SOMATIC HYPERMUTATION
SOMATIC HYPERMUTATION
Desh Bandhu
10/pbt/006
Contents
1-Introduction
2-Molecules involve in SHM
3-Model of SHM
4-Future Directions
Introduction
• somatic hypermutation (SHM) is a diversity
generating, regulated cellular mechanism
displayed by the adaptive immune response.
• Somatic Hypermutation adds diversity in already
Rearranged Gene Segments.
• Somatic hypermutation occurs at a frequency of
10¯3/base pair/ generation, than the spontaneous
mutation rate about 10⁻8/bp/generation.
• This Rate is higher hence the name, hypermutation.
• These mutations occur mostly at “hotspots” in the DNA, known as hypervariable regions.
• These regions correspond to the complementarity determining regions, the sites involved in antigen recognition on the antibody.
• These mutation result from nucleotide substitution rather than addition or deletion.
• They influence the process of affinity maturation of B cells.
• Affinity maturation leads to increase the affinity of antibodies for a particular antigen.
Molecules involved in SHM
• IgM antibodies expressing V regions that have undergone SHM, as well as IgG and IgA antibodies with no somatic mutations.
• Activation-induced cytidine deaminase: A B cell-specific protein required for SHM.
• Uracil N-glycosylase: Removing uracil generated by AID deamination.
• Mismatch repair proteins: Mismatch repair (MMR) normally maintains genomic integrity.
• MMR eliminates mutations that arise spontaneously in the genome.
• Error-prone DNA polymerases: increase mutation rate.
Model of somatic hypermutation
Future directions
Evolving protein in mammalian cell using SHM
SHM cell with the target gene integrated in the genome
cell population with the target gene mutated
cells with the desired phenotype amplified cells with the desired phenotype
isolate and characterize
SHM Plateform
To Produce New Fluorescent Proteins
• Tsien’s group has cloned a red fluorescent protein (RFP) into human B-cells and allowed them to make variants that could then be isolated based on their colors by flow-cytometry.
Questions??