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Krafsur ES, Maudlin I. Tsetse fly evolution, genetics and the trypanosomiases - A review. INFECTION GENETICS AND EVOLUTION 2018; 64:185-206. [PMID: 29885477 DOI: 10.1016/j.meegid.2018.05.033] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 05/30/2018] [Accepted: 05/31/2018] [Indexed: 01/27/2023]
Abstract
This reviews work published since 2007. Relative efforts devoted to the agents of African trypanosomiasis and their tsetse fly vectors are given by the numbers of PubMed accessions. In the last 10 years PubMed citations number 3457 for Trypanosoma brucei and 769 for Glossina. The development of simple sequence repeats and single nucleotide polymorphisms afford much higher resolution of Glossina and Trypanosoma population structures than heretofore. Even greater resolution is offered by partial and whole genome sequencing. Reproduction in T. brucei sensu lato is principally clonal although genetic recombination in tsetse salivary glands has been demonstrated in T. b. brucei and T. b. rhodesiense but not in T. b. gambiense. In the past decade most genetic attention was given to the chief human African trypanosomiasis vectors in subgenus Nemorhina e.g., Glossina f. fuscipes, G. p. palpalis, and G. p. gambiense. The chief interest in Nemorhina population genetics seemed to be finding vector populations sufficiently isolated to enable efficient and long-lasting suppression. To this end estimates were made of gene flow, derived from FST and its analogues, and Ne, the size of a hypothetical population equivalent to that under study. Genetic drift was greater, gene flow and Ne typically lesser in savannah inhabiting tsetse (subgenus Glossina) than in riverine forms (Nemorhina). Population stabilities were examined by sequential sampling and genotypic analysis of nuclear and mitochondrial genomes in both groups and found to be stable. Gene frequencies estimated in sequential samplings differed by drift and allowed estimates of effective population numbers that were greater for Nemorhina spp than Glossina spp. Prospects are examined of genetic methods of vector control. The tsetse long generation time (c. 50 d) is a major contraindication to any suggested genetic method of tsetse population manipulation. Ecological and modelling research convincingly show that conventional methods of targeted insecticide applications and traps/targets can achieve cost-effective reduction in tsetse densities.
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Affiliation(s)
- E S Krafsur
- Department of Entomology, Iowa State University, Ames, IA 50011, USA.
| | - Ian Maudlin
- School of Biomedical Sciences, The University of Edinburgh, Scotland, UK
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Borst P. Maxi-circles, glycosomes, gene transposition, expression sites, transsplicing, transferrin receptors and base J. Mol Biochem Parasitol 2016; 205:39-52. [DOI: 10.1016/j.molbiopara.2016.03.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 03/22/2016] [Accepted: 03/22/2016] [Indexed: 01/05/2023]
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Ersfeld K. Nuclear architecture, genome and chromatin organisation in Trypanosoma brucei. Res Microbiol 2011; 162:626-36. [PMID: 21392575 DOI: 10.1016/j.resmic.2011.01.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Accepted: 01/29/2011] [Indexed: 11/29/2022]
Abstract
The nucleus of the human pathogen Trypanosoma brucei not only has unusual chromosomal composition, characterised by the presence of megabase, intermediate and minichromosomes, but also chromosome and gene organisation that is unique amongst eukaryotes. Here I provide an overview of current knowledge of nuclear structure, chromatin organisation and chromosome dynamics during interphase and mitosis. New technologies such as chromatin immunoprecipitation, in combination with new generation sequencing and proteomic analysis of subnuclear fractions, have led to novel insights into the organisation of the nucleus and chromatin. In particular, we are beginning to understand how universal mechanisms of chromatin modifications and nuclear position effects are deployed for parasite-specific functions and are centrally involved in genomic organisation and transcriptional regulation. These advances also have a major impact on progress in understanding the molecular basis of antigenic variation.
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Affiliation(s)
- Klaus Ersfeld
- Department of Biological Sciences and Hull York Medical School, University of Hull, Hull HU6 7RX, UK.
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Matsunaga S, Endo T, Yagita K, Hirukawa Y, Tomino S, Matsugo S, Tsuruhara T. Chromosome size polymorphisms in the genus acanthamoeba electrokaryotype by pulsed-field gel electrophoresis. Protist 2009. [PMID: 23194715 DOI: 10.1016/s1434-4610(98)70039-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Twenty-eight strains from 12 species from the genus Acanthamoeba, including five isolates from amoebic keratitis patients, were subjected to molecular karyotyping by pulsed-field gel electrophoresis. 9 to 21 chromosome-sized DNA bands ranging from 200 kb to 3 Mb in size were detected. Molecular karyotypes also showed a wide multifariousness, i.e. there existed inter- and intraspecific heterogeneity. The five isolates from amoebic keratitis patients did not exhibit characteristic molecular karyotypes distinguishable from environmental isolates. Although karyotypic heterogeneity was observed within group I amoeba, they are distinguishable from those of group II and III. Strains having identical restriction fragment length polymorphism profiles of mtDNA did not have an identical molecular karyotype, i.e. weak correlation was found between molecular karyotypes and mtDNA restriction fragment length polymorphism profiles.
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Affiliation(s)
- S Matsunaga
- Department of Biology, Tokyo Gakugei University, Koganei-shi, Tokyo 184-8501, Japan
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Cooper A, Tait A, Sweeney L, Tweedie A, Morrison L, Turner CMR, MacLeod A. Genetic analysis of the human infective trypanosome Trypanosoma brucei gambiense: chromosomal segregation, crossing over, and the construction of a genetic map. Genome Biol 2008; 9:R103. [PMID: 18570680 PMCID: PMC2481433 DOI: 10.1186/gb-2008-9-6-r103] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2008] [Revised: 05/20/2008] [Accepted: 06/22/2008] [Indexed: 11/29/2022] Open
Abstract
A high-resolution genetic linkage map of the STIB 386 strain of Trypanosoma brucei gambiense is presented. Background Trypanosoma brucei is the causative agent of human sleeping sickness and animal trypanosomiasis in sub-Saharan Africa, and it has been subdivided into three subspecies: Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, which cause sleeping sickness in humans, and the nonhuman infective Trypanosoma brucei brucei. T. b. gambiense is the most clinically relevant subspecies, being responsible for more than 90% of all trypanosomal disease in humans. The genome sequence is now available, and a Mendelian genetic system has been demonstrated in T. brucei, facilitating genetic analysis in this diploid protozoan parasite. As an essential step toward identifying loci that determine important traits in the human-infective subspecies, we report the construction of a high-resolution genetic map of the STIB 386 strain of T. b. gambiense. Results The genetic map was determined using 119 microsatellite markers assigned to the 11 megabase chromosomes. The total genetic map length of the linkage groups was 733.1 cM, covering a physical distance of 17.9 megabases with an average map unit size of 24 kilobases/cM. Forty-seven markers in this map were also used in a genetic map of the nonhuman infective T. b. brucei subspecies, permitting comparison of the two maps and showing that synteny is conserved between the two subspecies. Conclusion The genetic linkage map presented here is the first available for the human-infective trypanosome T. b. gambiense. In combination with the genome sequence, this opens up the possibility of using genetic analysis to identify the loci responsible for T. b. gambiense specific traits such as human infectivity as well as comparative studies of parasite field populations.
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Affiliation(s)
- Anneli Cooper
- Wellcome Centre for Molecular Parasitology, Glasgow Biomedical Research Centre, University Place, Glasgow G12 8TA, UK.
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Dreesen O, Cross GAM. Telomere length in Trypanosoma brucei. Exp Parasitol 2007; 118:103-10. [PMID: 17910953 PMCID: PMC2233935 DOI: 10.1016/j.exppara.2007.07.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 07/12/2007] [Accepted: 07/16/2007] [Indexed: 01/09/2023]
Abstract
Trypanosoma brucei thwarts the host immune response by replacing its variant surface glycoprotein (VSG). The actively transcribed VSG is located in one of approximately 20 telomeric expression sites (ES). Antigenic variation can occur by transcriptional switching, reciprocal translocations, or duplicative gene conversion events among ES or with the large repertoire of telomeric and non-telomeric VSG. In recently isolated strains, duplicative gene conversion occurs at a high frequency and predominates, but the switching frequency decreases dramatically upon laboratory-adaptation. Uniquely, T. brucei telomeres grow--apparently indefinitely--at a steady rate of 6-12 base pairs (bp) per population doubling (PD), but the telomere adjacent to an active ES undergoes frequent truncations. Using two-dimensional gel electrophoresis, we demonstrate that all of the chromosome classes of fast-switching and minimally propagated T. brucei have shorter telomeres than extensively propagated Lister 427 clones, suggesting a link between laboratory adaptation, telomere growth, and VSG switching rates.
