What are Parasites

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What are Parasites?
Dependence on another organism that does harm to
the host.
Fundamental discoveries made in parasitic
systems Trans splicing RNA editing GPI
anchor structure Antigenic variation Endosymbi
osis Drug resistance mechanisms
Fleas Ticks Lice
Worms
Protozoa
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Eukaryotic Tree of Life
Apicomplexans
Entameoba
Kinetoplastids
Microsporidia
Trichomonas
S. Baldauf
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Apicomplexa

• Apically specialized
• Related to Alveolates
• gt5,000 species
• Intracellular parasites

Baldauf et al., Science 2000
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Apicomplexans
Cryptosporidium
Toxoplasma
Plasmodium
Eimeria
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Kinetoplastidae
Trypanosoma brucei spp. Extracellular
African Sleeping Sickness Trypanosoma cruzi
Intracellular Chagas Disease
Leishmania spp. Intracellular Cutaneous
vs. Visceral disease
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Developmental Stages of Leishmania
Metacyclic promastigote
Procyclic promastigote
in vitro, in culture
procyclic promastigotes non-infectious
Sand fly Mammal
metacyclic promastigotes infectious
Transmitted during Sand fly blood meal
amastigotes infectious
Amastigote
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Parasite Genomics

• Mitochondria and plastids

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Apicomplexan Genomes
Mitochondrial 6 kb tandem repeat CO1, COII,
Cyb Fragmented rRNA
Nuclear Genome 14 chromosomes 65 x 106 bp
haploid Map unit 100 kb
Apicoplast 35 kb genome Plastid like rRNA rpoB,
tufA, clpC
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Apicoplast

• Remnant endosymbiont
• Algal origin
• Non-photosynthetic
• Functions
• ferridoxin
• fatty acids
• Isoprenoids
• Target of antibiotics

Maréchal et al. 2001
Plasmodium
Toxoplasma
Blastodinium
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Origin of the Apicomplast
Secondary endosymbiosis
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Metabolic Pathways in Plasmodium
Gardner et al., Nature 2003
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Targeting Signals for Import into the Apicoplast
Foth et al., Science 2003
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Loss of Mitochondria in some Protists
Secondary loss presence of genes normally found
in mitochondria GAPDH Giardia Hsp60 Entamoeba
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Parasite Genomics

• Genome organization and regulation
• Apicomplexans

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Sequenced Genomes
Toxoplasma. Eimeria, Theileria
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Plasmodium Life Cycle
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Two-color Microarray Hybridization
Prepare total RNAs Sample 1 Sample 2
Prepare Microarray
cDNAs
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Z. Bozdech et al. 2003 PloS
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Transcription
Translation
Energy
Replication
Plastid
Invasion
Z. Bozdech et al. 2003 PloS
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Z. Bozdech et al. 2003 PloS
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Summary of gene regulation in Plasmodium

• Genes are expressed in a phasic pattern with a
  single maximum and minimum per intracellular
  cycle.
• Genes located in close proximity on chromosomes
  are not coordinately regulated.
• Co-regulation of genes based on common function,
  despite being physically separated.
• Gene expression program resembles phage or virus.
• Translationgtenergy metabolismgt DNA
  synthesisgtplastidgtinvasion

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Parasite Genomics

• Genome organization and regulation
• Kinetoplastida

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Transcription is constant across all genes and
possibly across development
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chr 1
yet, mRNA levels vary
Postranscription regulation
stability, processing translation, etc
Trans-splicing ? polyadenylation are coupled, a
downstream splice site dictates the upstream
site of polyadenylation
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Polycistronic Transcription and Trans-splicing
of mRNAs in Trypanosomatids
Spliced leader
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RNA editing in Trypanosomes
Prsts r smrtr thn y thnk!!!
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gtGuide RNAs are encoded by minicircles gtUsed as
templates for editing transcripts on
maxicircles gtDiscovered in Tryps and Leishmania,
now known from many organisms
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RNA Editing Complex
Rigaut et al., 1999 Nat. Biotech.
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Summary of gene expression in Kinetoplastids

• Gene expression is polycistronic
• Few conventional promoters
• Transplicing of leader RNA occurs simultaneously
  with polyA addition
• Message abundance controlled post-transcriptionall
  y
• Mitochondrial genome extensive editing

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Next time.
Adhesion
.Antigenic variation
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Reading List

• R. Dzikowski et al., Variant antigen gene
  expression in malaria. Cell Mico, 2006 8
  1371-1381.
• J.E. Taylor, G. Rudenko, Switching trypanosome
  coats whats in the wardrobe. Trends Genet. 22
  614-620.
• B.J. Foth et al., Dissecting apicoplast targeting
  in the malaria parasite Plasmodium falciparum.
  Science 2003, 299 705-708.