The role of Hedgehog transcription factor Gli1 in late stage SP thymocyte maturation 3521

Abstract Description Background The thymus is essential for the development of functional, mature T lymphocytes. Hedgehog (Hh) signalling components are present in the thymus, but their precise expression and the role of the pathway in thymocyte differentiation and maturation remains poorly understood. Experimental approach: We analysed the expression of the Hh pathway in thymocytes, in space and time, and performed immunophenotypic profiling, scRNA-Seq analysis and functional assays to study thymic differentiation in mice deficient for Gli1 (Gli1KO) and wildtype controls. Key Findings: Thymocytes expressed only one of three Hh ligands, Ihh, and one Hh transcription factor, Gli1. Analysis of Gli1KO mice showed no gross abnormalities in thymic structure or cellularity, but revealed a significant reduction in SP thymocytes able to upregulate Qa2, a maturation marker of endpoint differentiation in the thymic medulla. This defect in Qa2 was not associated with any defects in markers of functional maturation, but persisted in recent thymic emigrants. Using scRNA-Seq, we identified a population of SP thymocytes with active type I IFN signalling, which was defective in the absence of Gli1. This confirmed a requirement for type I IFN signalling in late stage thymic maturation and importantly, a novel role for the Hh transcription factor Gli1 in this process. Significance to field: Our research has shown a previously unknown role for Hh signalling in both thymocyte maturation and type I IFN signalling. Funding Sources The work was supported by Cancer Research UK (MdlR (A22257)); Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (MdlR [107609/Z/15/Z]) and a Wellcome Trust Discovery Award (MdlR [227432/Z/23/Z]) Topic Categories Hematopoiesis and Immune System Development (HEM)