title: Restricted STAT5 activation dictates appropriate thymic B versus T cell lineage commitment.
abstract: The molecular mechanisms regulating lymphocyte lineage commitment remain poorly characterized. To explore the role of the IL7R in this process, we generated transgenic mice that express a constitutively active form of STAT5 (STAT5b-CA), a key downstream IL7R effector, throughout lymphocyte development. STAT5b-CA mice exhibit a 40-fold increase in pro-B cells in the thymus. As documented by BrdU labeling studies, this increase is not due to enhanced B cell proliferation. Thymic pro-B cells in STAT5b-CA mice show a modest increase in cell survival ( approximately 4-fold), which correlates with bcl-x(L) expression. However, bcl-x(L) transgenic mice do not show increases in thymic B cell numbers. Thus, STAT5-dependent bcl-x(L) up-regulation and enhanced B cell survival are not sufficient to drive the thymic B cell development observed in STAT5b-CA mice. Importantly, thymic pro-B cells in STAT5b-CA mice are derived from early T cell progenitors (ETPs), suggesting that STAT5 acts by altering ETP lineage commitment. Supporting this hypothesis, STAT5 binds to the pax5 promoter in ETPs from STAT5b-CA mice and induces pax5, a master regulator of B cell development. Conversely, STAT5b-CA mice exhibit a decrease in the DN1b subset of ETPs, demonstrating that STAT5 activation inhibits early T cell differentiation or lineage commitment. On the basis of these findings, we propose that the observed expression of the IL-7R on common lymphoid progenitors, but not ETPs, results in differential STAT5 signaling within these distinct progenitor populations and thus helps ensure appropriate development of B cells and T cells in the bone marrow and thymic environments, respectively.
authors.affiliation: Center for Immunology, Cancer Center, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Christine A
authors.initials: CA
authors.lastname: Goetz
authors.forename: Ian R
authors.initials: IR
authors.lastname: Harmon
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: O'Neil
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Burchill
authors.forename: Tanner M
authors.initials: TM
authors.lastname: Johanns
authors.forename: Michael A
authors.initials: MA
authors.lastname: Farrar
mesh_terms: D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D019070:Cell Lineage / Q000235:genetics / Q000276:immunology; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006131:Growth Inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008894:Milk Proteins / Q000235:genetics / Q000378:metabolism*; D051757:PAX5 Transcription Factor; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013234:Stem Cells / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology; D051020:bcl-X Protein
chemical_list: C494812:Bcl2l1 protein, mouse; D004268:DNA-Binding Proteins; D006131:Growth Inhibitors; D008894:Milk Proteins; D051757:PAX5 Transcription Factor; C497282:Pax5 protein, mouse; D019253:Proto-Oncogene Proteins c-bcl-2; D050799:STAT5 Transcription Factor; C494096:Stat5b protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D051020:bcl-X Protein