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Affiliation(s)
| | - George A. M. Cross
- * Corresponding author. Tel.: +1 212-327-7571; fax: +1 212-327-7845. E-mail address:
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Sádlová J, Volf P, Victoir K, Dujardin JC, Votýpka J. Virulent and attenuated lines of Leishmania major: DNA karyotypes and differences in metalloproteinase GP63. Folia Parasitol (Praha) 2006. [DOI: 10.14411/fp.2006.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Ngaira JM, Njagi ENM, Ngeranwa JJN, Olembo NK. PCR amplification of RoTat 1.2 VSG gene in Trypanosoma evansi isolates in Kenya. Vet Parasitol 2004; 120:23-33. [PMID: 15019140 DOI: 10.1016/j.vetpar.2003.12.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2003] [Revised: 10/15/2003] [Accepted: 12/09/2003] [Indexed: 10/26/2022]
Abstract
A direct card agglutination test for Trypanosoma evansi, CATT/T. evansi based on the predominant variable antigen-type (pVAT) RoTat 1.2 was evaluated previously in the field in Isiolo District, Kenya. Sixteen out of 51 (31.4%) parasitologically positive camels were negative by the antibody detection test. In the present study, trypanosomes isolated from the camels were analysed in an attempt to determine the cause of the false negative results of CATT/T. evansi. A total of 20 field isolates comprised 16 stocks from camels that were negative by CATT/T. evansi, and 4 from CATT/T. evansi-positive camels. In addition, 15 known T. evansi and four T. brucei were used as reference. Purified DNA samples were tested using an established RoTat 1.2-based polymerase chain reaction (PCR) that yields a 488 bp product for the specific detection of T. evansi. Antibodies to RoTat 1.2 variant surface glycoprotein (VSG) were used in Western blotting to detect RoTat 1.2 VSG linear epitopes. Results of PCR and Western blot showed that the 16 stocks isolated from CATT/T. evansi-negative camels fell into three groups. In Group 1, both the RoTat 1.2 VSG gene and the VSG were absent in three stocks. In five trypanosome stocks in Group 2, the RoTat 1.2 VSG gene was detected, but Western blot was negative indicating absence of the expressed VSG. Five other stocks containing the RoTat 1.2 VSG gene were also in this group. The RoTat 1.2 VSG gene was detected and Western blot was positive in all four trypanosome stocks in Group 3. All four stocks from CATT/T. evansi-positive camels contained the RoTat 1.2 VSG gene and the expressed VSG. The reference T. evansi KETRI 2479 lacked the RoTat 1.2 VSG gene and there was no immune reactivity detected by Western blot. The rest of the reference T. evansi stocks examined contained the RoTat 1.2 VSG gene. All the four T. brucei samples examined were negative by PCR and Western blot. In conclusion, this study showed that the RoTat 1.2 VSG gene was absent from some T. evansi trypanosomes in Kenya.
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Affiliation(s)
- J M Ngaira
- Department of Biochemistry, Kenyatta University, P.O. Box 43844, Nairobi, Kenya.
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Berriman M, Hall N, Sheader K, Bringaud F, Tiwari B, Isobe T, Bowman S, Corton C, Clark L, Cross GAM, Hoek M, Zanders T, Berberof M, Borst P, Rudenko G. The architecture of variant surface glycoprotein gene expression sites in Trypanosoma brucei. Mol Biochem Parasitol 2002; 122:131-40. [PMID: 12106867 DOI: 10.1016/s0166-6851(02)00092-0] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Trypanosoma brucei evades the immune system by switching between Variant Surface Glycoprotein (VSG) genes. The active VSG gene is transcribed in one of approximately 20 telomeric expression sites (ESs). It has been postulated that ES polymorphism plays a role in host adaptation. To gain more insight into ES architecture, we have determined the complete sequence of Bacterial Artificial Chromosomes (BACs) containing DNA from three ESs and their flanking regions. There was variation in the order and number of ES-associated genes (ESAGs). ESAGs 6 and 7, encoding transferrin receptor subunits, are the only ESAGs with functional copies in every ES that has been sequenced until now. A BAC clone containing the VO2 ES sequences comprised approximately half of a 330 kb 'intermediate' chromosome. The extensive similarity between this intermediate chromosome and the left telomere of T. brucei 927 chromosome I, suggests that this previously uncharacterised intermediate size class of chromosomes could have arisen from breakage of megabase chromosomes. Unexpected conservation of sequences, including pseudogenes, indicates that the multiple ESs could have arisen through a relatively recent amplification of a single ES.
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Fu G, Melville SE. Polymorphism in the subtelomeric regions of chromosomes of Kinetoplastida. Trans R Soc Trop Med Hyg 2002; 96 Suppl 1:S31-40. [PMID: 12055849 DOI: 10.1016/s0035-9203(02)90049-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Leishmania spp. and the related kinetoplastid Trypanosoma brucei are single-celled parasites. In Leishmania, the nuclear genome comprises 36 diploid chromosomes and occasional amplified minichromosomes, while the T. brucei nucleus contains 11 larger diploid chromosomes and a variable number of intermediate-sized and minichromosomes. This paper primarily describes the subtelomeric structure of the larger diploid chromosomes of L. major and T. brucei, although some aspects may also apply to smaller chromosomes. The diploid chromosomes contain most protein-coding genes and vary in size. The telomeric sequence is common to both species, but adjacent subtelomeric repeats vary between species and chromosomes. It is possible that some of the complex repeats described here play a role in stabilizing replication and copy number of the chromosomes. The subtelomeric regions of T. brucei chromosomes differ from those of other protozoan parasites, as they are dedicated to expression sites for variant surface glycoprotein genes, used by the parasite to evade immune destruction by antigenic variation. Variation in these sites creates segmental aneuploidy in many T. brucei chromosomes.
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Affiliation(s)
- Guoliang Fu
- Imperial College School of Medicine, Hammersmith Hospital, London, W12 0NN, UK
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Dujardin JC, Victoir K, De Doncker S, Guerbouj S, Arévalo J, Le Ray D. Molecular epidemiology and diagnosis of Leishmania: what have we learnt from genome structure, dynamics and function? Trans R Soc Trop Med Hyg 2002; 96 Suppl 1:S81-6. [PMID: 12055856 DOI: 10.1016/s0035-9203(02)90056-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
This paper reviews our exploration of the dynamics of the Leishmania genome and its contribution to epidemiology and diagnosis. We used as a model Peruvian populations of L. (Viannia) braziliensis and L. (V.) peruviana, 2 species very close phylogenetically, but phenotypically very different in biotope and pathology. We initially focused on karyotype analysis. Our data showed that chromosomes were subject to a fast rate of evolution, and were sensitive indicators of genetic drift. Therefore, molecular karyotyping appeared an adequate tool for monitoring (i) emergence of close species, (ii) ecogeographical differentiation at the intraspecific level, and (iii) strain 'fingerprinting'. Chromosome size variation was mostly due to the number of tandemly repeated genes (rDNA, mini-exon, gp63, and cysteine proteinase genes), and could involve the deletion of unique genes (L. (V.) braziliensis-specific gp63 families). Considering the importance of these genes in parasitism, their rearrangement might have functional implications: adaptation to different environments and pleomorphic pathogenicity. Our knowledge of genome structure and dynamics was used to develop new polymerase chain reaction (PCR) techniques. Amplification of gp63 genes followed by cleavage with restriction enzymes and study of restriction fragment length polymorphism (gp63 PCR-RFLP) allowed the discrimination of all species tested, even directly in biopsies with 95% sensitivity (compared with PCR amplification of kinetoplast deoxyribonucleic acid). At the intra-specific level, RFLP was also observed and corresponded to mutations in major immunogen domains of gp63. These seem to be under strong selection pressure, and the technique should facilitate addressing how the host's immune pressure may modulate parasite population structure. Altogether, gp63 PCR-RFLP represents a significant operational improvement over the other techniques for molecular epidemiology and diagnosis: it combines sensitivity, discriminatory power and prognostic value.
