E13 ETPs have a transcriptional LTi signature and are required for the maturation (CD80⁺) of mTECs. (A) Single-cell multiplex qPCR analyzed by hierarchical clustering of single E13 and E18 ETPs (80 cells each) for the expression of ILC lineage-specific transcripts (right margin). Each column represents a cell (E13 ETP in salmon, E18 ETP in blue) and each row represents 1 gene (of 41 genes). Highlighted are ILC-associated transcripts (black) and LTi-associated transcripts (in red). Analysis was done by normalizing expression to 2 independent housekeeping genes (Gapdh and Actinb) in R package Phenograph as in Perchet et al⁶³  and represented in a code color where red represents high expression and blue low expression. Data are pooled from 2 independent experiments. (B) Pregnant female mice were injected at E10.5, E12.5, and E14.5 with 1 mg of anti-IL-7Ra antibody A7R34 (red arrows indicate time points of anti–IL-7Ra injections and purple arrows indicate time points of analysis). Thymic lobes were analyzed at E16.5 for the presence of ETP (Lin⁻CD117⁺CD44⁺CD24^low), for Vγ5Vδ1 γδT cells, and for LTi (CD127⁺CCR6⁺TcR⁻CD3⁻ cells) (n = 6), or at P2 for the presence of DN (CD4⁻CD8⁻γδ⁻), DP(CD4⁺CD8⁺), CD4⁺ thymocytes, and of Vγ5Vδ1 γδT cells, for LTi (CD127⁺CCR6⁺TcR⁻CD3⁻ cells), and for CD80⁺ mTECs (EpCAM⁺Ly51⁻UEA.1⁺CD45⁻) (n = 24). Plots show numbers of the respective populations per thymus. Data from 2 independent experiments. ****P < .0001.