Biomedical subjects

G M Wright

Publications and source records attributed to G M Wright.

At least 37 records · Page 2Linked to original sources

PubMed1998

Spatial and temporal distribution of proopiomelanotropin and proopiocortin mRNA during the life cycle of the sea lamprey: a qualitative and quantitative in situ hybridization study.

Two POMC-like pituitary prohormones proopiocortin (POC) and proopiomelanotropin (POM) have been characterized from adult sea lampreys (Petromyzon marinus). POC encodes a nasohypophysial factor (NHF), ACTH, an MSH, and beta-END; and POM encodes MSH-A, MSH-B, and beta-END. Two radiolabeled riboprobes, one encoding a unique portion of POC mRNA and the other encoding the MSH-B domain unique to POM mRNA, were generated in order to examine the expression of POC and POM during the life cycle of the sea lamprey by in situ hybridization. POC expression appears evenly distributed throughout most cells of the rostral pars distalis (RPD) during the entire life cycle. POC expression also occurs in scattered cells of the caudal (proximal) pars distalis (CPD) at stage 5 of metamorphosis. By the prespawner period, POC expression is mainly distributed in the dorsal aspect of this region. POM expression was completely confined to most cells of the pars intermedia (PI) at all periods examined. Quantitative, computer-assisted, image analysis of POM expression revealed high signal densities in all larvae which decreased by early metamorphosis, steadily increased and reached high levels by late metamorphosis (stages 6 and 7), and attained even higher levels in prespawners. Volumetric analysis revealed that the net volume of POM expressing cells is at its lowest in larvae and increases during subsequent development. Analysis of signal density and volumetric measurements of POC expression revealed that POC expression in the RPD is low in larvae and steadily increases during subsequent intervals of the life cycle reaching very high levels by the prespawning period. POC expression in the CPD, first visible at stage 5, increases steadily throughout the remainder of metamorphosis and reaches the highest levels of expression in prespawning animals. These results would implicate the role of POM and POC in some developmental processes but not in the initiation of metamorphosis. The very high levels of POM and POC expression in prespawner animals suggest that the two genes may have important roles at this time in the life cycle of lampreys.

Animals↗

PubMed1998

Somite number and vertebrate evolution.

Variation in segment number is an important but neglected feature of vertebrate evolution. Some vertebrates have as few as six trunk vertebrae, while others have hundreds. We examine this phenomenon in relation to recent models of evolution and development. Surprisingly, differences in vertebral number are foreshadowed by different somite counts at the tailbud stage, thought to be a highly conserved (phylotypic) stage. Somite number therefore violates the 'developmental hourglass' model. We argue that this is because somitogenesis shows uncoupling or dissociation from the conserved positional field encoded by genes of the zootype. Several other systems show this kind of dissociation, including limbs and feathers. Bmp-7 expression patterns demonstrate dissociation in the chick pharyngeal arches. This makes it difficult to recognise a common stage of pharyngeal development or 'pharyngula' in all species. Rhombomere number is more stable during evolution than somite number, possibly because segmentation and positional specification in the hindbrain are relatively interdependent. Although developmental mechanisms are strongly conserved, dissociation allows at least some major evolutionary changes to be generated in phylotypic stages.

Animals↗

PubMed1997

Microfibrils provide non-linear elastic behaviour in the abdominal artery of the lobster Homarus americanus.

1. Microfibrils are becoming increasingly recognized as an important component of the extra-cellular matrix. However, almost nothing is known about their mechanical role in the diversity of tissues in which they are found. 2. Microfibrils form the principal structural component in the wall of the abdominal artery of the lobster Homarus americanus. We have used previous estimates of the mechanical properties of these microfibrils, estimates of the fraction of the aorta wall volume occupied by the microfibrils, and their angular distribution as a function of strain in a numerical model that predicts the macroscopic mechanical properties of the whole tissue. 3. Microfibrils alone, when their reorientation and deformation are accounted for, characterize the stress-strain behaviour of the vessel. Evidence of the evolutionary conservation of fibrillin between medusans, echinoderms and vertebrates implies that the mechanical properties of lobster microfibrils may apply to microfibrillar function in other taxa. This will have profound implications on the perceived roles of microfibrils in development, physiology and disease.

Animals↗

PubMed1997

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development.

Embryos of different species of vertebrate share a common organisation and often look similar. Adult differences among species become more apparent through divergence at later stages. Some authors have suggested that members of most or all vertebrate clades pass through a virtually identical, conserved stage. This idea was promoted by Haeckel, and has recently been revived in the context of claims regarding the universality of developmental mechanisms. Thus embryonic resemblance at the tailbud stage has been linked with a conserved pattern of developmental gene expression - the zootype. Haeckel's drawings of the external morphology of various vertebrates remain the most comprehensive comparative data purporting to show a conserved stage. However, their accuracy has been questioned and only a narrow range of species was illustrated. In view of the current widespread interest in evolutionary developmental biology, and especially in the conservation of developmental mechanisms, re-examination of the extent of variation in vertebrate embryos is long overdue. We present here the first review of the external morphology of tailbud embryos, illustrated with original specimens from a wide range of vertebrate groups. We find that embryos at the tailbud stage - thought to correspond to a conserved stage - show variations in form due to allometry, heterochrony, and differences in body plan and somite number. These variations foreshadow important differences in adult body form. Contrary to recent claims that all vertebrate embryos pass through a stage when they are the same size, we find a greater than 10-fold variation in greatest length at the tailbud stage. Our survey seriously undermines the credibility of Haeckel's drawings, which depict not a conserved stage for vertebrates, but a stylised amniote embryo. In fact, the taxonomic level of greatest resemblance among vertebrate embryos is below the subphylum. The wide variation in morphology among vertebrate embryos is difficult to reconcile with the idea of a phyogenetically-conserved tailbud stage, and suggests that at least some developmental mechanisms are not highly constrained by the zootype. Our study also highlights the dangers of drawing general conclusions about vertebrate development from studies of gene expression in a small number of laboratory species.

Amphibians↗

PubMed1997

In vitro infection of a cell line from Ictalurus nebulosus with Piscirickettsia salmonis.

Piscirickettsia salmonis, the etiologic agent of salmonid rickettsial septicemia (SRS), affects several species of salmonids. Previous reports using the appearance of cytopathic effect (CPE) as the criterion for susceptibility, showed that Piscirickettsia salmonis (ATCC strain) can be grown in vitro in some cells lines derived from salmonid fish, but not in BB cells from brown bullhead (Ictalurus nebulosus) and BF-2 cells from bluegill (Lepomis macrochirus). In this study we describe growth of P. salmonis (ATCC strain VR 1361) in a cell line previously believed to be nonpermissive for this organism. CPE was first detected in chinook salmon embryo (CHSE-214) and epithelioma papulosum ciprini (EPC) cell lines at 6 d postinfection (dpi). In contrast, using BB cell line, CPE was first detected 45 dpi and the monolayer completed CPE by 78 dpi. Electron microscopic examination of BB cells 78 dpi revealed free, intracytoplasmic and extracellular localization of the agent. P. salmonis was also observed within membrane-bounded vacuoles in BB cells, similar to that described in CHSE 214 cells. Contrary to earlier reports, results from the present study show that the BB cell line, is susceptible to Piscirickettsia salmonis infection. The delayed onset of CPE in BB cells in comparison to other permissive cell lines suggests that BB cells are not ideal hosts for P. salmonis. Interestingly, however, these results demonstrate that P. salmonis can infect non-salmonid cell lines, and raises the possibility that non-salmonid fish may play a role in the persistence and transmission of SRS in the natural environment.

Animals↗

PubMed1996

The modulus of elasticity of lobster aorta microfibrils.

The presence of elastic fibres in the extracellular matrix (ECM) provides physiologically important elastic properties for many tissues. Until recently, microfibrils, one component of the ECM, were thought primarily to serve as a scaffolding on which elastin is deposited during development to form elaunin fibres [1]. The most prominent protein that forms mammalian microfibrils is fibrillin. It is known that mutations in the fibrillin gene cause a heterogenous connective tissue disease called Marfan syndrome [2], so information on mechanical properties of microfibrils or their role in tissue function would be useful. Microfibrils are also found in the ECM of some invertebrate tissues, and there is growing evidence that the protein forming the structure is homologous to mammalian fibrillin [3,4]. It has been shown that the microfibril-based arterial wall of the lobster has viscoelastic properties [5], and we have now utilized this primitive artery to measure the modulus of elasticity of microfibrils. It is similar to that of the rubber-like protein elastin.

Animals↗

PubMed1996

Spatial and temporal distribution of lamprin mRNA during chondrogenesis of trabecular cartilage in the sea lamprey.