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Affiliation(s)
- J C Dujardin
- Prins Leopold Instituut voor Tropische Geneeskunde, Protozoologie, 155 Nationalestraat, B-2000 Antwerpen, Belgium.
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Alsford S, Wickstead B, Ersfeld K, Gull K. Diversity and dynamics of the minichromosomal karyotype in Trypanosoma brucei. Mol Biochem Parasitol 2001; 113:79-88. [PMID: 11254956 DOI: 10.1016/s0166-6851(00)00388-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The genome of African trypanosomes contains a large number of minichromosomes. Their only proposed role is in the expansion of the parasites' repertoire of telomeric variant surface glycoprotein (VSG) genes as minichromosomes carry silent VSG gene copies in telomeric locations. Despite their importance as VSG gene donors, little is known about the actual composition of the minichromosomal karyotype and the stability of its inheritance. In this study we show, by using high-resolution pulsed-field electrophoresis, that a non-clonal trypanosome population contains an extremely diverse pattern of minichromosomes, which can be resolved into less complex clone-specific karyotypes by non-selective cloning. We show that the minichromosome patterns of such clones are stable over at least 360 generations. Furthermore, using DNA markers for specific minichromosomes, we demonstrate the mitotic stability of these minichromosomes within the population over a period of more than 5 years. Length variation is observed for an individual minichromosome and is most likely caused by a continuous telomeric growth of approximately 6 bp per telomere per cell division. This steady telomeric growth, counteracted by stochastic large losses of telomeric sequences is the most likely cause of minichromosome karyotype heterogeneity within a population.
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Affiliation(s)
- S Alsford
- School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK
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Thomas MC, Olivares M, Escalante M, Marañón C, Montilla M, Nicholls S, López MC, Puerta C. Plasticity of the histone H2A genes in a Brazilian and six Colombian strains of Trypanosoma cruzi. Acta Trop 2000; 75:203-10. [PMID: 10708660 DOI: 10.1016/s0001-706x(00)00061-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The analysis of three recombinant clones containing the histone H2A locus isolated from a genomic library of Trypanosoma cruzi DNA shows that the H2A gene loci are formed by 1.2 and 0.76 kb long intercalated units organized in a head-to-tail tandem array. The difference in length between the two gene units is due to the presence of a short interspersed nucleotide element (SINE)-like DNA sequence inserted at the 3' end of some of these units. Southern, northern and chromosomal blot analysis of a Brazilian Y strain and six Colombian strains demonstrated the existence of polymorphisms regarding the relative copy number of the H2A gene units, the relative abundance of the H2A transcripts and their chromosomal location. These results show the existence of a dynamic organization in the H2A loci among T. cruzi strains in which a SINE-like sequence may be involved and support the fact that T. cruzi has a high degree of plasticity in its genome.
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MESH Headings
- Animals
- Blotting, Northern
- Blotting, Southern
- Brazil
- Cloning, Molecular
- Colombia
- DNA, Protozoan/analysis
- Electrophoresis, Gel, Pulsed-Field
- Escherichia coli/metabolism
- Gene Dosage
- Genes, Protozoan
- Genetic Vectors
- Genome, Protozoan
- Histones/biosynthesis
- Histones/genetics
- Humans
- Polymorphism, Genetic
- RNA, Protozoan/analysis
- Recombinant Proteins/biosynthesis
- Short Interspersed Nucleotide Elements
- Trypanosoma cruzi/genetics
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Affiliation(s)
- M C Thomas
- Instituto de Parasitología y Biomedicina 'López Neyra', Consejo Superior de Investigaciones Científicas, Calle Ventanilla 11, 18001, Granada, Spain
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Hope M, MacLeod A, Leech V, Melville S, Sasse J, Tait A, Turner CM. Analysis of ploidy (in megabase chromosomes) in Trypanosoma brucei after genetic exchange. Mol Biochem Parasitol 1999; 104:1-9. [PMID: 10589977 DOI: 10.1016/s0166-6851(99)00103-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The megabase chromosomes of Trypanosoma brucei are normally diploid, but the extent to which this ploidy is maintained when parasites undergo genetic exchange is not known. To investigate this issue, a panel of 30 recombinant clones resulting from the co-transmission through tsetse flies of three different parental T. brucei lines in all pair-wise combinations (STIB 247, STIB 386 and TREU 927/4) were examined. These clones are products of 28 different mating events; four of them result from self-fertilisation and the others are F1 hybrids. DNA contents of the three parental lines were determined by flow cytometry and shown to differ only slightly with DNA content increasing in the order 927/4 < 247 < 386. Flow cytometry of the recombinant clones indicated DNA contents were similar to the parents in 28 clones and raised approximately 1.5 times the parental values in only two. The two F1 hybrid progeny with raised DNA contents were shown by marker analysis to be trisomic for seven independent loci indicating that they were probably triploid whereas progeny with DNA contents similar to parental values inherited a single allele from each parent for four independent loci indicating that they were diploid.
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Affiliation(s)
- M Hope
- Division of Infection and Immunity, I.B.L.S., Glasgow University, Scotland, UK
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Abstract
The only trypanosomatid so far proved to undergo genetic exchange is Trypanosoma brucei, for which hybrid production after co-transmission of different parental strains through the tsetse fly vector has been demonstrated experimentally. Analogous mating experiments have been attempted with other Trypanosoma and Leishmania species, so far without success. However, natural Leishmania hybrids, with a combination of the molecular characters of two sympatric species, have been described amongst both New and Old World isolates. Typical homozygotic and heterozygotic banding patterns for isoenzyme and deoxyribonucleic acid markers have also been demonstrated amongst naturally-occurring T. cruzi isolates. The mechanism of genetic exchange in T. brucei remains unclear, although it appears to be a true sexual process involving meiosis. However, no haploid stage has been observed, and intermediates in the process are still a matter for conjecture. The frequency of sex in trypanosomes in nature is also a matter for speculation and controversy, with conflicting results arising from population genetics analysis. Experimental findings for T. brucei are discussed in the first section of this review, together with laboratory evidence of genetic exchange in other species. The second section covers population genetics analysis of the large body of data from field isolates of Leishmania and Trypanosoma species. The final discussion attempts to put the evidence from experimental and population genetics into its biological context.
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Affiliation(s)
- W Gibson
- School of Biological Sciences, University of Bristol, UK
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Ersfeld K, Melville SE, Gull K. Nuclear and genome organization of Trypanosoma brucei. PARASITOLOGY TODAY (PERSONAL ED.) 1999; 15:58-63. [PMID: 10234187 DOI: 10.1016/s0169-4758(98)01378-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In this article, Klaus Ersfeld, Sara Melville and Keith Gull review current understanding of the structural organization of the nucleus of Trypanosoma brucei, and summarize recent data pertinent to the organization of its genome. Until recently, the cell biology of the trypanosome nucleus and issues of DNA organization and gene expression have often been treated as separate themes. However, recent work emphasizes the need for a more holistic approach to understanding these aspects of the biology of this parasite.
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Affiliation(s)
- K Ersfeld
- University of Manchester, School of Biological Sciences, 2.205 Stopford Building, Oxford Road, Manchester, UK M13 9PT.
