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S W Wilson

Publications and source records attributed to S W Wilson.

At least 55 records · Page 3Linked to original sources
PubMed1994

Regulatory gene expression boundaries demarcate sites of neuronal differentiation in the embryonic zebrafish forebrain.

During development of the zebrafish forebrain, a simple scaffold of axon pathways is pioneered by a small number of neurons. We show that boundaries of expression domains of members of the eph, forkhead, pax, and wnt gene families correlate with the positions at which these neurons differentiate and extend axons. Analysis of genetically or experimentally altered forebrains indicates that if a boundary is maintained, there is appropriate neural differentiation with respect to the boundary. Conversely, in the absence of a boundary, there is concomitant disruption of neural patterning. We also show that a strip of cells within the dorsal diencephalon shares features with ventral midline cells. This strip of cells fails to develop in mutant fish in which specification of the ventral CNS is disrupted, suggesting that its development may be regulated by the same inductive pathways that pattern the ventral midline.

Animals↗
PubMed1994

Spatially regulated expression of three receptor tyrosine kinase genes during gastrulation in the zebrafish.

We describe the isolation and early developmental expression of three novel zebrafish genes (rtk1-3) that encode members of the eph family of receptor tyrosine kinases. At the onset of gastrulation, rtk1 is expressed in the shield region corresponding to the future dorsal side of the embryo. As gastrulation proceeds, both rtk1 and rtk2 are expressed within the axial hypoblast along the entire axis of the embryo. After the gastrula stage is complete, expression of both genes is maintained in precursor cells of the notochord in the tail bud but is downregulated in other regions of the axial hypoblast, rtk3 is expressed in anterior axial hypoblast including the 'pillow' at the anterior tip of the hypoblast and in paraxial tissue in posterior regions of the embryo. We show that the precise spatial regulation of expression of rtk genes, ntl and goosecoid along the anteroposterior axis is maintained in embryos that have no dorsoventral axis. This indicates that the mechanisms that regulate gene expression along the anteroposterior and dorsoventral axes of the hypoblast may be independent.

Amino Acid Sequence↗
PubMed1993

Border disputes: do boundaries play a role in growth-cone guidance?

One of the earliest indications of regional patterning in the CNS is the spatially restricted expression of regulatory genes within the neuroepithelium. Many of these genes encode transcription factors and, although little is known of their downstream targets, it seems likely that they control the identity of cells in different regions of the CNS. This review discusses how the expression of these patterning genes might influence the location at which the first axon pathways in the CNS are pioneered. Evidence is described that suggests that the boundary regions between adjacent domains of regulatory gene expression influence where the first axons will extend.

Animals↗
PubMed1992

Axonal trajectories and distribution of GABAergic spinal neurons in wildtype and mutant zebrafish lacking floor plate cells.

The role of the midline floor plate cells in the neuronal differentiation of the spinal cord was examined by comparing putative GABAergic neurons in wildtype zebrafish embryos with those in cyc-1 mutant embryos. The mutation produces a pleiotropic recessive lethal phenotype and is severe in rostral brain regions, but its direct effect in the caudal hindbrain and the spinal cord is apparently restricted to the depletion of the midline floor plate cells. In wildtype embryos, an antibody against the neurotransmitter GABA labeled the cell bodies, axons, and growth cones of three classes of previously identified neurons; dorsal longitudinal neurons (DoLA), commissural secondary ascending neurons (CoSA), and ventral longitudinal neurons (VeLD). A novel ventral cell type, Kolmer-Agduhr (KA) neurons, was also labeled. In the cyc-1 mutant, abnormalities were observed in some, but not all, of the GABAreactive CoSA, VeLD, and KA axons, while the axonal trajectories of DoLA neurons were not affected. Furthermore, the number of KA cells was reduced in the mutant while the numbers of the other GABAreactive cells were unperturbed. These observations corroborate our earlier hypothesis that the floor plate cells are one of several guidance cues that direct axonal outgrowth near the ventral midline of the spinal cord. They also suggest that the floor plate cells may play a role in the cellular differentiation of the spinal cord of zebrafish embryos.

Animals↗
PubMed1992

Zebrafish pax[b] is involved in the formation of the midbrain-hindbrain boundary.

