A novel selection system for chromosome translocations in Saccharomyces cerevisiae

Chromosomal translocations are common genetic abnormalities found in both leukemias and solid tumors. While much has been learned about the effects of specific translocations on cell proliferation, much less is known about what causes these chromosome rearrangements. This article describes the development and use of a system that genetically selects for rare translocation events using the yeast Saccharomyces cerevisiae. A translocation YAC was created that contains the breakpoint cluster region from the human MLL gene, a gene frequently involved in translocations in leukemia patients, flanked by positive and negative selection markers. A translocation between the YAC and a yeast chromosome, whose breakpoint falls within the MLL DNA, physically separates the markers and forms the basis for the selection. When RAD52 is deleted, essentially all of the selected and screened cells contain simple translocations. The detectable translocation rates are the same in haploids and diploids, although the mechanisms involved and true translocation rates may be distinct. A unique double-strand break induced within the MLL sequences increases the number of detectable translocation events 100- to 1000-fold. This novel system provides a tractable assay for answering basic mechanistic questions about the development of chromosomal translocations.     

Partial trisomy for the distal part of the short arm of chromosome 11 due to paternal translocations 11/5]

A girl with partial trisomy for the short arm of chromosome 11 resulting from an unbalanced translocation 46,XX,der 5, t(5,11) (p 15,p14) pat is described. The clinical findings are compared with those of other patients with partial trisomy 11p. The translocation in the balanced form was present in the fater, the brother, and the grandmother of the proposita.     

A strategy for generation and balancing of autosome: Y chromosome translocations

We describe a method for generation and maintenance of translocations that move large autosomal segments onto the Y chromosome. Using this strategy we produced (2;Y) translocations that relocate between 1.5 and 4.8 Mb of the 2^nd chromosome.. All translocations were easily balanced over a male-specific lethal 1 (msl-1) mutant chromosome. Both halves of the translocation carry visible markers, as well as P-element ends that enable molecular confirmation. Halves of these translocations can be separated to produce offspring with duplications and with lethal second chromosome deficiencies . Such large deficiencies are otherwise tedious to generate and maintain.     

A strategy for generation and balancing of autosome: Y chromosome translocations

We describe a method for generation and maintenance of translocations that move large autosomal segments onto the Y chromosome. Using this strategy we produced (2;Y) translocations that relocate between 1.5 and 4.8 Mb of the 2^nd chromosome.. All translocations were easily balanced over a male-specific lethal 1 (msl-1) mutant chromosome. Both halves of the translocation carry visible markers, as well as P-element ends that enable molecular confirmation. Halves of these translocations can be separated to produce offspring with duplications and with lethal second chromosome deficiencies . Such large deficiencies are otherwise tedious to generate and maintain.     

Mouse models for psychiatric disorders

Genes involved in psychiatric disorders are difficult to identify, and those that have been proposed so far remain ambiguous. As it is unrealistic to expect the development of, say, a ‘schizophrenic’ or ‘autistic’ mouse, mice are unlikely to have the same role in gene identification in psychiatry as circling mice did in the discovery of human deafness genes. However, many psychiatric disorders are associated with intermediate phenotypes that can be modeled and studied in mice, including physiological or anatomical brain changes and behavioral traits. Mouse models help to evaluate the effect of a human candidate gene mutation on an intermediate trait, and to identify new candidate genes. Once a gene or pathway has been identified, mice are also used to study the interplay of different genes in that system.     

A dynamic study in two new cases of X chromosome translocations

Summary The authors discuss the clinical and cytogenetic problems raised in two new cases of X-chromosome translocations.The first case involves a child who presented marked growth retardation, behavioral anomalies, and discrete facial malformations at age 3 months. Chromosome analysis revealed the presence of a translocation between a 22 and X chromosome resulting in partial X monosomy and partial trisomy 22: 46,X,der(X),t(X;22)(q112;q13)mat. The balanced translocation form was detected in the mother. Dynamic study after 5-Brdu treatment revealed inactivation of the translocated X chromosome in the proband, while in the mother the normal X chromosome was inactivated.In addition to magnesium dependent hypocalcemia resulting from a specific absorption anomaly, Case 2 presented discrete malformations and psychomotor retardation. Chromosome analysis revealed an apparently balanced translocation between a 9 and X chromosome: 46,X,r(9;X)(q12; p22). Treatment with 5-Brdu demonstrated that the translocated X chromosome was inactivated but that inactivation did not extend to the translocated part of chromosome 9. Finally, a pericentric inversion of a 9 chromosome was detected in the father, grandfather, and brother of the proband.     

AID is required for c-myc/IgH chromosome translocations in vivo

Chromosome translocations between c-myc and immunoglobulin (Ig) are associated with Burkitt's lymphoma in humans and with pristane- and IL6-induced plasmacytomas in mice. These translocations frequently involve Ig switch regions, suggesting that they might be the result of aberrant Ig class switch recombination (CSR). However, a direct link between CSR and chromosome translocations has not been established. We have examined c-myc/IgH translocations in IL6 transgenic mice that are mutant for activation induced cytidine deaminase (AID), the enzyme that initiates CSR. Here we report that AID is essential for the c-myc/IgH chromosome translocations induced by IL6.     

