Search PubMed⌕ Search

Biomedical subjects

K B Avraham

Publications and source records attributed to K B Avraham.

50 records · Page 3Linked to original sources
PubMed1993

Molecular diversity of the SCG10/stathmin gene family in the mouse.

SCG10 is a neuronal growth-associated protein that shares an amino acid sequence similarity with an 18- to 19-kDa phosphoprotein named stathmin (also called p19, p18, Op18, pp17, prosolin, pp20, 19K, and leukemia-associated phosphoprotein, Lap18), which is more broadly expressed in a variety of cell types of the neural, immune, and reproductive systems. The sequence similarity has suggested that SCG10 and stathmin have been derived from structurally and evolutionarily related genes. To explore the structural and evolutionary relationships between these genes, we have isolated a series of cosmid and phage clones that covers the entire region of the mouse stathmin gene and most of the mouse SCG10 gene. The SCG10 transcription unit spans at least 30 kb, while the stathmin gene is 6 kb in length. Both genes consist of five exons, and many of the intron/exon boundaries fall into the homologous regions of conserved domains of these two proteins. However, the promoter-proximal regions are distinct in the two genes, suggesting that they have evolved by fusion of the duplicated coding exons to unique promoters. Southern blot analysis indicates that SCG10 mRNA is encoded by a single gene in the mouse genome, while stathmin cDNA probes detect multiple genes. Chromosome mapping experiments reveal that the SCG10 gene is localized at the proximal region of mouse chromosome 3 and is linked to Il-7, while the stathmin gene loci are distributed to three chromosomes; the authentic stathmin gene lies on chromosome 4, whereas the loci on chromosomes 9 and 17 are likely to be pseudogenes. These data are consistent with the idea that the neuron-specific SCG10 gene evolved by duplication and modification of the more broadly expressed stathmin/Lap18 gene.

Amino Acid Sequence↗
PubMed1993

Expression of manganese superoxide dismutase is not altered in transgenic mice with elevated level of copper-zinc superoxide dismutase.

In evaluating the relative expression of copper-zinc and manganese superoxide dismutase (CuZnSOD and MnSOD) in vivo in states like Down syndrome in which one dismutase is present at increased levels, we measured activities of both enzymes, in tissues of control and transgenic mice constitutively expressing increased levels of CuZnSOD, during exposure to normal and elevated oxygen tensions. Using SOD gel electrophoresis assay, CuZnSOD and MnSOD activities of brain, lung, heart, kidney, and liver from mice exposed to either normal (21%) or elevated (> 99% oxygen, 630 torr) oxygen tensions for 120 h were compared. Whereas CuZnSOD activity was elevated in tissues of transgenic relative to control mice under both normoxic or hyperoxic conditions, MnSOD activities in organs of transgenic mice were remarkably similar to those of controls under both conditions. To confirm the accuracy of this method in quantitating MnSOD relative to CuZnSOD expression, two other methods were utilized. In lung, which is the organ exposed to the highest oxygen tension during ambient hyperoxia, a sensitive, specific ELISA for MnSOD was used. Again, MnSOD protein was not different in transgenic relative to control mice during exposure to air or hyperoxia. In addition, lung MnSOD protein was not changed significantly by exposure to hyperoxia in either group. In kidney, a mitochondrion-rich organ, SOD assay, before and after inactivation of CuZnSOD with diethyldithiocarbamate, was used. MnSOD activity was not different in organs from air-exposed transgenic relative to control mice. The data indicated that expression of MnSOD in vivo was not affected by overexpression of the CuZnSOD and, therefore, the two enzymes are probably regulated independently.

Animals↗
PubMed1992

Murine chromosomal location of four hepatocyte-enriched transcription factors: HNF-3 alpha, HNF-3 beta, HNF-3 gamma, and HNF-4.

The genes for rat hepatocyte nuclear factors 3 and 4 (HNF-3 alpha, HNF-3 beta, HNF-3 gamma, and HNF-4) have been mapped in mouse by analysis of restriction fragment length polymorphisms in interspecific backcross mice. These hepatocyte-enriched transcription factors are positive-acting transcription factors with binding sites in regulatory regions of many genes expressed in hepatocytes. Both HNF-3 alpha, beta, and gamma and HNF-4 are also expressed in intestine. They have recently been implicated as potential participants in endodermal development from early gut cells because of their close homology to Drosophila genes, which themselves are expressed in the developing gut. Despite having similar functional roles and highly conserved DNA binding domains, the three loci from the Hnf-3 family of genes mapped to three different mouse chromosomes, suggesting that the Hnf-3 family has become widely dispersed during evolution and implying the necessity for independent activation of each member of the HNF-3 family.

Animals↗
PubMed1991

Down's syndrome: morphological remodelling and increased complexity in the neuromuscular junction of transgenic CuZn-superoxide dismutase mice.

