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R W Williams

Publications and source records attributed to R W Williams.

At least 73 records · Page 4Linked to original sources
PubMed1997

Decreased retinal ganglion cell number and misdirected axon growth associated with fissure defects in Bst/+ mutant mice.

PURPOSE: The autosomal semidominant mutation Bst (belly spot and tail) is often associated with small and atrophic optic nerves in adult mice and shares several important attributes with heritable optic nerve atrophy in humans. In this article, the authors present adult and developmental studies on the retinal phenotype in Bst/+ mice. METHODS: Retinal ganglion cells in adult Bst/+ mice were labeled retrogradely with horseradish peroxidase injected into the right optic tract. Labeled ganglion cells were mapped in whole-mounted retinas ipsilateral and contralateral to the injection site. The number of axons in optic nerves of these and other cases were quantified using an electron microscopic method. Eyes of neonatal, embryonic day 15 (E15), and embryonic day 12 (E12) Bst/+ mutants were examined histologically to understand the etiology of the retinal phenotype. RESULTS: Approximately 60% of adult Bst/+ mice have deficient direct pupillary light responses. This neurologic phenotype is associated with a reduction in the number of retinal ganglion cells from the wild-type average of 67,000 to less than 20,000 in Bst/+ mutants. Ganglion cells with crossed projections are more severely affected than those with uncrossed projections. Histologic analysis of eyes from E12 mice reveals a delayed closure of the optic fissure. Despite this abnormality, other ocular structures appear relatively normal. However, some E15 mutants exhibit marked disorganization of the retinal neuroepithelium, and ganglion cell axons are found between pigmented and neural retina. At birth, optic nerves of affected mice are smaller than those of wild-type mice, ectopic axons are found within the eyes, and the ganglion cell layer contains many dying cells. CONCLUSIONS: The expression of the retinal phenotype in Bst/+ mutants is highly variable-ranging from a complete absence of ganglion cells to numbers comparable to that in wild-type mice. The reduction in ganglion cell number in affected adult Bst/+ mice is attributable to the failure of ganglion cell axons to reach the optic nerve head early in development. Delayed fusion of the fissure is consistently associated with the Bst/+ genotype and probably contributes to the failure of ganglion cell axons to grow out of the eye.

Animals↗
PubMed1996

Genetic and environmental control of variation in retinal ganglion cell number in mice.

How much of the remarkable variation in neuron number within a species is generated by genetic differences, and how much is generated by environmental factors? We address this problem for a single population of neurons in the mouse CNS. Retinal ganglion cells of inbred and outbred strains, wild species and subspecies, and F1 hybrids were studied using an unbiased electron microscopic method with known technical reliability. Ganglion cell numbers among diverse types of mice are highly variable, ranging from 32,000 to 87,000. The distribution of all cases (n = 252) is close to normal, with a mean of 58,500 and an SD of 7800. Genetic factors are most important in controlling this variation; 76% of the variance is heritable and up to 90% is attributable to genetic factors in a broad sense. Strain averages have an unanticipated bimodal distribution, with distinct peaks at 55,500 and 63,500 cells. Three pairs of closely related strains have ganglion cell populations that differ by > 20% (10,000 cells). These findings indicate that different alleles at one or two genes have major effects on normal variation in ganglion cell number. Nongenetic factors are still appreciable and account for a coefficient of variation that averages approximately 3.6% within inbred strains and isogenic F1 hybrids. Age- and sex-related differences in neuron number are negligible. Variation within isogenic strains appears to be generated mainly by developmental noise.

Aging↗
PubMed1996

Changes in mutagenicity during crude oil degradation by fungi.

Two fungal strains, Cunninghamella elegans and Penicillium zonatum, that grow with crude oil as a sole carbon source were exposed to three crude oils that exhibit a range of mutagenic activity. At regular time intervals following fungal incubation with the various crude oils, extracts were tested for the presence of mutagenic activity using the spiral Salmonella assay. When the most mutagenic of the oils, Pennsylvania crude oil, was degraded by C. elegans or by P. zonatum, its mutagenicity was significantly reduced; corresponding uninoculated (weathered) controls of Pennsylvania crude remained mutagenic. West Texas Sour crude oil, a moderately mutagenic oil, exhibited little change in mutagenicity when incubated with either C. elegans or P. zonatum. Swanson River Field crude oil from Cook Inlet, Alaska is a slightly mutagenic oil that became more mutagenic when incubated with C. elegans; weathered controls of this oil showed little change in mutagenicity. Mycelial mat weights measured during growth on crude oils increased corresponding to the biodegradation of about 25% of the crude oil.

Biodegradation, Environmental↗
PubMed1996

Clonal architecture of the mouse retina.

