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Molecular mechanisms in lymphoid restriction: securing the B lineage fate
Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the work in this thesis I have aimed to deepen the understanding of the mechanisms behind the development of different blood cell lineages with a specific focus on B cell development.

To understand the interplay between extracellular signaling and transcription factor networks in early lymphoid development we investigated the functional collaborations of FLT3 and IL7R. We found that signaling via FLT3 and IL7R act in powerful synergy on proliferation of common lymphoid progenitors (CLPs). In addition to a role in expansion of progenitor cells we provided evidence for that IL7R signaling play a crucial role in B-cell commitment. IL7 deficient mice display a dramatic block in development before functional lineage restriction in the Ly6D+ CLP-compartment. The few Ly6D+CLPs that do develop have reduced mRNA levels of transcription factor EBF1, a protein with crucial functions in lineage restriction and activation of the B-lymphoid program. One crucial function of EBF1 is to activate Pax5. Even though Pax5 deficient fetal liver cells upon transplantation to congenic hosts will generate an abundance of cells with an activated B-lineage transcriptional program, the pro-B cells have disrupted regulation of non-B-lineage transcripts and a propensity to develop into T- and NK-cells in vitro. Both the activation of the B-lineage program and lineage restriction was dependent on the dose of transcription factors. Mice carrying a heterozygous mutation for the transcription factor E2A had slightly reduced relative frequency of progenitor cells and an impaired B-lineage specification in CLPs. Loss of one allele of Ebf1 resulted in reduced surface expression of IL2Rα and pre-B cell receptor (BCR), reduced IL7-response in vitro, and disrupted cell cycle dynamics in pro- and pre-B cells. While heterozygous loss of Pax5 did not result in any dramatic phenotype,  the combined loss of one allele of Pax5 and one allele of Ebf1 (Pax5+/-Ebf1+/-) had a dramatic effect on lineage plasticity in B-cell progenitors compared to the single heterozygotes. Furthermore, these Pax5+/-Ebf1+/- mice developed spontaneous, transplantable pro-B cell tumors and had a significantly reduced probability to survive over time. The transformed cells show high in vitro plasticity and tumor cells with induced overexpression of intracellular Notch1 can transform into T-lineage cell in vivo.

The data presented in this thesis add important pieces of information to the field of developmental hematopoiesis. By increasing the analytical depth of development in normal circumstances, and by understanding the consequence of genetic mutations in relation to cell type, we hope to contribute to the understanding of hematopoietic development in health and disease.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 55 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1422
National Category
Microbiology in the medical area
Identifiers
URN: urn:nbn:se:liu:diva-114273DOI: 10.3384/diss.diva-114273ISBN: 978-91-7519-226-0 (print)OAI: oai:DiVA.org:liu-114273DiVA: diva2:788639
Public defence
2014-12-12, Victoriasalen, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2015-02-16 Created: 2015-02-16 Last updated: 2016-06-22Bibliographically approved
List of papers
1. Interleukin-7-induced Stat-5 Acts in Synergy with Flt-3 Signaling to Stimulate Expansion of Hematopoietic Progenitor Cells
Open this publication in new window or tab >>Interleukin-7-induced Stat-5 Acts in Synergy with Flt-3 Signaling to Stimulate Expansion of Hematopoietic Progenitor Cells
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2010 (English)In: JOURNAL OF BIOLOGICAL CHEMISTRY, ISSN 0021-9258, Vol. 285, no 47, 36275-36284 p.Article in journal (Refereed) Published
Abstract [en]

The development of lymphoid cells from bone marrow progenitors is dictated by interplay between internal cues such as transcription factors and external signals like the cytokines Flt-3 ligand and Il-7. These proteins are both of large importance for normal lymphoid development; however, it is unclear if they act in direct synergy to expand a transient Il-7R(+)Flt-3(+) population or if the collaboration is created through sequential activities. We report here that Flt-3L and Il-7 synergistically stimulated the expansion of primary Il-7R(+)Flt-3(+) progenitor cells and a hematopoietic progenitor cell line ectopically expressing the receptors. The stimulation resulted in a reduced expression of pro-apoptotic genes and also mediated survival of primary progenitor cells in vitro. However, functional analysis of single cells suggested that the anti-apoptotic effect was additive indicating that the synergy observed mainly depends on stimulation of proliferation. Analysis of downstream signaling events suggested that although Il-7 induced Stat-5 phosphorylation, Flt-3L caused activation of the ERK and AKT signaling pathways. Flt-3L could also drive proliferation in synergy with ectopically expressed constitutively active Stat-5. This synergy could be inhibited with either receptor tyrosine kinase or MAPK inhibitors suggesting that Flt-3L and Il-7 act in synergy by activation of independent signaling pathways to expand early hematopoietic progenitors.