Transgenic mice carrying the human CuZn-superoxide dismutase gene were used to investigate whether CuZn-superoxide dismutase gene dosage is involved in the signs of neuromuscular junction deterioration associated with Down's syndrome. Three parameters of neuromuscular junction morphology were studied in hindlimb muscles of CuZn-superoxide dismutase-transgenic mice and their non-transgenic littermates: nerve terminal length, number of nerve terminal branching points and incidence of sprouting that results in synapse formation. These parameters increased with advanced age and the increase occurred earlier in CuZn-superoxide dismutase-transgenic mice. Therefore, the data is in line with the possibility that CuZn-superoxide dismutase-transgenic mice are undergoing premature ageing with respect to neuromuscular junction morphology, most probably owing to a gene dosage effect of CuZn-superoxide dismutase.

Aging↗
PubMed1991

Transgenic mice with expression of elevated levels of copper-zinc superoxide dismutase in the lungs are resistant to pulmonary oxygen toxicity.

To test the hypothesis that increases in lung superoxide dismutase can cause tolerance to pulmonary oxygen toxicity, we studied transgenic mice which constitutively express elevated levels of the human copper-zinc SOD (CuZnSOD). Upon exposure to hyperoxia (greater than 99% O2, 630 torr) the transgenic CuZnSOD mice showed increased survival, decreased morphologic evidence of lung damage such as edema and hyaline membrane formation, and reduction in the number of lung neutrophils. During continuous exposure to oxygen, both control and transgenic animals who successfully adapted to hyperoxia showed increased activity of lung antioxidant enzymes such as glutathione peroxidase (GPX), glutathione reductase (GR), and glucose-6-phosphate dehydrogenase (G6PD), whereas superoxide dismutase activity remained unchanged. The results show that expression of elevated levels of CuZnSOD decreases pulmonary oxygen toxicity and associated histologic damage and mortality.

Animals↗
PubMed1990

Down syndrome clinical symptoms are manifested in transfected cells and transgenic mice overexpressing the human Cu/Zn-superoxide dismutase gene.

Down syndrome (DS), the phenotypic expression of human trisomy 21, is presumed to result from overexpression of certain genes residing on chromosome 21 at the segment 21q22-the Down locus. The "housekeeping" enzyme CuZn-superoxide dismutase (CuZnSOD) is encoded by a gene from that region and its activity is elevated in DS patients. To investigate the possible involvement of CuZnSOD gene dosage in the etiology of the syndrome we have developed both cellular and animal models which enabled us to investigate the physiological consequences resulting from overexpression of the CuZnSOD gene. 1. Rat PC12 cells expressing elevated levels of transfected human CuZnSOD gene were generated. These transformants (designated PC12-hSOD) closely resembled the parental cells in their morphology, growth rate, and response to nerve growth factor, but showed impaired neurotransmitter uptake. The lesion was localized to the chromaffin granule transport mechanism. We found that the pH gradient (delta pH) across the membrane, which is the main driving force for amine transport, was diminished in PC12-hSOD granules. These results show that elevation of CuZnSOD activity interferes with the transport of biogenic amines into chromaffin granules. Since neurotransmitter uptake plays an important role in many processes of the central nervous system, CuZnSOD gene-dosage may contribute to the neurobiological abnormalities of Down's syndrome. 2. As an approach to the development of an animal model for Down syndrome, several strains of transgenic mice that carry the human CuZnSOD gene have been prepared. These animals express the transgene in a manner similar to that of humans, with 0.9 and 0.7-kilobase transcripts in a 1:4 ratio, and synthesize the human enzyme in an active form capable of forming human-mouse enzyme heterodimers. CuZnSOD activity is increased from 1.6 to 6.0-fold in the brains of four transgenic strains and to an equal or lesser extent in several other tissues. 3. To investigate the possible involvement of CuZnSOD gene dosage in the neuropathological symptoms of Down's syndrome, we analyzed the tongue muscle of the transgenic mice that express elevated levels of human CuZnSOD. The tongue neuromuscular junctions (NMJ) in the transgenic animals exhibited significant pathological changes, namely, withdrawal and destruction of some terminal axons and the development of multiple small terminals. The ratio of terminal axon area to postsynaptic membrane decreased, and secondary folds were often complex and hyperplastic. The morphological changes in the transgenic NMJ were similar to those previously seen in muscles of aging mice and rats as well as in tongue muscle of patients with Down's syndrome.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Diminished serotonin uptake in platelets of transgenic mice with increased Cu/Zn-superoxide dismutase activity.

Reduced levels of the neurotransmitter serotonin in blood platelets is a clinical symptom characteristic of individuals with Down's syndrome. To investigate the possible involvement of the Cu/Zn-superoxide dismutase (CuZnSOD) gene, which resides at the Down locus on chromosome no. 21, in the etiology of that symptom, we examined blood platelets of transgenic mice harboring the human CuZnSOD gene. It was found that platelets of transgenic CuZnSOD animals, which overexpress the transgene, contain lower levels of serotonin than nontransgenic littermate mice, due to a reduced rate of uptake of the neurotransmitter by the dense granules of the platelets. We found that the pH gradient (delta pH) across the dense granule membrane, which is the main driving force for serotonin transport, was diminished in dense granules of transgenic-CuZnSOD. Furthermore, a significantly lower than normal serotonin accumulation rate was also detected in dense granules isolated from blood platelets of Down's syndrome individuals. These findings suggest that CuZnSOD gene dosage is affecting the dense granule transport system and is thereby involved in the depressed level of blood serotonin found in patients born with Down's syndrome.

