Global transcriptional analysis of primitive thymocytes reveals accelerated dynamics of T cell specification in fetal stages

Nikolai N Belyaev,Alexandre J Potocnik,Judit Biró,Dimitrios Athanasakis,Delmiro Fernandez-Reyes

doi:10.1007/s00251-012-0620-6

Abstract

T cell development constitutes a multistage process allowing the dissection of events resulting in cellular commitment and functional specification in a specialized microenvironment. This process is guided by the appropriate expression of regulatory genetic factors like transcriptional activators or repressors which are, in part, dependent on instructive signals of the microenvironment. To date, it remains unclear whether exactly the same genetic mechanism acts in adult compared to fetal T cell development. In order to directly compare T cell commitment during adult and fetal differentiation, we isolated subsequent stages of intrathymic subpopulations starting with early canonical T cell progenitors up to irreversibly committed T cell precursors. The genome-wide analysis revealed several distinct gene clusters with a specific pattern of gene regulation for each subset. The largest cluster contained genes upregulated after transition through the most primitive pool into the next transitory population with a consistently elevated expression of elements associated with ongoing T cell fate specification, like Gata3 and Tcf7, in fetal progenitors. Furthermore, adult and fetal T cell progenitors occupied distinct “transcriptional territories” revealing a precise land map of the progression to final T cell commitment operating in different developmental windows. The presence and/or elevated expression of elements associated with an ongoing establishment of a T cell signature in the most primitive fetal subset is highly suggestive for an extrathymic initiation of T cell specification and underlines the fundamental differences in fetal versus adult lymphopoiesis.Electronic supplementary materialThe online version of this article (doi:10.1007/s00251-012-0620-6) contains supplementary material, which is available to authorized users.

Highlights

The hematopoietic system provides an exceptional platform to study cellular differentiation since developmentally arranged populations with prospective functional potential could be identified and isolated
To establish side-by-side phenotypic differences between adult and fetal T cell development, expression of surface antigens was assessed in early thymic progenitor” (ETP), DN2 and DN3 populations (Fig. 1b)
Expression of CD90.2 was homogeneously intermediate in adult DN1 ETPs, whereas this expression was heterogeneous on the analogous fetal population defining a CD90.2lo/int and a CD90.2hi population

Summary

Introduction

The hematopoietic system provides an exceptional platform to study cellular differentiation since developmentally arranged populations with prospective functional potential could be identified and isolated. Originating from a hematopoietic stem cell (HSC), which can sustain the life-long production of all blood cells, hematopoietic development proceeds by several distinct maturation steps characterized by stepwise restriction of alternative lineage options and the accompanying acquisition of functional competence. Functional maturation of T cells is compartmentalized to a specific anatomical site, namely, the thymus, where T cell differentiation takes place in highly specified stromal compartments (Petrie and Zúñiga-Pflücker 2007). T cell precursors—not necessarily restricted to the T cell lineage—seed the thymus at an early stage of their development (Ceredig and Rolink 2002; Shortman and Wu 1996). Further differentiation of T cell progenitors depends crucially on the thymic stroma which is exemplified by the absence of a functional T cell repertoire in “nude” mice carrying a mutation in the forkhead transcription factor Foxn (Nehls et al 1994)

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Conclusion