Abundant and equipotent founder cells establish and maintain acute lymphoblastic leukaemia.

High frequencies of blasts in primary acute lymphoblastic leukaemia (ALL) samples have the potential to induce leukaemia and to engraft mice. However, it is unclear how individual ALL cells each contribute to drive leukaemic development in a bulk transplant and the extent to which these blasts vary functionally. We used cellular barcoding as a fate mapping tool to track primograft ALL blasts in vivo. Our results show that high numbers of ALL founder cells contribute at similar frequencies to leukaemic propagation over serial transplants, without any clear evidence of clonal succession. These founder cells also exhibit equal capacity to home and engraft to different organs, although stochastic processes may alter the composition in restrictive niches. Our findings enhance the stochastic stem cell model of ALL by demonstrating equal functional abilities of singular ALL blasts and show that successful treatment strategies must eradicate the entire leukaemic cell population.

Long-term in vitro maintenance of clonal abundance and leukaemia-initiating potential in acute lymphoblastic leukaemia.

Lack of suitable in vitro culture conditions for primary acute lymphoblastic leukaemia (ALL) cells severely impairs their experimental accessibility and the testing of new drugs on cell material reflecting clonal heterogeneity in patients. We show that Nestin-positive human mesenchymal stem cells (MSCs) support expansion of a range of biologically and clinically distinct patient-derived ALL samples. Adherent ALL cells showed an increased accumulation in the S phase of the cell cycle and diminished apoptosis when compared with cells in the suspension fraction. Moreover, surface expression of adhesion molecules CD34, CDH2 and CD10 increased several fold. Approximately 20% of the ALL cells were in G0 phase of the cell cycle, suggesting that MSCs may support quiescent ALL cells. Cellular barcoding demonstrated long-term preservation of clonal abundance. Expansion of ALL cells for >3 months compromised neither feeder dependence nor cancer initiating ability as judged by their engraftment potential in immunocompromised mice. Finally, we demonstrate the suitability of this co-culture approach for the investigation of drug combinations with luciferase-expressing primograft ALL cells. Taken together, we have developed a preclinical platform with patient-derived material that will facilitate the development of clinically effective combination therapies for ALL.

Differential expression of miR-17~92 identifies BCL2 as a therapeutic target in BCR-ABL-positive B-lineage acute lymphoblastic leukemia.

Despite advances in allogeneic stem cell transplantation, BCR-ABL-positive acute lymphoblastic leukaemia (ALL) remains a high-risk disease, necessitating the development of novel treatment strategies. As the known oncomir, miR-17~92, is regulated by BCR-ABL fusion in chronic myeloid leukaemia, we investigated its role in BCR-ABL translocated ALL. miR-17~92-encoded miRNAs were significantly less abundant in BCR-ABL-positive as compared to -negative ALL-cells and overexpression of miR-17~19b triggered apoptosis in a BCR-ABL-dependent manner. Stable isotope labelling of amino acids in culture (SILAC) followed by liquid chromatography and mass spectroscopy (LC-MS) identified several apoptosis-related proteins including Bcl2 as potential targets of miR-17~19b. We validated Bcl2 as a direct target of this miRNA cluster in mice and humans, and, similar to miR-17~19b overexpression, Bcl2-specific RNAi strongly induced apoptosis in BCR-ABL-positive cells. Furthermore, BCR-ABL-positive human ALL cell lines were more sensitive to pharmacological BCL2 inhibition than negative ones. Finally, in a xenograft model using patient-derived leukaemic blasts, real-time, in vivo imaging confirmed pharmacological inhibition of BCL2 as a new therapeutic strategy in BCR-ABL-positive ALL. These data demonstrate the role of miR-17~92 in regulation of apoptosis, and identify BCL2 as a therapeutic target of particular relevance in BCR-ABL-positive ALL.

Evc regulates a symmetrical response to Shh signaling in molar development.