Targeted mutagenesis tools for modelling psychiatric disorders

Hes genes are required to maintain diverse progenitor cell populations during embryonic development. Loss of Hes1 results in a spectrum of malformations of pharyngeal endoderm-derived organs, including the ultimobranchial body (progenitor of C cells), parathyroid, thymus and thyroid glands, together with highly penetrant C-cell aplasia (81%) and parathyroid aplasia (28%). The hypoplastic parathyroid and thymus are mostly located around the pharyngeal cavity, even at embryonic day (E) 15.5 to E18.5, indicating the failure of migration of the organs. To clarify the relationship between these phenotypes and neural crest cells, we examine fate mapping of neural crest cells colonized in pharyngeal arches in Hes1 null mutants by using the Wnt1-Cre/R26R reporter system. In null mutants, the number of neural crest cells labeled by X-gal staining is markedly decreased in the pharyngeal mesenchyme at E12.5 when the primordia of the thymus, parathyroid and ultimobranchial body migrate toward their destinations. Furthermore, phospho-Histone-H3-positive proliferating cells are reduced in number in the pharyngeal mesenchyme at this stage. Our data indicate that the development of pharyngeal organs and survival of neural-crest-derived mesenchyme in pharyngeal arches are critically dependent on Hes1. We propose that the defective survival of neural-crest-derived mesenchymal cells in pharyngeal arches directly or indirectly leads to deficiencies of pharyngeal organs.     

A comparative map of chicken chromosome 24 and human chromosome 11

To improve the physical and comparative map of chicken chromosome 24 (GGA24; former linkage group E49C20W21) bacterial artificial chromosome (BAC) contigs were constructed around loci previously mapped on this chromosome by linkage analysis. The BAC clones were used for both sample sequencing and BAC end sequencing. Sequence tagged site (STS) markers derived from the BAC end sequences were used for chromosome walking. In total 191 BAC clones were isolated, covering almost 30% of GGA24, and 76 STS were developed (65 STS derived from BAC end sequences and 11 STS derived within genes). The partial sequences of the chicken BAC clones were compared with sequences present in the EMBL/GenBank databases, and revealed matches to 19 genes, expressed sequence tags (ESTs) and genomic clones located on human chromosome 11q22-q24 and mouse chromosome 9. Furthermore, 11 chicken orthologues of human genes located on HSA11q22-q24 were directly mapped within BAC contigs of GGA24. These results provide a better alignment of GGA24 with the corresponding regions in human and mouse and identify several intrachromosomal rearrangements between chicken and mammals.     

Gene order on the short arm of human chromosome 11: regional assignment of the LDH A gene distal to catalase in two translocations

Summary Leukemic cells with reciprocal translocations involving 11p13 and 14q13 were obtained from two patients with T-cell acute lymphoblastic leukemia and fused with mouse Ltk^- cells. DNA from independent hybrid clones was screened by Southern blot and hybridization to molecular probes for the human catalase and Ha-ras-1 genes. Several clones showed segregation of these two genes, indicating the presence of either the der 11 or der 14 human chromosomes. When DNA from these hybrid clones was examined for the presence of the human genes for calcitonin and γ-globin, both genes were found to segregate with the Ha-ras-1 gene and the der14 chromosome indicating that they lie distal to catalase. When the hybrid clones were examined for the presence of human lactate dehydrogenase A (LDH A) activity, only those clones containing the der14 chromosome expressed activity indicating that the LDH A gene is also distal to catalase on the short arm of chromosome 11.     

A deletion in chromosome 22 can cause digeorge syndrome

Summary An association between DiGeorge's syndrome and an unbalanced chromosomal rearrangement leading to trisomy 20pter20q11 and monosomy 22pter22q11 was found in four individuals belonging to one family. These and other data from the literature are interpreted to suggest that DiGeorge's syndrome can be caused by deletion of a gene located in chromosome 22, probably in band 22q11.     