The study of chimeric retinas has yielded insight on the early development of retina. The close match in chimerism ratios between right and left retinas is significant and supports the idea that both retinas originate from a common population of progenitors. We are able to estimate numbers of progenitor cells that contribute to the formation of the retina and the approximate time at which this small group is isolated from surrounding prosencephalic cell fields. These cells undergo at least five rounds of division before the first retinal neurons are generated. The mouse retina is not build from the center outward. There is simultaneous expansion and differentiation in all parts of the retina and as a result clones are not arranged in wedges. Instead the mouse retina is a patchwork of clones that do not differ greatly in size from center to periphery. The most consistent radial feature in mouse retina is a raphe left at the line of fusion of the margins of the ventral fissure. Processes that shape the clonal patchwork are both passive and active, intrinsic and extrinsic. Certain features of the clonal architecture of the retina, such as the size differences of clones are primarily passive responses to extrinsic forces on progenitor cells and their progeny. The fifteen-fold range in the size of cohorts is not due to intrinsic differences in the proliferative capacity of individual progenitor cells, but is due to the extent of cell movement and mixing at early stages of development. In contrast, active or intrinsic processes are illustrated by the partial (and still controversial) restriction of retinal progenitors, the possible clonal differences between ganglion cells with crossed and uncrossed projections, and the consistent differences in ratios of albino and pigmented genotypes in peripheral and central retina.

Animals↗
PubMed1995

Hepatitis core antigen produced in Escherichia coli: subunit composition, conformational analysis, and in vitro capsid assembly.

The production and biochemical and physiocochemical analysis are described of recombinant-produced hepatitis B virus core antigen (HBcAg capsid) and the corresponding particle produced by a deletion mutant missing the C-terminal 39 residues (HBeAg). Conditions for producing HBeAg from HBcAg capsids by in vitro proteolysis are also described. The morphology and masses of these capsids were determined by scanning transmission electron microscopy. Both HBcAg and HBeAg capsids comprise two size classes that correspond to icosahedral lattices with triangulation numbers (T) of 3 and 4, containing 180 and 240 subunits per capsid, respectively. This dimorphism was confirmed by sedimentation equilibrium and sedimentation velocity measurements on a Beckman Optima XL-A analytical ultracentrifuge. More than 60% of HBcAg capsids were T = 4, whereas only 15-20% of HBeAg capsids were of this size class: the remainder, in each case, were T = 3. Circular dichroism and Raman spectroscopy were used to determine the overall secondary structures of HBcAg and HBeAg capsids. Both have high alpha-helical contents, implying that this capsid protein does not conform to the canonical beta-barrel motif seen for all plant and animal icosahedral viral capsids solved to date. We suggest that the C-terminal domain of HBcAg has a random coil conformation. In vitro dissociation of HBeAg capsids under relatively mild conditions yielded stable dimers. The reassociation of HBeAg dimers into capsids appears to be driven by hydrophobic processes at neutral pH. Capsid assembly is accompanied by little change in subunit conformation as judged by circular dichroism and fluorescence spectroscopy. The thermal stability of HBcAg capsids was compared calorimetrically with that of in vitro assembled HBeAg capsids. Both have melting temperatures > 90 degrees C, implying that the C-terminal region makes little difference to the thermal stability of HBcAg: nevertheless, we discuss its possible role in facilitating disassembly and the release of viral nucleic acid.

Calorimetry, Differential Scanning↗
PubMed1995

Genetic control of retinal projections in inbred strains of albino mice.

Mutations in the tyrosinase gene are often associated with a misrouting of retinal ganglion cell axons at the optic chiasm. In albinos, tyrosinase activity is lost and some ganglion cell axons that would normally project into the ipsilateral optic tract instead cross midline and project into the contralateral tract. The developmental mechanisms that cause this modification in neuronal connectivity are unknown. In this study, we screened six diverse strains of albino mice (strains 129, A, AKR, BALB/c, C57BL/6-c/c, and CD-1) to discover genetically determined variations and possible gene loci that might affect the severity of the albino decussation abnormality. Ganglion cells were retrogradely labeled with horseradish peroxidase, and the ipsilaterally and contralaterally projecting cells were counted. The average number of ipsilaterally projecting ganglion cells in the six albino strains varies from 1,000 to 1,300. Despite this variation, 1.8-1.9% of the total population projects ipsilaterally in each strain. In comparison, 2.8% project ipsilaterally in the pigmented strain, C57BL/6(-)+/+. However, the percentage of displaced, ipsilaterally projecting cells varies substantially among albino strains--from a low of 4% in strain CD-1 to a high of nearly 10% in C57BL/6-c/c. We conclude that even with large differences in genetic background and in absolute numbers of ganglion cells, there is no appreciable variation in the magnitude of decussation error among albino mice. The consistent effect of null alleles at tyrosinase suggests a comparably tight linkage between the biochemical activity of this enzyme and the mechanisms that control decussation phenotype.

