Abstract 1564: A YY1-containing Complex Drives Cardiac Cushion Mesenchyme and Schwann Cell-Specific Periostin Expression
Periostin is a fasciclin-containing adhesive glycoprotein that facilitates the migration and differentiation of cells undergoing epithelial-mesenchymal-transformation (EMT) in the embryonic heart and peripheral nervous system. Despite the importance of EMT as a general developmental mechanism, little is known about how periostin’s embryonic expression patterns are controlled. To help resolve this deficiency, periostin’s 3.9 kb proximal promoter was isolated and using a transgenic approach found to drive embryonic, tissue-specific expression in schwann cells and in a sub-population of periostin-expressing cells in the cardiac out-flow tract mesenchyme. In order to identify the factor(s) responsible for this expression pattern, in vitro promoter dissection was undertaken utilizing dual-luciferase luminometry. Serially and internally truncated fragments of the proximal promoter were used to drive expression of firefly luciferase following transfection into RT4-D6P2T rat schwannoma cells. A 304 bp enhancer element was identified and was shown to drive in vivo expression that recapitulated the pattern generated by the full-length 3.9 kb promoter. Mutation of two evolutionarily-conserved YY1-like binding sites with the 304 bp fragment and subsequent EMSA analysis helped identify a core 37 bp region that specifically binds RT4-D6P2T nuclear extract protein and is essential for in vivo activity of the full length promoter. YY1-programed reticulocyte protein lysate was found to specifically bind the 37 bp fragment and co-transfection studies demonstrated that YY1 protein modulates periostin expression via one of the identified sites. Therefore, these studies identify a highly-conserved YY1-binding 37 bp region within a 304 bp fragment that drives tissue-specific embryonic expression of periostin in the cardiac outflow-tract cushion mesenchyme and schwann cells.