Elizabeth Egan

All Publications

• A forward genetic screen identifies erythrocyte CD55 as essential for Plasmodium falciparum invasion. SCIENCE Egan, E. S., Jiang, R. H., Moechtar, M. A., et al 2015; 348: 711-714
• Host-parasite interactions that guide red blood cell invasion by malaria parasites CURRENT OPINION IN HEMATOLOGY Paul, A. S., Egan, E. S., Duraisingh, M. T. 2015; 22 (3): 220-226

  Abstract

  Malaria is caused by the infection and proliferation of parasites from the genus Plasmodium in red blood cells (RBCs). A free Plasmodium parasite, or merozoite, released from an infected RBC must invade another RBC host cell to sustain a blood-stage infection. Here, we review recent advances on RBC invasion by Plasmodium merozoites, focusing on specific molecular interactions between host and parasite.Recent work highlights the central role of host-parasite interactions at virtually every stage of RBC invasion by merozoites. Biophysical experiments have for the first time measured the strength of merozoite-RBC attachment during invasion. For P. falciparum, there have been many key insights regarding the invasion ligand PfRh5 in particular, including its influence on host species tropism, a co-crystal structure with its RBC receptor basigin, and its suitability as a vaccine target. For P. vivax, researchers identified the origin and emergence of the parasite from Africa, demonstrating a natural link to the Duffy-negative RBC variant in African populations. For the simian parasite P. knowlesi, zoonotic invasion into human cells is linked to RBC age, which has implications for parasitemia during an infection and thus malaria.New studies of the molecular and cellular mechanisms governing RBC invasion by Plasmodium parasites have shed light on various aspects of parasite biology and host cell tropism, and indicate opportunities for malaria control.

  View details for DOI 10.1097/MOH.0000000000000135

  View details for Web of Science ID 000352793900005

  View details for PubMedID 25767956

  View details for PubMedCentralID PMC4418178

• Plasmodium falciparum transmission stages accumulate in the human bone marrow SCIENCE TRANSLATIONAL MEDICINE Joice, R., Nilsson, S. K., Montgomery, J., Dankwa, S., Egan, E., Morahan, B., Seydel, K. B., Bertuccini, L., Alano, P., Williamson, K. C., Duraisingh, M. T., Taylor, T. E., Milner, D. A., Marti, M. 2014; 6 (244)

  Abstract

  Transmission of Plasmodium falciparum malaria parasites requires formation and development of gametocytes, yet all but the most mature of these sexual parasite forms are absent from the blood circulation. We performed a systematic organ survey in pediatric cases of fatal malaria to characterize the spatial dynamics of gametocyte development in the human host. Histological studies revealed a niche in the extravascular space of the human bone marrow where gametocytes formed in erythroid precursor cells and underwent development before reentering the circulation. Accumulation of gametocytes in the hematopoietic system of human bone marrow did not rely on cytoadherence to the vasculature as does sequestration of asexual-stage parasites. This suggests a different mechanism for the sequestration of gametocytes that could potentially be exploited to block malaria transmission.

  View details for DOI 10.1126/scitranslmed.3008882

  View details for Web of Science ID 000338713000005

  View details for PubMedID 25009232

• Optimization of flow cytometric detection and cell sorting of transgenic Plasmodium parasites using interchangeable optical filters MALARIA JOURNAL Vorobjev, I. A., Buchholz, K., Prabhat, P., Ketman, K., Egan, E. S., Marti, M., Duraisingh, M. T., Barteneva, N. S. 2012; 11

