Poorly rearranging VH genes are associated with dimethylated H3/K9 in pro-B cells. ChIP assays were performed on (A) adult BM pro-B cells (B220+), (B) thymocytes, and (C) NIH-3T3 fibroblasts. Analysis was performed by real-time PCR. Data are expressed relative to the actin gene (actin = 1). The neuregulin values for pro-B cells, thymocytes and NIH-3T3 fibroblasts were 15.79±2.83, 15.01±3.51, and 5.59±1.6, respectively Results represent the mean ± SEM of 2 independent ChIP preparations.