Alterations in Genome Organization in Lymphoma Cell Nuclei due to the Presence of the t(14;18) Translocation.

Chromosomal rearrangements have been shown to alter genome organization, consequently having an impact on gene expression. Studies on certain types of leukemia have shown that gene expression can be exacerbated by the altered nuclear positioning of fusion genes arising from chromosomal translocations. However, studies on lymphoma have been, so far, very limited. The scope of this study was to explore genome organization in lymphoma cells carrying the t(14;18)(q32;q21) rearrangement known to results in over-expression of the BCL2 gene. In order to achieve this aim, we used fluorescence in situ hybridization to carefully map the positioning of whole chromosome territories and individual genes involved in translocation in the lymphoma-derived cell line Pfeiffer. Our data show that, although there is no obvious alteration in the positioning of the whole chromosome territories, the translocated genes may take the nuclear positioning of either of the wild-type genes. Furthermore, the BCL2 gene was looping out in a proportion of nuclei with the t(14;18) translocation but not in control nuclei without the translocation, indicating that chromosome looping may be an essential mechanism for BCL2 expression in lymphoma cells.

From FISH to Hi-C: The Chromatin Architecture of the Chromosomal Region 7q36.3, Frequently Rearranged in Leukemic Cells, Is Evolutionary Conserved.

Fluorescence in situ hybridization (FISH) and Hi-C methods are largely used to investigate the three-dimensional organization of the genome in the cell nucleus and are applied here to study the organization of genes (LMBR1, NOM1, MNX1, UBE3C, PTPRN2) localized in the human 7q36.3 band. This region contains the MNX1 gene, which is normally not expressed in human lymphocytes beyond embryonic development. However, this homeobox gene is frequently activated in leukemic cells and its expression is associated with an altered gene positioning in the leukemia cell nuclei. In this study, we used FISH on 3D-preserved nuclei to investigate the nuclear positioning of MNX1 in the leukemia-derived cell line K562. Of the five copies of the MNX1 gene present in K562, four alleles were positioned in the nuclear periphery and only one in the nuclear interior. Using the Juicebox's Hi-C dataset, we identified five chromatin loops in the 7q36.3 band, with different extensions related to the size and orientation of the genes located here, and independent from their expression levels. We identified similar loops in 11 human and three mouse cell lines, showing that these loops are highly conserved in different human cell lines and during evolution. Moreover, the chromatin loop organization is well conserved also during neuronal cell differentiation, showing consistency in genomic organization of this region in development. In this report, we show that FISH and Hi-C are two different approaches that complement one another and together give complete information on the nuclear organization of specific chromosomal regions in different conditions, including cellular differentiation and genetic diseases.

Genomic properties of chromosomal bands are linked to evolutionary rearrangements and new centromere formation in primates.

Chromosomal rearrangements in humans are largely related to pathological conditions, and phenotypic effects are also linked to alterations in the expression profile following nuclear relocation of genes between functionally different compartments, generally occupying the periphery or the inner part of the cell nuclei. On the other hand, during evolution, chromosomal rearrangements may occur apparently without damaging phenotypic effects and are visible in currently phylogenetically related species. To increase our insight into chromosomal reorganisation in the cell nucleus, we analysed 18 chromosomal regions endowed with different genomic properties in cell lines derived from eight primate species covering the entire evolutionary tree. We show that homologous loci, in spite of their evolutionary relocation along the chromosomes, generally remain localised to the same functional compartment of the cell nuclei. We conclude that evolutionarily successful chromosomal rearrangements are those that leave the nuclear position of the regions involved unchanged. On the contrary, in pathological situations, the effect typically observed is on gene structure alteration or gene nuclear reposition. Moreover, our data indicate that new centromere formation could potentially occur everywhere in the chromosomes, but only those emerging in very GC-poor/gene-poor regions, generally located in the nuclear periphery, have a high probability of being retained through evolution. This suggests that, in the cell nucleus of related species, evolutionary chromosomal reshufflings or new centromere formation does not alter the functionality of the regions involved or the interactions between different loci, thus preserving the expression pattern of orthologous genes.

