Panayiotis A. Ioannou

Transgenes encompassing dual-promoter CpG islands from the human TBP and HNRPA2B1 loci are resistant to heterochromatin-mediated silencing.

The genetic elements that are responsible for establishing a transcriptionally competent, open chromatin structure at a region of the genome that consists only of ubiquitously expressed, housekeeping genes are currently unknown. We demonstrate for the first time through functional analysis in stably transfected tissue culture cells that transgenes containing methylation-free CpG islands spanning the dual divergently transcribed promoters from the human TATA binding protein (TBP)-proteasome component-B1 (PSMB1) and heterogeneous nuclear ribonucleoprotein A2/B1 (HNRPA2B1)-heterochromatin protein 1Hs-gamma (chromobox homolog 3, CBX3) gene loci are sufficient to prevent transcriptional silencing and a variegated expression pattern when integrated within centromeric heterochromatin. In addition, only transgene constructs extending over both the HNRPA2B1 and the CBX3 promoters, and not the HNRPA2B1 promoter alone, were able to confer high and stable long-term EGFP reporter gene expression. These observations suggest that methylation-free CpG islands associated with dual, divergently transcribed promoters possess an independent dominant chromatin opening function and may therefore be major determinants in establishing and maintaining a region of open chromatin at housekeeping gene loci.

A knock-out mouse model for methylmalonic aciduria resulting in neonatal lethality.

Methylmalonic aciduria is a human autosomal recessive disorder of organic acid metabolism resulting from a functional defect in the activity of the enzyme methylmalonyl-CoA mutase. Based upon the homology of the human mutase locus with the mouse locus, we have chosen to disrupt the mouse mutase locus within the critical CoA binding domain using gene-targeting techniques to create a mouse model of methylmalonic aciduria. The phenotype of homozygous knock-out mice (mut-/-) is one of early neonatal lethality. Mice appear phenotypically normal at birth and are indistinguishable from littermates. By 15 h of age, they develop reduced movement and suckle less. This is followed by the development of abnormal breathing, and all of the mice with a null phenotype die by 24 h of age. Urinary levels of methylmalonic and methylcitric acids are grossly increased. Measurement of acylcarnitines in blood shows elevation of propionylcarnitine with no change in the levels of acetylcarnitine and free carnitine. Incorporation of [14C]propionate in primary fibroblast cultures from mut-/- mice is reduced to approximately 6% of normal level, whereas there is no detectable synthesis of mut mRNA in the liver. This is the first mouse model that recapitulates the key phenotypic features of mut0 methylmalonic aciduria.

Targeted modification of a human β-globin locus BAC clone using GET Recombination and an I-Scei counterselection cassette

There is a need for better approaches to allow precise engineering of large genomic BAC DNA fragments, to facilitate the use of intact genomic loci for therapeutic and biotechnology applications. We report an efficient method to insert any modification in any genomic locus, using a human beta-globin locus BAC clone as a model system. The modifications can range from single base changes to large insertions or deletions and leave no operational sequences. A counterselection cassette, consisting of an inducible I-SceI gene, its recognition site, and an antibiotic resistance gene, is inserted into the targeted region using GET Recombination. A PCR fragment carrying the modification but no selectable marker replaces the counterselection cassette in a second round of GET Recombination. The unique I-SceI site in the counterselection cassette is cut by I-SceI endonuclease, strongly selecting against nonrecombinant clones and yielding up to 30% correct recombinants.

Construction of bacterial artificial chromosome (BAC/PAC) libraries.

