ABSTRACT
The basic helix-loop-helix (HLH) E2A transcription factors bind to DNA as homodimers or as heterodimers formed with other basic HLH factors, activate gene expression, and promote differentiation of muscle, lymphoid, neuronal, and other cell types. These E2A functions can be inhibited by the Id proteins, HLH factors that sequester E2A in non-DNA binding dimers. Here we describe the direct interaction of E2A with Daxx, a broadly expressed non-HLH protein previously associated with apoptosis and transcriptional repression. Daxx inhibits E2A function, but not via an Id-like mechanism; rather, it recruits histone deacetylase activity to E2A-dependent promoters. Increased Daxx expression during muscle differentiation inhibits E2A-dependent expression of key myogenic genes and reduces myotube formation, while decreased Daxx expression promotes myotube formation. These results identify a new mechanism for limiting E2A activity and establish a link between Daxx-mediated gene regulation and control of cellular differentiation.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Basic Helix-Loop-Helix Transcription Factors/metabolism , Cell Differentiation/genetics , Nuclear Proteins/metabolism , Transcription, Genetic , Animals , Mice , Molecular Chaperones , Muscle Fibers, Skeletal/cytology , Muscle Fibers, Skeletal/metabolism , Myoblasts, Skeletal/cytology , Myoblasts, Skeletal/metabolism , NIH 3T3 Cells , RatsABSTRACT
OBJECTIVES: Whole-blood RNA for microarray analysis is easily accessible but contains a large proportion of globin mRNA that interferes with the accurate assessment of other genes. This study investigated the biological significance of genes whose expression was unmasked by globin mRNA reduction in peripheral blood. DESIGN AND METHODS: Samples were collected from healthy subjects using the PAXgene Blood RNA System, and globin mRNA was depleted using GLOBINclear. Genes exhibiting consistent changes in expression on Affymetrix HU133A 2.0 arrays were characterized in three main areas of gene ontology--molecular function, biological process, and cellular component. RESULTS: Globin reduction permitted detection of 2652+/-395 additional genes per assay. Genes unmasked by globin reduction include low abundance transcripts that function primarily as molecular binding proteins and catalytic enzymes in biological processes including transcription, replication, and intracellular transport and signalling. Protein products of these genes are preferentially associated with membranes and the nucleus. CONCLUSIONS: Additional genes detectable only after globin reduction in whole-blood RNA function in a variety of biological processes that may be important to diverse fields of study.
