The role of homeobox gene in leukaemia

Abstract

Homeobox genes are known to be active during development and they are turned off after the early stages of developmental life. The HLXB9/MNX1 gene is a homeobox gene localized on human chromosome 7 and is involved in the development of pancreas and the nervous system. However, some leukaemia research groups have reported an over-expression of HLXB9 in leukaemia patients who carry the t(7;12) and in the GDM-1 cell line that carries the t(6;7). The mechanisms of leukaemogenesis in t(7;12) patients are still unclear. The t(7;12) is one of the recurrent cytogenetic abnormalities that is associated with infant acute myeloid leukaemia (AML) patients and has been linked to poor prognosis. The aim of this study was (i) to determine the involvement of HLXB9 in cell lines known to express this gene at the transcript level and (ii) to investigate the position on HLXB9 in AML patients with abnormalities of chromosome 7. This aim was achieved through a series of experiments involving the use of both conventional and molecular cytogenetics. In the first place, the chromosomal abnormalities in leukaemia and lymphoma cell lines (GDM-1, K562 and Pfeiffer) have been analysed using G-banding and Multiplex FISH (M-FISH) techniques. Furthermore, FISH using whole chromosome painting technique was performed on 7 AML patients to investigate chromosome 7 rearrangements. Thirdly, the involvement of the homeobox gene HLXB9 has been investigated in the acute myeloid leukaemia (AML) derived cell line GDM-1 and in 4 AML patients. Fluorescence in situ hybridization (FISH) analysis was carried out using a specific probe for the HLXB9 gene on the AML patients in single and dual colour FISH in combination with an additional probe distal to HLXB9 on the GDM-1 cell line. FISH analysis showed no involvement of the HLXB9 gene in any rearrangement or breaks at chromosomal level on the AML cell line (GDM-1) and AML patients. Nevertheless, a breakpoint either proximal or distal to HLXB9 has been identified. In particular, the breakpoint in the GDM-1 cell line has been confirmed on between the two probes used. This thesis poses the basis for further studies to investigate the mechanisms of oncogenesis in leukaemias with over-expression of HLXB9 in relation to possible breakage of chromosome 7 in the vicinity of the gene