Biomedical subjects

S E Lewis

Publications and source records attributed to S E Lewis.

At least 19 recordsLinked to original sources

PubMed2002

Apollo: a sequence annotation editor.

The well-established inaccuracy of purely computational methods for annotating genome sequences necessitates an interactive tool to allow biological experts to refine these approximations by viewing and independently evaluating the data supporting each annotation. Apollo was developed to meet this need, enabling curators to inspect genome annotations closely and edit them. FlyBase biologists successfully used Apollo to annotate the Drosophila melanogaster genome and it is increasingly being used as a starting point for the development of customized annotation editing tools for other genome projects.

Animals↗

PubMed1992

Changes in chromatin proteins during optic nerve regeneration in the goldfish.

Regeneration of the goldfish optic nerve involves massive changes in the structure and pattern of macro-molecular synthesis in the retinal ganglion cells. To explore the mechanisms that underlie these events, we investigated the changes in chromatin proteins during the course of regeneration. Three major retinal chromatin proteins, two with apparent molecular weights of 58 kDa (C1 and C2) and one at 51 kDa (C3), all having isoelectric points around 5.5, showed a fourfold increase in their synthesis and/or accumulation by 14 days of regeneration. Synthesis of C1 and C3 decreased by day 32, the time at which the axons have grown back to the optic tectum and have formed many of their synapses; synthesis of C2 remained high through day 32. All three proteins bound to DNA-cellulose and required high salt concentrations (0.2-0.5 M KCl) to be eluted. C1 and C2 had similar proteolytic digestion patterns and reacted with monoclonal antibodies that recognize the goldfish intermediate filament proteins of the ON complex. The proteins identified here could be involved in structural alterations in the chromatin, or might serve as transcription factors to regulate gene expression during nerve regeneration.

Animals↗

PubMed1992

ENU mutagenesis in the mouse electrophoretic specific-locus test. 2. Mutational studies of mature oocytes.

Experiments were conducted using the biochemical specific-locus test to assess the mutagenicity of N-ethyl-N-nitrosourea (ENU) in mature oocytes of mice. C57Bl/6J females were treated with 100 mg/kg ENU by intraperitoneal injection and mated to untreated DBA males for 1 week following treatment. 1447 progeny were screened for evidence of mutations affecting the electrophoretic mobility of 32 different proteins; two mutants were detected by electrophoretic analyses. These results provide evidence that ENU is a germ-cell mutagen in mouse mature oocytes, although the frequency of mutants is somewhat lower than that obtained from spermatogonia treated with the same dose.

Animals↗

PubMed1992

Ethylene dibromide: negative results with the mouse dominant lethal assay and the electrophoretic specific-locus test.

Ethylene dibromide (1,2-dibromoethane; EDB) was tested for the induction of dominant lethal and electrophoretically-detectable specific-locus mutations in the germ cells of DBA/2J male mice. Males were treated with a single intraperitoneal injection of 100 mg/kg EDB and mated to two C57BL/6J females. In the dominant lethal assay, matings were carried out to measure the effect of EDB on meiotic and postmeiotic stages; germ cells representing spermatogonial stem cells were analyzed in the electrophoretic specific-locus test. Neither of these germ cell tests produced any evidence that EDB is a germ cell mutagen. It appears from these data and those reported in the literature that EDB, a genotoxic carcinogen that affects male fertility in some mammalian species, is not mutagenic in the germ cells of the male mouse.

Animals↗

PubMed1992

The influence of age and chronic restricted feeding on protein synthesis in the small intestine of the rat.

Rates of protein synthesis (measured in vivo) and growth of the small intestine were studied as a function of age in ad libitum fed (control) and chronic dietary-restricted rats. At weaning, the fractional rates of synthesis in the mucosal and muscularis externa and serosal layers of the small intestine of control animals were similarly high (90-100% per day). Although these rates subsequently declined with age in the muscularis externa and serosa, they remained constant in the mucosa. Restricted feeding (50% reduced intake), when imposed from weaning onwards, significantly extends the maximum life span of rodents. However, the change in nutritional status slows the accumulation of protein, RNA, and DNA in both layers of the small intestine. Although underfeeding did not prevent the age-related fall in muscularis externa and serosal protein synthesis, significantly higher rates (both fractional and per ribosome) were found when compared age for age with controls. Mucosal fractional synthetic rates were similarly increased by the reduced food intake. These changes in protein turnover in the small intestine are consistent with the higher rates of whole body turnover previously observed in chronically underfed rats.

Aging↗

PubMed1992

A malic enzyme probe detects cross-hybridizing sequences closely linked to loci encoding other metabolic enzymes.

The cytoplasmic malic enzyme (Mod-1) catalyzes the oxidative decarboxylation of malate: malate + NADP+----pyruvate + CO2 + NADPH + H+. Using a cDNA clone of Mod-1 as a probe, two new DNA markers not at the Mod-1 locus (restriction fragment length polymorphisms, RFLP) were detected by Southern blot analysis that showed extensive homology to Mod-1 sequences. Linkage of each restriction fragment length polymorphism to loci other than Mod-1 was assessed using the BXD (C57BL/6J x DBA/2J) recombinant inbred strains and confirmed by backcrosses. One polymorphic site, designated D9Rti1, was found to be closely linked to the phosphoglucomutase (Pgm-3) locus on Chromosome 9. The other hybridization site, designated D1Rti2, was closely linked to the isocitrate dehydrogenase (Idh-1) locus on Chromosome 1. The data presented imply that Mod-1 homologous sequences are tightly linked to three different metabolic enzymes.

Animals↗

PubMed1991

The biochemical specific-locus test and a new multiple-endpoint mutation detection system: considerations for genetic risk assessment.

The importance of studying the generation of mutations in mouse germ cells is emphasized, and the utility of the biochemical specific-locus test in detecting germinal mutations is described. All experiments performed to date using this test are listed. The relevance of dominant mutations to human genetic risk is also discussed. Finally, the value of using multiple tests for the study of in vivo germinal mutations is discussed, and the design for a new multiple-endpoint system is presented.

Animals↗

PubMed1991

ENU mutagenesis in the mouse electrophoretic specific-locus test, 1. Dose-response relationship of electrophoretically-detected mutations arising from mouse spermatogonia treated with ethylnitrosourea.

The mouse electrophoretic specific-locus test for induced germ-cell mutations, was used to determine the response of spermatogonial stem cells to a series of doses of the germ cell mutagen N-ethyl-N-nitrosourea (ENU). Male DBA/2J and C57B1/6J mice were treated with doses of 50, 100, 200 or 250 mg/kg ENU and their progeny screened for electrophoretically-detectable mutations at 32 separate loci. As expected, increasing doses of ENU led to increasing mutant frequencies. The differences in mutant frequencies between treated DBA/2J and C57B1/6J males were not statistically significant.

Alleles↗

PubMed1991

Electrophoretic variation in multiple recessive tester, T, stock mice.

The multiple recessive tester stock, homozygous for seven recessive visible markers, has been used since the 1950s in the specific locus test of mutagenicity in the mouse. The stock was developed by W.L. Russell in Oak Ridge, sent to the MRC Radiobiology Unit (Harwell) in 1953 and then passed to Research Triangle Institute (RTI) in 1988. Stocks are maintained by random mating in all three centres. and in addition stocks that have been selected for homozygosity at certain enzyme and protein markers are kept at both Harwell and RTI. The extent of electrophoretic variation was investigated in the random bred tester stocks at Harwell in 1981 and 1990, and in both random bred and fixed tester stocks at RTI in 1990. Altogether 44 loci were scored and eight of these (Acy-1, Es-3, Gpi-1, Hba, Hbb, Idh-1, Mod-1 and Pgd) have been polymorphic in one or more colonies at various times. Three loci (Es-3, Hbb and Mod-1) had low levels of polymorphism in 1981 and had become monomorphic by 1990. Despite this slight loss of variation, overall the tester stocks show considerable variability. The proportion of polymorphic loci and mean heterozygosity is of the same order of magnitude as island populations of wild mice or other isolated random bred laboratory populations. Contamination of tester stocks with other stocks can be ruled out, and thus tester stocks can be considered to be characteristic island populations. The retention of an appreciable amount of genetic variability in tester stocks is of practical importance in designing new mutation tests involving these mice. When using these stocks, care must be taken to ensure that they are homozygous for the loci under test.

Alleles↗

PubMed1991

The effects of age and chronic restricted feeding on protein synthesis and growth of the large intestine of the rat.

1. In vivo rates of protein synthesis and growth of the large intestine were studied in ad libitum fed control and chronic diet restricted rats between 3 and 149 weeks post partum. 2. Restricted feeding (50% reduced intake) when imposed from weaning significantly extends the life span of rodents through an unknown biochemical mechanism. 3. The change in nutritional status slows the accumulation of RNA, DNA and protein in the large intestine but does not modify the fractional rate of protein synthesis. 4. It was therefore deduced, that intracellular protein degradation, or the rate of mucosal cell extrusion into the gut lumen, is accelerated by chronic restricted feeding.

Age Factors↗

PubMed1990

Synthesis, axonal transport, and turnover of the high molecular weight microtubule-associated protein MAP 1A in mouse retinal ganglion cells: tubulin and MAP 1A display distinct transport kinetics.

Microtubule-associated proteins (MAPs) in neurons establish functional associations with microtubules, sometimes at considerable distances from their site of synthesis. In this study we identified MAP 1A in mouse retinal ganglion cells and characterized for the first time its in vivo dynamics in relation to axonally transported tubulin. A soluble 340-kD polypeptide was strongly radiolabeled in ganglion cells after intravitreal injection of [35S]methionine or [3H]proline. This polypeptide was identified as MAP 1A on the basis of its co-migration on SDS gels with MAP 1A from brain microtubules; its co-assembly with microtubules in the presence of taxol or during cycles of assembly-disassembly; and its cross-reaction with well-characterized antibodies against MAP 1A in immunoblotting and immunoprecipitation assays. Glial cells of the optic nerve synthesized considerably less MAP 1A than neurons. The axoplasmic transport of MAP 1A differed from that of tubulin. Using two separate methods, we observed that MAP 1A advanced along optic axons at a rate of 1.0-1.2 mm/d, a rate typical of the Group IV (SCb) phase of transport, while tubulin moved 0.1-0.2 mm/d, a group V (SCa) transport rate. At least 13% of the newly synthesized MAP 1A entering optic axons was incorporated uniformly along axons into stationary axonal structures. The half-residence time of stationary MAP 1A in axons (55-60 d) was 4.6 times longer than that of MAP 1A moving in Group IV, indicating that at least 44% of the total MAP 1A in axons is stationary. These results demonstrate that cytoskeletal proteins that become functionally associated with each other in axons may be delivered to these sites at different transport rates. Stable associations between axonal constituents moving at different velocities could develop when these elements leave the transport vector and incorporate into the stationary cytoskeleton.

Animals↗

PubMed1990