Among the genes thought to be involved in patterning the nervous system are a family of developmentally regulated paired box-containing (Pax) genes. Mutations in some of these Pax genes lead to severe developmental abnormalities. Zebrafish pax[b](pax[zf-b]) is a member of the Pax gene family that is expressed in the presumptive posterior midbrain from the end of gastrulation and, at later stages, in other localized regions of the developing embryo. Here we show that injection of antibodies raised against the pax[b] protein causes a localized malformation at the midbrain-hindbrain boundary. In situ hybridizations demonstrate that antibody injection causes downregulation of pax[b] transcripts in the posterior midbrain and alteration of wnt-1 and eng-2 expression in this area. The data demonstrate an involvement of pax[b] in the formation of the midbrain-hindbrain junction.

Animals↗
PubMed1992

Acquisition of regional and cellular identities in the developing zebrafish nervous system.

In the past year, several new techniques have been used with great success in the study of nervous system development in the zebrafish. Perhaps the most exciting results have come from experiments in which single identified cells or small groups of cells have been transplanted between embryos in order to examine cell determination and the site of action of genetic mutations.

Animals↗
PubMed1991

A pioneering growth cone in the embryonic zebrafish brain.

During development of the nervous system, growth cones navigate very precisely to their appropriate, often distant, targets. In insects, the task of establishing the earliest pathways is accomplished by a small number of neurons, termed pioneers. These neurons have axons that lay down an early scaffold, which provides a substrate for many later-developing axons. Here we show that a similar type of cell exists in the embryonic vertebrate brain. Using light- and electron-microscopic techniques we have examined the formation of one of the earliest tracts in the zebrafish brain. We find that it is pioneered at a precise time by the growth cone of a single neuron present in a predictable location. These observations show a fundamental similarity in the establishment of axonal pathways in the central nervous systems of both invertebrates and vertebrates.

Animals↗
PubMed1991

Continuous growth of the motor system in the axolotl.

During growth of the axolotl, motor neurons, and muscle fibres are added to the motor system. By double labelling neurons with tritiated thymidine and retrogradely transported HRP, we show that some motor neurons are born at postembryonic stages. Further analysis of motor neurons with the aid of HRP reveals this population of newly born cells relatively frequently in small (5-7 cm long) axolotls, but only rarely in large (7-13 cm long) axolotls. Evidence is presented that suggests that these immature cells are in the process of migrating from close to the ependyma out to the ventral horn. HRP transport also reveals growth cones of advancing axons within spinal nerves in animals up to 6 cm in length. Cell counts by light and electron microscopic methods show that muscle fibres are generated throughout larval life in the iliotibialis, a typical limb muscle. This analysis provides data consistent with the notion that new muscle fibres are added from a localised growth zone situated at the superficial edge of the muscle. These results are discussed in terms of the correlation between continuous growth of the motor system and the ability of the axolotl to functionally repair lesions to the peripheral nervous system.

Ambystoma↗
PubMed1991

Cloning and characterization of the gene for an additional extracellular serine protease of Bacillus subtilis.

We have purified a minor extracellular serine protease from a strain of Bacillus subtilis bearing null mutations in five extracellular protease genes: apr, npr, epr, bpr, and mpr (A. Sloma, C. Rudolph, G. Rufo, Jr., B. Sullivan, K. Theriault, D. Ally, and J. Pero, J. Bacteriol. 172:1024-1029, 1990). During purification, this novel protease (Vpr) was found bound in a complex in the void volume after gel filtration chromatography. The amino-terminal sequence of the purified protein was determined, and an oligonucleotide probe was constructed on the basis of the amino acid sequence. This probe was used to clone the structural gene (vpr) for this protease. The gene encodes a primary product of 806 amino acids. The amino acid sequence of the mature protein was preceded by a signal sequence of approximately 28 amino acids and a prosequence of approximately 132 amino acids. The mature protein has a predicted molecular weight of 68,197; however, the isolated protein has an apparent molecular weight of 28,500, suggesting that Vpr undergoes C-terminal processing or proteolysis. The vpr gene maps in the ctrA-sacA-epr region of the chromosome and is not required for growth or sporulation.

Amino Acid Sequence↗
PubMed1991

Stereotyped pathway selection by growth cones of early epiphysial neurons in the embryonic zebrafish.

