Quiz 5 part 2

Question 1

when is the rearrangement of heavy chain gene segments happening

Answer 1

in early pro-B and late pro-B

Question 2

is it likely that heavy chain rearrangement will succeed or fail?
EXPLAIN

Answer 2

there is a high probability that it will fail.

junctional diversity (P and N nucleotides) can shift the reading frame of the nucleotide sequence, resulting in a non multiple of 3 and nonfunctional genes

Question 3

explain why junctional diversity (P&N nucleotides) is both good and bad

Answer 3

good – it can generate a lot of diversity

bad — high probability of a frameshift mutation and ultimate failure

Question 4

what is the probability of Pro-B cell rearrangements failing/succeeding

Answer 4

66% chance of NONproductive rearrangements
33% chance of productive rearrangements and development proceeding

Question 5

between early pro-B and late pro-B, which has a better chance of a productive rearrangement?

EXPLAIN

Answer 5

early pro-B has a better chance at productive rearrangement
this is so because early pro-B is DJ recombination and D gene segments are functional in all 3 reading frames

the variable region only has ONE reading frame for the V-DJ recombination, so it’s less likely to be productive (1/3 chance)

Question 6

explain how chromosomes play a role in heavy chain recombination

Answer 6

in early pro-b, since there’s a high chance of development, recombination happens on BOTH loci (chromosomes)

however, in late pro-b, recombination happens at 1 locus at a time. if rearrangement is not productive on one chromosome, we move to another and try again

Question 7

if heavy chain rearrangement is successful, what happens?

Answer 7

the B cell differentiates into LARGE, dividing B cells, producing mu heavy chain

Question 8

approximately what% of large pre B cells produce a functional mu heavy chain?
what happens if unsuccessful?

Answer 8

~50%
apoptosis

Question 9

what is the checkpoint for late pro-B cells

Answer 9

testing to see if produced mu heavy chain is functional (productive)

tested if it’s able to associate with light chain

Question 10

HOW is this checkpoint of the mu heavy chain conducted?

Answer 10

cells produce a SURROGATE light chain

VpreB — similar to variable region of light chain
lambda5 — similar to constant region of light chain

mu chain homodimers assemble with surrogate light chain, Iga and IgB IN THE ER

Question 11

explain what the pre-B cell receptor is

Answer 11

the pre-B cell receptor IS THE CHECKPOINT PROCESS to test the mu heavy chain

mu heavy chain homodimers assemble with surrogate light chain, and coreceptors Iga and IgB IN THE ER

Question 12

If the first checkpoint is passed, (the newly made mu functional chain CAN FORM A large pre B cell receptor)

WHAT HAPPENS

Answer 12

Iga and IgB have cytoplasmic tails that signals to the pro-b cell to:

-terminate gene rearrangements. no longer needed

-stimulate several rounds of cell division

-VpreB and lambda5 promote pre b cell receptor oligomerization

Question 13

if the first checkpoint is NOT passed, what happens?

Answer 13

Iga and Igb do NOT give survival signals and the cell undergoes apoptosis

Question 14

upon successful passing of the first checkpoint, several important signals are sent via transcription factors to stop further recombination.
explain this further

Answer 14

RAG complex proteins are ceased to be expressed

Degradation of existing RAG complex proteins

chromatin structure is remodeled, INHIBITING transcription

Question 15

what is the purpose of these important signals, sent via transcription factors, to STOP FURTHER RECOMBINATION?

Answer 15

ALLELIC EXCLUSION

– no heavy chain rearrangement on the second locus

if both loci were allowed to produce heavy chains, B cell receptor binding would be suboptimal (low avidity)

Question 16

allelic exclusion gives _______ B cell receptors with high avidity binding

Answer 16

HOMOGENEOUS

Question 17

NO allelic exclusion gives ____ B cell receptors with low avidity binding

Answer 17

heterogeneous

Question 18

structurally, what exactly are large pre-B cells?

Answer 18

large oligomers of repeating preBCRs

Question 19

what happens to large pre-B cells?

Answer 19

they divide, producing ~100 clones of small pre-B cells.
this is called CLONAL EXPANSION

Question 20

the large pre-B cells divide, producing ~100 clones of small pre-B cells (clonal expansion)

are all of these small pre-B cells producing the same heavy chain?

Answer 20

YES – -we turned everything off to prevent transcription of another heavy chain

Question 21

do small pre-B cells still express the surrogate light chain?

Answer 21

NO – it was just a test

Question 22

WHERE are small pre-B cells producing their heavy chain?

Answer 22

in the ER – the heavy chains are ready to assemble

Question 23

is the small pre-b cell still expressing preBCR?

Answer 23

NO

Question 24

in small pre-B cells, the rearrangement of _____ begins

Answer 24

light chain (VJ) rearrangement

Question 25

in order for small pre-B cells to do light chain rearrangement, what has to happen?

Answer 25

RAG complex proteins must be reactivated

Question 26

small pre-B cells are ______ of ______ with identical ________

Answer 26

small pre-B cells are HUNDREDS of CLONES with IDENTICAL HEAVY CHAINS

Question 27

does the light chain rearrange 1 locus at a time or both? explain

Answer 27

one locus at a time

K rearranges first.
if unsuccessful, lambda locus is rearranged

Question 28

light chains are able to produce _____ rearrangements. explain this

Answer 28

SUCCESSIVE rearrangements

if the first attempt fails, rearrangement occurs on the same allele until the gene segment availability is exhausted

Question 29

what is the success rate of light chain rearrangement?

Answer 29

85% success rate

Question 30

light chain successive rearrangements usually results in more ____ chains than _______ chains

Answer 30

more kappa chains than lambda chains

Question 31

there is EXCLUSIVE lambda chain expression where?

Answer 31

IgD in upper respiratory tract

Question 32

light chain rearrangement with K light chain on one chromosome was not successful.
explain the chain of events that happens now (successive rearrangement process)

Answer 32

we will move to K region on the other chromosome.
if this is also unsuccessful, we will recombine the lambda light chain

Question 33

true or false:

the majority of the time, light chain rearrangement will be successful

Answer 33

true – 85% of the time

Question 34

what is the second checkpoint?

Answer 34

can the new light chain form a functional B cell receptor with the mu chains in the ER?

Question 35

at the time of the second checkpoint, are mu ready chains in the ER and ready to be assembled?

Answer 35

YES

Question 36

If the second checkpoint is passed, (the new light chain can form a functional BCR with the mu heavy chain) what will happen?

Answer 36

the BCR will be formed

further assembly of Iga and Igb allows expression on the cell surface

this surface expression initiates signaling to HALT LIGHT CHAIN REARRANGEMENTS

Question 37

If the second checkpoint is not passed, what happens?

(new light chain is not able to form a BCR with mu heavy chain)

Answer 37

the cell undergoes apoptosis

Question 38

out of the 100 clones of small pre-b that were formed, around how many will become fully formed?

Answer 38

around 85

Question 39

the expression of the BCR on the surface with a light chain and a heavy chain and all rearrangements are stopped.

what B cell is this?

Answer 39

immature B cell

Question 40

all the heavy chains are ____ and all the light chains are ___

Answer 40

all the heavy chains are IDENTICAL and all the light chains are DIFFERENT

–diverse population of antigenically distinct B cells