  Abstract

  Malaria remains a major cause of morbidity and mortality worldwide. Flow cytometry-based assays that take advantage of fluorescent protein (FP)-expressing malaria parasites have proven to be valuable tools for quantification and sorting of specific subpopulations of parasite-infected red blood cells. However, identification of rare subpopulations of parasites using green fluorescent protein (GFP) labelling is complicated by autofluorescence (AF) of red blood cells and low signal from transgenic parasites. It has been suggested that cell sorting yield could be improved by using filters that precisely match the emission spectrum of GFP.Detection of transgenic Plasmodium falciparum parasites expressing either tdTomato or GFP was performed using a flow cytometer with interchangeable optical filters. Parasitaemia was evaluated using different optical filters and, after optimization of optics, the GFP-expressing parasites were sorted and analysed by microscopy after cytospin preparation and by imaging cytometry.A new approach to evaluate filter performance in flow cytometry using two-dimensional dot blot was developed. By selecting optical filters with narrow bandpass (BP) and maximum position of filter emission close to GFP maximum emission in the FL1 channel (510/20, 512/20 and 517/20; dichroics 502LP and 466LP), AF was markedly decreased and signal-background improve dramatically. Sorting of GFP-expressing parasite populations in infected red blood cells at 90 or 95% purity with these filters resulted in 50-150% increased yield when compared to the standard filter set-up. The purity of the sorted population was confirmed using imaging cytometry and microscopy of cytospin preparations of sorted red blood cells infected with transgenic malaria parasites.Filter optimization is particularly important for applications where the FP signal and percentage of positive events are relatively low, such as analysis of parasite-infected samples with in the intention of gene-expression profiling and analysis. The approach outlined here results in substantially improved yield of GFP-expressing parasites, and requires decreased sorting time in comparison to standard methods. It is anticipated that this protocol will be useful for a wide range of applications involving rare events.

  View details for DOI 10.1186/1475-2875-11-312

  View details for Web of Science ID 000313865200001

  View details for PubMedID 22950515

• Independent control of replication initiation of the two Vibrio cholerae chromosomes by DnaA and RctB JOURNAL OF BACTERIOLOGY Duigou, S., Knudsen, K. G., Skovgaard, O., Egan, E. S., Lobner-Olesen, A., Waldor, M. K. 2006; 188 (17): 6419-6424

  Abstract

  Although the two Vibrio cholerae chromosomes initiate replication in a coordinated fashion, we show here that each chromosome appears to have a specific replication initiator. DnaA overproduction promoted overinitiation of chromosome I and not chromosome II. In contrast, overproduction of RctB, a protein that binds to the origin of replication of chromosome II, promoted overinitiation of chromosome II and not chromosome I.

  View details for DOI 10.1128/JB.00565-06

  View details for Web of Science ID 000240250200043

  View details for PubMedID 16923911

  View details for PubMedCentralID PMC1595377

• Autorepression of RctB, an initiator of Vibrio cholerae chromosome II replication JOURNAL OF BACTERIOLOGY Egan, E. S., Duigou, S., Waldor, M. K. 2006; 188 (2): 789-793

  Abstract

  The RctB protein binds to the origin of replication of Vibrio cholerae chromosome II (chrII) and is required for oriCIIVc-based replication. Here, we found that RctB acts as an autorepressor, inhibiting rctB transcription. Integration host factor promotes rctB transcription, while Dam and DnaA, factors required for replication of both V. cholerae chromosomes, influence RctB autorepression. Thus, RctB appears to regulate chrII replication as both an initiator and a transcription repressor, and its synthesis is modulated by factors that govern replication of both chromosomes.

  View details for Web of Science ID 000234677400045

  View details for PubMedID 16385068

• Divided genomes: negotiating the cell cycle in prokaryotes with multiple chromosomes MOLECULAR MICROBIOLOGY Egan, E. S., Fogel, M. A., Waldor, M. K. 2005; 56 (5): 1129-1138

  Abstract

  Historically, the prokaryotic genome was assumed to consist of a single circular replicon. However, as more microbial genome sequencing projects are completed, it is becoming clear that multipartite genomes comprised of more than one chromosome are not unusual among prokaryotes. Chromosomes are distinguished from plasmids by the presence of essential genes as well as characteristic cell cycle-linked replication kinetics; unlike plasmids, chromosomes initiate replication once per cell cycle. The existence of multipartite prokaryotic genomes raises several questions regarding how multiple chromosomes are replicated and segregated during the cell cycle. These divided genomes also introduce questions regarding chromosome evolution and genome stability. In this review, we discuss these and other issues, with particular emphasis on the cholera pathogen Vibrio cholerae.

