Lecture B2 - Introduction to Biology of Trypanosoma brucei

Question 1

What is the classification of Trypanosoma?

Answer 1

Domain - Eukaryota
Kingdom - Excavata
Phylum - Euglenozoa
Class - Kinetoplastida
Order - Trypanosomatida
Genus - Trypanosoma

Question 2

Describe the life cycle of T. brucei.

Answer 2

Very simple.
Vector is a tsetse fly, host is a human.
Tsetse fly takes a blood meal and its saliva releases the parasite (epimanstigote) that can swim inside the blood.
Once inside the parasite replicates and divides and spread throughout the host causing disease, it is mainly extracellular.

Question 3

What are the 2 major switches in the T brucei life cycle?

Answer 3

Slender to stumpy bloodstream form - density sensing could be important or ‘differentiation division’
The bloodstream form to pro cyclic (tse tse midgut form) - the in vitro process is stimulated by citrate and cis-aconitate and a reduction in temp from 37 to 27

Question 4

Why do trypanosomes have to have good evasion mechanisms?

Answer 4

They mainly live extracellularly in the blood so they are very susceptible to the immune system.

Question 5

How do trypanosomes evade the immune system?

Answer 5

Masters of disguise.
Multiple coats/cloaks
Switching mechanisms - trans-splicing and GPI-anchors.

Question 6

Describe the antigenic variation in trypanosomes.

Answer 6

Infection characterised by waves of parasitemia.
Each wave represents a single antigenic ally different clone or serotype.
Antibodies produced in the first week against clone A will not react with clone B.
The changing display of different antigens is called antigenic variation and is an important part of immune evasion.

Question 7

What causes sleeping sickness?

Answer 7

Trypanosoma brucei - complex life cycle.

Question 8

How many chromosomes, mini chromosomes and intermediate chromos are found in Trypanosome brucei?

Answer 8

11 regular chromosome pairs of mega base size chromosomes per genome.
100 mini chromosomes.
5 intermediate size chromos

Question 9

How many predicted genes, pseudogenes and T. brucei specific genes are in the Trypanosome brucei genome?

Answer 9

9000 predicted genes
900 pseudogenes
1700 T brucei specific

Question 10

What is a pseudogene?

Answer 10

Don’t code for a function product.

Question 11

How many VSG genes are in the Trypanosome brucei genome?

Answer 11

806 VSG genes (most are pseudogenes).

Question 12

What do the VSG genes do?

Answer 12

Variant surface glycoprotein genes allowing for lots of protein colours so it can switch between them to avoid the host immune system. Ectopic recombination allows for new antigenic ally diverse proteins.

Question 13

What is the kinetoplast?

Answer 13

Like a mitochondria for the trypanosome, kDNA compromises 10-20% of total DNA.

Question 14

Describe the nucleolus of the Trypanosome.

Answer 14

Most distinctive nuclear compartment.
Ribosome biogenesis - 45S ribosomal repeats cluster here. Pre-rRNA synthesised and processed, 40S and 60S complexes assembled here.
Ribosomal RNA genes and RNA Pol1 large su concentrated at periphery of nuceloulus.
TOR1 kinase depleted to disperse the nucleolus and RNA Pol1

Question 15

What are nuclear pores for?

Answer 15

Gaps in the membrane where the nucleolus can travel in and out.

Question 16

Describe trypanosome chromatin.

Answer 16

Ultrastructural compartmentalisation of the trypanosome nucleolus.
Distinct electron-lucent (1 eurochormatin) and electron-dense (2 heterochromatin) regions.
Nuclear pores (200-300 per nucleus).
More loosely packed.