AID mutates a non-immunoglobulin transgene independent of chromosomal position.
It is unknown how activation-induced cytidine deaminase (AID) targets immunoglobulin (Ig) genes during somatic hypermutation. Results to date are difficult to interpret: while some results argue that Ig genes have special sequences that mobilize AID, other work shows that non-Ig transgenes mutate. In this report, we have examined the effects of the intronic mu enhancer on the somatic hypermutation rates of a retroviral vector. For this analysis, we used centroblast-like Ramos cells to capture as much of the natural process as possible, used AIDhi and AIDlow Ramos variants to ensure that mutations are AID induced, and measured mutation of a GFP-provirus to achieve greater sensitivity. We found that mutation rates of the non-Ig provirus were AID-dependent, were similar at different genomic loci, but were approximately 10-fold lower than the V-region suggesting that AID can mutate non-Ig genes at low rates. However, the intronic mu enhancer did not increase the mutation rates of the provirus. Interestingly, exogenous over-expression of AID revealed that the V-region mutation rate can be saturated by lower levels of AID than the provirus, suggesting that selective mutation of Ig sequences is compromised in cells that over-express AID.
Department of Immunology, University of Toronto, Medical Sciences Bldg., Toronto, Canada M5S 1A8.
Jahan-Yar
JY
Parsa
Wajiha
W
Basit
Clifford L
CL
Wang
Jennifer L
JL
Gommerman
James R
JR
Carlyle
Alberto
A
Martin
D000818:Animals; D045744:Cell Line, Tumor; D002877:Chromosomes, Human; D003564:Cytidine Deaminase / Q000235:genetics* / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005803:Genes, Immunoglobulin; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000235:genetics*; D051379:Mice; D011533:Proviruses; D012190:Retroviridae; D027041:Somatic Hypermutation, Immunoglobulin; D019076:Transgenes; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D007135:Immunoglobulin Variable Region; D049452:Green Fluorescent Proteins; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase