Cloning and gene mapping of the mouse homologue of the CBFA2T1 gene associated with human acute myeloid leukemia

Analysis of Rex1 (zfp42) function in embryonic stem cell differentiation

Rex1 (zfp42) is a zinc finger protein expressed primarily in undifferentiated stem cells, both in the embryo and the adult. Upon all-trans retinoic acid induced differentiation of murine embryonic stem (ES) cells, Rex1 mRNA levels decrease several fold. To characterize the function(s) of Rex1 more extensively, we generated Rex1 double knockout ES cell lines. The disruption of the Rex1 gene enhanced the expression of ectoderm, mesoderm, and endoderm markers as compared to wild-type (Wt) cells. We propose that Rex1 acts to reduce retinoic acid induced differentiation in ES cells. We performed microarray analyses on Wt and Rex1-/- cells cultured in the presence or absence of LIF to identify potential Rex1 targets. We also evaluated gene expression in a Wt line that overexpresses Rex1 and in a Rex1-/- line in which Rex1 expression was restored. These data, taken together, suggest that Rex1 influences differentiation, cell cycle regulation, and cancer progression.

Genetic control of severe egg-induced immunopathology and IL-17 production in murine schistosomiasis

Infection with the trematode parasite Schistosoma mansoni results in a distinct heterogeneity of disease severity, both in humans and in an experimental mouse model. Severe disease is characterized by pronounced hepatic egg-induced granulomatous inflammation in a proinflammatory cytokine environment, whereas mild disease corresponds with reduced hepatic inflammation in a Th2 skewed cytokine environment. This marked heterogeneity indicates that genetic differences play a significant role in disease development, yet little is known about the genetic basis of dissimilar immunopathology. To investigate the role of genetic susceptibility in murine schistosomiasis, quantitative trait loci analysis was performed on F(2) progeny derived from SJL/J and C57BL/6 mice, which develop severe and mild pathology, respectively. In this study, we show that severe liver pathology in F(2) mice 7 wk after infection significantly correlated with an increase in the production of the proinflammatory cytokines IL-17, IFN-gamma, and TNF-alpha by schistosome egg Ag-stimulated mesenteric lymph node cells. Quantitative trait loci analysis identified several genetic intervals controlling immunopathology as well as IL-17 and IFN-gamma production. Egg granuloma size exhibited significant linkage to two loci, D4Mit203 and D17Mit82, both of which were inherited in a BL/6 dominant manner. Furthermore, a significant reduction of hepatic granulomatous inflammation and IL-17 production in interval-specific congenic mice demonstrated that the two identified genetic loci have a decisive effect on the development of immunopathology in murine schistosomiasis.

The ETO (MTG8) gene family

Cloning and characterization of the 8;21 chromosomal breakpoint identified AML1 on chromosome 21 and ETO (MTG8) on chromosome 8, and the resultant chimeric gene product, AML-1/ETO. The ETO gene family now includes three human members encoding proteins composed of four evolutionarily conserved domains termed nervy homology regions (NHR) 1-4. ETO associates with N-CoR/Sin3a/HDAC complexes in vivo and acts as a corepressor for the promyelocytic zinc finger protein. Moreover, ETO is nuclear matrix attached at sites coincident with histone deacetylase enzymes and mSin3a. These data suggest that ETO proteins function as transcriptional corepressors. This review focuses on the ETO gene family in terms of expression and function. Specifically, the role of ETO as a co-repressor will be detailed. Additionally, the impact of this recent discovery on treatment of t(8;21)-containing leukemia will be discussed.