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Melville SE, Leech V, Gerrard CS, Tait A, Blackwell JM. The molecular karyotype of the megabase chromosomes of Trypanosoma brucei and the assignment of chromosome markers. Mol Biochem Parasitol 1998; 94:155-73. [PMID: 9747967 DOI: 10.1016/s0166-6851(98)00054-1] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We present the molecular karyotype of the megabase chromosomes of Trypanosoma brucei stock TREU927/4 (927). We have identified 11 diploid chromosomes ranging in size from 1 to 5.2 Mb approximately and pairs of homologues differ in size by up to 15%. A total of 401 cDNA probes were hybridised to T. brucei stock 927 chromosomes and 168 chromosome-specific markers were defined. Most of these markers were hybridised to the separated chromosomal DNA of two other cloned field isolates and four F1 progeny clones from a laboratory cross. The chromosomes vary in size by up to two and a half times between stocks and the DNA content of the 11 pairs of homologues varies by up to 33% in different stocks. Stock 927 contains the smallest chromosomes and the least nuclear genomic DNA. Nevertheless, all 11 syntenic groups of cDNA probes are maintained in all stocks. In the F1 hybrids only we have identified one extra PFG band to which none of our probes hybridise. We have shown that probes thought to be specific for the bloodstream-form variant surface glycoprotein expression sites hybridise to different chromosomes in different stocks and may hybridise to either one or both of a homologous pair of chromosomes. We have also determined the chromosomal location of the ribosomal RNA gene arrays.
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Affiliation(s)
- S E Melville
- Department of Pathology, University of Cambridge, UK.
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Cross M, Taylor MC, Borst P. Frequent loss of the active site during variant surface glycoprotein expression site switching in vitro in Trypanosoma brucei. Mol Cell Biol 1998; 18:198-205. [PMID: 9418867 PMCID: PMC121476 DOI: 10.1128/mcb.18.1.198] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
African trypanosomes undergo antigenic variation of their variant surface glycoprotein (VSG) coat to avoid being killed by their mammalian hosts. The active VSG gene is located in one of many telomeric expression sites. Replacement of the VSG gene in the active site or switching between expression sites can give rise to a new VSG coat. To study Trypanosoma brucei VSG expression site inactivation rather than VSG gene switching, it is useful to have an in vitro negative-selection system independent of the VSG. We have achieved this aim by using a viral thymidine kinase (TK) gene. Following integration of the TK gene downstream of the 221a VSG expression site promoter, transformant cell lines became sensitive to the nucleoside analog 1-(2-deoxy-2-fluoro-8-D-arabinofuranosyl)-5-iodouracil. These TK trypanosomes were able to revert to resistance at a rate approaching 10(-5) per cell per generation. The majority of revertants expressed a new VSG gene even though there had been no selection against the VSG itself. Analysis of these switched variants showed that some had shut down TK expression via an in situ expression site switch. However, most variants had the complete 221 expression site deleted and another VSG expression site activated. We speculate that a new VSG expression site cannot switch on without inactivation of the old site.
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Affiliation(s)
- M Cross
- Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam
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21
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Mulugeta W, Wilkes J, Mulatu W, Majiwa PA, Masake R, Peregrine AS. Long-term occurrence of Trypanosoma congolense resistant to diminazene, isometamidium and homidium in cattle at Ghibe, Ethiopia. Acta Trop 1997; 64:205-17. [PMID: 9107367 DOI: 10.1016/s0001-706x(96)00645-6] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Ten trypanosome isolates were collected at random from cattle at Ghibe, Ethiopia, in February 1993 and all shown to be savannah-type Trypanosoma congolense. When inoculated into naïve Boran (Bos indicus) calves, all 10 isolates were resistant to diminazene aceturate (Berenil), isometamidium chloride (Samorin) and homidium chloride (Novidium) at doses of 7.0 mg/kg body weight (b.w.), 0.5 mg/kg b.w. and 1.0 mg/kg b.w., respectively. In order to determine whether this multiple-drug resistance was expressed by individual trypanosomes, clones were derived from two of the isolates and characterised in mice for their sensitivity to the three compounds; by comparison to drug-sensitive populations, the two clones expressed high levels of resistance to all 3 trypanocides. In experiments to characterise the uptake kinetics of [14C]-Samorin, the maximal rates of uptake (Vmax) for 4 Ghibe isolates ranged from 9.2 to 15.0 ng/10(8) trypanosomes/min. In contrast, Vmax for the isometamidium-sensitive clone T. congolense IL 1180 was 86.7 +/- 8.6 ng/10(8) trypanosomes/min. Lastly, molecular karyotypes were determined for eight isolates: seven different chromosome profiles were observed. These data indicate that in February 1993 there was a high prevalence of drug-resistant trypanosome populations with different chromosome profiles in cattle at Ghibe. Since a similar situation existed at the same site in July 1989, this suggests that the drug-resistance phenotype of trypanosomes at Ghibe had not altered over a 4 year period.
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Affiliation(s)
- W Mulugeta
- International Livestock Research Institute (ILRI), Nairobi, Kenya
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22
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Melville SE. Parasite genome analysis. Genome research in Trypanosoma brucei: chromosome size polymorphism and its relevance to genome mapping and analysis. Trans R Soc Trop Med Hyg 1997; 91:116-20. [PMID: 9196744 DOI: 10.1016/s0035-9203(97)90189-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Before the development of pulsed field gel electrophoresis (PFGE), little was known of the chromosomal organization of Trypanosoma brucei. This technique first revealed that the nuclear genome was subdivided into distinct size classes of chromosomes, subsequently shown to have disparate genetic roles in the life cycle of the parasite. PFGE also facilitated the determination of chromosome ploidy and the observation that apparent homologues often differed significantly in size within and between isolates. While the biological reasons underlying this plasticity may prove very interesting, nevertheless it could pose real problems for the global analysis of the T. brucei genome. Therefore, before undertaking large scale physical mapping, it is necessary to determine the number and size of chromosomes in the reference stock; to compare these to the chromosomes of other stocks to determine the relative sizes of homologues; and to investigate the deoxyribonucleic acid content of the size of polymorphic regions in order to assess how these may affect the execution of a physical mapping programme.
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Affiliation(s)
- S E Melville
- University of Cambridge, Department of Pathology, UK
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23
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Navarro M, Cross GA. DNA rearrangements associated with multiple consecutive directed antigenic switches in Trypanosoma brucei. Mol Cell Biol 1996; 16:3615-25. [PMID: 8668178 PMCID: PMC231357 DOI: 10.1128/mcb.16.7.3615] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Changes in variant surface glycoprotein (Vsg) expression allow Trypanosoma brucei to elude the immune response. The expressed vsg is always located at the telomeric end of a polycistronic transcription unit known as an expression site (ES). Although there are many ESs, only one is active at any particular time. The mechanisms regulating ES transcription and switching are unknown. Chromosome rearrangements within or upstream of the ES have been described to occur in occasional switch events, but no changes have been consistently associated with switching. We inserted the drug resistance genes neo and ble, conferring resistance to G418 and phleomycin, respectively, 1 kb downstream of "silent" ES promoters. This demonstrated that short-range transcription could be achieved from a silent ES promoter. From one initial transformant clone, panels of independent consecutive on-off-on switch clones were generated and analyzed. The first activation of the neo-targeted ES was always associated with deletion of the upstream tandem promoter in this ES, but no further rearrangements were detected in consecutive off-on switches of this ES. On the other hand, direct analysis of ES promoters showed that deletions and duplications occurred elsewhere. Activation of a ble-tagged 300-kb chromosome could not be achieved, but phleomycin-resistant clones could be obtained. One such clone arose from recombination between three ESs. Taken together, our experiments suggest that ES switching may occur after a period of chromosomal interactivity that may or may not leave tangible evidence in the form of detectable sequence changes.
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Affiliation(s)
- M Navarro
- Laboratory of Molecular Parasitology, The Rockefeller University, New York, New York 10021-6399, USA
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24
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Patnaik PK, Axelrod N, Van der Ploeg LH, Cross GA. Artificial linear mini-chromosomes for Trypanosoma brucei. Nucleic Acids Res 1996; 24:668-75. [PMID: 8604308 PMCID: PMC145704 DOI: 10.1093/nar/24.4.668] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
We have constructed artificial linear mini- chromosomes for the parasitic protozoan Trypanosoma brucei. These chromosomes exist at approx. 2 copies per cell, are indefinitely stable under selection but are lost from 50% of the transformed population in approx. 7 generations when grown in the absence of selective pressure. Consistent with results obtained earlier with natural chromosomes in T.brucei, the telomeres on these artificial chromosomes grow, adding approx. 1- 1.5 telomeric repeats per generation. The activity of a procyclic acidic repetitive protein (parp) gene promoter on these elements is unaffected by its proximity to a telomere, implying the lack of a telomere-proximal position effect (TPE) in procyclic trypanosomes. Among other things, these autonomously replicating dispensable genetic elements will provide a defined system for the study of nuclear DNA replication, karyotypic plasticity and other aspects of chromosomal behavior in this ancient eukaryotic lineage.
