The Lineage Differentiation and Dynamic Heterogeneity of Thymic Epithelial Cells During Thymus Organogenesis.

Hanchao Gao,Yangyang Li,Yang Yang,Jinmei Wu,Lixia Liu,Wenna Fan,Xinyu Cheng,Huimin Sun,Chunpei Ou,Cuilan Xia,Chuntao Xie,Pengfei Chen,Ming Ni,Kai Deng,Lisha Mou,Lin Li-Zhong ,Meiqun Cao ,Jingyu Song ,Dinggen Huang,Xiaofang Deng

doi:10.3389/fimmu.2022.805451

Abstract

Although much progress has been made recently in revealing the heterogeneity of the thymic stromal components, the molecular programs of cell lineage divergency and temporal dynamics of thymic epithelial cell (TEC) development are largely elusive. Here, we constructed a single-cell transcriptional landscape of non-hematopoietic cells from mouse thymus spanning embryonic to adult stages, producing transcriptomes of 30,959 TECs. We resolved the transcriptional heterogeneity of developing TECs and highlighted the molecular nature of early TEC lineage determination and cortico-medullary thymic epithelial cell lineage divergency. We further characterized the differentiation dynamics of TECs by clarification of molecularly distinct cell states in the thymus developing trajectory. We also identified a population of Bpifa1+ Plet1+ mTECs that was preserved during thymus organogenesis and highly expressed tissue-resident adult stem cell markers. Finally, we highlighted the expression of Aire-dependent tissue-restricted antigens mainly in Aire+ Csn2+ mTECs and Spink5+ Dmkn+ mTECs in postnatal thymus. Overall, our data provided a comprehensive characterization of cell lineage differentiation, maturation, and temporal dynamics of thymic epithelial cells during thymus organogenesis.

Highlights

The thymus, a primary lymphoid organ, forms a complex threedimensional meshwork structure that provides the microenvironment to drive the differentiation, proliferation, and selection of T lymphocytes [1,2,3,4,5]
To aid with mechanical isolation of the early embryonic thymi, E11.5 and E12.5 thymi were dissected from Foxn1-driven enhanced green fluorescent protein (EGFP) reporter mice in which expression of EGFP was fused with Foxn1
Thymic epithelial cells (TEC) are rare in the total thymic cellularity, with the proportion of less than 1% in adult and less than 10% in embryonic thymus except for E11.5 and E12.5 (Figure S1A)

Summary

Introduction

The thymus, a primary lymphoid organ, forms a complex threedimensional meshwork structure that provides the microenvironment to drive the differentiation, proliferation, and selection of T lymphocytes [1,2,3,4,5]. Thymic rudiment arises from the third pharyngeal pouch region in the mouse embryo at embryonic day 10.5 of gestation (E10.5) with specific expression of Foxn transcription factor [12,13,14,15] Transplantation studies in both birds and mice showed that cTECs and mTECs all originated from endodermal cells [14]. Reverting a nonfunctional Foxn allele to a functional one in a single postnatal TEPC reawakened its development into a neo-thymi tissue with normal medullary and cortical organization [17] These results clearly demonstrated the existence of TEPC in embryonic (at E12.5, Epcam+) [16] and postnatal (K14+) [17] thymus that produced both mTECs and cTECs. Characterization of the TEPCs has been intensively studied in the recent two decades. The differentiation capacity of TEPC was clarified, the differentiation model of TEPC to generate cTECs and mTECs is still elusive

Methods

Results

Conclusion