Search PubMed⌕ Search

Biomedical subjects

T Friedmann

Publications and source records attributed to T Friedmann.

At least 127 records · Page 7Linked to original sources
PubMed1988

Human retinoblastoma susceptibility gene: genomic organization and analysis of heterozygous intragenic deletion mutants.

A gene in chromosome region 13q14 has been identified as the human retinoblastoma susceptibility (RB) gene on the basis of altered gene expression found in virtually all retinoblastomas. In order to further characterize the RB gene and its structural alterations, we examined genomic clones of the RB gene isolated from both a normal human genomic library and a library made from DNA of the retinoblastoma cell line Y79. First, a restriction and exon map of the RB gene was constructed by aligning overlapping genomic clones, yielding three contiguous regions ("contigs") of 150 kilobases total length separated by two gaps. At least 20 exons were identified in genomic clones, and these were provisionally numbered. Second, two overlapping genomic clones that demonstrated a DNA deletion of exons 2 through 6 from one RB allele were isolated from the Y79 library. To confirm and extend this result, a unique sequence probe from intron 1 was used to detect similar and possibly identical heterozygous deletions in genomic DNA from three retinoblastoma cell lines, thereby explaining the origins of their shortened RB mRNA transcripts. The same probe detected genomic rearrangements in fibroblasts from two hereditary retinoblastoma patients, indicating that intron 1 includes a frequent site for mutations conferring predisposition to retinoblastoma. Third, this probe also detected a polymorphic site for BamHI with allele frequencies near 0.5/0.5. Identification of commonly mutated regions will contribute significantly to genetic diagnosis in retinoblastoma patients and families.

Cell Line↗
PubMed1988

Approaches to gene therapy in disorders of purine metabolism.

Model studies with gene transfer technology using retroviral vectors expressing the cloned human genes for adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), and hypoxanthine guanine phosphoribosyltransferase (HPRT) indicate that these disorders may eventually be treated by the introduction of the normal gene into defective cells. The autologous transplantation of bone marrow infected in vitro with retroviral vectors is the most developed approach at this time. The potential usefulness of this and other approaches for each of these three disorders of purine metabolism are discussed.

Adenosine Deaminase↗
PubMed1987

Grafting genetically modified cells to the brain: possibilities for the future.

Diagnostic and therapeutic approaches to disorders of the central nervous system (CNS) are particularly difficult to develop because of the relative inaccessibility of the mammalian brain to study and chemical treatment, the complexity and interconnectedness of CNS subsystems, and the profound and continued lack of fundamental understanding of the relationship between structure and function in the CNS. Neural grafting in the CNS has recently suggested a potential approach to CNS therapy through the selective replacement of cells lost as a result of disease or damage. Independently, studies aimed at direct genetic therapy in model systems have recently begun to suggest conceptually new approaches to the treatment of several kinds of human genetic disease, especially those caused by single-gene enzyme deficiencies. We suggest that a combination of these two approaches, namely the grafting into the CNS of genetically modified cells, may provide a new approach toward the restoration of some functions in the damaged or diseased CNS. We present evidence for the feasibility of this approach, including a description of some current techniques for mammalian cell gene transfer and CNS grafting, and several possible approaches to clinical applications.

Brain↗
PubMed1987

Epitope insertion into the human hypoxanthine phosphoribosyltransferase protein and detection of the mutant protein by an anti-peptide antibody.

The translational stop codon TAA of the human hypoxanthine phosphoribosyltransferase (HPRT) cDNA has been changed to GAA by site-specific mutagenesis. This modification extends the open reading frame to a downstream stop codon and results in the addition of a unique negatively charged hexapeptide to the C terminus of human HPRT protein. The mutated cDNA was transferred into HPRT-deficient rodent cells by retroviral vector infection, and the expressed enzyme was found to be fully active. An antibody against a synthetic octapeptide corresponding to the mutated HPRT C terminus precipitated the HPRT protein specifically from cells infected with the mutant virus and not infected with the wild-type HPRT virus. The technique of inserting a novel epitope into a protein by site-directed mutagenesis should be generally applicable in studies of the regulation of gene expression in vitro and in vivo.

Epitopes↗
PubMed1987

Expression of retrovirally transduced genes in primary cultures of adult rat hepatocytes.

Differentiated primary rat hepatocyte cultures have been infected with retroviral vectors expressing human hypoxanthine/guanine phosphoribosyltransferase or the transposon Tn5 neomycin-resistance gene. Expression of the markers was detected only after infection of the cells during a short period of cell replication and transient dedifferentiation from days 1 to 5 of culture. Provirus integrated during that period remains fully expressed during the entire subsequent stationary period of culture up to at least 25 days. Selection with the neomycin analogue G418 of cells infected with the neomycin vector led to the appearance of cells with hepatocyte morphology in which newly synthesized albumin was detectable by immunoprecipitation, indicating successful infection of hepatocytes.

Animals↗
PubMed1987

Gene expression from transcriptionally disabled retroviral vectors.

Retroviral vectors are used for the efficient transfer of foreign genes into mammalian cells. We report here the construction of murine retrovirus-based vectors carrying the full-length cDNA for human hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) and from which the enhancer sequences, the "CAAT box," and the "TATA box" in the long terminal repeats (LTRs) have been deleted. After infection of HPRT-deficient rat cells by the vectors, transcriptional activity from the 5' LTR was undetectable and expression of the HPRT cDNA was dependent on an internal promoter. Removal of the LTR regulatory elements increased HPRT gene expression from an internal promoter, indicating interference between the two sets of transcriptional signals. Such disabled vectors may reduce the likelihood of undesirable genetic changes through insertional mutagenesis in cells infected with retroviral vectors.

