Spatial (Tbata) expression in mature medullary thymic epithelial cells

Abstract

The Spatial gene is expressed in highly polarized cell types such as testis germ cells, brain neurons and thymic epithelial cells (TEC). Its expression was documented in testis and brain but poorly characterized in thymus. Here, we characterize for the first time Spatial-expressing TEC throughout ontogeny and adult mouse thymus. Spatial is expressed in thymicfated domain by embryonic day E10.5 and persists in subcapsular, cortical, medullary epithelial cells and in MTS24 1 progenitor TEC. Using mouse strains in which thymocyte development is blocked at various stages, we show that Spatial expression is independent of thymocyte-derived signals during thymus organogenesis. Analyses on purified thymic cell subsets show that Spatial short isoforms are expressed in cortical TEC (cTEC) and mature medullary TEC (mTEC). Spatial long isoforms were detected in the same TEC population. Spatial presents a nuclear distribution specific to mature mTEC expressing UEA1 and Aire. Aire-and RANKL-deficient mice revealed that Spatial expression is drastically reduced in the thymus of these mutants. These findings reveal a critical function of Aire in regulating Spatial expression, which is compatible with promiscuous Spatial gene expression. 530 IntroductionThe vertebrate thymus is responsible for the production of functional nonautoreactive T lymphocytes. In this primary lymphoid organ, T-cell precursors commonly called thymocytes undergo a series of developmental stages through interactions with thymic stromal cells, resulting in the generation of mature T lymphocytes that are exported to the periphery [1,2]. The unique function of the thymus resides mainly in the thymic epithelium, which forms the major subcompartment of the stroma [3,4]. The thymic epithelium itself is commonly divided into two main regions, the cortex and the medulla, and each of these regions contains several ultrastructurally and phenotypically distinct types of thymic epithelial cells (TEC) [5,6]. TEC are required both for thymus organogenesis and for the promotion of most if not all stages of thymocyte maturation [3,4]. Understanding the molecular mechanisms regulating TEC differentiation and function provides crucial insights into mechanisms controlling T-cell development in the thymus.Using DNA chip technology we isolated the Spatial gene (Stromal Protein Associated with Thymii and Lymph node), also known as Tbata (thymus, brain and testes associated), by an approach based on differential screening between different knock-out mice models exhibiting distinct thymic immunodeficiencies [7]. This analysis led to the identification of three adult variants of the Spatial gene expressed in the thymus [8]. In addition, we also described two other isoforms isolated in the testis [8][9][10]. According to the size of alternative spliced variants, we have respectively named Spatial isoforms: Spatial-a (1035 bp), Spatial-b (1002 bp), Spatial-g (933 bp) for the short isoforms identified in the thymus; Spatial-d (1353 bp) and Spatial-e (1454 bp) for the long isoforms ...

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