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Affiliation(s)
- P K Patnaik
- Laboratory of Molecular Parasitology, The Rockefeller University, New York, NY 10021-6399 USA
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25
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Victoir K, Dujardin JC, de Doncker S, Barker DC, Arevalo J, Hamers R, Le Ray D. Plasticity of gp63 gene organization in Leishmania (Viannia) braziliensis and Leishmania (Viannia) peruviana. Parasitology 1995; 111 ( Pt 3):265-73. [PMID: 7567095 DOI: 10.1017/s0031182000081828] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The genomic organization of gp63 genes in 4 and 7 isolates of Leishmania braziliensis and L. peruviana, respectively was studied by RFLP analysis with 3 restriction enzymes (Bgl I, Sal I and Apa I). Our results showed a marked polymorphism among isolates. Some characters were specific to L. braziliensis or to L. peruviana, and others specific to the respective biogeographical populations of L. peruviana. The average minimum copy number of gp63 genes was found to be higher in L. braziliensis (71) than in L. peruviana (46), suggesting that deletion of gp63 genes might be partially involved in the size decrease of the chromosome bearing gp63 genes, observed between those 2 species (from 700 to 610 kb). Our results may suggest the existence of at least 2 arrays of heterologous gp63 repeats, varying in relative copy number between L. braziliensis and L. peruviana, and among isolates of the latter species. Rearrangement of the gp63 genes was observed during long-term in vitro maintenance of a reference strain of L. braziliensis. These observations document the existence of a dynamic gp63 gene organization in Leishmania of the braziliensis complex.
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Affiliation(s)
- K Victoir
- Instituut voor Tropische Geneeskunde Prince Leopold, Antwerpen, Belgium
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26
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Dujardin JC, Bañuls AL, Llanos-Cuentas A, Alvarez E, DeDoncker S, Jacquet D, Le Ray D, Arevalo J, Tibayrenc M. Putative Leishmania hybrids in the Eastern Andean valley of Huanuco, Peru. Acta Trop 1995; 59:293-307. [PMID: 8533665 DOI: 10.1016/0001-706x(95)00094-u] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
During an outbreak of tegumentary leishmaniasis that developed in the 1990s in the Eastern Andean valley of Huanuco, Peru, the coexistence of Andean (uta) and sylvatic leishmaniases was suspected for ecological and geographical reasons, and sympatric sampling was carried out. Seven human isolates of Leishmania were characterized by multilocus enzyme electrophoresis, random amplification of polymorphic DNA and molecular karyotyping. The three methods identified 3 isolates as L. braziliensis, and 4 isolates as putative hybrids with characters of L. braziliensis and L. peruviana. Data from Huanuco are compared to previous results from other areas endemic for uta. Biological and epidemiological implications are discussed.
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Affiliation(s)
- J C Dujardin
- Laboratory of Protozoology, Institute of Tropical Medicine, "Prince Leopold", Antwerp, Belgium
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27
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Lanzer M, Fischer K, Le Blancq SM. Parasitism and chromosome dynamics in protozoan parasites: is there a connection? Mol Biochem Parasitol 1995; 70:1-8. [PMID: 7637690 DOI: 10.1016/0166-6851(95)00021-r] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Genomic plasticity is a hallmark of many protozoan parasites, including Plasmodium spp, Trypanosoma spp, Leishmania ssp and Giardia lamblia. Strikingly, there is a common theme regarding the structural basis of this karyotype variability. Chromosomes are compartmentalized into conserved central domains and polymorphic chromosome ends. Since antigen-encoding genes frequently reside in telomere-proximal domains, it is tempting to speculate that the genetic flexibility of chromosome ends has been recruited as a tool in immune evasion strategies by some parasitic protozoa.
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Affiliation(s)
- M Lanzer
- Zentrum für Infektionsforschung, Würzburg, Germany
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28
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Waitumbi JN, Murphy NB, Peregrine AS. Genotype and drug-resistance phenotype of Trypanosoma evansi isolated from camels in northern Kenya. ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 1994; 88:677-83. [PMID: 7893184 DOI: 10.1080/00034983.1994.11812921] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- J N Waitumbi
- International Laboratory for Research on Animal Diseases (ILRAD), Nairobi, Kenya
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29
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Wilson K, Berens RL, Sifri CD, Ullman B. Amplification of the inosinate dehydrogenase gene in Trypanosoma brucei gambiense due to an increase in chromosome copy number. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)62002-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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30
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Béjà O, Schwartz D, Michaeli S. Karyotype analysis of the monogenetic trypanosomatid Leptomonas collosoma. Mol Biochem Parasitol 1994; 66:71-81. [PMID: 7984189 DOI: 10.1016/0166-6851(94)90037-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In order to develop a genetic system for the monogenetic trypanosomatids, we have analyzed the molecular karyotype of Leptomonas collosoma based on chromosome separation by clamped homogeneous electric field (CHEF) gel electrophoresis. The chromosome location of 5 RNA coding genes (SL, U6, 5S, 7SL and rRNA) and 2 protein coding genes (for HSP83 and alpha-tubulin) was determined. All of the L. collosoma genes examined were found on at least 2 chromosomes, which differ in size in the range of 100-500 kb, suggesting that the organism is diploid. The weighted sum of L. collosoma chromosomes separated by CHEF analysis was approximately 62 +/- 3 Mb, whereas the genome size determined by FACS was estimated at approx. 80 Mb. This suggests that some of the homologous chromosomes differ in their size. The analysis presented here may facilitate studies on the function of individual genes, and on the genetic stability of this organism.
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Affiliation(s)
- O Béjà
- Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel
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31
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Waitumbi JN, Young JR. Electrophoretic karyotyping is a sensitive epidemiological tool for studying Trypanosoma evansi infections. Vet Parasitol 1994; 52:47-56. [PMID: 8030187 DOI: 10.1016/0304-4017(94)90034-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Thirty-six isolates of trypanozoon trypanosomes collected from camels in Northern Kenya during the dry season sporadic infections of 1986 and during the wet season epidemic infections of 1987 were identified as Trypanosoma evansi by the homogeneity of their kinetoplast DNA minicircles. Although the minicircles of all the isolates were indistinguishable, polymorphism in chromosome-sized DNA molecules detected by electrophoresis was extensive. The isolates could be grouped into eight distinct electrophoretic karyotypes which could be distinguished from three additional karyotypes identified among earlier T. evansi isolates. In one camel herd with a long history of trypanocide application, which was continued during the present study, all isolates bar one belonged to one karyotype group. From a second herd, in which trypanosomosis management was by individual treatment of proven parasitaemic cases, isolates with diverse karyotypes were obtained. Some of the karyotypes identified during the dry season sporadic infections were re-isolated in the subsequent wet season epidemic. These observations indicate that distinguishing T. evansi isolates by molecular electrophoretic karyotypes is more discriminating than kDNA analysis. Observations of karyotype patterns recurring in isolates from herds kept under chemoprophylaxis could help in the identification of drug-resistant parasites.
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Affiliation(s)
- J N Waitumbi
- Kenya Trypanosomiasis Research Institute, Kikuyu
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32
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Orozco E, Lazard D, Sanchez T, Sanchez MA, Hernandez R, Silva EF. A variable DNA region of Entamoeba histolytica is expressed in several transcripts which differ in genetically related clones. MOLECULAR & GENERAL GENETICS : MGG 1993; 241:271-9. [PMID: 8246880 DOI: 10.1007/bf00284678] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A highly variable DNA region (EhVR1), isolated from Entamoeba histolytica clone A, strain HM1:IMSS, is transcribed into several transcripts, which differ in genetically related clones. EhVR1 (3.5 kb) is composed of two contiguous fragments; one of these 1.9 kb long, at the 3' end, identified similar transcripts in clones A, L6 and C2 (all derived from strain HM1:IMMS), the other of 1.6 kb, at the 5' end, detected 0.5, 0.6 and 0.7 kb transcripts only in clone A. Variability of the 1.6 kb fragment was found even within the same clone maintained under different conditions. EhVR1 was localized to 1.3 and 1.4 Mb linear chromosomes and also found in circular molecules. The sequence of the 1.6 kb fragment revealed the presence of a large number of different repeats, including inverted and palindromic repeats. A p145 sequence, previously detected in episomal DNA of the amoeba, was found at the 5' end of EhVR1. The presence of EhVR1 in linear and circular molecules, its high number of repeats, and its variability in genetically related clones suggest the existence of DNA regions that undergo dynamic non-reciprocal recombination between circular episomes and linear chromosomes, and may thus contribute to variability in the trophozoite genome.