This unit describes the construction of BAC and PAC libraries. Two vectors, pCYPAC2 and pPAC4 have been used for preparing PAC libraries, and a new BAC vector pBACe3.6 has been developed for construction of BAC libraries. A support protocol describes preparation of PAC or BAC vector DNA for cloning by digestion with BamHI or EcoRI, simultaneous dephosphorylation with alkaline phosphatase, and subsequent purification through pulsed‐field gel electrophoresis (PFGE). For the preparation of high‐molecular weight DNA for cloning, support protocols provide procedures for embedding total genomic DNA from lymphocytes or animal tissue cells, respectively, in InCert agarose. Another support protocol details the next steps for the genomic DNA: partial digestion with MboI or with a combination of EcoRI endonuclease and EcoRI methylase, and subsequent size fractionation by preparative PFGE. The final support protocol covers the isolation of BAC and PAC plasmid DNA for analyzing clones.

The potential of bone marrow stem cells to correct liver dysfunction in a mouse model of Wilson's disease

Metabolic liver diseases are excellent targets for correction using novel stem cell, hepatocyte, and gene therapies. In this study, the use of bone marrow stem cell transplantation to correct liver disease in the toxic milk (tx) mouse, a murine model for Wilsons disease, was evaluated. Preconditioning with sublethal irradiation, dietary copper loading, and the influence of cell transplantation sites were assessed. Recipient tx mice were sublethally irradiated (4 Gy) prior to transplantation with bone marrow stem cells harvested from normal congenic (DL) littermates. Of 46 transplanted tx mice, 11 demonstrated genotypic repopulation in the liver. Sublethal irradiation was found to be essential for donor cell engraftment and liver repopulation. Dietary copper loading did not improve cell engraftment and repopulation results. Both intravenously and intrasplenically transplanted cells produced similar repopulation successes. Direct evidence of functionality and disease correction following liver repopulation was observed in the 11 mice where liver copper levels were significantly reduced when compared with mice with no liver repopulation. The reversal of copper loading with bone marrow cells is similar to the level of correction seen when normal congenic liver cells are used. Transplantation of bone marrow cells partially corrects the metabolic phenotype in a mouse model for Wilsons disease.

Humanized β-Thalassemia Mouse Model Containing the Common IVSI-110 Splicing Mutation

Splicing mutations are common causes of β-thalassemia. Some splicing mutations permit normal splicing as well as aberrant splicing, which can give a reduced level of normal β-globin synthesis causing mild disease (thalassemia intermedia). For other mutations, normal splicing is reduced to low levels, and patients are transfusion-dependent when homozygous for the disease. The development of therapies for β-thalassemia will require suitable mouse models for preclinical studies. In this study, we report the generation of a humanized mouse model carrying the common IVSI-110 splicing mutation on a BAC including the human β-globin (huβ-globin) locus. We examined heterozygous murine β-globin knock-out mice (muβth-3/+) carrying either the IVSI-110 or the normal huβ-globin locus. Our results show a 90% decrease in huβ-globin chain synthesis in the IVSI-110 mouse model compared with the mouse model carrying the normal huβ-globin locus. This notable difference is attributed to aberrant splicing. The humanized IVSI-110 mouse model accurately recapitulates the splicing defect found in comparable β-thalassemia patients. This mouse model is available as a platform for testing strategies for the restoration of normal splicing.

Multicenter Study of the Molecular Basis of Thalassemia Intermedia in Different Ethnic Populations