Nuclear Repositioning of the Non-Translocated HLXB9 Allele in the Leukaemia Cell Line GDM-1 Harbouring a t(6;7)(q23;q36).

Transcriptionally active and inactive topologically associated domains (TADs) occupy different areas in the cell nucleus, and chromosomal rearrangements relocating TADs could determine ectopic expression of the repositioned genes. In this study, we investigated the HLXB9 gene in a myeloid leukaemia cell line, GDM-1, known to harbour a rearrangement involving chromosome 7 with a breakpoint distal to HLXB9, highly expressed in these cells. We used FISH to target the regions involved in the translocation and to distinguish the translocated chromosome from the non-translocated one in interphase nuclei. Two-dimensional analysis of the interphase FISH data indicated that the 2 HLXB9 alleles had a different localisation in the cell nuclei, with the translocated allele consistently positioned in the nuclear periphery and the normal one in the more internal portion of the nucleus, known as the transcriptionally active compartment. Our data may indicate that HLXB9 transcripts in the GDM-1 cell line do not arise from the allele located in rearranged chromosome 7, suggesting that regulation of gene expression in cancer cells harbouring chromosomal translocations might be more complex than previously thought, paving the path to further investigations on mechanisms of gene expression.

Effect of MYC and PARP Inhibitors in Ovarian Cancer Using an In Vitro Model.

BACKGROUND/AIM: The 8q24 chromosomal region, which contains the MYC and PVT1 candidate oncogenes, is amplified in carcinomas. Both genes have been involved in the etiopathogenesis of ovarian cancer (OC). In this study, we used an in vitro OC model with a known 8q24 copy number increase and in silico tools to investigate the expression of MYC/PVT1 loci and copy number variation in OC. We also assessed the effects of rucaparib (a PARP inhibitor) in the presence or absence of 10058F4 (a MYC inhibitor) on the expression of MYC/linear PVT1/circular PVT1. MATERIALS AND METHODS: Tissue culture, chromosome preparation, RNA extraction, RT-qPCR, FISH, and wound healing assays were employed. OncoDB, cBioportal, UALKAN, and ROC Plotter in silico tools were also utilized. RESULTS: Although PVT1 and MYC expression levels remained unaltered in OC, putative copy number alterations across all cancers showed a marked difference between the two genes, particularly in gain and amplification for MYC. PVT1 expression demonstrated prognostic value for the treatment of patients with serous and endometrioid OC. Both genes correlated with PARP10, FAM83H, and DEPTOR. The use of rucaparib in the presence or absence of the MYC inhibitor (10058F4) in vitro, led to a significant down-regulation in the expression of MYC, linear, and circular PVT1. CONCLUSION: Our data provide a novel insight into the potential interactions of MYC and PVT1 with other genes. Moreover, we identified a new PARP inhibition mechanism down-regulating MYC, as well as the linear and circular PVT1 transcripts. Future work should expand on clinical studies to better understand the prognostic role of PVT1 in OC.

Mechanisms associated with t(7;12) acute myeloid leukaemia: from genetics to potential treatment targets.

Acute myeloid leukaemia (AML), typically a disease of elderly adults, affects 8 children per million each year, with the highest paediatric incidence in infants aged 0-2 of 18 per million. Recurrent cytogenetic abnormalities contribute to leukaemia pathogenesis and are an important determinant of leukaemia classification. The t(7;12)(q36;p13) translocation is a high-risk AML subtype exclusively associated with infants and represents the second most common abnormality in this age group. Mechanisms of t(7;12) leukaemogenesis remain poorly understood. The translocation relocates the entire MNX1 gene within the ETV6 locus, but a fusion transcript is present in only half of the patients and its significance is unclear. Instead, research has focused on ectopic MNX1 expression, a defining feature of t(7;12) leukaemia, which has nevertheless failed to produce transformation in conventional disease models. Recently, advances in genome editing technologies have made it possible to recreate the t(7;12) rearrangement at the chromosomal level. Together with recent studies of MNX1 involvement using murine in vivo, in vitro, and organoid-based leukaemia models, specific investigation on the biology of t(7;12) can provide new insights into this AML subtype. In this review, we provide a comprehensive up-to-date analysis of the biological features of t(7;12), and discuss recent advances in mechanistic understanding of the disease which may deliver much-needed therapeutic opportunities to a leukaemia of notoriously poor prognosis.

