igtcr基因重排原理及多样性

Chapter4The generation of lymphocyteantigen receptorsPrimary immunoglobulin gene rearrangement Antibody repertoire : 1011 in human- The total number of antibody specificitiesavailable to an individual Ig gene rearrangement in antibody producing cells- Southern blot analysisnon lymphoid cell : V,C in the distant fragmentsmature B cell : V,C in the same fragments somatic recombination Figure 4.1- V gene rearrangement Figure 4.2V region of light chain : V gene segment(VL protein) (VL gene)J gene segment(JL gene)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 segmentsfor the V region of human heavy and light chains pseudogenes : not functional proteinFigure 4.3- The germline organization of the Ig genes gene familyFigure 4.4 Rearrangement of V,D,J gene segments- DNA rearrangements are guided by conserved 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(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 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- RAG are only expressed in developing lymphocytes- Other ubiquitously expressed DNA-modifying proteins DNA ligase IV : joins the processed ends together with XRCC4 DNA-dependent protein kinase (DNA-PK) Ku : a heterodimer Ku70 : Ku80 Ku+DNA-PK+Artemis complex: a protein involved in the opening of covalently closed DNA hairpin structures- terminal deoxynucleotidyl transferase (TdT) randomly adding nucleotides- RAG genes, DNA-PK, TdT gene deficiency Severe combined immune deficiency(SCID) mouse Signal joint and coding jointFigure 4.7 The diversity of the Ig repertoire : four main process- combinatorial diversity multiple gene segments different combination different combination of H,L chain- Junctional diversity- Somatic hypermutation Combinatorial diversitykappa chain 40 5 = 200lambda chain 30 4 = 120H chain 40 25 6 = 6000- Combinatorial diversity is likely to be less from the theoretical calculation3201.9106 Junctional diversity- The diversity of CDR3 in H,L chains is 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 end of the gene segment N-nucleotides : non template-encoded- Addition of P,N nucleotide is a random process Productive or nonproductive rearrangement TCR gene segments and rearrangementFigure 4.9- The same enzyme for Ig ge