We studied 325 thalassemia intermedia patients from Iran, India, Pakistan, Thailand, Mauritius and Cyprus to examine factors which influence the phenotype. The β-thalassemia (thal) mutations were determined for 219 β-thal/β-thal and 106 β-thal/Hb E [β26(B8)Glu→Lys, GAG→AAG] thalassemia intermedia patients. Thirty-one different mutations were identified, and their combination gave rise to more than 44 different genotypes, of which 14 (31.8%) had the β0/β0, 21 (47.7%) the β0/β+ and nine (20.5%) the β+/β+ types. Thus, the β+-thal mutations were present in 68.2% of patients. α-Thalassemia mutations were present in frequencies higher than in the general population of all ethnic groups studied, as 45% of the patients carried α-thal mutations. Correlation of α-thal mutations with β-globin mutations showed that the α-thal mutations were mainly co-inherited with the β+-thal mutations. The XmnI Gγ polymorphic site at −158 (C→T) was positive (T) in nine (8.8%) of 102 patients of the β+/β+ genotype, and the percentage of both XmnI Gγ polymorphism [+/−] (T/C) and [+/+] (T/T) genotypes increased to 42.9 and 87.3, respectively, in the β0/β+ and β0/β0 patients. This polymorphism was found in the majority of β+-thal/Hb E compound heterozygote patients (88.6%), and β0-thal/Hb E patients (84.8%), suggesting that it could be linked to the Hb E chromosome. Therefore, the XmnI Gγ polymorphism at −158 (C→T) was associated with β0-thal mutations as well as the Hb E chromosome. The present study demonstrates that in cases of thalassemia intermedia with β+ mutations, the common ameliorating factor is the presence of α-thal mutations, while in cases with β0 mutations, the common ameliorating factor is the presence of the XmnI Gγ polymorphism at −158 (C→T).

Atomic force microscopy imaging of DNA-cationic liposome complexes optimised for gene transfection into neuronal cells

Cationic liposomes represent an important gene delivery system due to their low immunogenicity, but are relatively inefficient, with optimisation of DNA–liposome complexes (lipoplexes) for transfection necessary for each cell type of interest. There have been few studies examining optimisation in neuronal cell types or determining how the structure of lipoplexes affects transfection efficiency.

Complementation of α-thalassaemia in α-globin Knockout Mice with a 191 kb Transgene Containing the Human α-Globin Locus

Abstractα-Thalassaemia is an inherited blood disorder caused by a decrease in the synthesis of α-globin due to mutations in one or both of the α-globin genes located on human chromosome 16. A 191 kb transgene derived from a sequenced bacterial artificial chromosome (BAC) clone carrying the human α-globin gene cluster, together with about 100 kb of sequence upstream of DNase1 hypersensitive site HS-40 and 30 kb downstream of the α1-globin gene, was introduced into fertilised mouse oocytes by pronuclear microinjection. Three transgenic founder mice were obtained. Analysis of one transmitting line by fluorescent in situ hybridisation and quantitative PCR demonstrated a single copy integration of the human α-globin transgene on chromosome 1. Analysis of haemoglobins from the peripheral blood by cellulose acetate electrophoresis and high performance liquid chromatography (HPLC) demonstrated synthesis of human α-globin to about 36% of the level of each mouse α-globin locus. Breeding of transgenic mice with mice heterozygous for a knockout (KO) deletion of both murine α-globin genes showed that the human α-globin locus restored haemoglobin levels and red cell distribution width to normal in double heterozygous mice and significantly normalised other haematological parameters. Interestingly the human transgene also induced a significant increase in red cell production and haematocrit above wild type values. This is the first report demonstrating complementation of a murine α-globin KO mutation by human α-globin gene expression from an intact human α-globin locus. The transgenic mouse model described in this report should be very useful for the study of human α-globin gene regulation and for the development of strategies to down regulate α-globin production as a means of ameliorating the severity of β-thalassaemia.

Development of a novel bacterial artificial chromosome cloning system for functional studies.

Bacterial artificial chromosome (BAC) cloning systems currently in use generate high quality genomic libraries for gene mapping, identification, and sequencing. However, the most commonly used BAC cloning systems do not facilitate functional studies in eukaryotic cells. To overcome this limitation, we have developed pEBAC190G, a new BAC vector that combines the features of the first generation PAC/BAC vectors with eukaryotic elements that facilitate the transfection, episomal maintenance, and functional analysis of large genomic fragments in eukaryotic cells. A number of different cloning strategies may be used to retrofit genomic fragments from existing libraries into the new vector. The system was tested by the retrofitting of a 170kb NotI genomic fragment from the RPCI-11 BAC library into the NotI site of pEBAC190G. Clones from any eukaryotic genomic library harboured in this vector can be transferred from bacteria directly to eukaryotic cells for functional analysis.