Tooth morphogenesis involves patterning through the activity of epithelial signaling centers that, among other molecules, secrete Sonic hedgehog (Shh). While it is known that Shh responding cells need intact primary cilia for signal transduction, the roles of individual cilia components for tooth morphogenesis are poorly understood. The clinical features of individuals with Ellis-van Creveld syndrome include various dental anomalies, and we show here that absence of the cilial protein Evc in mice causes various hypo- and hyperplasia defects during molar development. During first molar development, the response to Shh signaling is progressively lost in Evc-deficient embryos and, unexpectedly, the response consistently disappears in a buccal to lingual direction. The important role of Evc for establishing the buccal-lingual axis of the developing first molar is also supported by a displaced activity of the Wnt pathway in Evc mutants. The observed growth abnormalities eventually manifest in first molar microdontia, disruption of molar segmentation and symmetry, root fusions, and delayed differentiation. Analysis of our data indicates that both spatially and temporally disrupted activities of the Shh pathway are the primary cause for the variable dental anomalies seen in patients with Ellis-van Creveld syndrome or Weyers acrodental dysostosis.

Identification of a mutation in synapsin I, a synaptic vesicle protein, in a family with epilepsy.

A four generation family is described in which some men of normal intelligence have epilepsy and others have various combinations of epilepsy, learning difficulties, macrocephaly, and aggressive behaviour. As the phenotype in this family is distinct from other X linked recessive disorders linkage studies were carried out. Linkage analysis was done using X chromosome microsatellite polymorphisms to define the interval containing the causative gene. Genes from within the region were considered possible candidates and one of these, SYN1, was screened for mutations by direct DNA sequencing of amplified products. Microsatellite analysis showed that the region between MAOB (Xp11.3) and DXS1275 (Xq12) segregated with the disease. Two point linkage analysis demonstrated linkage with DXS1039, lod score 4.06 at theta = 0, and DXS991, 3.63 at theta = 0. Candidate gene analysis led to identification of a nonsense mutation in the gene encoding synapsin I that was present in all affected family members and female carriers and was not present in 287 control chromosomes. Synapsin I is a synaptic vesicle associated protein involved in the regulation of synaptogenesis and neurotransmitter release. The SYN1 nonsense mutation that was identified is the likely cause of the phenotype in this family.

A phenotype map of the mouse X chromosome: models for human X-linked disease.

The identification of many of the transcribed genes in man and mouse is being achieved by large scale sequencing of expressed sequence tags (ESTs). Attention is now being turned to elucidating gene function and many laboratories are looking to the mouse as a model system for this phase of the genome project. Mouse mutants have long been used as a means of investigating gene function and disease pathogenesis, and recently, several large mutagenesis programs have been initiated to fulfill the burgeoning demand of functional genomics research. Nevertheless, there is a substantial existing mouse mutant resource that can be used immediately. This review summarizes the available information about the loci encoding X-linked phenotypic mutants and variants, including 40 classical mutants and 40 that have arisen from gene targeting.

Mouse mutants carrying deletions that remove the genes mutated in Coffin-Lowry syndrome and lactic acidosis.

The mouse X-linked mutants lined and stripey are associated with lethality of affected males in utero and a striping of the coat in carrier females. We demonstrate that the underlying mutations are nested deletions which lie in the Phex-Amelx chromosomal segment conserved between man and mouse. The lined deletion contains less than approximately 0.7 cM of genetic material and includes the growth factor-regulated protein kinase gene, Rsk2. Stripey carries a larger deletion which removes approximately 2.0 cM of genetic material, including Rsk2 and the pyruvate dehydrogenase E1alpha subunit gene, Pdha1 . Since Coffin-Lowry syndrome and neonatal lactic acidosis are associated with mutations in the human homologues of Rsk2 and Pdha1 respectively, lined and stripey provide models for gene deficiencies in these disorders.

An integrated genetic and man-mouse comparative map of the DXHXS674-Pdha1 region of the mouse X chromosome.

The genes for ocular albinisim type 1 (OA1) and the Xenopus laevis-like apical protein (APXL) map between amelogenin (AMELX) and the pseudoautosomal boundary in the distal region of the human X chromosome short arm. The mouse homologues, Oa1 and Apxl, have recently been shown to lie proximal to their expected locations on the mouse X chromosome, but their positions with respect to critical gene loci in the vicinity have not been defined. By analyzing recombination events from (Mus musculus x Mus spretus) x M. musculus backcrosses, we have constructed a detailed mouse genetic map that encompasses Oa1, five other genes, and 13 microsatellite loci. The order of genes and evolutionary breakpoints (EB) is defined as centromere-(EB)-(DXHXS674, DXHXS679)-Smcx-(EB)-Oa1-(EB)-Phex (3'-->5')-Pdha1-telomere. Thus Oa1 lies in a region between two previously characterized conserved segments.