The temporal and spatial expression patterns of lamprin, the principle structural protein in lamprey cartilages, were examined by in situ hybridization during chondrogenesis of trabecular cartilage in day 17-33 post-fertilization prolarval lampreys. Lamprin mRNA transcripts were first detected during day 19, concomitant with the end of the condensation phase of chondrogenesis and the initiation of matrix synthesis as indicated by light microscopic examination. In the stages which followed, the hybridization signal increased with progressive intensity, paralleling matrix synthesis, suggesting transcriptional control of lamprin gene expression. Spatially, lamprin expression patterns mirrored the rostrocaudal development of the trabecular cartilage rudiment. No signal was detected over adjacent tissues or control sections. Some similarities exist between the temporal patterns of lamprin expression and the expression of matrix proteins such as elastin and collagen of higher vertebrates. It is concluded that certain aspects of chondrogenesis are critical to the normal development of a functional cartilaginous matrix and are conserved throughout the vertebrate taxa.

Animals↗

PubMed1995

Microsurgical vasovasostomy in military personnel.

This paper details the operative techniques, results and reasons for reversals of vasectomy in military personnel. Fifty-two reversals were performed by two surgeons (AC & DW) over a 7 year period. Data collection was by (i) retrospective analysis of service documents, surgical registers and laboratory records and (ii) response to a questionnaire. The interval between original vasectomy and reversal varied from 5 months to 16 years. Change of sexual partner was the most common reason for requesting the procedure. There were two recorded postoperative infections and no postoperative mortality. Post-reversal semen analysis proved anastomotic success in 49 out of 51 cases (96%). Semen analysis was not returned for the remaining case. Of the couples who had been trying for at least 18 months, 28 out of 42 (67%) had conceived, including one miscarriage. A further seven cases had been trying for less than 18 months, or had no opportunity due to physical separation. Two of these seven patients ended their relationship soon after operation. Pregnancy outcome was unknown in three cases.

Adult↗

PubMed1995

The structure and physical properties of invertebrate and primitive vertebrate arteries.

Light and electron microscopy and in vitro inflation experiments were conducted on the aortae of three different invertebrate species: the lobster Homarus americanus, the horseshoe crab Limulus polyphemus and the whelk Busycon contrarium. Inflation experiments were also performed on the aortae of two species of primitive vertebrates, the sea lamprey Petromyzon marinus and the Atlantic hagfish Myxine glutinosa. The inflation experiments demonstrated similar overall biomechanical properties in each case, despite the existence of differences in tissue structure. The vessels were compliant at low strains, but demonstrated nonlinear elasticity, increasing in stiffness as strains increased; this property could act as protection against artery wall rupture. The vessels of the lamprey, hagfish and lobster are capable of acting as fairly efficient elastic reservoirs and of smoothing blood flow during circulation as they had low hysteresis values (13-18%). The aortae of the horseshoe crab and whelk, if performing this function, have much higher energy losses, up to more than 30% per cycle. The microscopy studies of the aortae of the lobster, horseshoe crab and whelk revealed tissue structures which differ widely from each other as well as from the structures of the lamprey and hagfish. None of these arteries contained elastin, but all contained fibrillar material which differed in appearance, size and arrangement between species. These materials were conjectured to contribute to the elastic properties of the tissue.

Animals↗

PubMed1993

Characterization of lamprin, an unusual matrix protein from lamprey cartilage. Implications for evolution, structure, and assembly of elastin and other fibrillar proteins.

Lamprin, an insoluble non-collagen, non-elastin protein, is the major connective tissue component of the fibrillar extracellular matrix of lamprey annular cartilage. Here we demonstrate that the soluble monomer of lamprin is a family of highly hydrophobic, self-aggregating proteins with molecular masses of 12 and 10 kDa. Two mRNAs for soluble lamprin were identified (0.9 and 2 kilobases), differing principally in the length of their 3'-untranslated tails. Variants of soluble lamprin appear to arise both as the products of multiple genes and by alternate splicing. Although not generally homologous to any other protein, soluble lamprins contain a tandemly repeated peptide sequence (GGLGY) which is present in both silkmoth chorion proteins and spider dragline silk. Strong homologies to this repeat sequence are also present in several mammalian and avian elastins. Monoclonal antibodies to VGVAPG, a repeated sequence in human elastin, also cross-react with lamprin. We suggest that these proteins share a structural motif which promotes self-aggregation and fibril formation in proteins through interdigitation of hydrophobic side chains in beta-sheet/beta-turn structures, a motif that has been preserved in recognizable form over several hundred million years of evolution.

Amino Acid Sequence↗

PubMed1993

Production of monoclonal antibodies specific for antigens derived from tissue of chinook salmon (Oncorhynchus tshawytscha) affected with plasmacytoid leukemia.

