Multi-transcription factor reporter mice delineate early precursors to the LTi and ILC lineages

Transcription factor (TF) reporter mice have proved integral to the characterization of murine innate lymphoid cell (ILC) development and function. Here, we implemented a CRISPR/Cas9-generated combinatorial reporter approach for the simultaneous resolution of several key TFs throughout ILC development in both the fetal liver and adult bone marrow. We demonstrate that the Tcf7-expressing early innate lymphoid progenitor (EILP) and the common helper innate lymphoid progenitor (CHILP) both contain a heterogeneous mixture of committed ILC and Lymphoid Tissue-inducer (LTi) precursors, rather than a shared precursor to these lineages. Moreover, the earliest specified precursor to the LTi lineage was identified upstream of these populations, prior to the expression of Tcf7. These findings match dynamic changes in chromatin accessibility associated with the expression of key TFs (ie. Gata3 and Rorc), highlighting the distinct origins of ILC and LTi lineages at the epigenetic and functional levels, and provide a revised map for ILC development. Overall design: ATAC-seq was performed in ILC and LTi precursors from E15 Fetal Liver of Zbtb16-EGFP or Zbtb16-EGFP Tcf7-mCherry Rorc-Thy1.1 reporter mice