Unifying hypothesis for the motoneuronal code in neurological disorders

The elucidation of the motoneuronal code in disorders characterized by prominent motor deficits, such as stroke, Parkinson disease (PD), chronic cerebellar degeneration (CCD) and amyotrophic lateral sclerosis (ALS), would have major impacts for early diagnosis, understanding of disease progression, monitoring the effects of conventional or emerging therapies, and rehabilitation. We propose that the fundamental rules of motoneuronal coding are violated in these neurological diseases. Unraveling of the motoneuronal signatures will lead to a new classification of movement disorders. We suggest that: (1) paresia due to a stroke is associated with a reduction in the mean motor unit firing rates (MUFR), abnormal commonality between pairs of motor units (MU), and an abnormal MU/force relationship; (2) in PD, MU do not discharge at the appropriate MUFR at given recruitment thresholds due to underactivity of the motor cortex. Treatment restores the linear relationship between recruitment threshold and MUFR; (3) in CCD, the hierarchical organization of MU is impaired, the commonality between pairs of MU is deregulated, the derecruitment of MU is abnormal, and EMG discharges show periods of electrical silences in MU discharges (ESIMUD); (4) in the early stages of ALS, a premature recruitment of high-threshold MU at low force levels occurs. The hierarchical organization is lost. Fluctuations in timing intervals between successive discharges of given MU are increased. Impaired MU contractile properties resulting from upper motor neuron disease are associated with decreased maximal M wave following lower motor neuron disease. The decline in mechanical force output following fatigue is associated with frequency shifts in the myoelectric signal and reduced muscle fiber conduction velocity. We suggest that patterns of MU discharges are distinct in acute diseases and in chronic neurological conditions, as a result of plasticity, compensatory patterns and reorganization of motor cortex output involving changes in functional connectivity in the central nervous system (CNS).     

Dissecting cause and effect in the pathogenesis of psychiatric disorders: genes, environment and behaviour

It has long been established that the development of psychiatric illness results from a complex interplay between genetic and environmental factors. Postmortem and genetic linkage studies have identified a number of promising candidate genes which have been reinforced by replication and functional studies. However, the fact that concordance rates for monozygotic twins rarely approach 100% highlights the involvement of environmental factors. Whilst epidemiological studies of psychiatric cohorts have demonstrated potential risk factors, such studies are clearly limited and in many cases the potential mechanism linking a given risk factor with pathogenesis remains unclear. A very powerful method of elucidating the mechanisms underlying gene-environment interactions is the use of appropriate animal models of psychiatric pathology. Whilst animals cannot be used to map the entire complexity of diseases such as schizophrenia, dissecting the symptom profile into more simply encapsulated traits or endophenotypes has proved to be a successful approach. Such endophenotypes provide a measurable link between aetiological factors and phenotypic outcome. Given the potential for the careful control and modification of an experimental animal's environment, the combination of studies of candidate genes with investigations of environmental factors is an effective heuristic tool, allowing examination of behavioural endophenotypes in conjunction with cellular and molecular outcomes. This review will consider the extant genetic, molecular, pharmacological and lesion-based models of psychiatric disorders, and the relevant methods of environmental manipulation appearing in the literature. We will discuss studies where such models have been combined, and the potential for future experimentation in this area.     

A cluster of chromosome 11p13 translocations found via distinct D-D and D-D-J rearrangements of the human T cell receptor delta chain gene.

Human T cell tumours have few consistently occurring translocations which provide markers for this disease. The translocation t(11;14)(p13;q11), however, seems to be an exception, since it has been repeatedly observed in T-ALL. We have analysed a number of T-ALL samples carrying the t(11;14) with a view to assessing the nature of the translocated sequences on chromosomes 11 and 14. Three of the tumours studied have breakpoints, at 14q11, within the T cell receptor delta chain locus, while a fourth appears to break in the J alpha region. The TCR delta sequences involved in the translocation junctions are made from D delta-D delta-J delta joins or from D delta-D delta joins, allowing us to define distinct human D delta and J delta segments. These results allow us to make a comparison between the human and mouse TCR delta loci, both as regards sequence and rearrangement hierarchies. The disparate translocation breakpoints at chromosome 14q11 contrast with the marked clustering of breaks at chromosome 11p13; in all four cases, the breakpoint occurs within a region of less than 0.8 kb of chromosome 11. The analysis of junctional sequences at the 11p13 breakpoint cluster region only shows a consensus heptamer-like sequence in one out of four tumours analysed. Therefore, recombinase-mediated sequence specific recognition is not the only cause of chromosomal translocation.     

The Giemsa-11 technique for species-specific chromosome differentiation

Summary Oxidizing Methylene Blue and adding the reaction products to Eosin Y and Azure B makes possible a highly reliable Giemsa-11 technique for discrimination of chromosomes in hybrid cells according to their parental origin. This staining can be combined in a sequential procedure with a fluorescent banding technique allowing the exact identification of the chromosomes.     

Argininosuccinic aciduria. A new case revealed by psychiatric disorders

The case of a 4 years old boy, hospitalized for an unexplained coma, is reported. He is the first child of a non-consanguin couple. The psychomotor development of this child was considered as normal up to the age of 18 months; then, a delay in language development, behaviour disorders with an important instability interrupted by episodes of somnolence, were observed. This child was treated for psychotic disorders. At the age of 3 and half, he had two episodes of seizures associated with fever. He was hospitalized for a 24 hours coma (4 years old). An hepatomegaly and a dry, brittle hair were then observed. Hyperammonemia was made obvious by a protein tolerance test. The diagnosis of argininosuccinate lyase (ASAL) deficiency was based on the increased levels of ASA in plasma and urine. The deficiency was proved by a fibroblast culture. With protein restriction, hepatomegaly disappeared, hair became normal, the behaviour disorders and the delay in language development was improved. However, some school difficulties persist. This case shows that an hereditary metabolic syndrome can be revealed by psychotic like symptoms in childhood.