These features were critical to our ability to utilize this model to assess the dynamic changes in 5-hmC marks and gene expression that accompany hematopoietic stem cell commitment to definitive erythropoiesis

These features were critical to our ability to utilize this model to assess the dynamic changes in 5-hmC marks and gene expression that accompany hematopoietic stem cell commitment to definitive erythropoiesis. == Physique 1. paradigm for stem cell differentiation. Accumulated evidence has demonstrated the ability of a single hematopoietic cell to lose multilineage potential and commit to a specific blood cell GR-203040 type, a complex GR-203040 process involving extrinsic and intrinsic signals heavily influenced by the stem cell microenvironment (Ogawa, 1993;Smith et al., 1991;Spradling et al., 2001). Lineage commitment by stem cells is usually characterized by initiating a specific transcriptional program while simultaneously silencing large numbers of genes that maintain the self-renewal characteristics of the stem cell compartment. Although accumulated data underscore the importance of extrinsic factors in lineage commitment, very little is known about the epigenetic changes that accompany lineage commitment and differentiation. Ten-Eleven-Translocation (TET) family members are dioxygenases that catalyze the conversion of 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine (5-hmC) and other covalent cytosine modifications, which have the potential to provide additional complexity to overall gene regulation (Kriaucionis and Heintz, 2009;Tahiliani et al., 2009). Controversy exists as to whether Tet1 is required for pluripotency, with Rabbit Polyclonal to TNF12 some studies showing thatTet1knockdown leads to spontaneous differentiation of mouse embryonic stem cells (ESCs) (Ito et al., 2010) and others failing to demonstrate compromised self-renewal capacity (Dawlaty et al., 2011;Koh et al., 2011;Williams et al., 2011). Genome-wide mapping of 5-hmC in mouse ESCs exhibited an association with active chromatin marks as well as the enrichment of 5-hmC at transcriptional start sites and within enhancer regions, suggesting that 5-hmC plays a role in transcriptional regulation (Pastor et al., 2011;Stroud et al., 2011;Williams et al., 2011;Wu et al., 2011;Wu and Zhang, 2011b). Many studies have demonstrated a role for 5-hmC and GR-203040 the Tet enzymes in DNA methylation reprogramming in the mammalian zygote (Ficz et al., 2011;Gu et al., 2011;Iqbal et al., 2011;Wossidlo et al., 2011). However, whether 5-hmC functions as an intermediate in active or passive demethylation pathways, confers its own epigenetic function, or both, is not defined. Furthermore, many studies have examined 5-mC versus 5-hmC in cells in a single differentiation state and, therefore, have not been able to test how 5-hmC distribution changes during the course of differentiation. Until recently, most studies employed approaches that cannot distinguish 5-mC from 5-hmC, making it difficult to map dynamic changes precisely in the epigenetic landscape during stem cell commitment to a particular lineage. The current study provides comprehensive analysis of 5-hmC changes in a dynamic fashion during human stem/early progenitor cell commitment to the erythroid lineage and during subsequent differentiation, providing a valuable resource for understanding the relationship between epigenetic modifications and transcription factor (TF) binding as well as the generation of molecular hypotheses regarding stem cell commitment. == RESULTS == == Global Levels of 5-hmC Change Dramatically during Erythropoiesis == To decipher the precise role(s) of 5-hmC in stem cell commitment, we chose a well-defined erythroid commitment and differentiation model (Kang et al., 2008;Tamez et al., 2009;Uddin et al., 2004), in which primary human hematopoietic stem/early progenitor cells differentiate during 17 days of in vitro culture in a replicative, synchronous, and orderly progression through all of the known erythroid intermediates (Figures 1A,S1A, and S1B). The day 0 starting cell population was highly enriched for stem/early progenitor cells (74.8% 6.8% CD34+/CD90+) and was devoid of cells expressing myeloid or lymphoid markers (Determine S1A; Table S1). Our culture conditions were permissive for erythroid-lineage commitment by day 3 as confirmed by expression ofEPOR,GATA1, andHBB, all highly representative genes for erythroid cells (Physique S1C). These features were critical to our ability to utilize this model to assess the dynamic changes in 5-hmC marks and gene expression that accompany hematopoietic stem cell commitment to definitive erythropoiesis. == Physique 1. Dynamic Changes in 5-hmC and 5-mC Levels during Erythroid Differentiation. == (A) Photomicrographs of hematoxylin and benzidine-stained cells cytospun onto slides on the days indicated. Changes in cellular morphology as well as acquisition of HB (brown) during the differentiation program are seen in the micrographs. (B and C) Total 5-hmC (B) and 5-mC (C) content in cells at days 0, 3, 7, 10, 13, and 17 during in.