Study of position effect as a mechanism arising from chromosomal translocations in leukaemia

Abstract

The chromosomal translocation of t(14;18)(14q32;18q21) is a characteristic aberration of follicular lymphoma and Diffuse Large B cells lymphoma. By PCR, it was proved that the rearrangement of chromosomes 14 and 18 leads to an overexpression of BCL2, an anti-apoptotic protein, which is one of the factors responsible for the maturation of the diseases. The translocation involves the promoter region of IGH gene and the transcriptional unit of BCL2 gene. Previous studies carried out in Dr Tosi’s lab showed a looping out of the BCL2 gene from its chromosome territory in 15% of the nuclei analysed. This looping out could be possibly responsible for the transcriptional activity of the gene. A further relevant finding concerns the spatial distribution of the genes involved in the translocation in the interphase nuclei. In the Pfeiffer cell line, harbouring the t(14;18) rearrangement, the translocated BCL2 gene was positioned in the cell nuclei according to a bimodal distribution. One could speculate that the distribution in the periphery and in the centre of the nuclei could divide the Pfeiffer cell line in two different subpopulations, consequently from the transcriptional activity. These preliminary data set the ground for more experimental work to test whether genes associated with the nuclear interior were transcriptionally active as opposed to the genes positioned towards the nuclear periphery, transcriptionally inactive. The work here presented focuses on this investigation using RNA-DNA FISH (Fluorescence in situ hybridization). My work enabled the detection of IGH, BCL2 and t(14;18) genes along with their transcripts inside of the nuclei of Pfeiffer cell line. Contrary to what had been hinted by previous work, my results showed multiple nuclear positions of transcriptionally active IGH/BCL2 translocation. The result will need to be further supported by software analysis in order to define its specific nuclear position and to ensure the perfect localization of the genes inside each nucleus.