In this report we have examined the development of one of the earliest projections in the embryonic zebrafish brain, that from the epiphysis. Epiphysial axons and growth cones were labelled anterogradely in whole-mounted brains, using either the carbocyanine dye, diI, or horseradish peroxidase (HRP). Some embryos were also either stained with anti-acetylated tubulin or HNK-1 antibodies to reveal other axons in the brain, or were secondarily sectioned for light and electron microscopy. The epiphysial axons have a very specific projection pattern and virtually all axons grow precisely to their target regions without error. The first epiphysial growth cone extends ventrally from the epiphysis into the dorsoventral diencephalic tract at 19-20 h post-fertilisation (h PF). Several hours later, it turns rostrally to grow alongside axons in the tract of the postoptic commissure. The morphology of the leading growth cone changes in predictable ways at different locations along its pathway and these changes correlate with differences in the local environment that it encounters. In contrast to other published descriptions of other developing systems, the epiphysial growth cone is no more complex either when pioneering a pathway, or when encountering divergent axonal pathways. Indeed, it is most complex (i.e. has the greatest number of processes) when it first starts to follow the tract of the postoptic commissure. The presence and selective retention of filopodia within other axonal pathways suggests that growth cones have access to these pathways but do not select them. These observations support the notion that local guidance cues exist within the early scaffold of brain tracts. Subsequent epiphysial axons form a tight fascicle within the dorsoventral diencephalic tract, but abruptly defasciculate from each other upon turning rostrally into the tract of the postoptic commissure. Epiphysial growth cones that enter this tract at abnormal locations still turn in the appropriate direction. Therefore, guidance cues are not restricted solely to the normal intersections but may be distributed along the length of the tracts. The epiphysial growth cones and axons have very characteristic spatial relations to other axons in the tracts of the developing brain. They are restricted to the dorsal region of the tract of the postoptic commissure and the rostral region of the postoptic commissure. At early developmental stages, the epiphysial axons are the only axons within the dorsoventral diencephalic tract and they are located very superficially within the neuroepithelium. At later stages, they are displaced to deeper regions of the neuropil by non-epiphysial axons.

Animals↗
PubMed1990

The development of a simple scaffold of axon tracts in the brain of the embryonic zebrafish, Brachydanio rerio.

We have examined neuronal differentiation and the formation of axon tracts in the embryonic forebrain and midbrain of the zebrafish, between 1 and 2 days postfertilisation. Axons were visualised with three techniques; immunocytochemistry (using HNK-1 and antiacetylated tubulin antibodies) and horseradish peroxidase (HRP) labelling in whole-mounted brains, and transmission electron microscopy. Differentiation was monitored by histochemical staining for acetylcholinesterase (AChE). These independent methods demonstrated that a simple grid of tracts and commissures forms the initial axon scaffold of the brain. At 1 day, the olfactory nerve, four commissures, their associated tracts and three other non-commissural tracts are present. By 2 days, these tracts and commissures have all greatly enlarged and, in addition, the optic nerve and tract, and three new commissures and their associated tracts have been added. Small applications of HRP at various sites revealed the origins and projections of some of these earliest axons. Retrogradely labelled cell bodies originated from regions that were also positive for AChE activity. At 1 day, HRP-labelled axons were traced: (1) from the olfactory placode through the olfactory nerve to the dorsal telencephalon; (2) from the telencephalon into the tract of the anterior commissure and also to the postoptic region of the diencephalon; (3) from the hindbrain through the ventral midbrain and diencephalon to the postoptic commissure; (4) from the dorsal diencephalon (in or near the epiphysis) to the tract of the postoptic commissure; (5) from ventral and rostral midbrain through the posterior commissure. Three new projections were demonstrated at 2 days: (1) from the retina through the tract of the postoptic commissure to the tectum; (2) from the telencephalon to the contralateral diencephalon; and (3) from the telencephalon to the ventral flexure. These results show that at 1 day, the zebrafish brain is impressively simple, with a few small, well-separated tracts but by 2 days the brain is already considerably more complex. Most of the additional axons added onto pre-existent tracts rather than pioneered new ones supporting the notion that other axons play a crucial role in the guidance of early central nervous system (CNS) axons.