Animals↗
PubMed1988

Down's syndrome: abnormal neuromuscular junction in tongue of transgenic mice with elevated levels of human Cu/Zn-superoxide dismutase.

To investigate the possible involvement of Cu/Zn-superoxide dismutase (CuZnSOD) gene dosage in the neuropathological symptoms of Down's syndrome, we analyzed the tongue muscle of transgenic mice that express elevated levels of human CuZnSOD. The tongue neuromuscular junctions (NMJ) in the transgenic animals exhibited significant pathological changes, namely, withdrawal and destruction of some terminal axons and the development of multiple small terminals. The ratio of terminal axon area to postsynaptic membrane decreased, and secondary folds were often complex and hyperplastic. The morphological changes in the transgenic NMJ were similar to those previously seen in muscles of aging mice and rats as well as in tongue muscle of patients with Down's syndrome. The findings suggest that CuZnSOD gene dosage is involved in the pathological abnormalities of tongue NMJ observed in Down's syndrome patients.

Age Factors↗
PubMed1988

Premature aging changes in neuromuscular junctions of transgenic mice with an extra human CuZnSOD gene: a model for tongue pathology in Down's syndrome.

We examined the tongue muscles in several strains of transgenic mice carrying the human Zn-Cu superoxide dismutase (CuZnSOD) gene. The presence of the extra gene was confirmed in mated progeny and the gene product activity was measured in the tongue and found to be much higher than in normal littermate controls. Using electron microscopic morphometry, the neuromuscular junctions of the transgenic mice showed significant changes resembling excessive aging, with atrophy, degeneration, withdrawal, and sometimes destruction of the terminal axons, as well as the development of multiple small terminals. The myofibers showed little change except for slight hypertrophy and an increased variability in size. They also had more megamitochondria, fat droplets and lipofuscin bodies. Excess CuZnSOD generates H2O2 and hydroxyl radicals which affect both NMJ membranes and plasticity, and which may produce premature aging. The findings resemble those observed in tongues of patients with Down's syndrome, in whom an extra CuZnSOD gene is present as part of the trisomy of chromosome 21.

Aging↗
PubMed1987

Transgenic mice with increased Cu/Zn-superoxide dismutase activity: animal model of dosage effects in Down syndrome.

Down syndrome, the phenotypic expression of human trisomy 21, is presumed to result from a 1.5-fold increase in the expression of the genes on human chromosome 21. As an approach to the development of an animal model for Down syndrome, several strains of transgenic mice that carry the human Cu/Zn-superoxide dismutase gene have been prepared. These animals express the transgene in a manner similar to that of humans, with 0.9- and 0.7-kilobase transcripts in a 1:4 ratio, and synthesize the human enzyme in an active form capable of forming human-mouse enzyme heterodimers. Cu/Zn-superoxide superoxide dismutase activity is increased from 1.6- to 6.0-fold in the brains of four transgenic strains and to an equal or lesser extent in several other tissues. These animals provide a unique system for studying the consequences of increased dosage of the Cu/Zn-superoxide dismutase gene in Down syndrome and the role of this enzyme in a variety of other pathological processes.

Alzheimer Disease↗
PubMedDate not supplied

Tailchaser (Tlc): a new mouse mutation affecting hair bundle differentiation and hair cell survival.

We have undertaken a phenotypic approach in the mouse to identifying molecules involved in inner ear function by N-ethyl-N-nitrosourea mutagenesis followed by screening for new dominant mutations affecting hearing or balance. The pathology and genetic mapping of the first of these new mutants, tailchaser (Tlc), is described here. Tlc/+ mutants display classic behavioural symptoms of a vestibular dysfunction, including head-shaking and circling. Behavioural testing of ageing mice revealed a gradual deterioration of both hearing and balance function, indicating that the pathology caused by the Tlc mutation is progressive, similar to many dominant nonsyndromic deafnesses in humans. Based on scanning electron microscopy (SEM) studies, Tlc clearly plays a developmental role in the hair cells of the cochlea since the stereocilia bundles fail to form the characteristic V-shape pattern around the time of birth. By young adult stages, Tlc/+ outer hair bundles are grossly disorganised although inner hair bundles appear relatively normal by SEM. Increased compound action potential thresholds revealed that the Tlc/+ cochlear hair cells were not functioning normally in young adults. Similar to inner hair cells, the hair bundles of the vestibular hair cells also do not appear grossly disordered. However, all types of hair cells in the Tlc/+ inner ear eventually degenerate, apparently regardless of the degree of organisation of their hair bundles. We have mapped the Tlc mutation to a 12 cM region of chromosome 2, between D2Mit164 and D2Mit423. Based on the mode of inheritance and map location, Tlc appears to be a novel mouse mutation affecting both hair cell survival and stereocilia bundle development.

Animals↗