Base Sequence↗
PubMed1986

The organization of the human HPRT gene.

The organization of the X-linked gene for human hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8.) has been determined by a combination of restriction endonuclease mapping, heteroduplex analysis and DNA sequence analysis of overlapping genomic clones. The entire gene is 42 kilobases in length and split into 9 exons. The sizes of the 7 internal exons and the exon-intron boundaries are identical to those of mouse HPRT gene. The 5' end of the gene lacks the prototypical 5' transcriptional regulatory sequence elements but contains extremely GC-rich sequences and five GC hexanucleotide motifs (5'-GGCGGG-3'). These structural features are very similar to those found in the mouse HPRT gene and to some of the regulatory signals common to a class of constitutively expressed "housekeeping" genes. Several transcriptional start sites have been identified by nuclease protection studies. Extensive sequence homology between the mouse and human genes is found in the 3' non-coding portion of the gene.

Animals↗
PubMed1986

Variable stability of a selectable provirus after retroviral vector gene transfer into human cells.

Human lymphoblasts deficient in the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) were infected with an amphotropic helper-free retroviral vector expressing human HPRT cDNA. The stability and expression of the HPRT provirus in five cell lines with different proviral integration sites were examined by determining HPRT mutation and reversion frequencies and by blot hybridization studies. Mutation to the HPRT-negative phenotype occurred at frequencies of approximately 4 X 10(-5) to 3 X 10(-6) per generation. Most mutations in each of the five cell lines were associated with partial or complete deletions or rearrangements of the provirus. Several mutants retained a grossly intact HPRT provirus, and in one such mutant HPRT shutdown resulted from a revertible epigenetic mechanism that was not associated with global changes in proviral methylation. Therefore, mutation and shutdown of the HPRT provirus in human lymphoblasts result from mechanisms similar to those reported for several other avian and mammalian replication-competent retroviruses.

Cell Line↗
PubMed1986

Comparison of the opioid activity of CAM and kappa agonists.

CAM has been shown to produce opiate agonist and antagonist activities. Based on its potent agonist activity in rabbit vas deferens and the low potency of naloxone to antagonize its agonist effect in the guinea pig ileum and mouse vas deferens, CAM can be considered as kappa agonist. It is further supported by its diuretic effect and the estimated "apparent pA2" values with naloxone and Mr-2266BS. However, in the rabbit ear artery and cat nictitating membrane, ethylketazocine (EK) produced agonist activity, while CAM produced antagonist activity. Also, EK differs from CAM in mouse vas deferens in the presence of 4-aminopyridine. It is concluded, that CAM might be an agonist on kappa type (subtype) of opiate receptors, although its spectrum of activity was found to be different from EK or bremazocine.

Animals↗
PubMed1986

Primary structure of acetylcholinesterase: implications for regulation and function.

A cDNA encoding acetylcholinesterase (AChE) (EC 3.1.1.7) from Torpedo californica was isolated and from its nucleotide sequence the entire amino acid sequence of the processed protein and a portion of the leader peptide has been deduced. Approximately 70% of the tryptic peptides from the catalytic subunit of the 11 S form have been sequenced, and a comparison of the peptide sequences with the sequence inferred from the cDNA suggests that the cDNA sequence derives from mRNA for the 11 S form of the enzyme. The amino acid sequence is preceded by a hydrophobic leader peptide and contains an open reading frame encoding for 575 amino acids characteristic of a secreted globular protein. Eight cysteines, most of which are disulfide linked, are found along with four potential sites of N-linked glycosylation. The active-site serine is located at residue 200. Local homology is found with other serine hydrolases in the vicinity of the active site, but the enzyme shows striking global homology with the COOH-terminal portion of thyroglobulin. Further comparison of the amino acid sequences of the individual enzyme forms with other cDNA clones that have been isolated should resolve the molecular basis for polymorphism of the AChE species.

Acetylcholinesterase↗
PubMed1985

Retroviral vector-mediated gene transfer into human hematopoietic progenitor cells.

The transfer of the human gene for hypoxanthine phosphoribosyltransferase (HPRT) into human bone marrow cells was accomplished by use of a retroviral vector. The cells were infected in vitro with a replication-incompetent murine retroviral vector that carried and expressed a mutant HPRT complementary DNA. The infected cells were superinfected with a helper virus and maintained in long-term culture. The production of progeny HPRT virus by the bone marrow cells was demonstrated with a colony formation assay on cultured HPRT-deficient, ouabain-resistant murine fibroblasts. Hematopoietic progenitor cells able to form colonies of granulocytes or macrophages (or both) in semisolid medium in the presence of colony stimulating factor were present in the nonadherent cell population. Colony forming units cloned in agar and subsequently cultured in liquid medium produced progeny HPRT virus, indicating infection of this class of hematopoietic progenitor cell.

Animals↗
PubMed1984

Expression of a retrovirus encoding human HPRT in mice.

Transmissible retroviruses encoding human hypoxanthine phosphoribosyltransferase (HPRT) were used to infect mouse bone marrow cells in vitro, and the infected cells were transplanted into mice. Both active human HPRT-protein and chronic HPRT-virus production were detected in hematopoietic tissue of the mice, showing transfer of the gene. These results indicate the possible use of retroviruses for somatic cell therapy.

Animals↗