Alleles↗
PubMed1995

Analysis of the retinas and optic nerves of achiasmatic Belgian sheepdogs.

An autosomal recessive mutation carried in a family of black Belgian sheepdogs eliminates the optic chiasm--all retinal ganglion cell axons extend directly into the ipsilateral optic tract. One key issue we are trying to resolve is whether the retina or the chiasm is the principal site of mutant gene action. In this study, we have examined retinas of mutants to discover any associated changes in retinal structure. Retinas of mutant animals are relatively normal. Inner and outer nuclear layers are qualitatively indistinguishable from those of normal dogs. The principal difference is that the area centralis of mutants is smaller and had a lower peak ganglion cell density than that of normal dogs (8,100 vs 10,500/mm2, P < 0.05). This mutant phenotype is similar to that seen in retinas of Siamese cats and albino ferrets. Beyond area centralis, the central-to-peripheral gradient in ganglion cell density is normal in mutants. The size of the optic nerves, density of axons, and total number of axons do not differ between mutant and normal dogs. One of three mutant dogs had a small abnormal optic chiasm. Retrograde labeling of ganglion cells demonstrated that the residual crossed projection originated from cells in a widespread region in nasal retina and not solely from the peripheral nasal region, as might be expected of an anti-albino. Although our analysis does not rule out the retina as a site of mutant gene action, the modest differences between mutant and normal retinas suggest that the mutation either acts outside the retina or exerts a highly specific effect on ganglion cell trajectories alone.

Animals↗
PubMed1995

Atrazine treatment potentiates excretion of mutagenic urine in 2,6-dinitrotoluene-treated Fischer 344 rats.

Atrazine (ATZ), an s-triazine herbicide, is a widespread environmental contaminant. The hepatocarcinogenic component of technical grade dinitrotoluene, 2,6-dinitrotoluene (2,6-DNT, 19.5%), is a byproduct of trinitrotoluene synthesis and is found at production sites. This study explores the effect of ATZ treatment on the bioactivation of the promutagen, 2,6-DNT. Male Fischer 344 rats (5 weeks old) were administered 50 mg/kg of ATZ by gavage for 5 weeks. At 1, 3, and 5 weeks, both DMSO-control and ATZ-pretreated rats were treated p.o. with 75 mg/kg of 2,6-DNT and were housed in metabolism cages for urine collection. Sulfatase- and beta-glucuronidase-treated, concentrated urine was bioassayed for urinary mutagens in a microsuspension modification of the Salmonella assay with and without metabolic activation. No significant change in mutagen excretion was observed in ATZ-treated rats; however, an elevation in direct-acting urine mutagens from rats receiving ATZ and 2,6-DNT at weeks 1 (359 +/- 68 vs. 621 +/- 96 revertants/ml) and 5 (278 +/- 46 vs. 667 +/- 109 revertants/ml) of treatment was observed. The increase in production of urinary mutagens was accompanied by an elevation in small intestinal nitroreductase activity. Increases in large intestinal nitroreductase and beta-glucuronidase were observed after 5 weeks. There was no apparent effect of ATZ following 5 weeks of treatment on the production of 2,6-DNT-derived hepatic DNA adducts. ATZ treatment modifies intestinal enzymes responsible for promutagen bioactivation, and potentiates the excretion of mutagenic urine in 2,6-DNT-treated animals.

Animals↗
PubMed1995

Ocular motor abnormalities in achiasmatic mutant Belgian sheepdogs: unyoked eye movements in a mammal.

We studied the eye movements of several members of a family of Belgian sheepdogs that includes achiasmatic mutants. Our aim was to identify the types of nystagmus and other ocular motor abnormalities exhibited by the mutants. We also recorded from several unaffected heterozygous carriers of the genetic mutation and from a normal Irish Setter. Mutant dogs exhibited nystagmus waveforms that were occasionally similar to those of humans with congenital nystagmus (CN). Foveating and braking saccades and foveation periods were seen in some waveforms. More common were pendular oscillations of both eyes that were essentially independent in amplitude and phase. At some times there was a pendular nystagmus with a 180 deg phase shift between the movements of unaffected relatives did not reveal any saccadic instabilities. However, small saccadic intrusions could have been masked by quantization artifacts. Individual dogs from this family provide an animal model of the ocular motor consequences of the disturbed visual input caused by the absence of an optic chiasm and a novel model of CN. Despite any other ocular motor abnormalities present, the CN may be studied in isolation just as in humans it is studied when strabismus and other types of nystagmus are present. Further studies of ocular motor development and function in achiasmatic dogs have the potential to reveal both the organization of the control systems for each extraocular muscle and the role of yoking of the agonist muscles of the two eyes.

Animals↗
PubMed1995

Initial study of periodontal status in non-insulin-dependent diabetics in Mauritius.

