Cell Sorting Strategies:
For modified smart-seq2 data, mouse yolk sac, AGM and placenta at E11.0 were dissected and prepared for single cell suspensions. Single cell suspensions were stained with Ter119, CD45, CD41, CD31, CD44 and 7AAD. Living HE cells (CD44+-
CD31+CD45-Ter119-), non-HE cells (CD44-CD31+CD45-Ter119-) and ECs (CD31+CD45-Ter119-) were isolated by FACS into individual wells of a 96-well plate containing 2.5 ml cell lysis buffer. For smart-seq2-GFP data, Hoxa13+ lineages were obtained from the Rosa26mTmG; Hoxa13CreER placentas at E11.0, E12.0 and E13.5, were dissected and prepared for single cell suspensions, respectively. GFP+ single cell isolated by FACS into individual wells of a 96-well plate containing 2.5 ml cell lysis buffer