SRSF1 Deficiency Impairs the Late Thymocyte Maturation and the CD8 Single-Positive Lineage Fate Decision.

Ce Ji,Wenhui Guo,Xiao Cui,Juanjuan Liu,Jingjing Liu,Guotao Yu,Youmin Kang,Menghao You,Feng Chen,Fang Wang,Shuyang Yu,Shunzong Yuan,Zhihong Qi,Mingxia Feng,Li Bao,Zhao Wang

doi:10.3389/fimmu.2022.838719

Abstract

The underlying mechanisms of thymocyte development and lineage determination remain incompletely understood, and the emerging evidences demonstrated that RNA binding proteins (RBPs) are deeply involved in governing T cell fate in thymus. Serine/arginine-rich splicing factor 1 (SRSF1), as a classical splicing factor, is a pivotal RBP for gene expression in various biological processes. Our recent study demonstrated that SRSF1 plays essential roles in the development of late thymocytes by modulating the T cell regulatory gene networks post-transcriptionally, which are critical in response to type I interferon signaling for supporting thymocyte maturation. Here, we report SRSF1 also contributes to the determination of the CD8+ T cell fate. By specific ablation of SRSF1 in CD4+CD8+ double positive (DP) thymocytes, we found that SRSF1 deficiency impaired the maturation of late thymocytes and diminished the output of both CD4+ and CD8+ single positive T cells. Interestingly, the ratio of mature CD4+ to CD8+ cells was notably altered and more severe defects were exhibited in CD8+ lineage than those in CD4+ lineage, reflecting the specific function of SRSF1 in CD8+ T cell fate decision. Mechanistically, SRSF1-deficient cells downregulate their expression of Runx3, which is a crucial transcriptional regulator in sustaining CD8+ single positive (SP) thymocyte development and lineage choice. Moreover, forced expression of Runx3 partially rectified the defects in SRSF1-deficient CD8+ thymocyte maturation. Thus, our data uncovered the previous unknown role of SRSF1 in establishment of CD8+ cell identity.

Highlights

T cell development occurs in the thymus and consists of several ordered processes, such as T cell lineage commitment, T cell receptor (TCR) rearrangements, expression of diverse TCR repertoire, positive and negative selection, and the terminal maturation for acquisition of their functions as helper, cytotoxic or regulatory T cells [1,2,3,4]
The results indicated that CD8+ cell-specific genes were enriched in wild-type double positive (DP) cells relative to Serine/arginine-rich splicing factor 1 (SRSF1)-deficient DP cells, suggesting that the differentiation capacity of DP cell toward CD8+ single positive (SP) was more significantly reduced in absence of SRSF1, both CD4+ and CD8+ SP thymocyte-related genes exhibited the enrichment in wild-type DP cells (Figure S1D)
To address the potential role of SRSF1 involved in the lineage choice of CD4-versus-CD8 thymocytes, we established the genetic mouse model with conditional inactivation of SRSF1 in DP stage by crossing Srsf1fl/fl mice with Cd4-Cre mice [30], which is widely applied for the lineage determination analysis of late thymocytes (Figure S2A)

Summary

Introduction

T cell development occurs in the thymus and consists of several ordered processes, such as T cell lineage commitment, T cell receptor (TCR) rearrangements, expression of diverse TCR repertoire, positive and negative selection, and the terminal maturation for acquisition of their functions as helper, cytotoxic or regulatory T cells [1,2,3,4]. The dynamic expression of cell surface markers which are related to functional alterations is essential to delineate the stages of thymocyte development [6]. The thymocytes are stratified into distinct developmental stages defined by the expression of TCRb (or CD3e) and the activation marker CD69, representing preselection (TCRbloCD69lo), initial stage of selection (TCRbintCD69lo), undergoing selection (TCRbintCD69hi), post selected immature (TCRbhiCD69hi), and post selected mature (TCRbhiCD69lo) thymocytes, respectively [7,8,9]. The post selected TCRbhi thymocytes can be further compartmentalized by the dynamic expression level of CD69, CD24, CD4 and CD8 on their cell surface, reflecting the heterogeneity and defining the developmental stages of late thymocytes [11, 12]

Methods

Results

Conclusion