  View details for DOI 10.1111/j.1365-2958.2005.04622.x

  View details for Web of Science ID 000228975300002

  View details for PubMedID 15882408

• Synchronous replication initiation of the two Vibrio cholerae chromosomes CURRENT BIOLOGY Egan, E. S., Lobner-Olesen, A., Waldor, M. K. 2004; 14 (13): R501-R502

  View details for Web of Science ID 000222673700007

  View details for PubMedID 15242627

• Distinct replication requirements for the two vibrio cholerae chromosomes CELL Egan, E. S., Waldor, M. K. 2003; 114 (4): 521-530

  Abstract

  Studies of prokaryotic chromosome replication have focused almost exclusively on organisms with one chromosome. We defined and characterized the origins of replication of the two Vibrio cholerae chromosomes, oriCI(vc) and oriCII(vc). OriCII(vc) differs from the origin assigned by bioinformatic analysis and is unrelated to oriCI(vc). OriCII(vc)-based replication requires an internal 12 base pair repeat and two hypothetical genes that flank oriCII(vc). One of these genes is conserved among diverse genera of the family Vibrionaceae and encodes an origin binding protein. The other gene codes for an RNA and not a protein. OriCII(vc)- but not oriCI(vc)-based replication is negatively regulated by a DNA sequence adjacent to oriCII(vc). There is an unprecedented requirement for DNA adenine methyltransferase in both oriCI(vc)- and oriCII(vc)-based replication. Our studies of replication in V. cholerae indicate that microorganisms having multiple chromosomes may utilize unique mechanisms for the control of replication.

  View details for Web of Science ID 000184928800014

  View details for PubMedID 12941279

• An extraretinally expressed insect cryptochrome with similarity to the blue light photoreceptors of mammals and plants JOURNAL OF NEUROSCIENCE Egan, E. S., Franklin, T. M., Hilderbrand-Chae, M. J., McNeil, G. P., Roberts, M. A., Schroeder, A. J., Zhang, X. L., Jackson, F. R. 1999; 19 (10): 3665-3673

  Abstract

  Photic entrainment of insect circadian rhythms can occur through either extraretinal (brain) or retinal photoreceptors, which mediate sensitivity to blue light or longer wavelengths, respectively. Although visual transduction processes are well understood in the insect retina, almost nothing is known about the extraretinal blue light photoreceptor of insects. We now have identified and characterized a candidate blue light photoreceptor gene in Drosophila (DCry) that is homologous to the cryptochrome (Cry) genes of mammals and plants. The DCry gene is located in region 91F of the third chromosome, an interval that does not contain other genes required for circadian rhythmicity. The protein encoded by DCry is approximately 50% identical to the CRY1 and CRY2 proteins recently discovered in mammalian species. As expected for an extraretinal photoreceptor mediating circadian entrainment, DCry mRNA is expressed within the adult brain and can be detected within body tissues. Indeed, tissue in situ hybridization demonstrates prominent expression in cells of the lateral brain, which are close to or coincident with the Drosophila clock neurons. Interestingly, DCry mRNA abundance oscillates in a circadian manner in Drosophila head RNA extracts, and the temporal phasing of the rhythm is similar to that documented for the mouse Cry1 mRNA, which is expressed in clock tissues. Finally, we show that changes in DCry gene dosage are associated predictably with alterations of the blue light resetting response for the circadian rhythm of adult locomotor activity.

