During thymopoiesis, a unique program of gene expression promotes the development of CD4 regulatory T (T reg) cells. Although Foxp3 maintains a pattern of gene expression necessary for T reg cell function, other transcription factors are emerging as important determinants of T reg cell development. We show that the NF-κB transcription factor c-Rel is highly expressed in thymic T reg cells and that in c-rel−/− mice, thymic T reg cell numbers are markedly reduced as a result of a T cell–intrinsic defect that is manifest during thymocyte development. Although c-Rel is not essential for TGF-β conversion of peripheral CD4+CD25− T cells into CD4+Foxp3+ cells, it is required for optimal homeostatic expansion of peripheral T reg cells. Despite a lower number of peripheral T reg cells in c-rel−/− mice, the residual peripheral c-rel−/− T reg cells express normal levels of Foxp3, display a pattern of cell surface markers and gene expression similar to those of wild-type T reg cells, and effectively suppress effector T cell function in culture and in vivo. Collectively, our results indicate that c-Rel is important for both the thymic development and peripheral homeostatic proliferation of T reg cells.

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The putative role(s) of a mechanically gated (MG) cation channel in Xenopus oocyte growth, maturation, fertilization and embryogenesis has been examined. Using a pharmacological approach, we have tested the effects of the MG channel blockers, gadolinium, gentamicin and amiloride on the above developmental events. Our results indicate that oocyte maturation, fertilization and early embryogenesis (up to the free-swimming stage 45) can proceed normally in the presence of concentrations of agents that either completely abolish (i.e., > or = 10 microM Gd3+) or partially block (i.e., 1 mM gentamicin) single MG channel activity as measured by patch-clamp recording. However, we also find that higher concentrations of Gd3+ (> or = 50 microM) can lead to an increased percentage (> 20%) of axis-perturbed embryos compared with control (< 1%) and that amiloride (0.5 mM) reduces the success of fertilization (from 100% to < 50%) and increases mortality (by approximately 75%) in developing embryos. Furthermore, we find that all three agents inhibit oocyte growth in vitro. However, their order of effectiveness (amiloride > gentamicin > Gd3+) is opposite to their order for blocking MG channels (Gd3+ >> gentamicin > amiloride). These discrepancies indicated that the drugs effects occur by mechanisms other than, or in addition to, MG channel block. Our results provide no compelling evidence for the idea that MG channel activity is critical for development in Xenopus. This could mean that there are other mechanisms in the oocyte that can compensate when MG channel activity is blocked or that the protein that forms the channel can undergo additional interactions that result in a function insensitive to MG channel blockers.

The interleukin-8 receptors (CXCR1 and CXCR2) are specifically expressed at high levels in cells of the neutrophil lineage. In this work we identify promoter elements of the CXCR1 gene and the ets family transcription factor PU.1 as a major regulator for activation of the CXCR1 promoter. We first showed that the upstream sequence of CXCR1 (؊800 to ؉86 base pairs (bp)) directs myeloid-specific expression of reporter gene constructs. Second, we showed the presence of negative elements in the sequence from ؊800 to ؊128 bp and positive elements from ؊128 to ؉50 bp. Third, we demonstrated that the fragment ؊22 to ؉14 bp binds PU.1. Fourth, we showed that PU.1 transactivates the CXCR1 promoter. These data are the first demonstration of PU.1-mediated transcriptional regulation of a neutrophil chemoattractant G protein-coupled receptor.The molecular mechanisms regulating neutrophil development are not defined yet. Abnormal neutrophil development is related to several pathological conditions such as neutropenia, neutrophilia, and myelogenous leukemia (1-3). The regulation of this developmental process most likely involves the interplay of transcription factors with positive and negative cis-acting elements and cytokines interacting with their cognate receptors (4, 5). For example, disrupting either of the murine genes encoding the transcription factors PU.1 (Spi-1) and CCAAT enhancer-binding protein ␣ impairs neutrophil development (6 -8). Similarly, disruption of the gene encoding the cytokine granulocyte colony-stimulating factor (G-CSF) 1 inhibits neutrophil development (3). By contrast, disruption of the murine homolog of the chemotactic cytokine interleukin-8 (IL-8) receptor gene (CXCR2) causes neutrophilia (9). IL-8 receptor subtypes A and B (CXCR1 and CXCR2) are G-protein-coupled receptors expressed at high levels in a myeloid-specific fashion, in mature neutrophils and myeloid precursor cells (10 -12). IL-8 suppresses the proliferation of myeloid progenitor and precursor cells via activation of the IL-8 receptor (12, 13). In mature neutrophils, IL-8 is the major mediator for the recruitment of neutrophils from circulation to the sites of injury and infection. Despite the importance of the IL-8 receptor in myeloid development and its restrictive expression in myeloid cells, the transcriptional mechanisms regulating myeloid-specific expression of the IL-8 receptor genes are unknown.Previous studies have shown that CXCR1 and CXCR2 expression is under transcriptional control (14). The genomic organization and promoter regions of CXCR1 and CXCR2 have been previously mapped (15, 16). The CXCR1 gene consists of two exons interrupted by an intron of ϳ1.7 kilobases. The entire open reading frame is encoded in exon 2. Sprenger et al. (15) detected promoter activity in the T lymphoma cell line Jurkat when transfected with the chloramphenicol acetyltransferase reporter gene driven by 5Ј flanking sequences of the CXCR1 gene (Ϫ800 to ϩ21 bp). However, identification of regulatory elements and transcription factors regulating...