ABSTRACT
Coreceptor expression is tightly regulated during thymocyte development. Deletion of specific Cd8 enhancers leads to variegated expression of CD8alphabeta heterodimers in double-positive thymocytes. Here we show CD8 variegation is correlated with an epigenetic 'off' state, linking Cd8 enhancer function with chromatin remodeling of the adjacent genes Cd8a and Cd8b1 (Cd8). The zinc finger protein MAZR bound the Cd8 enhancer and interacted with the nuclear receptor corepressor N-CoR complex in double-negative thymocytes. MAZR was downregulated in double-positive and CD8 single-positive thymocytes. 'Enforced' expression of MAZR led to impaired Cd8 activation and variegated CD8 expression. Our results demonstrate epigenetic control of the Cd8 loci and identify MAZR as an important regulator of Cd8 expression.
Subject(s)
CD8 Antigens/biosynthesis , Neoplasm Proteins/metabolism , Repressor Proteins/metabolism , T-Lymphocytes/immunology , Animals , CD8 Antigens/genetics , CD8 Antigens/immunology , Chromatin/immunology , DNA Methylation , Down-Regulation , Electrophoretic Mobility Shift Assay , Enhancer Elements, Genetic/immunology , Epigenesis, Genetic , Flow Cytometry , Mice , Mice, Inbred C57BL , Mice, Knockout , Neoplasm Proteins/genetics , Neoplasm Proteins/immunology , Promoter Regions, Genetic , Repressor Proteins/genetics , Repressor Proteins/immunology , T-Lymphocytes/cytology , Transcription, GeneticABSTRACT
Developmental stage-, subset-, and lineage-specific CD8 enhancers have been identified recently by transgenic reporter analyses. Enhancer E8(II) (CIV-4,5) is active in both immature double-positive thymocytes (DP) and mature CD8 single-positive (SP) thymocytes and T cells, whereas E8(I) (CIII-1,2) directs expression only in mature cells. In mice lacking either E8(I) (CIII-1,2) or E8(II) (CIV-4,5), there was no effect on CD8 expression in DP thymocytes. However, deletion of both enhancers resulted in variegated expression of CD8, with appearance of CD4(+)CD8(-) SP thymocytes expressing surface markers characteristic of DP thymocytes. Consequently, fewer mature CD8(+) T cells developed from the reduced pool of DP cells. These results suggest that the initiation of CD8 expression is mediated by cis-regulatory elements that are distinct from any that may be involved in maintenance of expression.