  View details for Web of Science ID 000080162400003

  View details for PubMedID 10233998

• A genetic linkage map for zebrafish: Comparative analysis and localization of genes and expressed sequences GENOME RESEARCH GATES, M. A., Kim, L., Egan, E. S., Cardozo, T., Sirotkin, H. I., Dougan, S. T., Lashkari, D., Abagyan, R., Schier, A. F., Talbot, W. S. 1999; 9 (4): 334-347

  Abstract

  Genetic screens in zebrafish (Danio rerio) have isolated mutations in hundreds of genes with essential functions. To facilitate the identification of candidate genes for these mutations, we have genetically mapped 104 genes and expressed sequence tags by scoring single-strand conformational polymorphisms in a panel of haploid siblings. To integrate this map with existing genetic maps, we also scored 275 previously mapped genes, microsatellites, and sequence-tagged sites in the same haploid panel. Systematic phylogenetic analysis defined likely mammalian orthologs of mapped zebrafish genes, and comparison of map positions in zebrafish and mammals identified significant conservation of synteny. This comparative analysis also identified pairs of zebrafish genes that appear to be orthologous to single mammalian genes, suggesting that these genes arose in a genome duplication that occurred in the teleost lineage after the divergence of fish and mammal ancestors. This comparative map analysis will be useful in predicting the locations of zebrafish genes from mammalian gene maps and in understanding the evolution of the vertebrate genome.

  View details for Web of Science ID 000079904300003

  View details for PubMedID 10207156

• Zebrafish organizer development and germ-layer formation require nodal-related signals NATURE Feldman, B., GATES, M. A., Egan, E. S., Dougan, S. T., Rennebeck, G., Sirotkin, H. I., Schier, A. F., Talbot, W. S. 1998; 395 (6698): 181-185

  Abstract

  The vertebrate body plan is established during gastrulation, when cells move inwards to form the mesodermal and endodermal germ layers. Signals from a region of dorsal mesoderm, which is termed the organizer, pattern the body axis by specifying the fates of neighbouring cells. The organizer is itself induced by earlier signals. Although members of the transforming growth factor-beta (TGF-beta) and Wnt families have been implicated in the formation of the organizer, no endogenous signalling molecule is known to be required for this process. Here we report that the zebrafish squint (sqt) and cyclops (cyc) genes have essential, although partly redundant, functions in organizer development and also in the formation of mesoderm and endoderm. We show that the sqt gene encodes a member of the TGF-beta superfamily that is related to mouse nodal. cyc encodes another nodal-related proteins, which is consistent with our genetic evidence that sqt and cyc have overlapping functions. The sqt gene is expressed in a dorsal region of the blastula that includes the extraembryonic yolk syncytial layer (YSL). The YSL has been implicated as a source of signals that induce organizer development and mesendoderm formation. Misexpression of sqt RNA within the embryo or specifically in the YSL induces expanded or ectopic dorsal mesoderm. These results establish an essential role for nodal-related signals in organizer development and mesendoderm formation.

  View details for Web of Science ID 000075829900044

  View details for PubMedID 9744277

• Mutant rescue by BAC clone injection in zebrafish GENOMICS Yan, Y. L., Talbot, W. S., Egan, E. S., Postlethwait, J. H. 1998; 50 (2): 287-289

  Abstract

  Genes essential for vertebrate body plan specification, organ development, and organ function are likely to be shared between mammals and zebrafish, but only in zebrafish have large-scale, genome-wide mutagenesis screens been conducted to isolate embryonic lethal mutations. Discovering the roles played by these disrupted genes requires their molecular characterization, which would be facilitated by assaying large cloned genomic DNAs for their potential to rescue mutant phenotypes. Here we demonstrate that bacterial artificial chromosomes can rescue the phenotype of floating head (flh) mutants. Homozygous flh embryos lack a differentiated notochord and have a reduced, discontinuous floor plate. Mutant embryos injected with genomic clones containing the flh+ gene often had stretches of several to many notochord cells overlaid by a row of floor-plate cells. In contrast, control mutant embryos injected with artificial chromosomes lacking the flh+ gene failed to form notochord. We conclude that the injection of large-insert genomic clones will speed the isolation of zebrafish genes disrupted by mutation and hence the identification of gene functions necessary for development of vertebrate embryos.

