CHARTING AND PROBING THE ACTIVITY OF ADARS IN HUMAN DEVELOPMENT AND CELL-FATE SPECIFICATION

Adenosine deaminases acting on RNA (ADARs) impact diverse cellular processes and pathological conditions. While we possess important insights into their roles in adult tissues, their functions in early cell fate specification remain less understood. To address this, we devised a comprehensive framework to investigate ADARs in human development. We began by charting time-course RNA editing profiles in human organs from fetal to adult stages, enabling broad insights into RNA editing trends across diverse tissues. Next, we utilized hPSC differentiation to experimentally probe ADARs across specific tissue-types, harnessing brain organoids as neural specific, and teratomas as pan-tissue developmental models. We found that time-series teratomas faithfully recapitulated developmental trends observed in fetal tissue. Motivated by this, we conducted pan-tissue, single-cell CRISPR-KO screens of ADARs in teratomas to assess their role in cell-fate specification. Knocking out ADAR1 led to a global decrease in RNA editing across all germ-layers. Intriguingly, we observed a significant fitness defect in mesodermal tissues, and an enrichment of adipogenic cells, revealing a novel role for ADAR1 in mesenchymal differentiation. Collectively, we developed a multi-pronged framework charting time-resolved RNA editing profiles in fetal and fetal-like organ tissues, thereby shedding light on the role of ADARs in development and cell fate-specification.