Proper tissue-and developmental stage-specific transcriptional control over the five genes of the human ~-globin locus is elicited in part by the locus control region (LCR), but the molecular mechanisms that dictate this determined pattern of gene expression during human development are still controversial. By use of homologous recombination in yeast to generate mutations in the LCR within a yeast artificial chromosome (YAC) bearing the entire human 13-globin gene locus, followed by injection of each of the mutated YACs into murine ova, we addressed the function of LCR hypersensitive site (HS) elements 3 and 4 in human 13-globin gene switching. The experiments revealed a number of unexpected properties that are directly attributable to LCR function. First, deletion of either HS3 or HS4 core elements from an otherwise intact YAC results in catastrophic disruption of globin gene expression at all erythroid developmental stages, despite the presence of all other HS elements in the YAC transgenes. If HS3 is used to replace HS4, gene expression is normal at all developmental stages. Conversely, insertion of the HS4 element in place of HS3 results in significant expression changes at every developmental stage, indicating that individual LCR HS elements play distinct roles in stage-specific [~-type globin gene activation. Although the HS4 duplication leads to alteration in the levels of ¢-and ~/-globin mRNAs during embryonic erythropoiesis, total [3-type globin mRNA synthesis is balanced, thereby leading to the conclusion that all of the human [3-locus genes are competitively regulated. In summary, the human [3-globin HS elements appear to form a single, synergistic functional entity called the LCR, and HS3 and HS4 appear to be individually indispensable to the integrity of this macromolecular complex.

The five human beta-type-globin genes, epsilon, Ggamma, Agamma, delta and beta, are close together and are regulated by a locus control region (LCR) located at the 5' end of the locus. Here we investigate the functional consequences of this organization with respect to temporal regulation of the individual genes, by using recombination techniques to invert the order of either the genes or the LCR in vivo. Our analysis of transgenic mice bearing either normal or mutant transgenes leads to two new observations. First, the position of the epsilon-globin gene next to the LCR is mandatory for its expression during the yolk-sac stage of erythropoiesis. Second, LCR activity is orientation dependent, and so the LCR does not act as a simple enhancer to stimulate transcription of the globin genes. Thus, in the absence of any change in transgene integration position, transgene copy number, trans-acting factors or other resident genetic information, simple inversion of the human genes or the LCR fundamentally alters the transcription of beta-type globin genes.

BackgroundVitellogenin (Vg), a major reproductive protein, has been associated with infection-resistant response in fish. However, the underlying mechanisms by which Vg is involved in anti-infectious response are not understood.Methodology/ResultsBy both protein-microbe interaction analysis and enzyme-linked immunosorbent assay as well as phagocytosis test, we demonstrate for the first time that fish Vg acts as a pattern recognition molecule with multiple specificities that can recognize bacteria as well as fungus rather than self components from fish, and functions as an opsonin that can enhance macrophage phagocytosis.ConclusionsThis study shows that fish Vg plays an integrative function in regulating immunity via its pleiotropic effects on both recognizing pathogen-associated molecular patterns and promoting macrophage phagocytosis. It also supports the notion that factors normally involved in control of female reproduction are associated with immunity in organisms that rely on Vg for oocyte development.

The human ␤-globin locus control region (LCR) harbors both strong chromatin opening and enhancer activity when assayed in transgenic mice. To understand the contribution of individual DNase I hypersensitive sites (HS) to the function of the human ␤-globin LCR, we have mutated the core elements within the context of a yeast artificial chromosome (YAC) carrying the entire locus and then analyzed the effect of these mutations on the formation of LCR HS elements and expression of the genes in transgenic mice. In the present study, we examined the consequences of two different HS2 mutations. We first generated seven YAC transgenic lines bearing a deletion of the 375-bp core enhancer of HS2. Single-copy HS2 deletion mutants exhibited severely depressed HS site formation and expression of all of the human ␤-globin genes at every developmental stage, confirming that HS2 is a vital, integral component of the LCR. We also analyzed four transgenic lines in which the core element of HS2 was replaced by that of HS3 and found that while HS3 is able to restore the chromatin-opening activity of the LCR, it is not able to functionally replace HS2 in mediating high-level globin gene transcription. These results continue to support the hypothesis that HS2, HS3, and HS4 act as a single, integral unit to regulate human globin gene transcription as a holocomplex, but they can also be interpreted to say that formation of a DNase I hypersensitive holocomplex alone is not sufficient for mediating high-level globin gene transcription. We therefore propose that the core elements must productively interact with one another to generate a unique subdomain within the nucleoprotein holocomplex that interacts in a stage-specific manner with individual globin gene promoters.Locus control regions (LCRs) are highly specialized tissuespecific DNA regulatory elements that are able to confer position-independent and copy number-dependent expression of cis-linked genes when examined in transgenic mice. Since the discovery of the human ␤-globin LCR (13, 20), a growing number of genes or loci have been found to be regulated by LCR-like activities. Most LCRs appear to be composite elements and, perhaps not coincidentally, contain several DNase I hypersensitive sites (HS). The examples of genes regulated by such elements include the human ␤-globin (45), the T-cellspecific CD2 (18), the T-cell receptor ␣/␦ (41), and the chicken lysozyme loci (2). Higgs et al. (23) and Montoliu et al. (35) have shown that single HS located upstream of the ␣-globin or tyrosinase genes also bear multiple activities normally attributed to an LCR.The human ␤-globin LCR, located from approximately 8 to 22 kbp upstream of the ε-globin gene (13, 14, 47, 48) is composed of four erythroid cell-specific (HS1 to HS4) and one ubiquitous (HS5) DNase I HS. This region mediates chromatin opening over the whole ␤-globin gene locus and also is responsible for stimulating high-level expression of the globin genes throughout erythroid cell development (12). Perhaps most remarkably, the LCR ...

