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Title: Analysis of the LYL-1 null mutant mouse : a possible role in haematopoietic progenitor cell mobilisation
Author: King, Emerson Randall
ISNI:       0000 0001 3599 7136
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2002
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The gene that encodes the Lymphoblastic Leukemia protein 1 (LYL-1) (Cleary, et al, 1988) was identified originally through the characterisation of a tumor specific t(7;19) chromosomal translocation involving the T-cell receptor (TCR) C[beta] gene. The LYL-1 protein is a member of the class II basic helix-loop-helix (bHLH) family of transcriptional factors (Mellentin, et al, 1989; Massari and Murre, 2000). LYL-1 forms heterodimers, both in-vitro and in-vivo, with class I bHLH proteins E2A, and HEB (Miyamoto, et al, 1996), and has been shown to interact with motifs present in the NFκB1 precursor p105 (Ferrier, et al, 1999). LYL-1 mRNA is expressed primarily within the haematopoietic system (Kuo, et al, 1991) and displays a pattern of expression that overlaps considerably with stem cell leukemia protein (SCL) (Visvader, et al, 1991). Both SCL and LYL-1 mRNA are expressed in erythroid and myeloid cell lineages as well as in megakaryocytes, but not in normal T-cells (Mellentin, et al, 1989; Mouthon, et al, 1993). LYL-1, unlike SCL, is expressed in cell lines established from leukemias of B lymphocyte origin (Visvader, et al, 1991; Miyamoto, et al, 1996). The amino acid sequence of the LYL-1 protein shares 78% overall identity with it's human counterpart (Visvader, et al, 1991; Kuo, et al, 1991) and possess an identical bHLH domain except for a conservative amino acid substitution in the loop region. Although the role of LYL-1 protein in the oncogenic transformation of T-cells has not been defined, as a consequence of the translocation it's de-regulated expression may alter the precise balance of transcriptional regulators, and thereby precipitate leukaemogenic events in T-cell. The almost identical E-box DNA-binding site for SCL and LYL-1 bHLH heterodimers (Miyamoto, et al., 1996), in conjunction with the critical function SCL haematopoiesis (Begley and Green, 1999), suggests a role for LYL-1 within the haematopoietic cells. The function of LYL-1 in haematopoiesis was examined by disruption of the LYL-1 gene by homologous recombination in ES cells. A lacZ/ neomycin gene cassette was cloned in-frame into the fourth exon, replacing a 0.7kb Hpal fragment encoding the bHLH, as well as the entire 3'- end of die LYL-1 gene. The absence of a functional LYL-1 protein was associated with increased numbers of c-Kit-positive cells, early (BFU-e) and late (CFU-e) erythroid progenitors (approximately 3-5 times) in the spleen. These progenitors generated haemoglobinised erythroblasts in vitro. More BFU-e in the LYL-1−/− spleen responded to Epo only, and in the presence of Epo and SCF some of these BFU-e produced colonies that comprised a large number of erythroid cells. In vivo, splenic erythroid progenitors and precursors expressed SCL mRNA, GATA-1, TER-119, and haemoglobin, and were distributed throughout the red pulp. LYL-1−/− spleen comprised 5 to 10-fold more erythroblasts than normal, which were arranged into clusters that often contained megakaryocytes. There was a 2-fold increase in the number of CFU- GEMM in the LYL-1−/− spleen, but no change in CFU-G. The bone marrow of LYL-1−/− mice contained 1.4-fold more CFU-e compared to LYL-1+/+ controls, but there was no change in BFU-e number. The erythroblasts in the LYL-1−/− spleen were not apoptotic. The loss of a functional LYL-1 protein was further associated with a reduction in the number of erythrocytes, and the amount of stored iron, in the spleen, but no change in the number of erythrocytes in the peripheral circulation, or in the amount of stored iron in the bone marrow. The results presented suggest that LYL-1 has a role in events associated with mobilisation of haematopoietic progenitors from the bone marrow. Expression of a non-functional LYL-1 protein in LYL-1−/− mice induced mobilisation of erythroid progenitors, followed by their expansion in the spleen.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available