Two distinct monoclonal antibodies (MAB) were prepared for testing with kidney, spleen, and retrobulbar tissue imprints made from chinook salmon (Oncorhynchus tshawytscha) affected with plasmacytoid leukemia. (PL). Hybridomas were prepared from mice immunized with whole and lysed cells purified from renal or retrobulbar PL-positive tissues, which had been obtained from naturally and experimentally infected fish from British Columbia, Canada. The MAB reacted with at least 4 morphologically different cell types; fluorescence was associated with the plasma membrane and cytoplasm. The MAB also reacted with kidney imprints made from chinook salmon affected with a PL-like lymphoproliferative disease in California, indicating that these 2 diseases might be caused by a similar agent. The MAB did not react with any of the kidney or spleen imprints made from wild chinook salmon collected from a river in Ontario, Canada.

Animals↗

PubMed1993

Ultrastructure of granulosa lutein cells from rats fed hexachlorobenzene.

Corpora lutea from Sprague-Dawley rats that were orally administered 0.0 (control), 1.0, 10.0, and 100.0 mg/kg hexachlorobenzene (HCB) for 21 days were analyzed by electron microscopy. Granulosa lutein cells (GLC) from animals of the 10.0 mg group showed differences from the cells of animals that served as the controls. Golgi complexes and smooth endoplasmic reticulum appeared more conspicuous, possibly due to dilation resulting from hyperactivity. Free polysomes seemed more prominent in the cells of the 10.0 mg group. The GLC architecture from animals of the 1.0 and 100.0 mg groups was similar to that of the corresponding cells in the control group. Since smooth endoplasmic reticulum is involved in the synthesis of steroid hormones, and that free polysomes are engaged in synthesis of cytoplasmic proteins, it is suggested that HCB at a dose of 10.0 mg/kg given for 21 days may alter the synthetic activity of the GLC of the rat.

Animals↗

PubMed1992

Quantitative regional variation in the expression of major histocompatibility class II antigens in enterocytes of the mouse small intestine.

The qualitative and quantitative expression of major histocompatibility class II antigens was investigated in the absorptive epithelium of the duodenum, jejunum, and ileum from mice of C3H/He (H-2k haplotype) and C57BL/6 (H-2b haplotype) strains by peroxidase-antiperoxidase labelling and image analysis. Immunohistochemical labelling revealed that the expression of class II antigens was greatest in the ileum and decreased proximally towards the duodenum. The villus epithelium of the duodenum showed a granular staining pattern in the apices of some cells. In the jejunum, an increased expression was demonstrated in the apical and basal cytoplasm of all cells covering the villus. Cells at the tip of the villus, in addition, showed staining of the lateral surfaces. Ileal enterocytes demonstrated the most intense immunostaining appearing in the cytoplasm and along baso-lateral surface membranes. Quantitative analyses confirmed that a highly significant (p less than 0.0001) difference in expression of class II antigens occurred in the three regions of the small intestine, which corroborated the qualitative findings. This regional variation of class II molecules by the absorptive epithelium may influence regional differences in antigen presenting functions and immune responsiveness to ingested antigens.

Animals↗

PubMed1992

Changes in the ventral dermis and development of iridophores in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis: an ultrastructural study.

The ultrastructural changes that take place in the ventral dermis along with the development of iridophores were examined in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis. There is a disruption of all components of the ventral dermis and a reformation that results in a structure very similar to that prior to metamorphosis. Although not a dermal component, a layer of iridophores develops directly beneath the dermis during late metamorphosis. The dermal endothelium is lost by mid metamorphosis (stage 4) and the highly organized collagenous lamellae making up the bulk of the dermis become disrupted by the migration of fibroblasts into the region. Many of these fibroblasts are involved in the degradation of the lamellae. By stage 5 of metamorphosis some fibroblasts become highly active collagen synthesizing cuboidal shaped cells that align to form a layer above the reformed dermal endothelium. New lamellae are formed by these cuboidal cells which then divide and migrate into the lamellae where they assume the characteristic attenuated appearance of fibroblasts in the adult dermal lamellae region. Iridophores first appear during stage 5 directly beneath the dermal endothelium. Reflecting platelets develop from double membraned vesicles associated with the Golgi apparatus. By late metamorphosis, stacks of trapezoidal shaped platelets fill the cytoplasm of the iridophores. The significance of the changes in the dermis during metamorphosis are discussed. This work is part of a continuing series of studies on the connective tissues in the anadromous sea lamprey.

Animals↗

PubMed1992

Ultrastructural localisation of acid phosphatase in intestinal eosinophilic granule cells (EGC) of rainbow trout (Oncorhynchus mykiss) following degranulation with capsaicin.

