Guikema Jeroen E J, de Boer Conny, Haralambieva Eugenia, Smit Laura A, van Noesel Carel J M, Schuuring Ed, Kluin Philip M
Department of Pathology and Laboratory Medicine, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
Genes Chromosomes Cancer. 2006 Sep;45(9):808-19. doi: 10.1002/gcc.20345.
Most chromosomal t(8;14) translocations in sporadic Burkitt lymphomas (BL) are mediated by immunoglobulin class switch recombination (CSR), yet all tumors express IgM, suggesting an incomplete or exclusively monoallelic CSR event. We studied the exact configuration of both the nontranslocated IGH allele and the MYC/IGH breakpoint by applying a combination of low- and high-resolution methods (interphase FISH, DNA fiber FISH, long-distance PCR, and Southern blotting) on 16 BL. IGH class switch events involving the nontranslocated IGH allele were not observed. Thirteen cases had MYC/IGH breakpoints in or nearby IGH switch (S) sites, including five at Smu, three at Sgamma and five at Salpha. All eight translocations with a breakpoint at Sgamma or Salpha were perfectly reciprocal, without deletion of Cmu-Cdelta or other CH elements. Internal Smu deletions claimed to be a marker for CSR activity and implicated in stabilization of IgM expression were found in BL but did not correlate with downstream translocation events. This study shows that switch breakpoints in sporadic BL are exclusively resolved by a noncanonical recombination mechanism involving only one switch region.
