B cell development is a multistep process that is tightly regulated at the transcriptional level. In recent years, investigators have shed light on the transcription factor networks involved in all the differentiation steps comprising B lymphopoiesis. The interplay between transcription factors and the epigenetic machinery involved in establishing the correct genomic landscape characteristic of each cellular state is beginning to be dissected. The participation of “epigenetic regulator-transcription factor” complexes is also crucial for directing cells during reprogramming into pluripotency or lineage conversion. In this context, greater knowledge of epigenetic regulation during B cell development, transdifferentiation, and reprogramming will enable us to understand better how epigenetics can control cell lineage commitment and identity. Herein, we review the current knowledge about the epigenetic events that contribute to B cell development and reprogramming. 1. Introduction Hematopoietic stem cells (HSCs) give rise to mature B cells through the sequential differentiation of lymphoid progenitor cells. Long-term HSCs (LT-HSCs) have the ability to self-renew and reconstitute the entire immune system by differentiating into short-term HSCs (ST-HSCs). ST-HSCs differentiate into multipotent progenitors (MPPs) that then branch into common myeloid progenitors (CMPs) and lymphoid-primed multipotent progenitors (LMPPs). CMPs further differentiate into erythrocytes and megakaryocytes, whereas LMPPs retain the capability to give rise to myelomonocytic or lymphoid lineages [1, 2]. LMPPs become common lymphoid progenitors (CLPs) [3], which have the potential to differentiate into B and T lymphocytes as well as natural killer (NK) cells [4, 5]. Once committed to the lymphoid lineage, further differentiation steps lead to the formation of pro-B and pre-B cells, which are the early B cell precursors for immature B cells, the terminally differentiated plasma cells and germinal-center B cells (Figure 1). Figure 1: Scheme for B cell development. Successive stages of B cell differentiation and the key transcription factors and epigenetic regulators involved are shown. The epigenetic regulators that cooperate with specific transcription factors at every cell differentiation step are in purple. MicroRNA transcript targets are in green. Every step in B cell development is characterized by the activation of the specific genetic program characteristic of the new intermediate/progenitor generated and the repression/extinction of the genetic program of the previous cellular
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