2. How does this diversity achieved in
term of anti body production??
In a genetic recombination, which
happens in anti body light chain and
heavy chain, known as VDJ
recombination.
There are 51V , 27D, 6 J segments
3. VDJ RECOMBINATION
• V(D)J recombination is the
mechanism of somatic
recombination that occurs only in
developing lymphocyte during
the early stages of T and B cell
maturation.
4. Key Enzymes and Components
1. The process of V(D)J recombination is mediated by VDJ recombinase, which
is a diverse collection of enzymes. The key enzymes involved
are: Recombination activating genes 1 and 2 (RAG)
2. Terminal deoxynucleotidyl transferase (TdT)
3. Artemis nuclease, a member of non-homologous end joining (NHEJ) pathway
for DNA repair
4. DNA-dependent protein kinase (DNA-PK)
5. X-ray repair cross-complementing protein 4 (XRCC4)
6. DNA ligase IV
7. Non-homologous end-joining factor 1 (NHEJ1)
8. DNA polymerases λ and μ.
5. Recombination Signal Sequences (RSSs)
• To maintain the specificity of recombination, V(D)J recombinase
recognizes and binds to recombination signal sequences (RSSs)
flanking the variable (V), diversity (D), and joining (J) genes
segments.
• RSSs are composed of three elements:
1. a heptamer of seven conserved nucleotides
2. a spacer region of 12 or 23 basepairs in length
3. a nonamer of nine conserved nucleotides
10. Process
Progenitor lymphoid cell which through
VDJ recombination make an immature B
cell with unique antibody that binds to
specific antigen.
• This process occurs in two steps
1. Somatic recombination of heavy chain
2. Somatic recombination of light chain
12. STRUCTURE OF HEAVY CHAIN
The germ line DNA of progenitor B cell has some
genes for the heavy chains. Those will make
heavy chains of the Ab.
In the heavy chain gene we have: a leader
segment, V (variable) region, D (Diversity)
Segment, J (Joining) segment, and we have the
constant region.
VDJ recombination involves the VDJ segments.
There are many V segments, many D segments,
and many J segments.
On the heavy chain gene we have also some
constant region called as Constant u (Cu) that
make Ab for IgM.
13. J and C and in close proximity.
However the V region and D region are far away
from each other.
14. VDJ RECOMBINATION
1. In the developing B cell, the first recombination
event to occur is between one D and one J gene
segment of the heavy chain locus. Any DNA
between these two gene segments is deleted.
2. This D-J recombination is followed by the joining
of one V gene segment, from a region upstream of
the newly formed DJ complex, forming a
rearranged VDJ gene segment. All other gene
segments between V and D segments are now
deleted from the cell's genome.
3. Primary transcript (unspliced RNA) is generated
containing the VDJ region of the heavy chain and
both the constant mu and delta chains (Cμ and Cδ).
(i.e. the primary transcript contains the segments:
V-D-J-Cμ-Cδ).
4. The primary RNA is processed to add
a polyadenylated (poly-A) tail after the Cμ chain
and to remove sequence between the VDJ segment
and this constant gene segment.
5. Translation of this mRNA leads to the production
of the IgM heavy chain protein.
15. SOMATIC RECOMBINATION OF LIGHT
CHAIN
The first step of recombination for the light chains involves the joining
of the V and J chains to give a VJ complex before the addition of the
constant chain gene during primary transcription. Light chain don’t
have a D segment.
Two types of chains:
kappa and lambda chains, but the immunoglobin rearrange in a similar
way so, Both K and L don't have a Diversity segment.
J and C regions are close to each other but the variable(v)region is
faraway and V always have a leader sequence.
16. VJ recombination
First step is Shuffling, in which
any of the variable region shuffle
with the J segment.e-g.., Vk2
shuffle with Jk4.
The second step is Cutting, in
which the region between Vk2 and
Jk4 ,are deleted or removed.
The 3rd step is Joining, Vk2 and
Jk4 join together.
Transcription occur, DNA is
converted into pre-RNA. After
splicing, Pre-RNA is converted into
mature RNA. Finally the mature
RNA is translated into Igk light
chain(protein).
17. Assembly of the Ig μ heavy chain and one of
the light chains results in the formation of
membrane bound form of the
immunoglobulin IgM that is expressed on the
surface of the immature B cell.
18. Differnce in recombination
• When the recombination occurs in constant region. It gives idea
about “Which antibody is made”
IGG, IGM, IGA, IGE
• But when the recombination occurs in variable region
“Which subtype of antibody is made”
It makes the difference in the variable region. It makes 2 IgG
different from each other.