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Affiliation(s)
- E Orozco
- Department of Experimental Pathology, Centro de Investigacion y de Estudias Avonzados del I.P.N., Mexico, D.F
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33
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Sibley LD, Pfefferkorn ER, Boothroyd JC. Development of genetic systems for Toxoplasma gondii. ACTA ACUST UNITED AC 1993; 9:392-5. [PMID: 15463677 DOI: 10.1016/0169-4758(93)90091-s] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The protozoan parasite Toxoplasma gondii has recently emerged as an important opportunistic pathogen in humans. Toxoplasma also shares a number of biological features with Plasmodium and Eimeria, which are important pathogens of humans and animals. Because o f the ease o f experimental use, David Sibley, Elmer Pfefferkom and John Boothroyd have undertaken the development of genetics in Toxoplasma as a model intracellular parasite. Toxoplasma is presently the only parasitic protozoan where both classical and molecular genetics are feasible. The recent advances in this system are highlighted here, along with potential applications of genetics for understanding intracellular parasitism.
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Affiliation(s)
- L D Sibley
- Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA
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34
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Dujardin JC, Llanos-Cuentas A, Caceres A, Arana M, Dujardin JP, Guerrini F, Gomez J, Arroyo J, De Doncker S, Jacquet D. Molecular karyotype variation in Leishmania (Viannia) peruviana: indication of geographical populations in Peru distributed along a north-south cline. ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 1993; 87:335-47. [PMID: 8250624 DOI: 10.1080/00034983.1993.11812777] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Forty-one Leishmania peruviana isolates were selected along a north-south transect which crossed areas endemic for uta in three different biogeographical regions in the Peruvian Andes. The isolates were analysed by molecular karyotyping and hybridization with three chromosome-derived DNA probes. All the isolates could be distinguished from L. braziliensis by their pLb-134 hybridization patterns. However, the patterns with the other probes (pLb-168 and -22) could be used to cluster the Peruvian isolates in discrete groups (karyodemes) which varied in their level of similarity with L. braziliensis. The geographical distribution of these karyodemes supports the hypothesis that eco-graphical isolation has contributed to the heterogeneity of L. peruviana.
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Affiliation(s)
- J C Dujardin
- Laboratory of Protozoology, Institute of Tropical Medicine, Prince Leopold, Antwerpen, Belgium
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35
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Codjia V, Mulatu W, Majiwa PA, Leak SG, Rowlands GJ, Authié E, d'Ieteren GD, Peregrine AS. Epidemiology of bovine trypanosomiasis in the Ghibe valley, southwest Ethiopia. 3. Occurrence of populations of Trypanosoma congolense resistant to diminazene, isometamidium and homidium. Acta Trop 1993; 53:151-63. [PMID: 8098900 DOI: 10.1016/0001-706x(93)90026-8] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In July 1989, blood samples were collected from parasitaemic cattle in the Ghibe valley, Ethiopia, frozen in liquid nitrogen and transported to Nairobi, Kenya. Twelve of the stabilates were inoculated into individual Boran (Bos indicus) calves and characterised for their sensitivity, in turn, to diminazene aceturate (Berenil), isometamidium chloride (Samorin) and homidium chloride (Novidium). All 12 stabilates produced infections which were shown to be Trypanosoma congolense and resistant to treatment with diminazene aceturate at a dose of 7.0 mg kg-1 body weight (b.w.). Eleven of the infections were also resistant to isometamidium chloride at a dose of 0.5 mg kg-1 b.w. and homidium chloride at a dose of 1.0 mg kg-1 b.w. The drug-sensitivity phenotypes of three of the same isolates were also determined in goats which were each treated with only one of the three trypanocides: all expressed the same phenotypes as the populations expressed in the aforementioned Boran calves. Five clones were derived from one of the isolates which expressed a high level of resistance to all three trypanocides; each clone expressed high levels of resistance to all three trypanocides when characterised in mice. Thus, the multi-resistance phenotype of the parental isolate was associated with expression of mutli-resistance by individual trypanosomes. Finally, molecular karyotypes and electrophoretic variants of six enzymes were determined for seven and eight of the isolates, respectively. Six different karyotypes were observed and all eight of the latter isolates belonged to different zymodemes, indicating that the multi-resistance phenotype at Ghibe was associated with many genetically distinct populations.
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Affiliation(s)
- V Codjia
- International Laboratory for Research on Animal Diseases (ILRAD), Nairobi, Kenya
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36
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Abstract
The analysis of the differences between two complex genomes holds promise for the discovery of infectious agents and probes useful for genetic studies. A system was developed in which subtractive and kinetic enrichment was used to purify restriction endonuclease fragments present in one population of DNA fragments but not in another. Application of this method to DNA populations of reduced complexity ("representations") resulted in the isolation of probes to viral genomes present as single copies in human DNA, and probes that detect polymorphisms between two individuals. In principle, this system, called representational difference analysis (RDA), may also be used for isolating probes linked to sites of genomic rearrangements, whether occurring spontaneously and resulting in genetic disorders or cancer, or programmed during differentiation and development.
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37
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Unstable amplification of two extrachromosomal elements in alpha-difluoromethylornithine-resistant Leishmania donovani. Mol Cell Biol 1992. [PMID: 1448081 DOI: 10.1128/mcb.12.12.5499] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We describe the first example of unstable gene amplification consisting of linear extrachromosomal DNAs in drug-resistant eukaryotic cells. alpha-Difluoromethylornithine (DFMO)-resistant Leishmania donovani with an amplified ornithine decarboxylase (ODC) gene copy number contained two new extrachromosomal DNAs, both present in 10 to 20 copies. One of these was a 140-kb linear DNA (ODC140-L) on which all of the amplified copies of the odc gene were located. The second was a 70-kb circular DNA (ODC70-C) containing an inverted repeat but lacking the odc gene. Both ODC140-L and ODC70-C were derived from a preexisting wild-type chromosome, probably by a conservative amplification mechanism. Both elements were unstable in the absence of DFMO, and their disappearance coincided with a decrease in ODC activity and an increase in DFMO growth sensitivity. These results suggest the possibility that ODC70-C may play a role in DFMO resistance. These data expand the diversity of known amplification mechanisms in eukaryotes to include the simultaneous unstable amplification of both linear and circular DNAs. Further characterization of these molecules will provide insights into the molecular mechanisms underlying gene amplification, including the ability of linear amplified DNAs to acquire telomeres and the determinants of chromosomal stability.
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Wilson K, Beverley SM, Ullman B. Stable amplification of a linear extrachromosomal DNA in mycophenolic acid-resistant Leishmania donovani. Mol Biochem Parasitol 1992; 55:197-206. [PMID: 1359409 DOI: 10.1016/0166-6851(92)90140-f] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Pulsed field gel electrophoretic analysis of chromosomes of MPA100 cells, a strain of Leishmania donovani that possesses an approx. 15-fold amplified IMP dehydrogenase (IMPDH) gene copy number, revealed a new 280-kb extrachromosomal DNA, IMPDH-280, that was not present in wild type parental cells. Southern blots of these pulsed field gels revealed that the vast majority of the amplified impdh genes were localized on IMPDH-280. In addition to the 700-kb wild type chromosome, the impdh probe also recognized a 740-kb chromosome in the MPA100 genome. The pulse time-dependent relative mobility of IMPDH-280 in pulsed field gels, the failure of limited gamma-irradiation to generate a new discrete DNA fragment, and the susceptibility of IMPDH-280 to lambda-exonuclease digestion, demonstrated that IMPDH-280 was a linear molecule. IMPDH-280 was also recognized by a telomere probe but not by fragments derived from amplified DNAs found in other drug-resistant Leishmania. IMPDH-280 and the drug resistance phenotype remained stable when MPA100 cells were propagated in the absence of drug for 2 years. The appearance of IMPDH-280 in MPA100 cells represents one of the first examples of an amplification of a linear extrachromosomal DNA element mediating drug resistance in Leishmania and the first instance of a linear DNA amplification that is stable in the absence of selective pressure.
