HDAC HEMATOPOIESIS · Role of Class IIa Histone deacetylases in hematopoietic cell differentiation
FP7 — People (Marie Curie Actions)
- Duration
- 2007-09-01 → 2011-08-31
- EU contribution
- €100,000
- Participants
- 2
- Scheme
- MC-IRG
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Results in brief
Role of Class IIa Histone deacetylases in hematopoietic cell differentiation
Adult hematopoiesis is characterised by the generation of all blood cell types. To achieve this, Hematopoietic stem cells (HSCs) differentiate into Common myeloid progenitors (CMPs) and Lymphoid-primed multipotent progenitors (LMPPs). CMPs give rise to Megakaryocyte / erythrocyte progenitors (MEPs) and Granulocyte / macrophage progenitors (GMPs), whereas LMPPs still have the capacity to choose between the myelomonocytic and lymphoid lineages. Common lymphoid progenitors (CLPs) have the potential to differentiate into B and T lymphocytes, as well as Natural killer (NK) cells. Since the stability of every differentiation step is critical, each transition is tightly regulated at the transcriptional level through the action of lineage-restricted transcription factors that induce genes characteristic of particular cellular states. Surprisingly, very little is known on the role of gene transcriptional repressors, such as Histone deacetylases (HDACs), in the lineage specification and differentiation of hematopoietic cells. The goal of my research proposal was to investigate the role of HDAC7 in lineage commitment and differentiation of hematopoietic cells. The specific objectives of the Marie Curie IRG project are: - Objective 1. Identification of HDAC7 target genes in B cell precursors (pre-B cells) by ChIP-seq - Objective 2. Role of HDAC7 during the reprogramming of pre-B cells into macrophages - Objective 3. Role of HDAC7 in B cell development. We have observed that, similar to B cell specific genes, HDAC7 expression is dramatically downregulated during the transdifferentiation of pre-B cells into macrophages. Co-immunoprecipitation experiments show that HDAC7 interacts with MEF2C and not with IKAROS, PAX5 and E2A in pre-B cells. Chromatin immunoprecipitation (ChIP) experiments show that HDAC7 is recruited to the MEF2 binding sites present in the promoter of key genes for myeloid cells. Re-expression of HDAC7 interferes with the transdifferentiation of pre-B cells into macrophages at both the functional level and the establishement of the myeloid genetic program. To investigate the role of HDAC7 in B lymphocyte development in vivo we have performed a conditional knockout approach. We have observed that HDAC7 deletion in pro-B cells results in a block of B cell development at that developmental stage. Specifically we have found a diminished number of pre-B cells (CD43-) and a dramatic reduction of immature B cells (IgM+) in the bone marrow. In the spleen, we observe a severe impairment in the generation of B cells (B220+). No differences are observed in the number of thymocytes between knockout and littermate control mice. Taken together, these results demonstrate that HDAC7 is crucial for the development of B lymphocytes in vivo. With the execution of the project we have identified the first lineage specific transcriptional repressor in the hematopoietic system. We have demonstrated that HDAC7 is recruited to and represses lineage inappropriate genes in B cell precursors. The down-regulation of HDAC7 is a critical event for the proper transdifferentiation of pre-B cells into macrophages. Using conditional knockout mice we have demonstrated that specific deletion of HDAC7 in pro-B cells results in a dramatic block in B cells development at the pro-B cell stage in the bone marrow. Taken together, the findings obtained with the execution of the Marie Curie IRG grant demonstrate that HDAC7 is a key transcriptional repressor for the development and identity of B lymphocytes.
Data: CORDIS, © European Union
Project objective
Chromatin, the higher order structure of DNA and protein, forms a barrier for gene transcription. Modification of histones, a major component of the chromatin, is a critical mechanism by which the barrier is regulated. An important modification, which is thought to activate transcription, is the acetylation of histones. Regulation of histones acetylation is performed by the antagonistic activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Mammalian HDACs are divided into three distinct classes based on their homology to yeast proteins. Class I HDACs (HDAC1, 2, 3 and 8), Class II HDACs, which are subdivided into two families, Class IIa (HDAC4, 5, 7 and 9) and Class IIb (HDAC6 and 10) and Class III HDACs, also named sirtuins, which comprises Sirt1, 2, 3, 4, 5, 6 and 7. In contrast to other HDACs, Class IIa HDACs are expressed in a tissue specific manner and have been shown to play an important role in cell differentiation. The hematopoietic system is a complex and interesting model of cell commitment and differentiation. Hematopoietic lineages are specified by lineage-restricted transcription factors that result in a distinct gene expression pattern. However, little is known about the role of chromatin modifying enzymes in the hematopoietic system. It has been shown that HDAC5 and HDAC9 are expressed in hematopoietic cells. However, their role in commitment of hematopoietic cells has never been investigated. Here, I propose to study the role of HDAC5 and HDAC9 in lineage commitment of hematopoietic cells. By using a genomic approach, as well as, knock out and trangenic mouse models, I will elucidate the lineage compartment where they are expressed, the specific target genes repressed by both proteins and their role in hematopoietic cell differentiation. The elucidation of the molecular mechanisms involved in the lineage commitment of hematopoietic stem cells will suppose an important advance in regenerative medicine.
Original text from CORDIS.
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Data: CORDIS, © European Union