  View details for Web of Science ID 000074367700018

  View details for PubMedID 9653657

• Vertebrate genome evolution and the zebrafish gene map NATURE GENETICS Postlethwait, J. H., Yan, Y. L., GATES, M. A., Horne, S., Amores, A., Brownlie, A., Donovan, A., Egan, E. S., Force, A., Gong, Z. Y., Goutel, C., Fritz, A., Kelsh, R., Knapik, E., Liao, E., Paw, B., Ransom, D., Singer, A., Thomson, M., Abduljabbar, T. S., Yelick, P., Beier, D., Joly, J. S., Larhammar, D., ROSA, F., Westerfield, M., Zon, L. I., Johnson, S. L., Talbot, W. S. 1998; 18 (4): 345-349

  Abstract

  In chordate phylogeny, changes in the nervous system, jaws, and appendages transformed meek filter feeders into fearsome predators. Gene duplication is thought to promote such innovation. Vertebrate ancestors probably had single copies of genes now found in multiple copies in vertebrates and gene maps suggest that this occurred by polyploidization. It has been suggested that one genome duplication event occurred before, and one after the divergence of ray-finned and lobe-finned fishes. Holland et al., however, have argued that because various vertebrates have several HOX clusters, two rounds of duplication occurred before the origin of jawed fishes. Such gene-number data, however, do not distinguish between tandem duplications and polyploidization events, nor whether independent duplications occurred in different lineages. To investigate these matters, we mapped 144 zebrafish genes and compared the resulting map with mammalian maps. Comparison revealed large conserved chromosome segments. Because duplicated chromosome segments in zebrafish often correspond with specific chromosome segments in mammals, it is likely that two polyploidization events occurred prior to the divergence of fish and mammal lineages. This zebrafish gene map will facilitate molecular identification of mutated zebrafish genes, which can suggest functions for human genes known only by sequence.

  View details for Web of Science ID 000072755500016

  View details for PubMedID 9537416

• Genetic analysis of chromosomal rearrangements in the cyclops region of the zebrafish genome GENETICS Talbot, W. S., Egan, E. S., GATES, M. A., Walker, C., Ullmann, B., Neuhauss, S. C., Kimmel, C. B., Postlethwait, J. H. 1998; 148 (1): 373-380

  Abstract

  Genetic screens in zebrafish have provided mutations in hundreds of genes with essential functions in the developing embryo. To investigate the possible uses of chromosomal rearrangements in the analysis of these mutations, we genetically characterized three gamma-ray induced alleles of cyclops (cyc), a gene required for development of midline structures. We show that cyc maps near one end of Linkage Group 12 (LG 12) and that this region is involved in a reciprocal translocation with LG 2 in one gamma-ray induced mutation, cyc(b213). The translocated segments together cover approximately 5% of the genetic map, and we show that this rearrangement is useful for mapping cloned genes that reside in the affected chromosomal regions. The other two alleles, cyc(b16) and cyc(b229), have deletions in the distal region of LG 12. Interestingly, both of these mutations suppress recombination between genetic markers in LG 12, including markers at a distance from the deletion. This observation raises the possibility that these deletions affect a site required for meiotic recombination on the LG 12 chromosome. The cyc(b16) and cyc(b229) mutations may be useful for balancing other lethal mutations located in the distal region of LG 12. These results show that chromosomal rearrangements can provide useful resources for mapping and genetic analyses in zebrafish.

  View details for Web of Science ID 000071494000034

  View details for PubMedID 9475747

  View details for PubMedCentralID PMC1459804