OBJECTIVES: Investigation of Mauritian non-insulin diabetic periodontal health. METHODS: In Port Louis, the capital of Mauritius, 24 patients with non-insulin-dependent diabetes mellitus were matched by age with 24 controls. Because matching was incomplete for gender and race, the groups were treated as independent for data analysis. Operator-blind scores were recorded for the presence of plaque, bleeding on probing, probing depth, recession and probing attachment level. RESULTS: When variations in plaque and age were taken into account, there was a significant difference in probing attachment level between the groups (diabetic mean = 4.16 mm, control mean = 3.09 mm), and an effect of gender on gingival bleeding which may relate to tobacco smoking. CONCLUSION: In an isolated community with a 13% prevalence of NIDDM, this study confirms previous periodontal findings regarding the effect of the disease.

Adult↗
PubMed1995

Potentiation of 2,6-dinitrotoluene genotoxicity in Fischer 344 rats by pretreatment with coal tar creosote.

Pretreatment of male Fischer 344 rats for 5 wk with coal tar creosote, a coal distillation product that is widely used as a wood preservative, potentiated the excretion of urinary mutagens in 2,6-dinitrotoluene (DNT) treated rats. Creosote increased the bioactivation of DNT to significantly greater levels of urinary genotoxic metabolites and/or formed DNA adducts in the liver. A significant increase in the excretion of mutagenic DNT metabolites was observed after the first week of creosote treatment, peaked at wk 3, and then decreased by 33% after 5 wk of treatment. Nevertheless, there was a significant increase (66%) in the formation of DNT-derived DNA adducts in the livers of rats treated with DNT plus creosote at wk 5. Increased cecal beta-glucuronidase activity and reduced small intestinal nitroreductase activity may play roles in the bioactivation of DNT. The excretion of mutagenic DNT metabolites supplies useful information about the bioactivation of DNT; it does not provide a useful index of DNT-derived hepatic DNA adduct formation. Such interactions could be important to predictive risk assessment because the overall cancer risk of such chemical mixtures may exceed the sum of the component risks.

Analysis of Variance↗
PubMed1995

CDR molecular localization of possible anti-idiotypic anti-DNA antibodies in normal subjects, patients with SLE, and SLE first-degree relatives.

Patients with active systemic lupus erythematosus (SLE) with disease worsening or severe flares frequently show very low levels of serum immunoglobulin G (IgG) anti-F(ab')2 antibody. Anti-F(ab')2 antibody probably represents a polyclonal collection of generic anti-idiotypic antibodies involved in immune homeostasis. We synthesized the entire variable regions of the heavy and light chains (VH and VL) of two monoclonal anti-DNA antibodies, V88 and 2A4, as overlapping 7-mers on small polypropylene pins and tested these linear segments of anti-DNA V-regions for reactivity against serum samples from 10 normal subjects with high serum IgG anti-F(ab')2, 11 normal subjects with low anti-F(ab')2, 5 patients with SLE with active uncontrolled disease, 3 patients with SLE in remission, and 8 unaffected normal first-degree SLE relatives. VH and VL regions of a human monoclonal IgG anti-rabies antibody were also tested as a control. Concordant IgG antibody reacting with the same complementarity-determining regions (CDRs) was arbitrarily scored as indicative of the presence of anti-idiotypic antibody in test serum samples. Among normal subjects with either high or low serum anti-F(ab')2 levels, 10% to 21% showed strong concordant anti-CDR reactions with either the monoclonal anti-DNA or the control monoclonal anti-rabies V-region sequences. However, all patients with active SLE showed no detectable anti-CDR-reactive antibody. Patients with SLE in remission often showed return of strong concordant anti-CDR antibody. Normal unaffected SLE relatives also showed high levels of anti-CDR reactivity for both monoclonal anti-DNA and anti-rabies antibody sequences.

Adolescent↗
PubMed1994

Betadoublet: de novo design, synthesis, and characterization of a beta-sandwich protein.

How an amino acid sequence encodes the information necessary for a protein to adopt a unique tertiary structure remains unresolved. We are addressing this problem by designing "from scratch" protein molecules that will adopt predetermined three-dimensional structures. Based on this strategy, two identical four-stranded beta-sheets were designed to dimerize and form a beta-sandwich protein, called betadoublet. A synthetic gene encoding half the beta-sandwich protein was expressed in Escherichia coli, and the protein was purified to homogeneity. Biophysical characterization of betadoublet in aqueous solution demonstrated that the disulfide formed between the two sheets and that the dimer was a compact unaggregated globular protein, consisting predominantly of beta-sheet and stable to thermal denaturation. It has some backbone amide protons whose exchange is slow enough to be measured by NMR but binds more of the dye 1-anilinonaphthalene-8-sulfonate than a well-folded protein.

Amino Acid Sequence↗