The mouse X-linked developmental mutant, tattered, lies between DXMit55 and Xkh and is associated with hyperkeratinization.

The X-linked mouse mutant phenotype, tattered (Td), is associated with prenatal lethality of males and has been mapped previously to the proximal region of the mouse X chromosome. We report here a refined position for Td and demonstrate that it lies in the approximately 0.9-cM interval between DXMit55 and Xkh. This enables us to predict that the human homologue lies either between CLCN5 and the evolutionary breakpoint that lies between GATA1 and PFC or distal to XK and proximal to the evolutionary breakpoint that lies between XK and DMD. Histological analysis of dorsal skin taken from 5-day-old heterozygous animals revealed that the mutation was associated with patches of hyperkeratinzation in the epidermis and in the hair follicles, accompanied by a mild inflammatory infiltrate in the underlying dermis.

High-resolution comparative mapping of the proximal region of the mouse X chromosome.

The murine homologues of the loci for McLeod syndrome (XK), Dent's disease (CICN5), and synaptophysin (SYP) have been mapped to the proximal region of the mouse X chromosome and positioned with respect to other conserved loci in this region using a total of 948 progeny from two separate Mus musculus x Mus spretus backcrosses. In the mouse, the order of loci and evolutionary breakpoints (EB) has been established as centromere-(DXWas70, DXHXF34h)-EB-Clcn5-(Syp, DXMit55, DXMit26)-Tfe3-Gata1-EB-Xk-Cybb-telomere. In the proximal region of the human X chromosome short arm, the position of evolutionary breakpoints with respect to key loci has been established as DMD-EB-XK-PFC-EB-GATA1-C1CN5-EB-DXS1272E-ALAS2-E B-DXF34-centromere. These data have enabled us to construct a high-resolution genetic map for the approximately 3-cM interval between DXWas70 and Cybb on the mouse X chromosome, which encompasses 10 loci. This detailed map demonstrates the power of high-resolution genetic mapping in the mouse as a means of determining locus order in a small chromosomal region and of providing an accurate framework for the construction of physical maps.

A 2-Mb YAC contig encompassing three loci (DXF34, DXS14, and DXS390) that lie between Xp11.2 translocation breakpoints associated with incontinentia pigmenti type 1.

We demonstrate that all the repeat elements representing the conserved loci DXF34 and DXS390 lie between the X;9 and the X;17 translocation breakpoints associated with incontinentia pigmenti type 1 (IP1). Sequence-tagged sites (STSs) at DXF34S1, DXS14, and DXS390 have been used to isolate YAC clones containing these loci, and a contig of approximately 2 Mb has been constructed. Patterns of hybridization observed in the YAC clones indicate that DXS390 comprises two distinct regions (A and B). The STS at DXS390 detects the A region and includes a polymorphic CA repeat (PIC = 0.25). This expansion of the cloned region around DXF34 and DXS390 will enable the isolation of additional conserved sequences that will help in understanding both the lesions underlying the pathogenesis of IP1 and the size and extent of the man-mouse homologous block defined by DXF34.

New insights into the man-mouse comparative map of the X chromosome.

Two conserved loci, DXHX674h and DXHX679h, which map to Xp11.22-Xp11.21 on the human X chromosome short arm, have been positioned between the loci for proteolipid protein (Plp) and the E1a subunit of pyruvate dehydrogenase (Pdha1) in the distal region of the mouse X chromosome using Mus musculus x Mus spretus interspecific backcrosses. These data, together with previous comparative mapping studies on another conserved locus (DXF34) and the locus that encodes the erythroid transcription factor (GATA1), reveal that loci that map to the proximal region of the human X chromosome short arm lie in four different regions of the mouse X chromosome and that the human and mouse X chromosomes contain a minimum of eight conserved segments.