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Affiliation(s)
- K Wilson
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201-3098
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39
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Hanson S, Beverley SM, Wagner W, Ullman B. Unstable amplification of two extrachromosomal elements in alpha-difluoromethylornithine-resistant Leishmania donovani. Mol Cell Biol 1992; 12:5499-507. [PMID: 1448081 PMCID: PMC360487 DOI: 10.1128/mcb.12.12.5499-5507.1992] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
We describe the first example of unstable gene amplification consisting of linear extrachromosomal DNAs in drug-resistant eukaryotic cells. alpha-Difluoromethylornithine (DFMO)-resistant Leishmania donovani with an amplified ornithine decarboxylase (ODC) gene copy number contained two new extrachromosomal DNAs, both present in 10 to 20 copies. One of these was a 140-kb linear DNA (ODC140-L) on which all of the amplified copies of the odc gene were located. The second was a 70-kb circular DNA (ODC70-C) containing an inverted repeat but lacking the odc gene. Both ODC140-L and ODC70-C were derived from a preexisting wild-type chromosome, probably by a conservative amplification mechanism. Both elements were unstable in the absence of DFMO, and their disappearance coincided with a decrease in ODC activity and an increase in DFMO growth sensitivity. These results suggest the possibility that ODC70-C may play a role in DFMO resistance. These data expand the diversity of known amplification mechanisms in eukaryotes to include the simultaneous unstable amplification of both linear and circular DNAs. Further characterization of these molecules will provide insights into the molecular mechanisms underlying gene amplification, including the ability of linear amplified DNAs to acquire telomeres and the determinants of chromosomal stability.
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Affiliation(s)
- S Hanson
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201-3098
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40
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Abstract
We have identified a novel 75 kbp large extrachromosomal DNA (LED) which is stably maintained during developmental conversion of Trypanosoma cruzi. It has a covalently closed circular conformation and is not derived from the kinetoplast network. In all T. cruzi strains analysed, LED contains 18S rRNA and spliced leader (sl) sequences. LED from the T. cruzi Y strain contains a minimum of 15 copies of the sl repeat arrayed in a head-to-tail configuration and 50 copies of a 196 bp repeat. LED is also present in Trypanosoma dionisii (subgenus Schizotrypanosoma) and in other members of the family Trypanosomatidae. LED from different T. cruzi strains and from other members of the Trypanosomatidae differ in their content of large ribosomal subunit rRNA sequences and the 196 bp repeat. The presence of LED in four evolutionarily distant trypanosomatid species suggests that it plays an important role in the biology of these parasites.
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Affiliation(s)
- W Wagner
- Department of Microbiology and Immunology, Oregon Health Sciences University, Portland 97201-3098
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41
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Korman SH, Le Blancq SM, Deckelbaum RJ, Van der Ploeg LH. Investigation of human giardiasis by karyotype analysis. J Clin Invest 1992; 89:1725-33. [PMID: 1601983 PMCID: PMC295858 DOI: 10.1172/jci115774] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The patterns of transmission of Giardia lamblia and the potential contribution of strain differences to pathogenicity of infection is poorly understood. We used pulsed field gradient gel electrophoresis (PFGE) to separate chromosome-sized DNA molecules of 22 stocks of G. lamblia isolated from 13 individuals (6 symptomatic, 7 asymptomatic) living in Jerusalem. PGFE gels run under a variety of conditions revealed up to nine ethidium bromide-stained bands per isolate ranging in size from 0.7 to greater than 3 megabasepairs. Relative staining intensities indicated that some bands contained multiple chromosomes. Major differences in the number, size, and intensity of bands allowed a clear differentiation of the karyotypes of isolates from each of the different individuals. This is in contrast to previous studies where the karyotype of different isolates have been strikingly homogeneous. Hybridization of Southern blots with surface antigen, beta-tubulin, and ribosomal RNA genes revealed that these gene families were distributed to different sized chromosomes amongst the different isolates. PFGE thus revealed major differences in the karyotypes of different G. lamblia isolates that were obtained over a short period of time from a relatively confined geographic area. In contrast, karyotypes of isolates established either by direct cultivation of duodenal trophozoites or by excystation of stool cysts from the same individuals were almost identical. Also, isolates from the same individuals obtained over a prolonged period of time revealed only minor differences in their karyotype, suggesting that recurrent infection can be caused by genetically similar organisms. We conclude that chronic giardiasis can result from recurrence of occult infection or reinfection from a common source.
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Affiliation(s)
- S H Korman
- Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York 10032
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42
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Lun ZR, Brun R, Gibson W. Kinetoplast DNA and molecular karyotypes of Trypanosoma evansi and Trypanosoma equiperdum from China. Mol Biochem Parasitol 1992; 50:189-96. [PMID: 1311051 DOI: 10.1016/0166-6851(92)90215-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
We compared 12 stocks of Trypanosoma evansi and 1 recently isolated stock of Trypanosoma equiperdum from different regions of China by analysis of kinetoplast DNA (kDNA), nuclear DNA and molecular karyotypes. The T. equiperdum stock was remarkably similar to the T. evansi stocks, except for the possession of kDNA maxi-circles, suggesting a very close evolutionary relationship between T. evansi and T. equiperdum. The maxi-circles of the Chinese T. equiperdum stock were approximately 14.3 kb in size, i.e., about half the size of those of Trypanosoma brucei. This stock is thus similar to an old laboratory stock of T. equiperdum, which also has maxi-circles with a sizeable deletion. Both T. equiperdum and T. evansi kDNA mini-circles hybridised with a T. evansi-specific mini-circle fragment isolated from a Kenyan T. evansi stock. Our results extend the generality that T. evansi and T. equiperdum mini-circles are microheterogeneous rather than homogeneous. Molecular karyotypes obtained by pulsed field gradient gel electrophoresis provided a more sensitive way of distinguishing the T. evansi stocks than isoenzymes or restriction fragment length polymorphisms in kDNA mini-circles, genes for ribosomal RNAs and variant surface glycoproteins. Our results fit the general idea that T. evansi stocks worldwide have a single origin.
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Affiliation(s)
- Z R Lun
- Swiss Tropical Institute, Basel
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43
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Abstract
The advent of pulsed field electrophoresis has allowed a direct approach to the karyotype of Leishmania. The molecular karyotype thus obtained is a stable characteristic of a given strain, although minor modifications may occur during in vitro maintenance. Between 20 and 28 chromosomal bands can be resolved depending on the strain, ranging in size from approximately 250 to 2600 kb. The technique has revealed a striking degree of polymorphism in the size and number of the chromosomal bands between different strains, and this seems independent of the category (species, zymodeme, population) to which the strains belong. It appears that only certain strains originating from the same geographic area may share extensive similarities. This polymorphism can largely be accounted for by chromosome size variations, which can involve up to 25% of the chromosome length. As a result, homologous chromosomes can exist in versions of markedly different size within the same strain. When this occurs with several different chromosomes, the interpretation of PFE patterns appears difficult without prior identification of the size-variable chromosomes and of the chromosome homologies. DNA deletions and amplifications have been shown to account for some of these size modifications, but other mechanisms are probably involved; nevertheless, interchromosomal exchange does not seem to play a major role in these polymorphisms. These chromosomal rearrangements, yet in an early stage of characterization, exhibit two relevant features: they seem (1) to affect essentially the subtelomeric regions and (2) to occur in a recurrent nonrandom manner. Chromosomal rearrangements sharing the same characteristics have been identified in yeast and other protozoa such as Trypanosoma and Plasmodium. The significance of this hypervariability for the biology of the parasite remains unknown, but it can be expected that such mechanisms have been maintained for some purpose; genes specifically located near chromosome ends might benefit from rapid sequence change, alternating activation, or polymorphism of expression. The chromosomal plasticity could represent a general mode of mutation in these parasites, in parallel with genetic exchange which may be uncommon in nature. The molecular characterization of these rearrangements, the identification of each chromosome with the help of physical restriction maps and linkage maps, and the collation of such data on a number of strains and species should allow a significant progress in the understanding of the genetics of Leishmania, in particular as regards ploidy, generation of phenotypic diversity, and genome evolution. Finally, like other models, this is susceptible to improve our knowledge of DNA-DNA interactions and of the chromosome functional structure and dynamics.
