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Microbiota On Mucosal > B5- Antigenic Switch Trypanosoma > Flashcards

B5- Antigenic Switch Trypanosoma Flashcards

1
Q

What are the waves of parasitemia

A

The immunogenic response 5-7 days mounted then peak again when the 1% of cells changing have outgrown other populations

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2
Q

How does it cover surface

A

The final 23 aa are cleaved for a gpi anchor

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3
Q

How many gene copies of vsg

A

1000

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4
Q

What is the one expressed called

A

Expression linked copy

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5
Q

How many expression sites are there and why

A

20-44 because max of 44 telomeres in the 11 pairs of chr

Vsg lie in subtelomeric regiosnnonly in expression sites

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6
Q

Explain structure of vsg

A

About 500 aa

Signal sequence in n terminus

Central region is highly variable

C terminus is conserved

Final 17-23 aa are cleaved and replaced by gpi anchor

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7
Q

If they are highly diverse, are they diverse in tertiary structure

A

No, they have a highly conserved homodimer strucrure where each monomer held by hinge region at central region

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8
Q

What can cleave the gpi anchor to release coat for turnover

A

Pl-C

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9
Q

What is on the 5’ and 3’ of the vsg gene in the expression site at Subtelomeric regions

A

2 barren regions of repeats not targeted by RE
5’ is a 76bp repeat
3’ is the TTAGGG telomeric repeats

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10
Q

What other repeat can be present (only in blood form not metacyclic salivary gland) before promoter

A

50bp repeat

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11
Q

What is in between the promoter and 76bp repeat on blood form expression sites

A

Exp site associated genes polycistron (ESAGs)
Exp at the same time as the vsg

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12
Q

Give example of what this can be

A

Transferrin receptor for grabbing iron

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13
Q

How many Expressjon sites in blood form can be found

A

20

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14
Q

How does blood form es differ to salivary metacyclic forms of tsetse

A

They don’t have the 50bp repeats, promoter immediately 5’ of the vsg

No 76 bp repeat

No esags

In metacyclic only 20 vsg genes are ever expressed vs 1000 in bes

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15
Q

Where else can silent vsgs park

A

On the 100 mini chromosomes

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16
Q

What sort of repeats are here

A

5’ long 177 bp repeat and also telomerix 3’

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17
Q

What is the most common way of gene switching (all involve recombination)

A

Duplicative transposition

A gene not in telomeric region ie esag can form a loop (chr loops) and displace the vsg at the expression site telomere to become active
The other vsg discarded

Duplicative because the Solent vsg still kept in silent library

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18
Q

How is telomere conversion different

A

Where another gene at another telomere site will displace the active vsg-ES
It is copied and transposed into that spot

19
Q

What other 2 ways can occur

A

Telomere reciprocal exchange where both genes at a telomeric site switch places and 1 of them becomes in the active ES

In situ switch where promoter can become activated or inactivated

20
Q

Are the promoter sequences diff between active and inactive Es

A

No

21
Q

Give example of a enzyme for homologous recomb which ko can disrupt gene switching (but not fully) and how does it work

A

Rad51

Can insert ssdna into homologous dna duplexes and causes recombination events

22
Q

What sort of ptm modification associated with silenced ES enriched at telomere regions

A

Base J (modified base)

23
Q

In active vs inactive where are modified j bases (active shows loss in Es, inactive shows gain)

A

Active- only in 50bp repeats before promoter and at telomere ttaggg repeats

Inactive - along whole orf and the repeats including at the ESAGS and vsg site

24
Q

Was J base modification actually shown to control expression or not

A

It was later found to not affect expression despite different patterns in active and inactive vsgs but instead likely involved in switching and recombination

25
Q

How is telomeric position effect a factor in silencing (suggested by reporter cloning exp)

A

Closer the gene to the telomere the more silenced it is
Further away the reporter gene becomes expressed much more

independent of promoter (works with a constitutive promoter)

Suggesting active can switch further from telomere

26
Q

Which initiation factor associated with the active ES and increases occupancy of rna pol 1. (Enriched at active ES)

A

CIFTA

27
Q

What type of ptm is seen close to promoter and can increase occupancy in active ES

A

SUMOylation

28
Q

What protein displaces h1,2a and 3 in active ES and opens the chromatin structure for txn

A

Tdp1

29
Q

What does this show

A

Tertiary structure also a factor in expression

30
Q

Which methylation by dot1b associated with silent ES

A

Trimethylation at h3k76

31
Q

What was used which blocks rna pol II and Iii but not rna pol I and still found vsg expression confirming pol 1

A

A-amanitin

32
Q

Where is activity of rna pol 1 found usually (and only ever found for insect stages but not blood form)

A

Nucleolus periphery (for rrna txn)

33
Q

Where apart from nucleolus was active ES expression found by tagging with gfp aswell as rna pol activity - found only in the blood form.

A

Extranucleolar body

(Inactive vsg did not colocalise with rna pol in the extranucleolar body)

34
Q

How does this explain exclusion

A

1 chr / Es needs to find way to this Extranucleolar body and the rest are silenced

35
Q

Was this found in insect stage

A

No

36
Q

How did scientists looking at tertiary structure through hi-c and pacbio come to conclusion that chromatin compactness affects accessibility for switching AND exclusion

A

Subtelomeric vsg highly packaged chromatin in inactive state

When deleting the h3 and h4 variant histones they found increased exp of more than 1 vsg
Further identified vsgs were able to homologously recombine better in this state and switch vsgs that were active (usually low frequency / low rate switching)

37
Q

How could this potentially give a therapy

A

Target genome compact structure ? To increase exp of more vsgs

38
Q

Which protein part of the nucleoskeleton keeps stability of heterochromatin in silent vsg ES and what happens in knockdown of it

A

NUP-1

Knockdown shown to increase vsg switchinf and also results in reduced vsg silencing

Showing importance of tertiary structure

39
Q

What other proteins present in periphery help the heterochromstin stability of inactive ES (epigentic control in addition to dot1b)

A

Hdac3

40
Q

What is present in the Extranucleolar body that inactive Es don’t have access to

A

Sl-array (rna pol II whcih transcribes SLrna to donate sl for maturation of the active vsg)

41
Q

Why doesn’t telomeric position effect explain full story of gene exp

A

Because there will be a vsg that is the expression linked copy which will be expressed despite being close to telomeric regions

Suggests other factors of regulating like chromatin/ tertiary dna structures

42
Q

Why is pacbio particularly important to look at vsg genes in Subtelomeric regions

A

High amount of repeats = long sequences

43
Q

Which form of parasite is nuclear compartmentalisation extra nuclear body txn machinery specific to

A

Blood form

Microbiota On Mucosal (22 decks)

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