Hs.568769 and DNTT (TdT): ‘partners in crime’ in a novel t(5;10) translocation in ALL?
Molecular dissection of chromosome translocations has identified many genes important to the cause or progression of leukaemia. Aside from their diagnostic and prognostic value, the identification of these genes is critical to our understanding of leukaemogenesis and a necessary precedent to the design of targeted, less toxic treatments. However, the genetic basis of up to 40% of acute lymphoblastic leukaemia (ALL) cases remains unknown. We hypothesize that novel chromosome translocations may mark the location of genes potentially rearranged more frequently by cryptic submicroscopic mechanisms in leukaemia patients.
We have targeted the breakpoints of a novel t(5;10)(q22;q24) translocation found as the sole abnormality in the leukaemic cells of a 59 year old male with ALL. Our positional cloning efforts using a combination of fluorescent in situ hybridization, large-insert bacterial-, yeast- and P1-artificial chromosome (BAC, YAC, PAC) clones, end-sequencing, in silico analyses, leukemic t(5;10) metaphase studies, custom PCR analyses and Southern hybridization studies of patient DNA, have mapped the 10q24 breakpoint to a 700 bp genomic region, physically disrupting UniGene Hs.568769 which encodes a novel RNA transcript. Using RACE and Northern blot analyses we have confirmed the unique transcriptional activity of Hs.568769, a novel gene now newly implicated in this case of ALL.
Chromosome 5 sequences abnormally fused to Hs.568769 disrupts its normal transcription and unknown function, and potentially links it to the etiology of this ALL. In addition, Hs.568769 overlaps the promoter of the deoxynucleotidyltransferase terminal (DNTT) gene, transcribing from within, DNTT intron 1 in the opposite direction. This is a tightly regulated genomic region directly involved in lymphocyte development that has not previously been associated with leukaemia, although suspicions have previously fallen on DNTT which exhibits unexplained abnormal activity in many leukaemias.