Lithium treatment in ovo: effects on embryonic heart rate, natural death of ciliary ganglion neurons, and brain expression of a highly conserved chicken homolog of human MTG8/ETO

Understanding the action of the mood stabilizer lithium is dependent on availability of experimental models where lithium treatment at clinically relevant concentrations induces marked phenotypic and genotypic changes. Here we report on such changes in the chicken embryo. Lithium chloride (0.6 mM), applied in ovo 60 h after incubation, markedly delayed the heart rate increase observed from ED2.5 to ED5, and induced the brain expression of a new chicken gene cETO from ED7 to ED15. At the same time the overall developmental dynamics and embryo survival, or the expression of chicken gephyrin were not significantly affected. Furthermore, lithium treatment (0.3 mM, 48 h after incubation) abolished the difference in neuronal number between ED12 ciliary ganglia developing in the presence or absence of postganglionic target muscles. We show that cETO is a close homologue of the human transcription factor MTG8/ETO; named after its location on chromosome 8, and participation in chromosomal translocation 8;21 in myeloid leukemia. The mRNA and protein levels of ETO and gephyrin had a parallel course in chicken brain development suggesting that the expression of both genes is regulated mainly at the level of gene transcription. However, the patterns of expression were markedly different. ETO peaked at ED7 and decreased five-fold at ED15. In contrast, gephyrin levels increased five-fold from ED7 to ED15. We propose that the induction of ETO expression, in concert with lithium-induced upregulation of other genes, such as PEBP2beta and bcl-2, is participating in the neuroprotective effect of chronic lithium treatment.

Nuclear import and subnuclear localization of the proto-oncoprotein ETO (MTG8)

ETO (MTG8) was first described due to its involvement in the (8;21) translocation frequently observed in acute myeloid leukemias. In the t(8;21) the AML1 gene on chromosome 21 is fused to ETO on chromosome 8. The resultant hybrid protein is comprised of the DNA binding domain of AML-1 and the majority of ETO. This study examines the subnuclear distributions of ETO, AML-1B and AML-1/ETO proteins fused to green fluorescence protein in living cells using fluorescence microscopy. Further, we identified a 40 amino acid portion of ETO (amino acids 241-280) that was sufficient to cause nuclear import of green fluorescent protein. Mutational analysis demonstrated that lysine 265 and/or arginine 266 were required for nuclear import of ETO, but that the surrounding basic residues were not critical. ETO interacted with the nuclear import proteins importin-alpha and beta in vitro, and mutations in ETO that abolish nuclear localization also abolished the in vitro interaction with importin-alpha and beta. These data suggest that ETO enters the nucleus via an importin-mediated pathway. Additionally, ETO and AML-1/ETO co-localized to punctate nuclear bodies distinct from those containing promyelocytic leukemia protein. Nuclear body formation was dependent upon a region of ETO N-terminal to the nuclear localization signal. Thus, ETO and AML-1/ETO reside in potentially novel subnuclear compartments.

Chromosomal, in silico and in vitro expression analysis of cardiovascular-based genes encoding zinc finger proteins

Three hundred and sixty expressed sequence tags (ESTs) from human heart cDNA libraries corresponding to one hundred and twenty six unique zinc finger proteins (ZFPs) were annotated and classified into seven types of ZFPs as reported previously. Among these 126 cvbZFPs (cardiovascular-based ZFPs), the C(2)H(2)-type and the C(2)C(2)-type are the two major ZFP types which account for more than 80% of ZFP genes present in the cardiovascular system. The expression patterns of 11 randomly selected ZFP genes (at least one for each type) in normal fetal, adult and hypertrophic adult hearts, respectively, were determined using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. The results suggest that ZFPs may be involved in the processes of either developmental control (downregulated or upregulated expression) or basic cellular functional regulation (constant expression). Interestingly, PAF-1 (peroxisome assembly factor-1), a C(3)HC(4)-type ZFP (RING domain-containing ZFP) showing a downregulated expression pattern in normal tissues was found to be upregulated in hypertrophic adult heart, suggesting a possible role for this fetal gene in the pathogenesis of cardiac hypertrophy. In silico Northern analysis of 15 tissues showed that over 90% of cvbZFPs demonstrate widespread tissue distribution, suggesting the vast majority of ZFPs are functionally shared among tissues. The potential importance of transcriptional repressors in cardiovascular development and disease, such as HFHZ, was supported by the observation that one-third (39 of 126) of cvbZFPs possess this function. Of these, 26 are C(2)H(2)-type and the remaining 13 included 8 C(2)C(2)-type, 1 C(3)HC(4)-type, 1 C(2)HC(4)C(HD)-type, 2 C(3)H-type and 1 combination type. Of particular interest was the observation that ZFPs which contain a KRAB domain are the major subtype present (51. 3% of the total repressors in cvbZFPs). Chromosomal distribution analysis showed that mapping loci of cvbZFP genes are concentrated on chromosomes 1, 3, 6, 8, 10, 11, 12, 19 and X. In particular, chromosome 19 appears to be enriched in ZFP genes with C(2)H(2)-type as the predominant type present. Overall, this report provides a fundamental initial step toward understanding the potential role of ZFPs in regulating cadiac development and disease.

