The Polycomb group protein L3MBTL1 represses a SMAD5-mediated transcriptional program in human pluripotent stem cells

Epigenetic regulation of key transcriptional programs is a critical mechanism that controls hematopoietic development and thus aberrant expression patterns or mutations in epigenetic regulators occur frequently in hematologic malignancies. We demonstrate that the Polycomb protein L3MBTL1, which is monoallelically deleted in 20q- myeloid malignancies, represses the ability of stem cells to drive hematopoietic-specific transcriptional programs by regulating the expression of SMAD5 and impairing its recruitment to target regulatory regions. Indeed, knock-down of L3MBTL1 promotes the development of hematopoiesis and impairs neural cell fate in human pluripotent stem cells. We also found a role for L3MBTL1 in regulating SMAD5 target gene expression in mature hematopoietic cell populations, thereby affecting erythroid differentiation. Taken together, we have identified epigenetic priming of hematopoietic-specific transcriptional networks, which may assist in the development of therapeutic approaches for patients with anemia. The Polycomb protein L3MBTL1, deleted in 20q- myeloid malignancies, plays a regulatory role during differentiation of human iPS cells. Upon lentiviral knock-down of L3MBTL1, iPS cells stay poised for hematopoietic development and up-regulate expression of BMP/SMAD targets, which may also mediate impaired neural development. Human iPS cells at an undifferentiated stage of differentiation were lentivirally infected to express shRNAs targeting L3MBTL1. GFP+ cells were FACS sorted and subjected to RNA extraction and hybridized to Affymetrix U133plus 2.0 arrays, scanned, and subjected to quality control parameters. The data were normalized using MAS5.0.