Pan-Cancer Analysis Identifies MNX1 and Associated Antisense Transcripts as Biomarkers for Cancer.

The identification of diagnostic and prognostic biomarkers is a major objective in improving clinical outcomes in cancer, which has been facilitated by the availability of high-throughput gene expression data. A growing interest in non-coding genomic regions has identified dysregulation of long non-coding RNAs (lncRNAs) in several malignancies, suggesting a potential use as biomarkers. In this study, we leveraged data from large-scale sequencing projects to uncover the expression patterns of the MNX1 gene and its associated lncRNAs MNX1-AS1 and MNX1-AS2 in solid tumours. Despite many reports describing MNX1 overexpression in several cancers, limited studies exist on MNX1-AS1 and MNX1-AS2 and their potential as biomarkers. By employing clustering methods to visualise multi-gene relationships, we identified a discriminative power of the three genes in distinguishing tumour vs. normal samples in several cancers of the gastrointestinal tract and reproductive systems, as well as in discerning oesophageal and testicular cancer histological subtypes. Notably, the expressions of MNX1 and its antisenses also correlated with clinical features and endpoints, uncovering previously unreported associations. This work highlights the advantages of using combinatory expression patterns of non-coding transcripts of differentially expressed genes as clinical evaluators and identifies MNX1, MNX1-AS1, and MNX1-AS2 expressions as robust candidate biomarkers for clinical applications.

Alterations to Genome Organisation in Stem Cells, Their Differentiation and Associated Diseases.

The organisation of the genome in its home, the cell nucleus, is reliant on a number of different aspects to establish, maintain and alter its functional non-random positioning. The genome is dispersed throughout a cell nucleus in specific chromosome territories which are further divided into topologically associated domains (TADs), where regions of the genome from different and the same chromosomes come together. This organisation is both controlled by DNA and chromatin epigenetic modification and the association of the genome with nuclear structures such as the nuclear lamina, the nucleolus and nuclear bodies and speckles. Indeed, sequences that are associated with the first two structures mentioned are termed lamina-associated domains (LADs) and nucleolar-associated domains (NADs), respectively. The modifications and nuclear structures that regulate genome function are altered through a cell's life from stem cell to differentiated cell through to reversible quiescence and irreversible senescence, and hence impacting on genome organisation, altering it to silence specific genes and permit others to be expressed in a controlled way in different cell types and cell cycle statuses. The structures and enzymes and thus the organisation of the genome can also be deleteriously affected, leading to disease and/or premature ageing.

Engineered model of t(7;12)(q36;p13) AML recapitulates patient-specific features and gene expression profiles.

Acute myeloid leukaemia carrying the translocation t(7;12)(q36;p13) is an adverse-risk leukaemia uniquely observed in infants. Despite constituting up to 30% of cases in under 2-year-olds, it remains poorly understood. Known molecular features are ectopic overexpression of the MNX1 gene and generation of a fusion transcript in 50% of patients. Lack of research models has hindered understanding of t(7;12) biology, which has historically focused on MNX1 overexpression rather than the cytogenetic entity itself. Here, we employed CRISPR/Cas9 to generate t(7;12) in the human K562 cell line, and in healthy CD34+ haematopoietic progenitors where the translocation was not sustained in long-term cultures or through serial replating. In contrast, in K562 cells, t(7;12) was propagated in self-renewing clonogenic assays, with sustained myeloid bias in colony formation and baseline depletion of erythroid signatures. Nuclear localisation analysis revealed repositioning of the translocated MNX1 locus to the interior of t(7;12)-harbouring K562 nuclei - a known phenomenon in t(7;12) patients which associates with ectopic overexpression of MNX1. Crucially, the K562-t(7;12) model successfully recapitulated the transcriptional landscape of t(7;12) patient leukaemia. In summary, we engineered a clinically-relevant model of t(7;12) acute myeloid leukaemia with the potential to unravel targetable molecular mechanisms of disease.