Comprehensive review of adult acute myelogenous leukemia: cytomorphological, enzyme cytochemical, flow cytometric immunophenotypic, and cytogenetic findings

This study reports findings from a retrospective, comprehensive review of 80 cases of adult AML in regard to cytomorphology, enzyme cytochemistry (EC), flow cytometric immunophenotyping (FCI), and chromosomal analysis. From this review, we conclude that diagnostically challenging cases can only be subtyped by combining the cytomorphology with EC, FCI, and subsequent cytogenetic results. This is particularly true in recognizing the hypogranular variant of AML,M3 (AML, M3m) and distinguishing it from other subtypes. Nonlineage expression of markers (CD1, CD2, CD4, CD5, CD7, and CD56) was nonspecific as to AML subtype. Of interest, CD2 coexpression in acute myelomonocytic leukemia with eosinophilia (M4-Eo) was exclusively associated with inversion of chromosome 16 (inv 16) and was not observed in the other M4-Eo's without inv16. We also recognized a previously undescribed M3m with CD56 coexpression, heightening awareness of this entity which needs to be distinguished from the unique subtype of CD56+ AML with otherwise similar immunophenotypic and morphologic characteristics. In addition, nonlineage expression of CD19 alone was exclusively associated with the cytogenetic finding of t (8;21) (q22; q22) and thus may represent a favorable prognostic indicator by FCI.

Polymorphism in the 3' untranslated region of MTG8 is associated with obesity in Pima Indian males

Obesity has a genetic component and predisposes for the development of type 2 diabetes mellitus. One approach to identifying new candidate genes for obesity is to explore potential regulatory factors expressed in fat tissue that may play a role in adipocyte development or metabolic control. Because we found relatively abundant mRNA levels of the putative transcription factor MTG8 in human adipose tissue, a polymorphic microsatellite marker in the 3' untranslated region of this gene was genotyped in 281 Pima Indians, a population with one of the highest reported rates of obesity. We detected a male-specific association with age-adjusted percentage body fat (p = 0.0002), body mass index (p = 0.01), waist circumference (p = 0.008), and thigh circumference (p = 0.02). Comparative analysis of all 13 MTG8 exons in 30 Pimas did not reveal any genetic variants which could explain the association with obesity in males.

Structure and expression of the human MTG8/ETO gene

Translocations involving the putative proto-oncogene MTG8/ETO on 8q22 are frequently found in acute myeloid leukemia. To date, little is known of the genomic organization of this gene. Here, we report that the MTG8 gene consists of 13 exons distributed over 87 kb of genomic DNA. Two polymorphic microsatellite repeats are described, including one in intron 3 (three alleles; heterozygosity 0.34) and another in the 3'UTR (15 alleles; heterozygosity 0.89). Expression of MTG8 was detected in a variety of normal human tissues with the highest mRNA levels occurring in brain and heart. Previously, two mRNA forms produced by the alternative usage of the first exon have been reported. We now describe a novel, abundantly expressed, alternatively spliced transcript resulting from the inclusion of a 155-bp exon (designated 9a) that changes the reading frame and introduces a premature stop codon. Identical alternatively spliced mRNA variants were found to be produced by the highly conserved homologous gene (Cbfa2t1) in the mouse, suggesting an evolutionary significance.