A conserved transcriptional program for MAIT cells across mammalian evolution [Mdomestica_thymus_MAIT]. A conserved transcriptional program for MAIT cells across mammalian evolution [Mdomestica_thymus_MAIT]

Mucosal-Associated Invariant T (MAIT) cells recognize the riboflavin pathway-derived metabolite 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil (5-OP-RU) presented by the MHC-Ib molecule MR1. Both MR1 and the T cell receptor genes used by MAIT cells are under strong evolutionary pressure in mammals, suggesting an important role of 5-OP-RU-specific T cells across species. In humans and mice, MAIT cells acquire distinctive effector functions linked to the expression of the master transcription factor ZBTB16 (PLZF) during thymic development. Conservation of a unique differentiation program in 5-OP-RU-specific T cells from other species is unclear. Here, we used single-cell RNA sequencing to characterize the development of 5-OP-RU-specific T cells in 6 species spanning 110 million years of mammalian evolution. Cross-species comparative analyses revealed a conserved sequence of transcriptional events underlying the maturation of 5-OP-RU-specific thymocytes, marked by the early expression of ZBTB16 in all species. MAIT cells also co-expressed the transcription factors TBX21 (Tbet) and RORC (RORgt) in human, sheep, cattle and opossum. By contrast, Tbet and RORgt were expressed by distinct subsets of MAIT cells in the thymus of rodents, including pet mice and >30 genetically diverse mouse strains, dismissing a laboratory mouse artifact. In mice, RORgt+ MAIT cells further matured in the mesenteric lymph nodes and intestines to acquire a transcriptional program remarkably conserved in MAIT cells from non-rodent species and characterized by co-expression of type 1 and type 17 effector genes, but also genes associated with cytotoxicity and tissue repair. Thus, we define a deeply conserved transcriptional program for 5-OP-RU-specific T cells, which may help understand their functions. Overall design: Mdomestica_thymus_MAIT

黏膜相关恒定T细胞（Mucosal-Associated Invariant T, MAIT）可识别由MHC-Ib分子MR1呈递的、源自核黄素通路的代谢物5-(2-氧亚丙基亚氨基)-6-d-核糖胺基尿嘧啶(5-OP-RU)。MAIT细胞所使用的MR1与T细胞受体基因均在哺乳动物中受到强烈的进化选择压力，这提示5-OP-RU特异性T细胞在各物种中均发挥重要功能。在人类与小鼠体内，MAIT细胞在胸腺发育过程中会获得与主控转录因子ZBTB16(PLZF)表达相关的独特效应功能。目前尚不清楚其他物种的5-OP-RU特异性T细胞是否存在保守的独特分化程序。本研究利用单细胞RNA测序技术，对覆盖哺乳动物1.1亿年进化历程的6个物种体内5-OP-RU特异性T细胞的发育过程进行了表征。跨物种比较分析显示，5-OP-RU特异性胸腺细胞的成熟过程存在保守的转录事件序列，其共同特征为所有物种中均存在ZBTB16的早期表达。在人类、绵羊、牛与负鼠体内，MAIT细胞还会共表达转录因子TBX21(Tbet)与RORC(RORγt)。与之相反，在啮齿类动物（包括宠物小鼠及30余种遗传背景多样的小鼠品系）的胸腺中，Tbet与RORγt分别由不同的MAIT细胞亚群表达，这排除了实验小鼠特异性假象的可能。在小鼠体内，RORγt+ MAIT细胞会在肠系膜淋巴结与肠道中进一步成熟，获得一套在非啮齿类物种的MAIT细胞中高度保守的转录程序，该程序以1型和17型效应基因共表达为特征，同时还包含与细胞毒性及组织修复相关的基因。综上，本研究明确了一套针对5-OP-RU特异性T细胞的高度保守转录程序，这将有助于解析这类细胞的功能。总体实验设计：Mdomestica_thymus_MAIT