Regulation of gene expression in mast cells: micro-rNA expression and chromatin structural analysis of cytokine genes.

Despite deriving from two different compartments of the immune system (myeloid and lymphoid respectively), Th2 cells and mast cells produce the same panel of cytokines, interleukin (IL)4, IL5 and IL13. We have compared the chromatin structure of the RAD50/IL13/IL4 locus in Th2 cells and mast cells. Th2 and mast cells display strong overlap in their patterns of DNase I hypersensitivity throughout this locus, except that the first intron of the IL13 gene (MCHS) is DNase I hypersensitive only in mast cells and the conserved non-coding sequence (CNS)-1 in the IL4/IL13 intergenic region is DNase I hypersensitive only in Th2 cells (explaining why cytokine expression is impaired in Th2 cells but not in mast cells of CNS-1-deleted mice). We have also examined the role of micro-RNAs (miRNAs) in the development and activation of mast cells and T cells. miRNAs are 21- to 25-nucleotide small RNAs that regulate gene expression posttranscriptionally by targeting protein-coding mRNAs. Using oligonucleotide arrays to analyse miRNA expression in murine T cells and mast cells, we have identified distinctive cell type-specific patterns of miRNA expression as well as changes related to differentiation and cell activation. We are studying the biological functions of selected miRNAs.