Acetylcholinesterase↗
PubMed1987

Trace mineral supplementation of burn patients: a national survey.

Much research effort has been devoted to determination of caloric and protein requirements in burn patients. Although it is generally accepted that trace mineral requirements increase concomitantly with caloric and protein needs, little research has been conducted to document that assumption. Our survey was undertaken to assess current practice and identify research needs. One hundred ninety-six survey questionnaires were sent to burn units in North America. Forty percent (78) were returned. Ninety percent of respondents prescribe or recommend trace mineral supplements in their facilities. "Higher risk" was the single criterion most often mentioned as a basis for supplementation (54 [77%] of 70 respondents), with 49 of them indicating that they provide trace mineral supplements to patients receiving total parenteral nutrition support. Fifty-six respondents provided detailed information concerning trace mineral supplementation. Of that group, 88% prescribe zinc supplements, 75% prescribe iron supplements, and 26% prescribe chromium supplements. Thirteen percent supplement selenium. Less than 2% supplement molybdenum or vanadium and do so only when administering total parenteral nutrition. Many respondents expressed concern about the lack of guidelines for trace mineral supplementation in the burn patient, leading to the conclusion that further research in that area would benefit burn-injured patients and the health care providers who care for them.

Burns↗
PubMed1984

A new preparation for recording single-channel currents from skeletal muscle.

Spherical vesicles of sarcolemma (media diameter, 78 microns) were prepared from frog skeletal muscle by prolonged exposure to enzymes (collagenase, then protease) and to isotonic KCl solutions, which promote swelling of muscle fibres. Patch clamp recording was used to measure unitary K and Na currents from this preparation. Na and K channels had conductances around 15 pS and their kinetic properties appeared unaltered by vesicle formation.

Animals↗
PubMed1984

AppppA and related adenylylated nucleotides are synthesized as a consequence of oxidation stress.

AppppA , ApppGpp , AppppG , ApppG , and ApppA rapidly accumulate to high levels in Salmonella typhimurium following exposure to a variety of oxidizing agents, but not to a variety of other stresses. Among the agents inducing these adenylylated nucleotides are 1-chloro-2,4-dinitrobenzene, diamide, hydrogen peroxide, t-butyl hydroperoxide, N-ethyl maleimide, iodoacetamide, cadmium chloride, and a variety of quinones. Some of these oxidizing agents cause preferential synthesis of specific adenylylated nucleotides, e.g., N-ethyl maleimide induces ApppA and menadione induces ApppGpp . Our data, as well as other evidence in the literature, strongly suggest that oxidation stress is coupled to adenylylated nucleotide synthesis by aminoacyl-tRNA synthetases. Although adenylylated nucleotides are made by tRNA synthetases in vitro, their synthesis in vivo is not a simple consequence of inhibition of synthetase activity. Compounds that inhibit normal charging by aminoacyl-tRNA synthetases do not result in the synthesis of adenylylated nucleotides, nor do mutations in tRNA synthetase structural genes or tRNA structural, modifying, or processing genes. We propose that the family of adenylylated nucleotides are alarmones signaling the onset of oxidation stress, and that particular ones may be alarmones for specific oxidative stresses, e.g., ApppGpp for oxidative damage to amino acid biosynthesis.

Adenine Nucleotides↗
PubMed1984

Role of endoscopic retrograde cholangiopancreatography in the diagnosis and treatment of choledochocele.

Choledochocele is a rare abnormality involving the intramural segment of the common bile duct. It may present clinically as recurrent acute pancreatitis, biliary colic, or cholestatic jaundice. A choledochocele may be easily overlooked by the conventional diagnostic methods, such as upper gastrointestinal series, intravenous cholangiogram, abdominal ultrasound, and computed tomography. Endoscopic retrograde cholangiopancreatography is helpful in demonstrating a choledochocele. Additionally, in selected cases, a choledochocele may be effectively managed by endoscopic sphincterotomy. We present the clinical, endoscopic, and radiographic findings in a series of 8 patients with choledochocele. The radiologic technique most useful in demonstrating a choledochocele at the time of endoscopic retrograde cholangiopancreatography is detailed. The pathogenesis, differential diagnosis, and relevant current literature pertaining to choledochocele are discussed.

Aged↗