IgTCR基因重排原理及多样性

H chain
40 Ⅹ 25 Ⅹ 6 = 6000
1.9106
- Combinatorial diversity is likely to be less from the
theoretical calculation
• Junctional diversity
- The diversity of CDR3 in H,L chains is
closed DNA hairpin structures
- terminal deoxynucleotidyl transferase (TdT)
⇒ randomly adding nucleotides
- RAG genes, DNA-PK, TdT gene deficiency
⇒ Severe combined immune deficiency(SCID) mouse
Chapter4 The generation of lymphocyte
antigen receptors
Primary immunoglobulin gene rearrangement
• Antibody repertoire : 1011 in human - The total number of antibody specificities available to an individual
significantly increased by the addition and
deletion of nucleotides
Figure 4.8
- The added nucleotide are known as P-nucleotides
and N-nucleotides
• P-nucleotides : palindromic sequences at the
• Signal joint and coding joint
• The diversity of the Ig repertoire : four main process
- combinatorial diversity
• multiple gene segments ⇒ different combination
- RAG are only expressed in developing lymphocytes
- Other ubiquitously expressed DNA-modifying proteins
• DNA ligase IV : joins the processed ends together with XRCC4
- The germline organization of the Ig genes gene family Figure 4.4
• Rearrangement of V,D,J gene segments
- DNA rearrangements are guided by conserved
V region of heavy chain : V gene segment
(VH protein)
(VH gene)
D gene segment
(DH gene)
J gene segment
(JH gene)
- The numbers of functional gene segments for the V region of human heavy and light chains ′ pseudogenes ′ : not functional protein Figure 4.3
(12/23)
- 12/23 rule
- exception : D-D joining (fusion) in human ≈ 5%
- two mode of rearrangement
Figure 4.6
• looping out and deletion : more common • no deletion
• different combination of H,L chain
- ctional diversity
- Somatic hypermutation
• Combinatorial diversity
kappa chain 40Ⅹ 5 = 200 320 lambda chain 30Ⅹ 4 = 120
• Ig gene rearrangement in antibody producing cells
- Southern blot analysis
non lymphoid cell : V,C in the distant fragments
mature B cell : V,C in the same fragments
end of the gene segment
• N-nucleotides : non template-encoded
- Addition of P,N nucleotide is a random process
⇒ Productive or nonproductive rearrangement
noncoding DNA sequence
Figure 4.5
(recombination signal sequence, RSS)
• heptamer : contiguous with the coding sequence • space : 12 or 23 nucleotides long • nonamer : second conserved sequence - coding sequence-heptamer-space-nonamer
- The numbers of human TCR gene segment Figure 4.12
• Enzymatic steps in the gene rearrangement
- RAG (Recombination Activating Genes RAG-1,RAG-2)
protein complexes bind to RSSs
⇒ make single-strand DNA breaks at sites 5′ of each RSS
TCR gene rearrangement
• TCR gene segments and rearrangement Figure 4.9
- The same enzyme for Ig gene rearrangement can be used for TCR gene rearrangement Figure 4.10, Figure 4.11
• DNA-dependent protein kinase (DNA-PK)
• Ku : a heterodimer Ku70 : Ku80
Figure 4.7
• Ku+DNA-PK+Artemis ⇒ complex
: a protein involved in the opening of covalently
⇒ somatic recombination Figure 4.1
- V gene rearrangement
Figure 4.2
V region of light chain : V gene segment
(VL protein)
(VL gene)
J gene segment
(JL gene)