (n = 6) and ECs (CD41lo/−CD45−Ter119−ESAM+CD144 + CD31 + c-Kitlo/−) fractioned into TdT + and TdT− fractions. Sorted cells (placenta TdT + /TdT− = 1,136/2000 cells; UC TdT + /TdT− = 319/1817 cells; AGM TdT + /TdT− = 0/2000 cells) were plate in limiting range in five replicates, six dilutions. (C) Graph showing frequency of HECs in each sorted population. Frequencies are shown on top of each bar. (D) Experimental design. Placental labyrinth, umbilical cord and AGM were dissected from Runx1IRES-GFP/ + E10.5 embryos (n = 30). HPC + refers to wells containing round hematopoietic cells by visual inspection. (E) Sorted GFP + cells expressing endothelial markers (CD31 + CD144 + c-Kitlo/−CD41−CD45−) from each tissue (AGM, 600 cells; UC, 153 cells; Placenta, 885 cells) were plated in OP9 co-cultures in limiting range and screened for hematopoietic outgrowth by the appearance of round hematopoietic cells after 9 days. (F) The frequency of HECs in the populations described in panel E. HEC frequencies in C and F were determined using ELDA Limiting Dilution Software. UC, umbilical cord; PL, placenta, AGM, aorta–gonad–mesonephros. The schematic diagrams in panels A and D were generated using Biorender (https://www.biorender.com/academic-license). The data underlying this figure can be found in S1 Data.