Reassessment of interactions between hematopoietic receptors using common beta-chain and interleukin-3-specific receptor beta-chain-null cells: no evidence of functional interactions with receptors for erythropoietin, granulocyte colony-stimulating factor, or stem cell factor

Mice lacking both the gene encoding the shared receptor for granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 common beta-chain (B(c)) and the gene for the IL-3 specific receptor (BIL3) were generated. This was achieved by targeting the B(c) locus in embryonic stem cells that were heterozygous for a null mutation of BIL3. Cells from mice generated with the doubly targeted embryonic stem cells were unresponsive to all 3 cytokines. Considerable previous data suggested a role for common beta-chain (beta(c)) in modulating signaling of cytokines including erythropoietin (EPO), G-CSF, and stem cell factor (SCF). However, bone marrow cells from mice lacking beta(c) and beta(IL3) showed normal responsiveness to these cytokines. Thus, there was no evidence for a biologically significant interaction between signaling via beta(c) or beta(IL3) and signaling by EPO, G-CSF, or SCF. Previously documented biochemical phenomena, including receptor transmodulation, receptor transphosphorylation, and even direct physical interaction, involving the beta(c)/beta IL-3 receptor systems do not reflect genuine interactions of physiological significance in primary hematopoietic cells. This study provided results that challenge conclusions previously established using a variety of biochemical assays. (Blood. 2000;96:1588-1590)

SCL expression in the mouse embryo detected with a targeted lacZ reporter gene demonstrates its localization to hematopoietic, vascular, and neural tissues

The helix-loop-helix transcription factor SCL (TAL1) is indispensable for blood cell formation in the mouse embryo. We have explored the localization and developmental potential of cells fated to express SCL during murine development using SCL-lacZ mutant mice in which the Escherichia coli lacZ reporter gene was 'knocked in' to the SCL locus. In addition to the hematopoietic defect associated with SCL deficiency, the yolk sac blood vessels in SCL(lacZ/lacZ) embryos formed an abnormal primary vascular plexus, which failed to undergo subsequent remodeling and formation of large branching vessels. Intraembryonic vasculogenesis in precirculation SCL(lacZ/lacZ) embryos appeared normal but, in embryos older than embryonic day (E) 8.5 to E9, absolute anemia leading to severe hypoxia precluded an accurate assessment of further vascular development. In heterozygous SCL(lacZ/w) embryos, lacZ was expressed in the central nervous system, vascular endothelia, and primitive and definitive hematopoietic cells in the blood, aortic wall, and fetal liver. Culture of fetal liver cells sorted for high and low levels of beta galactosidase activity from SCL(lacZ/w) heterozygous embryos indicated that there was a correlation between the level of SCL expression and the frequency of hematopoietic progenitor cells.