L02 Flashcards
what gene segments encode the V region in H chain and TCR beta
V, D and J (V is the biggest)
what gene segments encode the V region in L chain and TCR alpha
V and J
In B cells (during their development in the bone marrow) the DNA containing the Ig gene segments is deliberately broken and the gene segments are rearranged (joined together) to form functional Ig genes
True
different rearrangement for each B cell (random breakage and rearrangement)
True
After DNA breakage what gene segments are joined in the light chain to encode the V region
single V and a single J
what 2 loci contain L chain genes
κ and λ
After DNA breakage what gene segments are joined in the H chain to encode the V region
V D and J
what is the order of ig rearrangements during B cell development
first H chain gene segments rearrange (D-J, then V-DJ (greater variability in H chain as V, D and J segments)
then light chain gene segments rearrange: κ segments (V-J) first
if κ rearrangement is unsuccessful, then gene segments (V-J) rearrange
how many gene segments are there for each chain
check slide 16 of the lecture
where is the H chain locus
chromosome 14
where is the κ chain locus
chromosome 2
where is the λ chain locus
chromosome 22
what are the steps for the somatic recombination process
Somatic recombination is the process where DNA is cut to join immunoglobulin genes together
RAG 1 and RAG 2 protein complexes bind to RSS and cut the genes removing RSS sites
Artemis, DNA-PK, Ku, and DNA Ligase + XRCC4 form a complex that binds the RAG proteins joining RSS into the signal joint
Hair pins at the end of the gene segments are cleaved and TdT adds additional nucleotides to the DNA strand and the other enzymes of the complex ligate the ends together
in each individual B cell, only one rearranged H chain gene from one chromosome (i.e. allele) is expressed
True
more than one rearranged L chain from one chromosome is expressed by each individual B cell
False
each B cell expresses either a rearranged kappa or lamda light chain; never both
True
what is combinatorial diversity
different V, D and J segments recombine to produce different sequences
what is junctional diversity
imprecise joining (small differences in sequences where V-D and D-J segments join)
N regions (random addition of nucleotides at junctions of V-D and D-J by terminal transferase)
what are the features of somatic hypermutation (SHM)
mutation frequency in antibody (H/L) V genes is orders of magnitude higher than that seen in all other areas of the genome
SHM occurs in germinal centres (GC) as B cells recognize Ag and proliferate/become activated
which enzyme performs SHM
activation-induced deaminase (AID)
how does activation-induced deaminase (AID)
work
AID acts on DNA to de-aminate cytosine to uracil
uracil is then recognized by error-prone DNA repair pathways leading to mutations
the membrane and secreted forms of BCR are produced by alternative RNA processing
true
what is the heavy chain C region gene for each Ig class
IgM —μ
IgD — δ
IgG — γ
IgA — α
IgE — ε
four γ chain gene segments correspond to the four IgG subclasses; similarly two α chain gene segments
True
which class is the first expressed in B cells
IgM
why is IgM the first class expressed in B cells
the Cμ segment is physically closest to the V, D and J gene segments
why can IgD be co expressed with IgM
Cδ is next to Cμ
how is IgD and IgM co expressed
differential processing of the RNA from the two C region genes
what does switching to different Ig classes require
further DNA recombination: guided by switch regions involving the enzyme AID
what steps insure AB diversity
there are multiple gene segments for each chain
combinatorial diversity
combinations of heavy and light chains
junctional diversity increases diversity further
somatic hypermutation (SHM)
how many possible light chain combinations can we have
300
which process ensures only 1 heavy and 1 light chains are expressed
allelic exclusion
RAG-1 and RAG-2 genes encode lymphoid-specific components of the recombinase
True
