Georgina F Miller

National Institutes of Health, Maryland, United States

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Publications (6)27.53 Total impact

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    ABSTRACT: LoxP-Cre technology was used to remove the selenocysteine tRNA gene, trsp, in either endothelial cells or myocytes of skeletal and heart muscle to elucidate the role of selenoproteins in cardiovascular disease. Loss of selenoprotein expression in endothelial cells was embryonic lethal. A 14.5-day-old embryo had numerous abnormalities including necrosis of the central nervous system, subcutaneous hemorrhage and erythrocyte immaturity. Loss of selenoprotein expression in myocytes manifested no apparent phenotype until about day 12 after birth. Affected mice had decreased mobility and an increased respiratory rate, which proceeded rapidly to death. Pathological analysis revealed that mice lacking trsp had moderate to severe myocarditis with inflammation extending into the mediastinitis. Thus, ablation of selenoprotein expression demonstrated an essential role of selenoproteins in endothelial cell development and in proper cardiac muscle function. The data suggest a direct connection between the loss of selenoprotein expression in these cell types and cardiovascular disease.
    Neuromuscular Disorders 03/2007; 17(2):135-42. · 3.46 Impact Factor
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    ABSTRACT: Sphingosine-1-phosphate (S1P), an important sphingolipid metabolite, regulates diverse cellular processes, including cell survival, growth, and differentiation. Here we show that S1P signaling is critical for neural and vascular development. Sphingosine kinase-null mice exhibited a deficiency of S1P which severely disturbed neurogenesis, including neural tube closure, and angiogenesis and caused embryonic lethality. A dramatic increase in apoptosis and a decrease in mitosis were seen in the developing nervous system. S1P(1) receptor-null mice also showed severe defects in neurogenesis, indicating that the mechanism by which S1P promotes neurogenesis is, in part, signaling from the S1P(1) receptor. Thus, S1P joins a growing list of signaling molecules, such as vascular endothelial growth factor, which regulate the functionally intertwined pathways of angiogenesis and neurogenesis. Our findings also suggest that exploitation of this potent neuronal survival pathway could lead to the development of novel therapeutic approaches for neurological diseases.
    Molecular and Cellular Biology 01/2006; 25(24):11113-21. · 5.04 Impact Factor
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    ABSTRACT: Bacillus anthracis edema toxin (ET), an adenylyl cyclase, is an important virulence factor that contributes to anthrax disease. The role of ET in anthrax pathogenesis is, however, poorly understood. Previous studies using crude toxin preparations associated ET with subcutaneous edema, and ET-deficient strains of B. anthracis showed a reduction in virulence. We report the first comprehensive study of ET-induced pathology in an animal model. Highly purified ET caused death in BALB/cJ mice at lower doses and more rapidly than previously seen with the other major B. anthracis virulence factor, lethal toxin. Observations of gross pathology showed intestinal intralumenal fluid accumulation followed by focal hemorrhaging of the ileum and adrenal glands. Histopathological analyses of timed tissue harvests revealed lesions in several tissues including adrenal glands, lymphoid organs, bone, bone marrow, gastrointestinal mucosa, heart, and kidneys. Concomitant blood chemistry analyses supported the induction of tissue damage. Several cytokines increased after ET administration, including granulocyte colony-stimulating factor, eotaxin, keratinocyte-derived cytokine, MCP-1/JE, interleukin-6, interleukin-10, and interleukin-1beta. Physiological measurements also revealed a concurrent hypotension and bradycardia. These studies detail the extensive pathological lesions caused by ET and suggest that it causes death due to multiorgan failure.
    American Journal Of Pathology 12/2005; 167(5):1309-20. · 4.60 Impact Factor
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    ABSTRACT: Cryptococcal meningoencephalitis develops as a result of hematogenous dissemination of inhaled Cryptococcus neoformans from the lung to the brain. The mechanism(s) by which C. neoformans crosses the blood-brain barrier (BBB) is a key unresolved issue in cryptococcosis. We used both an in vivo mouse model and an in vitro model of the human BBB to investigate the cryptococcal association with and traversal of the BBB. Exposure of human brain microvascular endothelial cells (HBMEC) to C. neoformans triggered the formation of microvillus-like membrane protrusions within 15 to 30 min. Yeast cells of C. neoformans adhered to and were internalized by the HBMEC, and they crossed the HBMEC monolayers via a transcellular pathway without affecting the monolayer integrity. The histopathology of mouse brains obtained after intravenous injection of C. neoformans showed that the yeast cells either were associated with endothelial cells or escaped from the brain capillary vessels into the neuropil by 3 h. C. neoformans was found in the brain parenchyma away from the vessels by 22 h. Association of C. neoformans with the choroid plexus, however, was not detected during up to 10 days of observation. Our findings indicate that C. neoformans cells invade the central nervous system by transcellular crossing of the endothelium of the BBB.
    Infection and Immunity 10/2004; 72(9):4985-95. · 4.07 Impact Factor
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    ABSTRACT: Until recently, Histoplasma capsulatum was believed to harbour three varieties, var. capsulatum (chiefly a New World human pathogen), var. duboisii (an African human pathogen) and var. farciminosum (an Old World horse pathogen), which varied in clinical manifestations and geographical distribution. We analysed the phylogenetic relationships of 137 individuals representing the three varieties from six continents using DNA sequence variation in four independent protein-coding genes. At least eight clades were idengified: (i) North American class 1 clade; (ii) North American class 2 clade; (iii) Latin American group A clade; (iv) Latin American group B clade; (v) Australian clade; (vi) Netherlands (Indonesian?) clade; (vii) Eurasian clade and (viii) African clade. Seven of eight clades represented genetically isolated groups that may be recognized as phylogenetic species. The sole exception was the Eurasian clade which originated from within the Latin American group A clade. The phylogenetic relationships among the clades made a star phylogeny. Histoplasma capsulatum var. capsulatum individuals were found in all eight clades. The African clade included all of the H. capsulatum var. duboisii individuals as well as individuals of the other two varieties. The 13 individuals of var. farciminosum were distributed among three phylogenetic species. These findings suggest that the three varieties of Histoplasma are phylogenetically meaningless. Instead we have to recognize the existence of genetically distinct geographical populations or phylogenetic species. Combining DNA substitution rates of protein-coding genes with the phylogeny suggests that the radiation of Histoplasma started between 3 and 13 million years ago in Latin America.
    Molecular Ecology 01/2004; 12(12):3383-401. · 6.28 Impact Factor
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    Yun C Chang, Georgina F Miller, K J Kwon-Chung
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    ABSTRACT: Cryptococcus neoformans is the etiologic agent of cryptococcosis. Two mating types exist in this fungus, MAT alpha and MATa. The CPRa gene of C. neoformans is a MATa strain-specific gene and encodes a putative seven-transmembrane domain pheromone receptor. Unlike the other reported fungal pheromone receptors, CPRa shows functional diversity. Deletion of CPRa drastically affects mating efficiency but does not abolish mating. CPRa expression is developmentally regulated and is not affected by deletion of the transcriptional regulator STE12a. The expression of CPRa is markedly increased by shifting cultures from liquid to solid media. CPRa also plays a significant role in virulence. Delta cpra cells produce smaller capsules in the brains of mice than the wild-type cells, and the mice infected with Delta cpra survive significantly longer than those receiving the wild-type strain. Our results suggest that the MATa pheromone receptor of C. neoformans is not only required for mating but also important for survival and growth of the fungus in host tissue.
    Infection and Immunity 10/2003; 71(9):4953-60. · 4.07 Impact Factor