Precise control of hematopoietic stem cell (HSC) proliferation and differentiation is needed to maintain a lifetime supply of blood cells. Using genome-wide ENU mutagenesis and phenotypic screening, we have identified a mouse line that harbors a point mutation in the transactivation (TA) domain of the transcription factor c-Myb (M303V), which reduces c-Myb-dependent TA by disrupting its interaction with the transcriptional coactivator p300. The biological consequences of the c-Myb(M303V/M303V) mutation include thrombocytosis, megakaryocytosis, anemia, lymphopenia, and the absence of eosinophils. Detailed analysis of hematopoiesis in c-Myb(M303V/M303V) mice reveals distinct blocks in T cell, B cell, and red blood cell development, as well as a remarkable 10-fold increase in the number of HSCs. Cell cycle analyses show that twice as many HSCs from c-Myb(M303V/M303V) animals are actively cycling. Thus c-Myb, through interaction with p300, controls the proliferation and differentiation of hematopoietic stem and progenitor cells.

CD8+ T cells can mediate eradication of established tumors, and strategies to amplify tumor-reactive T-cell numbers by immunization or ex vivo expansion followed by adoptive transfer are currently being explored in individuals with cancer. Generating effective CD8+ T cell-mediated responses to tumors is often impeded by T-cell tolerance to relevant tumor antigens, as most of these antigens are also expressed in normal tissues. We examined whether such tolerant T cells could be rescued and functionally restored for use in therapy of established tumors. We used a transgenic T-cell receptor (TCR) mouse model in which peripheral CD8+ T cells specific for a candidate tumor antigen also expressed in liver are tolerant, failing to proliferate or secrete interleukin (IL)-2 in response to antigen. Molecular and cellular analysis showed that these tolerant T cells expressed the IL-15 receptor alpha chain, and could be induced to proliferate in vitro in response to exogenous IL-15. Such proliferation abrogated tolerance and the rescued cells became effective in treating leukemia. Therefore, high-affinity CD8+ T cells are not necessarily deleted by encounter with self-antigen in the periphery, and can potentially be rescued and expanded for use in tumor immunotherapy.

Antigen receptor-mediated production of inositol-1,4,5-trisphosphate (Ins(1,4,5)P3) in lymphocytes triggers the release of Ca2+ from intracellular stores; this release of Ca2+ results in the opening of store-operated Ca2+ channels in the plasma membrane. Here we report that mice lacking Ins(1,4,5)P3 3-kinase B (Itpkb), which converts Ins(1,4,5)P3 to inositol-1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), had impaired B lymphocyte development and defective immunoglobulin G3 antibody responses to a T lymphocyte-independent antigen. Itpkb-deficient B lymphocytes had the phenotypic and functional features of tolerant B lymphocytes and showed enhanced activity of store-operated Ca2+ channels after B lymphocyte receptor stimulation, which was reversed by the provision of exogenous Ins(1,3,4,5)P4. Our data identify Itpkb and its product Ins(1,3,4,5)P4 as inhibitors of store-operated Ca2+ channels and crucial regulators of B cell selection and activation.

The colonic crypt is the functional unit of the colon mucosa with a central role in ion and water reabsorption. Under steady-state conditions, the distal colonic crypt harbors a single stem cell at its base that gives rise to highly proliferative progenitor cells that differentiate into columnar, goblet, and endocrine cells. The role of c-Myb in crypt homeostasis has not been elucidated. Here we have studied three genetically distinct hypomorphic c-myb mutant mouse strains, all of which show reduced colonic crypt size. The mutations target the key domains of the transcription factor: the DNA binding, transactivation, and negative regulatory domains. In vivo proliferation and cell cycle marker studies suggest that these mice have a progenitor cell proliferation defect mediated in part by reduced Cyclin E1 expression. To independently assess the extent to which c-myb is required for colonic crypt homeostasis we also generated a novel tissue-specific mouse model to allow the deletion of c-myb in adult colon, and using these mice we show that c-Myb is required for crypt integrity, normal differentiation, and steady-state proliferation.colon ͉ hypomorphs ͉ A33 ͉ stem cells ͉ p27

The hematopoietic stem cell (HSC) compartment is composed of long-term reconstituting (LTR) and short-term reconstituting (STR) stem cells. LTR HSC can reconstitute the hematopoietic system for life, whereas STR HSC can sustain hematopoiesis for only a few weeks in the mouse. Several excellent gene expression profiles have been obtained of the total hematopoietic stem cell population. We have used five-color FACS sorting to isolate separate populations of LTR and STR stem cell subsets. The LTR HSC has the phenotype defined as Lin ؊ Sca ؉ Kit ؉ 38 ؉ 34 ؊ ; two subsets of STR HSC were obtained with phenotypes of Lin ؊ Sca ؉ Kit ؉ 38 ؉ 34 ؉ and Lin ؊ Sca ؉ Kit ؉ 38 ؊ 34 ؉ . The microarray profiling study reported here was able to identify genes specific for LTR functions. In the interrogated genes (Ϸ12,000 probe sets corresponding to 8,000 genes), 210 genes are differentially expressed, and 72 genes are associated with LTR activity, including membrane proteins, signal transduction molecules, and transcription factors. Hierarchical clustering of the 210 differentially expressed genes suggested that they are not bone marrow-specific but rather appear to be stem cell-specific. Transcription factor-binding site analysis suggested that GATA3 might play an important role in the biology of LTR HSC.microarray ͉ regulation