28. Parasitic Eukaryotes

Protozoa: Amoeba example

Brain eating amoeba called N. fowleri

Does N. fowleri have rRNA operons

No, each N. fowleri cell has ~4,000 copies of a 14 kb circular plasmid that harbor rRNA genes.

Protozoa: Flagellates example

T. brucei which causes African sleeping sickness and transmitted by tsetse fly

VSG switching by T. brucei

variant surface glycoprotein expression to create antigenetic variation for immune evasion

VSG switching by T. brucei pattern

Variants arise with degree of regulation because antibodies act to remove early variants, but by then later variants are already emerging

VSG switching mechanism

altering which 15 BES within the genome is active

recombination or gene conversion-mediated feeding of new
VSG sequence

Variant surface glycoprotein (VSG) switching is the major
driver of antigenic variation in Trypanosoma brucei. One
mechanism of VSG switching is what?
(1) inversion of the bloodstream expression site (BES) promoter
such that it drives transcription of a VSG gene located upstream
in the opposite orientation
(2) the mutation of RNA polymerase such that it recognizes a
different gene promoter sequence, which switches which VSG
gene is transcribed
(3) inducing transcription of a VSG gene located within one of
the densely-packed tandem arrays of VSG genes located within
one of the mini-chromosomes
(4) differential gene expression in response to levels of
extracellular iron
(5) the gene conversion-mediated feeding of new VSG sequence
information into the expressed bloodstream expression site (BES)

the gene conversion-mediated feeding of new VSG sequence
information into the expressed bloodstream expression site (BES)

Plasmodium life cycle: Schizogany

asexual reproduction by
multiple fission, producing merozoites.
The merozoites are what generate the
clinical symptoms of malaria

The first Plasmodium chloroquine-resistant isolate was recovered in 1957. In 2025, how could you determine the molecular basis of resistance?

Metagenomic analysis to compare chloroquine-resistant and -sensitive isolates

What happened when comparing chloroquine-resistant and -sensitive isolates of P. falciparum?

identified a gene on chromosome 7 as the major resistance determinant

Hookworm genomics

shed some light on the remarkable ability of these organisms to
suppress the production of pro-inflammatory cytokines

Female schistosoma

heterogametic sex with ZW chromosome

Male schistosoma

Homogametic with ZZ pair

Analysis of male and female sex chromosomes in Schistosoma

suggests that there are distinct regions on the Z chromosome that differ between males and females, which could be indicative of sex-specific genetic variations or differences in chromosome structure and gene content

Tapeworm genome vs Flatworm distant relative

Although gene order has been lost, ancient chromosomal synteny is preserved among these parasitic flatworms

Genome data has been generated for several
species of hookworm. One insight to come
out of this data is what?
(1) insight into the mechanisms by which these
parasites can suppress production of pro-
inflammatory molecules
(2) observation that these parasites do not
express proteins on their surface, and hence no
vaccine can be developed
(3) observation that the rRNA operons of these
parasites are located on plasmids not as part of
one or more chromosomes
(4) that different hookworm species are
unrelated to each other, sharing as much
similarity to C. elegans as they do with each other
(5) that sequencing the genomes of these
multicellular eukaryotes is easy

insight into the mechanisms by which these
parasites can suppress production of pro-
inflammatory molecules