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Affiliation(s)
- P Bastien
- Laboratoire d'Ecologie Médicale et Pathologie Parasitaire, Annexe de la Faculté de Médecine, Montpellier, France
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44
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Affiliation(s)
- X Y Huang
- Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, NY 10032
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45
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Blaineau C, Bastien P, Rioux JA, Roizès G, Pagès M. Long-range restriction maps of size-variable homologous chromosomes in Leishmania infantum. Mol Biochem Parasitol 1991; 46:292-302. [PMID: 1922200 DOI: 10.1016/0166-6851(91)90053-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In order to clarify the interpretation of molecular karyotype polymorphisms in Leishmania, the three smallest chromosomes from five cloned strains of Leishmania infantum were identified by chromosome-specific anonymous DNA probes. The presence in the same clone of homologous chromosomes of a different size was demonstrated. The chromosome size polymorphism appeared even more dramatic, with size variations affecting up to 20% of the chromosome, and the two smallest bands in one strain being equivalent to six bands in another strain. Long-range restriction maps of five different-sized homologues of chromosome I showed the size-variation to be located to a terminal fragment in 4 out of 5 cases, and to a central fragment in one. The size-variable sequence was present on at least three other chromosomes as determined by hybridisation analysis. This suggests an instability of the subtelomeric regions such as that in Plasmodium falciparum. Lastly, the finding of several pairs of distinct-sized homologous chromosomes, together with other studies, strongly suggest that Leishmania is diploid in at least part of its chromosomal complement.
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Affiliation(s)
- C Blaineau
- Laboratoire d'Ecologie Médicale et de Pathologie Parasitaire, Faculté de Médecine, Montpellier, France
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46
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Characterization of VSG gene expression site promoters and promoter-associated DNA rearrangement events. Mol Cell Biol 1991. [PMID: 1708090 DOI: 10.1128/mcb.11.5.2467] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The expressed variant cell surface glycoprotein (VSG) gene of Trypanosoma brucei is located at the 3' end of a large, telomeric, polycistronic transcription unit or expression site. We show that the region 45 kb upstream of the VSG gene, in the expression site on a 1.5-Mb chromosome, contains at least two promoters that are arranged in tandem, directing the transcription of the expression site. DNA rearrangement events occur specifically, at inactivation of the expression site, and these events delete the most upstream transcribed region and replace it with a large array of simple-sequence DNA, leaving the downstream promoter intact. Because of the placement of simple-sequence DNA, the remaining downstream promoter now becomes structurally identical to previously described VSG promoters. The downstream promoter is repetitive in the genome, since it is present at several different expression sites. Restriction fragment length polymorphism mapping allows grouping of the expression sites into two families, those with and those without an upstream transcription unit, and the DNA rearrangement events convert the expression sites from one type to the other. Deletion of the upstream transcription unit also leads to the loss of several steady-state RNAs. The findings may indicate a role for promoter-associated DNA rearrangement events, and/or interactions between tandemly arranged promoters, in expression site transcriptional control.
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47
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Gottesdiener K, Chung HM, Brown SD, Lee MG, Van der Ploeg LH. Characterization of VSG gene expression site promoters and promoter-associated DNA rearrangement events. Mol Cell Biol 1991; 11:2467-80. [PMID: 1708090 PMCID: PMC360012 DOI: 10.1128/mcb.11.5.2467-2480.1991] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The expressed variant cell surface glycoprotein (VSG) gene of Trypanosoma brucei is located at the 3' end of a large, telomeric, polycistronic transcription unit or expression site. We show that the region 45 kb upstream of the VSG gene, in the expression site on a 1.5-Mb chromosome, contains at least two promoters that are arranged in tandem, directing the transcription of the expression site. DNA rearrangement events occur specifically, at inactivation of the expression site, and these events delete the most upstream transcribed region and replace it with a large array of simple-sequence DNA, leaving the downstream promoter intact. Because of the placement of simple-sequence DNA, the remaining downstream promoter now becomes structurally identical to previously described VSG promoters. The downstream promoter is repetitive in the genome, since it is present at several different expression sites. Restriction fragment length polymorphism mapping allows grouping of the expression sites into two families, those with and those without an upstream transcription unit, and the DNA rearrangement events convert the expression sites from one type to the other. Deletion of the upstream transcription unit also leads to the loss of several steady-state RNAs. The findings may indicate a role for promoter-associated DNA rearrangement events, and/or interactions between tandemly arranged promoters, in expression site transcriptional control.
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Affiliation(s)
- K Gottesdiener
- Department of Genetics and Development, Columbia University, New York, New York 10032
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48
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Abstract
Members of the Trypanosomatidae, which include the African trypanosomes, the American trypanosomes and the leishmanias, cause disease in vast proportions in man and his livestock and are a major detrimental factor to the social and economic well-being of the third world. Current research using the techniques of molecular biology has revealed two unusual types of mRNA processing in these protozoans; these are the addition of a shared leader sequence to the 5' ends of nuclear mRNAs by a mechanism of trans splicing, and the insertion and deletion of specific uridine residues in mitochondrial transcripts by RNA editing. The presence of these two mRNA processing pathways in the Trypanosomatidae has profound consequences for the organization and expression of their genetic information.
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49
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Abstract
The genome of the protozoan Trypanosoma brucei is known to be diploid. Karyotype analysis has, however, failed to identify homologous chromosomes. Having refined the technique for separating trypanosome chromosomes (L. H. T. Van der Ploeg, C. L. Smith, R. I. Polvere, and K. Gottesdiener, Nucleic Acids Res. 17:3217-3227, 1989), we can now provide evidence for the presence of homologous chromosomes. By determining the chromosomal location of different genetic markers, most of the chromosomes (14, excluding the minichromosomes), could be organized into seven chromosome pairs. In most instances, the putative homologs of a pair differed in size by about 20%. Restriction enzyme analysis of chromosome-sized DNA showed that these chromosome pairs contained large stretches of homologous DNA sequences. From these data, we infer that the chromosome pairs represent homologs. The identification of homologous chromosomes gives valuable insight into the organization of the trypanosome genome, will facilitate the genetic analysis of T. brucei, and suggests the presence of haploid gametes.
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50
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Gottesdiener K, Garciá-Anoveros J, Lee MG, Van der Ploeg LH. Chromosome organization of the protozoan Trypanosoma brucei. Mol Cell Biol 1990; 10:6079-83. [PMID: 2233733 PMCID: PMC361410 DOI: 10.1128/mcb.10.11.6079-6083.1990] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The genome of the protozoan Trypanosoma brucei is known to be diploid. Karyotype analysis has, however, failed to identify homologous chromosomes. Having refined the technique for separating trypanosome chromosomes (L. H. T. Van der Ploeg, C. L. Smith, R. I. Polvere, and K. Gottesdiener, Nucleic Acids Res. 17:3217-3227, 1989), we can now provide evidence for the presence of homologous chromosomes. By determining the chromosomal location of different genetic markers, most of the chromosomes (14, excluding the minichromosomes), could be organized into seven chromosome pairs. In most instances, the putative homologs of a pair differed in size by about 20%. Restriction enzyme analysis of chromosome-sized DNA showed that these chromosome pairs contained large stretches of homologous DNA sequences. From these data, we infer that the chromosome pairs represent homologs. The identification of homologous chromosomes gives valuable insight into the organization of the trypanosome genome, will facilitate the genetic analysis of T. brucei, and suggests the presence of haploid gametes.
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Affiliation(s)
- K Gottesdiener
- Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, New York 10032
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