Preclinical Studies on the Effect of Rucaparib in Ovarian Cancer: Impact of BRCA2 Status.

BACKGROUND: Approximately 50% of ovarian cancer patients harbour homologous recombination repair deficiencies. These deficiencies have been successfully targeted using poly (ADP-ribose) polymerase inhibitors (PARPi) particularly for patients harbouring BRCA1/2 mutations. The aim of this study is to assess the effects of the PARPi rucaparib in vitro using cell lines with BRCA2 mutations in comparison to those with BRCA2 wild type. METHODS: Cell proliferation assays, RT-qPCR, immunofluorescence, annexin V/PI assays were used to assess the effects of rucaparib in vitro. RESULTS: The BRCA2 mutant ovarian cancer cell line PEO1 exhibited higher PARP1 activity when treated with H2O2 compared to wild type cell lines. The migratory and proliferative capacity of PEO1 cells was compromised following treatment with rucaparib 10 µM compared to BRCA2 wild-type cell lines via a mechanism involving the mTOR pathway. Rucaparib treatment significantly increased DNA damage primarily in PEO1 cells and SKOV3 cells compared with wild type. CONCLUSIONS: Appropriate identification of robust predictive biomarkers for homologous recombination deficiency using 'liquid' biopsies would facilitate the identification of patients suitable for PARPi therapy. Preliminary efforts to undertake such testing are described here. This study also demonstrates the mechanisms of action of rucaparib (PARPi) which may involve elements of the mTOR pathway.

Chromosomal Rearrangements and Altered Nuclear Organization: Recent Mechanistic Models in Cancer.

The last decade has seen significant progress in understanding how the genome is organized spatially within interphase nuclei. Recent analyses have confirmed earlier molecular cytogenetic studies on chromosome positioning within interphase nuclei and provided new information about the topologically associated domains (TADs). Examining the nuances of how genomes are organized within interphase nuclei will provide information fundamental to understanding gene regulation and expression in health and disease. Indeed, the radial spatial positioning of individual gene loci within nuclei has been associated with up- and down-regulation of specific genes, and disruption of normal genome organization within nuclei will result in compromised cellular health. In cancer cells, where reorganization of the nuclear architecture may occur in the presence of chromosomal rearrangements such as translocations, inversions, or deletions, gene repositioning can change their expression. To date, very few studies have focused on radial gene positioning and the correlation to gene expression in cancers. Further investigations would improve our understanding of the biological mechanisms at the basis of cancer and, in particular, in leukemia initiation and progression, especially in those cases where the molecular consequences of chromosomal rearrangements are still unclear. In this review, we summarize the main milestones in the field of genome organization in the nucleus and the alterations to this organization that can lead to cancer diseases.

Mutations of NFKBIA, encoding IkappaB alpha, are a recurrent finding in classical Hodgkin lymphoma but are not a unifying feature of non-EBV-associated cases.

A consistent feature of the Hodgkin and Reed-Sternberg (HRS) cells in classical Hodgkin lymphoma (cHL) is the constitutive activation of NF-kappaB transcription factors. In Epstein-Barr virus (EBV)-associated cases of cHL, expression of viral antigens most probably leads to NF-kappaB activation but for non-EBV-associated cases, the mechanism is not clear. Previous small studies have demonstrated deleterious mutations of NFKBIA, the gene encoding IkappaB alpha, in HRS cells. In the present study, we aimed to establish the frequency of NFKBIA mutation in cHL by investigating a larger series of cases and to determine whether these mutations are a characteristic feature of non-EBV-associated cHL. Single HRS cells from 20 cases of cHL were analysed by PCRs covering all 6 exons of the gene. Clonal deleterious mutations were detected in 3 cases and in 1 case both alleles of the gene were shown to harbour mutations. NFKBIA mutations were detected only in non-EBV-associated cases but the majority of these cases had wild-type NFKBIA. It remains possible that defects in genes encoding other inhibitors of NF-kappaB, such as TNFAIP3 (A20) and CYLD, are involved in the latter cases, as described for one case in this series.

