ABNORMAL REARRANGEMENTS ASSOCIATED WITH V(D)J RECOMBINATION IN FANCONI-ANEMIA

The hallmark of Fanconi anemia (FA), a rare inherited cancer prone dis order, is a high level of chromosome breakage, spontaneous and induced by cross-linking agents. The increased genomic instability of FA is r eflected at the gene level by an overproduction of intragenic deletion s. Two of the eight FA genes have been cloned, however, their function remains unknown. We recently demonstrated that the lack of functional FA genes lead to a marked decrease in the fidelity of non-homologous end-joining, a pathway that mammalian cells predominantly use to repai r DNA double-strand breaks (DSB). Knowing that specific DSB are genera ted during V(D)J recombination, here we have examined the molecular fe atures of V(D)J rearrangements in normal and FA lymphoblasts belonging to complementation groups C and D. Using appropriate extrachromosomal recombination substrates, V(D)J coding and signal joint formation hav e been analysed quantitatively and qualitatively. Our results show tha t the frequency of coding and signal joint formation was not significa ntly different in normal and FA cells. However, when the fidelity of t he V(D)J reaction was examined, we found that in normal human lymphobl asts V(D)J recombination proceeds with high precision whereas, in FA c ells a several fold increase in the frequency of aberrant rearrangemen ts is associated with V(D)J coding joint formation. The abnormal recom binants that we recovered in FA are consistent with excessive degradat ion of DNA ends generated during the V(D)J reaction. On the basis of t hese findings, we propose a working model in which FA genes play a rol e in the control of the fidelity of rejoining of specific DNA ends. Su ch a defect may: explain several basic features of FA, such as chromos omal instability and deletion proneness. (C) 1998 Academic Press.