We explored the mechanism of definitive-stage -globin transcriptional inactivity within a human ␤-globin YAC expressed in transgenic mice. We focused on the globin CAC and CAAT promoter motifs, as previous laboratory and clinical studies indicated a pivotal role for these elements in globin gene activation. A high-affinity CAC-binding site for the erythroid krü ppel-like factor (EKLF) was placed in the -globin promoter at a position corresponding to that in the adult ␤-globin promoter, thereby simultaneously ablating a direct repeat (DR) element. This mutation led to EKLF-independent -globin transcription during definitive erythropoiesis. A second 4-bp substitution in the -globin CAAT sequence, which simultaneously disrupts a second DR element, further enhanced ectopic definitive erythroid activation of -globin transcription, which surprisingly became EKLF dependent. We finally examined factors in nuclear extracts prepared from embryonic or adult erythroid cells that bound these elements in vitro, and we identified a novel DR-binding protein (DRED) whose properties are consistent with those expected for a definitive-stage -globin repressor. We conclude that the suppression of -globin transcription during definitive erythropoiesis is mediated by the binding of a repressor that prevents EKLF from activating the -globin gene.

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Previous studies have defined transcriptional control elements, in addition to the promoters, that both lie near individual human ␤-globin locus genes and have been implicated in their differential stage-specific regulation during development (i.e., are believed to directly participate in hemoglobin switching). We have reinvestigated the activities during erythropoiesis that might be conferred by two of the more intensively analyzed of these elements, the -globin gene 5 silencer and the ␤-globin gene 3 enhancer, by deleting them from a yeast artificial chromosome that spans the human ␤-globin locus, and then analyzing transgenic mice for expression of all of the human genes. These studies show that sequences within the -globin ''silencer'' are not only required for silencing but are also required for activation of -globin transcription; furthermore, deletion of the silencer simultaneously reduced ␥-globin transcription during the yolk sac stage of erythroid development. Analysis of the adult ␤-globin gene 3 enhancer deletion showed that its deletion affects only that gene.

When the orphan nuclear receptors TR2 and TR4, the DNA-binding subunits of the DRED repressor complex, are forcibly expressed in erythroid cells of transgenic mice, embryos exhibit a transient mid-gestational anemia as a consequence of a reduction in the number of primitive erythroid cells. GATA-1 mRNA is specifically diminished in the erythroid cells of these TR2/TR4 transgenic embryos as it is in human CD34 + progenitor cells transfected with forcibly expressed TR2/TR4. In contrast, in loss-of-function studies analyzing either Tr2-or Tr4-germline-null mutant mice or human CD34 + progenitor cells transfected with force-expressed TR2 and TR4 short hairpin RNAs (shRNAs), GATA-1 mRNA is induced. An evolutionarily conserved direct repeat (DR) element, a canonical binding site for nuclear receptors, was identified in the GATA1 hematopoietic enhancer (G1HE), and TR2/TR4 binds to that site in vitro and in vivo. Mutation of that DR element led to elevated Gata1 promoter activity, and reduced promoter responsiveness to cotransfected TR2/TR4. Thus, TR2/TR4 directly represses Gata1/GATA1 transcription in murine and human erythroid progenitor cells through an evolutionarily conserved binding site within a well-characterized, tissue-specific Gata1 enhancer, thereby providing a mechanism by which Gata1 can be directly silenced during terminal erythroid maturation.