Place, publisher, year, edition, pages
The American Society for Biochemistry and Molecular Biology, 2010
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-62734 (URN)10.1074/jbc.M110.155531 (DOI)000284146100037 ()20829349 (PubMedID)
Available from: 2010-12-03 Created: 2010-12-03 Last updated: 2015-02-16
2. IL-7 mediates Ebf-1-dependent lineage restriction in early lymphoid progenitors
Open this publication in new window or tab >>IL-7 mediates Ebf-1-dependent lineage restriction in early lymphoid progenitors
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2011 (English)In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 118, no 5, 1283-1290 p.Article in journal (Refereed) Published
Abstract [en]

eficiencies in the IL-7 signaling pathway result in severe disruptions of lymphoid development in adult mice. To understand more about how IL-7 deficiency impacts early lymphoid development, we have investigated lineage restriction events within the common lymphoid progenitor (CLP) compartment in IL-7 knockout mice. This revealed that although IL-7 deficiency had a minor impact on the development of LY6D(-) multipotent CLPs, the formation of the lineage restricted LY6D(+) CLP population was dramatically reduced. This was reflected in a low-level transcription of B-lineage genes as well as in a loss of functional B-cell commitment. The few Ly6D(+) CLPs developed in the absence of IL-7 displayed increased lineage plasticity and low expression of Ebf-1. Absence of Ebf-1 could be linked to increased plasticity because even though Ly6D(+) cells develop in Ebf-1-deficient mice, these cells retain both natural killer and dendritic cell potential. This reveals that IL-7 is essential for normal development of Ly6D(+) CLPs and that Ebf-1 is crucial for lineage restriction in early lymphoid progenitors.

Place, publisher, year, edition, pages
American Society of Hematology, 2011
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-70104 (URN)10.1182/blood-2011-01-332189 (DOI)000293510000020 ()
Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2017-12-08
3. Single-cell analysis of early B-lymphocyte development suggests independent regulation of lineage specification and commitment in vivo
Open this publication in new window or tab >>Single-cell analysis of early B-lymphocyte development suggests independent regulation of lineage specification and commitment in vivo
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2012 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 39, 15871-15876 p.Article in journal (Refereed) Published
Abstract [en]

To better understand the process of B-lymphocyte lineage restriction, we have investigated molecular and functional properties in early B-lineage cells from Pax-5-deficient animals crossed to a B-lineage-restricted reporter mouse, allowing us to identify B-lineage-specified progenitors independently of conventional surface markers. Pax-5 deficiency resulted in a dramatic increase in the frequency of specified progenitor B-cellsmarked by expression of a lambda 5 (Igll1) promoter-controlled reporter gene. Gene expression analysis of ex vivo isolated progenitor cells revealed that Pax-5 deficiency has a minor impact on B-cell specification. However, single-cell in vitro differentiation analysis of ex vivo isolated cells revealed that specified B-lineage progenitors still displayed a high degree of plasticity for development into NK or T lineage cells. In contrast, we were unable to detect any major changes in myeloid lineage potential in specified Pax-5-deficient cells. By comparison of gene expression patterns in ex vivo isolated Pax-5-and Ebf-1-deficient progenitors, it was possible to identify a set of B-cell-restricted genes dependent on Ebf-1 but not Pax-5, supporting the idea that B-cell specification and commitment is controlled by distinct regulatory networks.

Place, publisher, year, edition, pages
National Academy of Sciences, 2012
Keyword
transcription, Notch-1, Deltex
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-85090 (URN)10.1073/pnas.1210144109 (DOI)000309604500070 ()
Note

Funding Agencies|Swedish Cancer Society||Swedish Research Council||Swedish Childhood Cancer Foundation||faculty of Medicine at Linkoping University||

Available from: 2012-11-02 Created: 2012-11-02 Last updated: 2017-12-07
4. Early B-cell Factor 1 Regulates the Expansion of B-cell Progenitors in a Dose-dependent Manner
Open this publication in new window or tab >>Early B-cell Factor 1 Regulates the Expansion of B-cell Progenitors in a Dose-dependent Manner
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2013 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 288, no 46, 33449-33461 p.Article in journal (Refereed) Published
Abstract [en]

Transcription factor doses are of importance for normal and malignant B-lymphocyte development; however, the understanding of underlying mechanisms and functional consequences of reduced transcription factor levels is limited. We have analyzed progenitor and B-lineage compartments in mice carrying heterozygote mutations in the E2a, Ebf1, or Pax5 gene. Although lymphoid progenitors from Ebf1 or Pax5 heterozygote mice were specified and lineage-restricted in a manner comparable with Wt progenitors, this process was severely impaired in E2a heterozygote mutant mice. This defect was not significantly enhanced upon combined deletion of E2a with Ebf1 or Pax5. Analysis of the pre-B-cell compartment in Ebf1 heterozygote mice revealed a reduction in cell numbers. These cells expressed Pax5 and other B-lineage-associated genes, and global gene expression analysis suggested that the reduction of the pre-B-cell compartment was a result of impaired pre-B-cell expansion. This idea was supported by a reduction in IL2R-expressing late pre-B-cells as well as by cell cycle analysis and by the finding that the complexity of the VDJ rearrangement patterns was comparable in Wt and Ebf1(+/-) pre-B-cells, although the number of progenitors was reduced. Heterozygote deletion of Ebf1 resulted in impaired response to IL7 in vitro and reduced expression levels of pre-BCR on the cell surface, providing possible explanations for the observed stage-specific reduction in cellular expansion. Thus, transcription factor doses are critical for specification as well as expansion of B-lymphoid progenitors, providing increased insight into the molecular regulation of B-cell development.

Place, publisher, year, edition, pages
American Society for Biochemistry and Molecular Biology, 2013
Keyword
Development; Differentiation; Immunology; Lymphocyte; Transcription Factors
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-103303 (URN)10.1074/jbc.M113.506261 (DOI)000328841700057 ()
Available from: 2014-01-17 Created: 2014-01-16 Last updated: 2017-12-06

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