Regulation of cell survival during B lymphopoiesis: apoptosis and Bcl-2/Bax content of precursor B cells in bone marrow of mice with altered expression of IL-7 and recombinase-activating gene-2.
B cell development in mouse bone marrow depends critically upon IL-7. To examine the possible in vivo trophic role of IL-7, we have quantitated apoptosis and Bcl-2 family proteins in populations of phenotypically defined B lineage cells in IL-7-deficient and IL-7-overexpressing mice. Using immunofluorescence labeling, multiparameter flow cytometry, and a short-term culture assay, we show that the apoptotic rates of precursor B cells, but not of more mature B cells, are enhanced by IL-7 gene deletion, associated with increased intracellular content of Bax and decreased Bcl-2, while, conversely, an IL-7 transgene suppresses precursor B cell apoptosis and produces low Bax and high Bcl-2 levels. During normal B cell development, high Bax/Bcl-2 ratios characterize cells undergoing greatest apoptotic cell death. Pro-B cells in RAG-2-/- mice, all destined to abort, show elevated Bax levels and Bax/Bcl-2 ratios. By comparison with the elevated rate of pro-B cell apoptosis in RAG-2-/- mice, provisional estimates have been made for the fraction of pro-B cells undergoing apoptosis in normal mice (70%), IL-7-/- mice (85%), and IL-7 transgenic mice (35%). The results demonstrate that IL-7 strongly promotes in vivo cell survival and maintains antiapoptotic Bcl-2/Bax ratios during the development of precursor B cells in mouse bone marrow.
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Department of Anatomy and Cell Biology, McGill University, Montreal, Canada.
Chaudhury
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Osmond
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D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000276:immunology*; D001402:B-Lymphocytes / Q000166:cytology* / Q000378:metabolism; D001854:Bone Marrow Cells / Q000166:cytology* / Q000378:metabolism; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D006410:Hematopoiesis / Q000235:genetics / Q000276:immunology; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D015851:Interleukin-7 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D008822:Mice, Transgenic; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000378:metabolism*; D019895:Transposases / Q000235:genetics; D051028:bcl-2-Associated X Protein