Identification of factors mediating the developmental regulation of the early acting-3.9 kb chicken lysozyme enhancer element

The chicken lysozyme gene -3.9 kb enhancer forms: a DNase I hypersensitive site (DHS) early in macrophage differentiation, but not in more primitive: multipotent myeloid precursor cells. A nucleosome! becomes precisely positi oned across the enhancer in parallel with DHS formation. In transfection as says, the 5'-part of the -3.9 kb element has ubiquitous: enhancer activity. The X-part has no stimulatory activity, but is necessary for enhancer repr ession in lysozyme non-expressing cells. Recent studies have shown that the chromatin fine structure of this region is affected by inhibition of histo ne deacetylase activity after Trichostatin A (TSA) treatment, but only in l ysozyme non-expressing cells. These results indicated a developmental modif ication of chromatin structure from a dynamic, but inactive, to a stabilise d, possibly hyperacetylated, active state. Here we have identified positive ly and negatively, acting transcription factors binding to the -3.9 kb enha ncer and determined their contribution to enhancer activity. Furthermore, w e examined the: influence of TSA treatment on enhancer activity in macropha ge cells and lysozyme non-expressing cells, including multipotent macrophag e precursors. Interestingly, TSA treatment was able to restore enhancer act ivity fully in macrophage precursors cells, but not in non-macrophage linea ge cells. These results suggest (i) that the transcription factors compleme nt of multipotent progenitor cells: is similar to that of lysozyme-expressi ng cells and (ii) that developmental regulation of the -3.9 kb enhancer! is mediated by the interplay of repressing and activating factors that respon d to or initiate changes in the chromatin acetylation state.