SOMATIC HYPERMUTATION OF A LAMBDA(2) TRANSGENE UNDER THE CONTROL OF THE LAMBDA-ENHANCER OR THE HEAVY-CHAIN INTRON ENHANCER

Previous experiments have suggested an important role for the Ig enhan cers and transcription in targeting somatic hypermutation. To determin e whether the requirement of the enhancers is Ig chain specific, we an alyzed two lambda(2) light chain transgenes under the control of diffe rent enhancers, either the lambda(2-4) enhancer or the heavy chain int ron enhancer, The transgenes were amplified and cloned from B220(+)PNA (high) B cells from either Peyer's patches (PP) or SRBC-immunized sple en, The lambda(2) transgene under the control of the lambda(2-4) enhan cer underwent mutation in both the PP and splenic & cell populations, but at a frequency lower than endogenous light chain genes, This requi rement for the lambda(2-4) enhancer could be replaced by the heavy cha in intron enhancer. interestingly, the heavy chain intron enhancer-dri ven lambda(2) construct showed evidence of statistically significant m utation in the PP B cell population, but not the spleen-derived popula tion, This difference in somatic hypermutation suggests that a lower m utation frequency can be more readily detected in B220(+)PNA(high) B c ells isolated from the PP, The ability of the heavy chain intron enhan cer to replace the lambda(2-4) enhancer shows that the requirement for the Ig enhancers in somatic hypermutation is not Ig locus specific, G iven that these Ig enhancers have very few elements in common, our res ults further suggest that the Ig enhancers are primarily important in the timing of transcription in the mutating B cell population.