Project description:Continuous thymic homing of hematopoietic progenitor cells (HPCs) via the blood is critical for normal T cell development. However, the nature and the differentiation program of the specialized thymic endothelial cells (ECs) controlling this process remain poorly understood. Here, using conditional gene-deficient mice, we find that lymphotoxin beta receptor (LTβR) directly controls thymic ECs to guide HPC homing. Interestingly, T cell deficiency or conditional ablation of T-cell-engaged LTβR signaling results in a defect in thymic HPC homing, suggesting the feedback regulation of thymic progenitor homing by thymic products. Furthermore, we identify and characterize a special thymic portal EC population with features that guide HPC homing. LTβR is essential for the differentiation and homeostasis of these thymic portal ECs. Finally, we show that LTβR is required for T cell regeneration upon irradiation-induced thymic injury. Together, these results uncover a cellular and molecular pathway that governs thymic EC differentiation for HPC homing.
Project description:The rat thymic medulla provides the microenvironment for negative selection, late thymocyte maturation, and thymocyte egress, and is generally characterized by widespread distribution of medullary thymic epithelial cells (mTECs). In contrast, rat thymic medulla contains medullary epithelium-free areas (mEFAs), but the cellular composition and functional significance of these regions remain unclear. Here, we combined spatial transcriptomics, scRNA-seq, and robust cell-type decomposition (RCTD) to characterize mEFAs in Lewis rat thymus. These analyses revealed that mature single-positive thymocytes, including CD4SP, CD8SP, and regulatory T-cell-lineage cells, were preferentially localized in mEFAs, whereas immature SP subsets were enriched in medullary epithelium-containing areas. Rat thymic mesenchymal cell-3 and -4 (TMC3 and TMC4) subsets were also enriched in mEFAs. These subsets were broadly similar to mouse medullary fibroblasts but displayed distinct predicted interactions with SP thymocytes, including costimulatory molecule–receptor, chemokine–receptor, and ECM–integrin axes. In addition, the venous endothelial cells (vECs) expressing portal endothelial cell markers were accumulated in mEFAs. The S1P transporter gene Spns2 was preferentially expressed in both TMC4 and vEC subsets, suggesting increased local concentration in mEFAs. These findings indicate that rat mEFAs are specialized medullary niches linking stromal organization, thymocyte maturation, and thymic egress.
Project description:The mechanism of egress of mature regulatory T cells (Tregs) from the thymus to the periphery remains enigmatic, as does the nature of those factors expressed in the thymic environment. Here, we examined the fate of thymic Tregs in TNFα/RelA double-knockout (TA-KO) mice, because TA-KO mice retain a Treg population in the thymus but have only a small Treg population at the periphery. Transplantation of whole TA-KO thymus to under the kidney capsule of Rag1 null mice failed to induce the production of donor-derived splenic Tregs expressing neuropilin-1 (Nrp1), which was reported to be a marker of naturally occurring Tregs, indicating that TA-KO thymic Tregs either do not leave the thymus or are lost at the periphery. We next transplanted enriched TA-KO thymic Tregs to the peripheries of TA-KO mice and traced mouse survival. Transplantation of TA-KO thymic Tregs rescued the lethality in TA-KO mice, demonstrating that TA-KO thymic Tregs remain functional at the periphery. The TA-KO thymic Treg population had highly demethylated CpG motifs in the foxp3 locus, indicating that the cells were arrested at a late-mature stage. Also, the population included a large subpopulation of Tregs expressing IL-7Rα, which is a possible marker of late-mature Tregs. Finally, TA-KO fetal liver chimeric mice developed an Nrp1+ splenic Treg population from TA-KO cells, suggesting that Treg arrest is caused by a lack of RelA in the thymic environment. Together, these results suggest that egress of mature Tregs from the thymus depends on RelA in the thymic environment. For the isolation of thymic Tregs, CD4+CD8α-CD25hi thymocytes were isolated from five 1.5- to 2-week-old TNFα-KO or TA-KO mice by using a FACSAria cell sorter. For the isolation of thymic stromal cells, 10 thymi from 1.5- to 2-week-old TNFα-KO or TA-KO mice were minced with scissors and treated with RPMI 1640 supplemented with 2% FCS, 0.2 mg/ml collagenase (Roche, Basel, Switzerland), 0.2 mg/ml dispase I (Roche), and 100 U/ml DNase I (Life Technologies) for 30 min with stirring. Digested thymi were centrifuged in a Percoll (GE Healthcare Bio-Sciences, Piscataway, NJ, USA) gradient (density, 1.115, 1.065, and PBS) at 1400g for 30 min. Cells in the upper layer were collected, and the CD45-EpCAM+ (thymic epithelial cells) and CD45+EpCAM- populations (enriched thymic stromal cells containing macrophages or dendritic cells) were sorted.
Project description:The mechanism of egress of mature regulatory T cells (Tregs) from the thymus to the periphery remains enigmatic, as does the nature of those factors expressed in the thymic environment. Here, we examined the fate of thymic Tregs in TNFα/RelA double-knockout (TA-KO) mice, because TA-KO mice retain a Treg population in the thymus but have only a small Treg population at the periphery. Transplantation of whole TA-KO thymus to under the kidney capsule of Rag1 null mice failed to induce the production of donor-derived splenic Tregs expressing neuropilin-1 (Nrp1), which was reported to be a marker of naturally occurring Tregs, indicating that TA-KO thymic Tregs either do not leave the thymus or are lost at the periphery. We next transplanted enriched TA-KO thymic Tregs to the peripheries of TA-KO mice and traced mouse survival. Transplantation of TA-KO thymic Tregs rescued the lethality in TA-KO mice, demonstrating that TA-KO thymic Tregs remain functional at the periphery. The TA-KO thymic Treg population had highly demethylated CpG motifs in the foxp3 locus, indicating that the cells were arrested at a late-mature stage. Also, the population included a large subpopulation of Tregs expressing IL-7Rα, which is a possible marker of late-mature Tregs. Finally, TA-KO fetal liver chimeric mice developed an Nrp1+ splenic Treg population from TA-KO cells, suggesting that Treg arrest is caused by a lack of RelA in the thymic environment. Together, these results suggest that egress of mature Tregs from the thymus depends on RelA in the thymic environment.
Project description:STN7-dependent phosphorylation of an as yet unknown thylakoid protein triggers the signaling events associated with the long-term acclimatory response (LTR). The LTR-associated signaling events regulate the expression of photosynthesis-related genes on the post-transcriptional level (nucleus), as indicated by transcript profiling in LTR mutants.