Organization/ Expression Lymphocyte Receptor Genes Flashcards
What do the letters in V (D) J stand for?
= gene segments
variable/ joining/ diversity
Where does V (D) J recombination occur?
primary organs = bone marrow/ thymus
Why is D in brackets V (D) J ?
not always present/ needed for recombination
- D only in heavy chain (not light)
How does V (D) J recombination occur?
random rearrangements
What is the result of V (D) J recombination?
novel amino acid sequences in antigen-binding regions of Igs/ TCRs
Why is V (D) J recombination important?
recognition of nearly all pathogens
- including altered self-cells
How do B cells create different possible antibodies in developing lymphocytes?
Recombination of gene segments
Can a B cell create different possible antibodies in a mature lymphocyte?
no
- only in developing lymphocyte/ not once activated
What segments are only used in heavy chains?
D
What variable segments are present in light chain?
V/J
What variable segments are present in heavy chain?
V/D/J
Why are different gene segment combinations important?
recognize different antigens
What is the constant region gene segment?
C
What is an immunoglobulin protein?
Antibody
What are the chains in an Ig protein?
2 identical heavy
2 identical light
What are the 2 possibilities for the 2 identical light chains on an Ig protein?
kappa/ lambda
Where is each set of gene families (kappa/ lambda/ heavy chain) encoded?
each on separate chromosomes
How do you know if you are looking at a heavy/ light chain?
no D= light
D= heavy
What do kappa light-chain genes pair?
V / J segments
What do lambda light-chain genes pair?
J / C segment
What segments does heavy-chain gene organization include?
VH/ DH/ JH/ CH
What is required to encode the variable region of the heavy chain of the Ig molecule?
recombination between 3 gene segments
- VH/ D/ JH
How is V (D) J recombination directed?
by a signal sequence (RSS)
What flanks each antibody gene segment?
RSSs = Recombination Signal Sequences
What happens to the spacer when 12 bp RSS and 23 bp RSS pair?
spacer removed
What is needed for recombination to occur?
12/23 rule
What is the 12/23 rule?
12 bp RSS must pair with a 23 bp RSS
What is a one-turn spacer?
12 bp RSS
What is a two-turn spacer?
23 bp RSS
What is the spacer?
RSS
What gene segment is the 12 bp RSS from?
V cluster
What gene segment is the 23 bp RSS from?
J cluster
What chain is a 2-step process for recombination?
Heavy
What enzyme joins gene segments?
RAG 1/2 recombinase
What does RAG stand for?
Recombination Activating Gene
What enzyme (RAG 1/2 recombinase) is needed for recombination?
both proteins
What RAG recombinase protein is more important?
RAG1
Why is RAG1 more important?
forms complex with RSS stabilized by binding RAG2
What is the role of RAG2?
binding stabilizes the RSS/ RAG1 complex
What is responsible for recognizing/ cutting DNA at the immunoglobulin-encoding region/ RSS?
RAG1/2 complex
What are the 10 well-defined steps of V(D)J recombination?
first 7 = both
8-10 = only heavy chain (D)
- RAG proteins recognize/ bind to RSS
- Cleavage of DNA
- Formation of hairpin at V / J region
- Ligation/ removal of signal ends
- Hairpin cleavage
- Overhang extension
- Ligation of light-chain V / J segments
- Exonuclease trimming
- N-nucleotide addition
- Ligation/ repair of heavy chain
What are the 5 mechanisms to generate antibody diversity in naive B cells?
Multiple gene segments
Combinatory diversity (light/ heavy chain)
Templated nucleotide addition
Exonuclease trimming
Non-templated nucleotide addition
What ensures each B cell synthesizes only 1 heavy/ 1 light chain?
Allelic exclusion
What happens to potentially autoreactive receptors in light-chains?
Receptor editing
What is the result of asymmetrical cleaving of hairpin structures?
Templated nucleotide addition
(uneven number bp)
What involves losing nucleotides/ changing reading frames?
Exonuclease trimming
(randomize to fill in)
What involves adding random nucleotides between joints?
Non-templated nucleotide addition
What is non-templated nucleotide addition mediated by?
TdT activity
