B and T Cell Rec. Genes Handout 2012

8/2/2019 B and T Cell Rec. Genes Handout 2012

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B- and T-cell receptor

genes

Dept of Cell and Molecular Biology!


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Immunoglobulin Variable regions


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RNA-DNAheteroduplex

analysis ofan immuno-globulin lightchain gene

Mouse H and L chain loci!


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Variability generating mechanisms inimmunoglobulin and TCR genes!

! Germline diversity; a large number of different V, D and J segmentswhich differ in nucleotide sequence.

! Combinatorial diversity; the different V, D, and J segments can freelycombine, resulting in a large number of possible combinations(VxDxJ).

! Junctional diversity; variation in the position of the cleavage site at thejunctions between V and J segments in the light chain and the V and Dand D and J in the heavy chain (approximately +3 to -3 nt).

! P-region diversity; difference in where the ligated loops are cleavedgenerates additional diversity at the V-J, V-D and D-J joining sites.

! N-region divesity; addition or removal of up to approximately 10 bp ateither side of the D segment in the IgH and TCR! and " genes, and at

a lesser extent at V- J junctions. Generated by the enzyme TdT(Terminal doeoxy nuclotide Transferase).

! Somatic mutations; random exchange of single nucleotides (one at atime) in and around the rearranged V region. Only found in the Iggenes and not in the TCR genes.

! Free combination of light and heavy chain polypeptides (TCR # and !or TCR $ and" polypeptides)


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Variability in immunoglobulinand TCR genes!

! Total potential diversity withjunctionaldiversity;

Immunoglobulins 10 11.

TCR #! 10 16 TCR $" 10 18

! Total potential diversity with somaticmutations ;Immunoglobulins 1015-16

Transcriptional activation of the %-light chain locus!


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Transcriptional activation of the heavy andlight chain locus!


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Differences between T cell recptorsand immunoglobulins during

somatic rearrangements!


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Switch Regions

G rich, simple repetitive sequences1-10 kb in length.

IgE (&) switch region approx. 1kb.IgG1 ($1) switch region approx 10 kb.

Short 5-7 nt repeats like, GAGCT, GGGGT, GGGCT

S , S & and S # are closely related with 20,40 and 80 bp repeat units respectively.

S $ the most divergent with 49-52 bp repeat units


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!1I-exon !4!3!2

Promoter

AAAAAA

Transcriptional activation ofun-rearranged locus

Germline Transcripts (GL) are essential for switchrecombination. Activated by IL-4 and CD40-CD40L interaction.GL transcripts stimulate recombination not only by openingof chromatin. The specific transcript or splicing is ofimportance, 10-100 fold higher switch frequency with theI exon (than irrelevant transcription)

Switch region (S&)!


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Membrane and secretory forms !


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B cell developmentEarly events!


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Surface markers on peripheral B cells

Documents

B and T Cell Rec. Genes Handout 2012