MLL-Rearranged Acute Leukemia with t(4;11)(q21;q23)-Current Treatment Options. Is There a Role for CAR-T Cell Therapy?

The MLL (mixed-lineage leukemia) gene, located on chromosome 11q23, is involved in chromosomal translocations in a subtype of acute leukemia, which represents approximately 10% of acute lymphoblastic leukemia and 2.8% of acute myeloid leukemia cases. These translocations form fusions with various genes, of which more than 80 partner genes for MLL have been identified. The most recurrent fusion partner in MLL rearrangements (MLL-r) is AF4, mapping at chromosome 4q21, accounting for approximately 36% of MLL-r leukemia and particularly prevalent in MLL-r acute lymphoblastic leukemia (ALL) cases (57%). MLL-r leukemia is associated with a sudden onset, aggressive progression, and notoriously poor prognosis in comparison to non-MLL-r leukemias. Despite modern chemotherapeutic interventions and the use of hematopoietic stem cell transplantations, infants, children, and adults with MLL-r leukemia generally have poor prognosis and response to these treatments. Based on the frequency of patients who relapse, do not achieve complete remission, or have brief event-free survival, there is a clear clinical need for a new effective therapy. In this review, we outline the current therapy options for MLL-r patients and the potential application of CAR-T therapy.

The RS4;11 cell line as a model for leukaemia with t(4;11)(q21;q23): Revised characterisation of cytogenetic features.

BACKGROUND: Haematological malignancies harbouring rearrangements of the KMT2A gene represent a unique subtype of leukaemia, with biphenotypic clinical manifestations, a rapid and aggressive onset, and a generally poor prognosis. Chromosomal translocations involving KMT2A often cause the formation of oncogenic fusion genes, such as the most common translocation t(4;11)(q21;q23) producing the KMT2A-AFF1 chimera. AIM: The aim of this study was to confirm and review the cytogenetic and molecular features of the KMT2A-rearranged RS4;11 cell line and put those in context with other reports of cell lines also harbouring a t(4;11) rearrangement. METHODS AND RESULTS: The main chromosomal rearrangements t(4;11)(q21;q23) and i(7q), described when the cell line was first established, were confirmed by fluorescence in situ hybridisation (FISH) and 24-colour karyotyping by M-FISH. Additional cytogenetic abnormalities were investigated by further FISH experiments, including the presence of trisomy 18 as a clonal abnormality and the discovery of one chromosome 8 being an i(8q), which indicates a duplication of the oncogene MYC. A homozygous deletion of 9p21 containing the tumour-suppressor genes CDKN2A and CDKN2B was also revealed by FISH. The production of the fusion transcript KMT2A-AFF1 arising from the der(11)t(4;11) was confirmed by RT-PCR, but sequencing of the amplified fragment revealed the presence of multiple isoforms. Two transcript variants, resulting from alternative splicing, were identified differing in one glutamine residue in the translated protein. CONCLUSION: As karyotype evolution is a common issue in cell lines, we highlight the need to monitor cell lines in order to re-confirm their characteristics over time. We also reviewed the literature to provide a comparison of key features of several cell lines harbouring a t(4;11). This would guide scientists in selecting the most suitable research model for this particular type of KMT2A-leukaemia.

Deletions of Chromosome 7q Affect Nuclear Organization and HLXB9Gene Expression in Hematological Disorders.