Enzyme cytochemistry was used to investigate possible lysosome involvement in capsaicin induced degranulation of the eosinophilic granule cell (EGC) of the rainbow trout intestine. Three adult rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with capsaicin in a saline vehicle (0.5 micrograms.g-1 body weight). Following a 2 hour period of incubation, the fish were killed, and a mid portion of the intestine was dissected and fixed in cold glutaraldehyde buffered with sodium cacodylate. Vibratome sections were incubated in either reaction medium containing beta-glycerophosphate and cerium chloride in acetate buffer or substrate (beta-glycerophosphate) deficient control medium. Sections were then refixed in osmium tetroxide and processed for electron microscopy. Acid phosphatase was found to be localised within lysosomes. The enzyme was not found in the large cytoplasmic granules under normal or capsaicin-stimulated conditions. EGCs which had migrated to the lamina propria in response to the capsaicin stimulation had a distinct multivesicular granule morphology. These multivesicular granules did not contain acid phosphatase suggesting that this form of EGC degranulation is not a lysosomally mediated event.

Acid Phosphatase↗

PubMed1992

Regional variation in ontogeny of class II antigens in enterocytes of mouse small intestine.

The ontogeny of major histocompatibility class II antigens in small intestine enterocytes of postnatal C3H/He mice was investigated. Cryosections of duodenal, jejunal, and ileal segments from 7-, 14-, 16-, 20-, 21-, 23-, 25-, 27-, 28-day-old and 7-week-old mice were stained for the class II antigens with MRC OX6 monoclonal antibodies by peroxidase-antiperoxidase labelling. In adults, the duodenum exhibited least expression of class II antigens that increased progressively towards the ileum. The expression in the villous epithelium was first seen in the duodenum and jejunum 21 days after birth but the ileal enterocytes did not exhibit any class II antigens. The earliest appearance (21 days postnatal) of class II antigens in the enterocytes coincides with the age of weaning which suggests that immunologic stimulation by ingested antigens after weaning may influence expression of these antigens. At day 28 after birth, the duodenum and jejunum expressed levels comparable to those in the adults. The first expression of the antigens seen in the ileum was at day 28 postpartum. Crypt epithelium of the three regions of the small intestine showed expression similar to that of corresponding regional villous enterocytes. We conclude that there is an age-dependent regional variation in the expression of class II antigens in enterocytes, and the expression increases with age. The variation in expression of the class II antigens in enterocytes of postnatal mice is attributed to the developmental status of the tissue. The nature of postnatal expression of the antigens is important since an early appearance of these antigens may have implications in autoimmunity.

Aging↗

PubMed1991

Degranulation of eosinophilic granule cells induced by capsaicin and substance P in the intestine of the rainbow trout (Oncorhynchus mykiss Walbaum).

Adult rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with capsaicin, substance P, serotonin, or a control of saline vehicle or bovine serum albumin (0.5 microgram/g body weight). Fish were sacrificed 30 min and 1, 2, and 4 h post-injection, the gut was dissected out, and a small section of the upper intestine was processed for electron microscopy. A significant proportion of eosinophilic granule cells (EGCs) of the intestine were in close association with non-myelinated neuronal bundles in all fish (4 fish per treatment and time period), but there was no significant difference between treatment or time, suggesting that the association was unaffected by these factors. Close examination of EGC ultrastructure showed that fish treated with capsaicin and substance P exhibited limited degranulation of the EGCs in the stratum compactum and extensive crinophagic-like degranulation in the lamina propria. Cells of the lamina propria contained characteristic multivesicular-like bodies. The degranulation was reminiscent of both mast cell degranulation and endocrine cell crinophagy. EGCs of fish treated with serotonin or a control were unaffected, suggesting that the serotoninergic neurons, believed to be involved in gut motility, were not responsible for degranulation. It is apparent that EGCs of the trout intestine may be under nervous control, as has been demonstrated previously for mammalian mast cells.

Animals↗

PubMed1990

Objective assessment in dementia: automated psychometric tests and the P3.

Event-related potentials have been shown to be closely correlated with cognitive functioning and it has been suggested that one such potential, the P3, can act as an objective and sensitive measure of the degree of dementia. The P3 is no longer thought of as a diagnostic tool in dementia; however, longitudinal changes in the P3 latency can be used to follow the course of a dementing illness or to assess effects of therapy. It is possible that the measurement of P3 latency may prove useful in the selection of patients with early dementia. Automated psychometric tests are also of considerable value in assessing large numbers of cognitively impaired subjects. The advantages of using these tests and their usefulness in multicentre drug trials is discussed.

Animals↗