The radial spatial positioning of individual gene loci within interphase nuclei has been associated with up- and downregulation of their expression. In cancer, the genome organization may become disturbed due to chromosomal abnormalities, such as translocations or deletions, resulting in the repositioning of genes and alteration of gene expression with oncogenic consequences. In this study, we analyzed the nuclear repositioning of HLXB9 (also called MNX1), mapping at 7q36.3, in patients with hematological disorders carrying interstitial deletions of 7q of various extents, with a distal breakpoint in 7q36. We observed that HLXB9 remains at the nuclear periphery, or is repositioned towards the nuclear interior, depending upon the compositional properties of the chromosomal regions involved in the rearrangement. For instance, a proximal breakpoint leading the guanine-cytosine (GC)-poor band 7q21 near 7q36 would bring HLXB9 to the nuclear periphery, whereas breakpoints that join the GC-rich band 7q22 to 7q36 would bring HLXB9 to the nuclear interior. This nuclear repositioning is associated with transcriptional changes, with HLXB9 in the nuclear interior becoming upregulated. Here we report an in cis rearrangement, involving one single chromosome altering gene behavior. Furthermore, we propose a mechanistic model for chromatin reorganization that affects gene expression via the influences of new chromatin neighborhoods.

Graft versus leukemia effect after haploidentical HSCT in a MLL-negative infant AML with HLXB9/ETV6 rearrangement.

Recently published data show an extremely poor survival of infants with AML and HLXB9/ETV6 rearrangement which is the fusion, resulting from the translocation t(7;12)(q36;p13). None of the patients reported survived a period of 3 years, including four patients who have received allogeneic hematopoietic stem cell transplantation (HSCT). Herein, we report the clinical course of an 8-month-old patient with acute myeloid leukemia, M2 subtype and with a HLXB9/TEL rearrangement. The patient received a haploidentical HSCT in relapse situation without any prior re-induction. The patient became MRD-negative over a period of 53 days after HSCT. This case reinforces the potential benefit of a graft-versus-leukemia effect in the haploidentical setting even in chemoresistant myeloid leukemias with poor-prognosis molecular features.

Detection of Helicobacter spp. DNA in the oral cavity of dogs.

The mode of acquisition of gastric Helicobacter spp. infection in dogs has not been determined. It is suspected that oral-oral and faecal-oral transmission may be involved. The present study sought to determine if Helicobacter spp. DNA is present in the oral cavity of healthy and vomiting dogs. Thirty-eight pet dogs (27 vomiting and 11 clinically healthy) were studied. The presence of Helicobacter spp. was determined by single and nested PCR evaluation of DNA extracted from saliva, dental plaque and gastric biopsy samples. Helicobacter spp. DNA was detected by nested PCR in 36 (94.7%) gastric biopsies, 17 (44.7%) dental plaque and 19 (50%) saliva samples out of the 38 dogs examined. Overall 27 (71.1%) dogs screened by nested PCR were found to harbour Helicobacter spp. DNA in the oral cavity (dental plaque and/or saliva). There was no significant difference in the prevalence of Helicobacter spp. DNA in the oral cavity of vomiting and healthy dogs, and the time from vomiting to oral sampling did not have significant impact. This study confirms the high prevalence of gastric Helicobacter spp. infection in dogs, and reveals that Helicobacter spp. DNA is detectable in the oral cavity of over 70% of dogs. These findings support the possibility of oral-oral transmission between dogs and that the canine oral cavity may act as source of non-pylori Helicobacter spp. infection for humans.

Folate deficiency as predisposing factor for childhood leukaemia: a review of the literature.

BACKGROUND: Folic acid and its derivates, known as folates, are chemoprotective micronutrients of great interest because of their essential role in the maintenance of health and genomic integrity. The supplementation of folic acid during pregnancy has long been known to reduce the risk of neural tube defects (NTDs) in the foetus. Folate metabolism can be altered by many factors, including adequate intake through diet. Folate deficiency can compromise the synthesis, repair and methylation of DNA, with deleterious consequences on genomic stability and gene expression. These processes are known to be altered in chronic diseases, including cancer and cardiovascular diseases. MAIN BODY: This review focuses on the association between folate intake and the risk of childhood leukaemia. Having compiled and analysed studies from the literature, we show the documented effects of folates on the genome and their role in cancer prevention and progression with particular emphasis on DNA methylation modifications. These changes are of crucial importance during pregnancy, as maternal diet has a profound impact on the metabolic and physiological functions of the foetus and the susceptibility to disease in later life. Folate deficiency is capable of modifying the methylation status of certain genes at birth in both animals and humans, with potential pathogenic and tumorigenic effects on the progeny. Pre-existing genetic polymorphisms can modify the metabolic network of folates and influence the risk of cancer, including childhood leukaemias. The protective effects of folic acid might be dose dependent, as excessive folic acid could have the adverse effect of nourishing certain types of tumours. CONCLUSION: Overall, maternal folic acid supplementation before and during pregnancy seems to confer protection against the risk of childhood leukaemia in the offspring. The optimal folic acid requirements and supplementation doses need to be established, especially in conjunction with other vitamins in order to determine the most successful combinations of nutrients to maintain genomic health and wellbeing. Further research is therefore needed to uncover the role of maternal diet as a whole, as it represents a main factor capable of inducing permanent changes in the foetus.

Paediatric acute myeloid leukaemia with the t(7;12)(q36;p13) rearrangement: a review of the biological and clinical management aspects.

The presence of chromosomal abnormalities is one of the most important criteria for leukaemia diagnosis and management. Infant leukaemia is a rare disease that affects children in their first year of life. It has been estimated that approximately one third of infants with acute myeloid leukaemia harbour the t(7;12)(q36;p13) rearrangement in their leukaemic blasts. However, the WHO classification of acute myeloid leukaemia does not yet include the t(7;12) as a separate entity among the different genetic subtypes, although the presence of this chromosomal abnormality has been associated with an extremely poor clinical outcome. Currently, there is no consensus treatment for t(7;12) leukaemia patients. However, with the inferior outcome with the standard induction therapy, stem cell transplantation may offer a better chance for disease control. A better insight into the chromosome biology of this entity might shed some light into the pathogenic mechanisms arising from this chromosomal translocation, that at present are not fully understood. Further work is needed to improve our understanding of the molecular and genetic basis of this disorder. This will hopefully open some grounds for possible tailored treatment for this subset of very young patients with inferior disease outcome. This review aims at highlighting the cytogenetic features that characterise the t(7;12) leukaemias for a better detection of the abnormality in the diagnostic setting. We also review treatment and clinical outcome in the cases reported to date.

Human homologue of a gene mutated in the slow Wallerian degeneration (C57BL/Wld(s)) mouse.

The slow Wallerian degeneration mouse (C57BL/Wld(s)) is a mutant strain of mouse, with the unique phenotype of prolonged survival of the distal axon following axotomy. The causative mutation is an 85 kb tandem triplication on distal mouse chromosome 4. The dominant slow Wallerian degeneration phenotype is conferred by a hybrid gene within the triplication, comprising a gene of previously unknown function, D4Cole1e, and the 5' end of ubiquitination factor E4B (Ube4b). It encodes an in-frame fusion protein consisting of the N-terminal 70 amino acids of Ube4b and 303 amino acids derived from the D4Cole1e gene. We have identified the human homologue of D4Cole1e, and mapped it to chromosome 1p36.2. Additional fluorescence in situ hybridisation signals indicate the presence of several homologous human sequences. Northern blot analysis shows two transcripts, widely expressed at varying levels in different human tissues. The human cDNA, which encodes a protein of 279 amino acids, has 80% nucleotide identity with the mouse cDNA. The derived human and mouse protein sequences share 78% amino acid identity and 82% amino acid similarity. The human cDNA and protein sequences are identical to the human nicotinamide mononucleotide adenylyltransferase (NMNAT). We have also determined the intron/exon structure of the gene, which will facilitate the screening of these exons for mutations in human neurodegenerative disorders.