In vitro gill cell monolayer successfully reproduces in vivo Atlantic salmon host responses to Neoparamoeba perurans infection

An in vitro model to study the host response to Neoparamoeba perurans, the causative agent of amoebic gill disease (AGD), was evaluated. The rainbow trout gill derived cell line, RTgill-W1, was seeded onto permeable cell culture supports and maintained asymmetrically with apical seawater. Cells were inoculated with either a passage attenuated or a recent wild clone of N. perurans. Amoebae, loaded with phagocytosed fluorescent beads, were observed associated with host cells within 20 min post inoculation (pi). By 6 h small foci of cytopathic effect appeared and at 72 h cytolysis was observed, with total disruption of the cell monolayer at 96 h pi. Due to cell monolayer disruption, the platform could not support proliferation of amoebae, which showed a 3-log reduction in parasite 18S rRNA mRNA after 72 h (10⁶ copies at 1 h to 10³ at 72 h pi). SEM observations showed amoebae-like cells with either short pseudopodia and a malleiform shape, or, long pseudopodia embedded within the gill cells and erosion of the cell monolayer. To study the host immune response, inoculated gill cells were harvested from triplicate inserts at 0, 1, 3, 6, 24 and 48 h pi, and expression of 12 genes involved in the Atlantic salmon response to AGD was compared between infected and uninfected cells and between amoebic clones. Both clones induced similar host inmate immune responses, with the up-regulation of proinflammatory cytokine IL1β, complement C3 and cell receptor MHC-1. The Th2 pathway was up-regulated, with increased gene expression of the transcription factor GATA3, and Th2 cytokines IL10, IL6 and IL4/13A. PCNA and AG-2 were also up-regulated. The wild clone induced significantly higher up-regulation of IL1β, MHC-1, PCNA, lysozyme and IL10 than the attenuated clone for at least some exposure times, but AG-2 gene expression was higher in cells inoculated with the attenuated one. A principal component analysis showed that AG-2 and IL10 were key genes in the in vitro host response to N. perurans. This in vitro model has proved to be a promising tool to study host responses to amoebae and may therefore reduce the requirement for in vivo studies when evaluating alternative therapeutants to AGD control.

Multiple cellulose synthase catalytic subunits are required for cellulose synthesis in Arabidopsis

The irregular xylem 1 (irx1) mutant of Arabidopsis has a severe deficiency in the deposition of cellulose in secondary cell walls, which results in collapsed xylem cells. This mutation has been mapped to a 140-kb region of chromosome 4. A cellulose synthase catalytic subunit was found to be located in this region, and genomic clones containing this gene complemented the irx1 mutation. IRX1 shows homology to a previously described cellulose synthase (IRX3). Analysis of the irx1 and irx3 mutant phenotypes demonstrates that both IRX1 and IRX3 are essential for the production of cellulose in the same cell. Thus, IRX1 and IRX3 define distinct classes of catalytic subunits that are both essential for cellulose synthesis in plants. This finding is supported by coprecipitation of IRX1 with IRX3, suggesting that IRX1 and IRX3 are part of the same complex.

Multiple cellulose synthase catalytic subunits are required for cellulose synthesis in Arabidopsis

The irregular xylem 1 (irx1) mutant of Arabidopsis has a severe deficiency in the deposition of cellulose in secondary cell walls, which results in collapsed xylem cells. This mutation has been mapped to a 140-kb region of chromosome 4. A cellulose synthase catalytic subunit was found to be located in this region, and genomic clones containing this gene complemented the irx1 mutation. IRX1 shows homology to a previously described cellulose synthase (IRX3). Analysis of the irx1 and irx3 mutant phenotypes demonstrates that both IRX1 and IRX3 are essential for the production of cellulose in the same cell. Thus, IRX1 and IRX3 define distinct classes of catalytic subunits that are both essential for cellulose synthesis in plants. This finding is supported by coprecipitation of IRX1 with IRX3, suggesting that IRX1 and IRX3 are part of the same complex.

The irregular xylem3 locus of Arabidopsis encodes a cellulose synthase required for secondary cell wall synthesis

The irregular xylem3 (irx3) mutant of Arabidopsis has a severe deficiency in secondary cell wall cellulose deposition that leads to collapsed xylem cells. The irx3 mutation has been mapped to the top arm of chromosome V near the marker nga106. Expressed sequence tag clone 75G11, which exhibits sequence similarity to cellulose synthase, was found to be tightly linked to irx3, and genomic clones containing the gene corresponding to clone 75G11 complemented the irx3 mutation. Thus, the IRX3 gene encodes a cellulose synthase component that is specifically required for the synthesis of cellulose in the secondary cell wall. The irx3 mutant allele contains a stop codon that truncates the gene product by 168 amino acids, suggesting that this allele is null. Furthermore, in contrast to radial swelling1 (rsw1) plants, irx3 plants show no increase in the accumulation of beta-1,4-linked glucose in the noncrystalline cell wall fraction. IRX3 and RSW1 fall into a distinct subgroup (Csa) of Arabidopsis genes showing homology to bacterial cellulose synthases.

The irregular xylem3 locus of Arabidopsis encodes a cellulose synthase required for secondary cell wall synthesis

The irregular xylem3 (irx3) mutant of Arabidopsis has a severe deficiency in secondary cell wall cellulose deposition that leads to collapsed xylem cells. The irx3 mutation has been mapped to the top arm of chromosome V near the marker nga106. Expressed sequence tag clone 75G11, which exhibits sequence similarity to cellulose synthase, was found to be tightly linked to irx3, and genomic clones containing the gene corresponding to clone 75G11 complemented the irx3 mutation. Thus, the IRX3 gene encodes a cellulose synthase component that is specifically required for the synthesis of cellulose in the secondary cell wall. The irx3 mutant allele contains a stop codon that truncates the gene product by 168 amino acids, suggesting that this allele is null. Furthermore, in contrast to radial swelling1 (rsw1) plants, irx3 plants show no increase in the accumulation of beta-1,4-linked glucose in the noncrystalline cell wall fraction. IRX3 and RSW1 fall into a distinct subgroup (Csa) of Arabidopsis genes showing homology to bacterial cellulose synthases.

Are anterior occlusal radiographs still indicated for orthodontic assessment?

OBJECTIVE

This study examined the question of taking anterior occlusal radiographs (AO) in addition to a dental panoramic tomogram (DPT) using the Planmeca PM Proline CC.

DESIGN

Retrospective single centre study.

SETTING

Dental hospital radiology department.

SUBJECTS

100 pairs of DPTs and AOs which had been requested for orthodontic assessment were examined between April and July 1995. All DPTs were taken on a Planmeca PM Proline CC machine.

RESULTS

The AO was assumed to be the gold standard and the diagnostic validity of the DPT can be assessed using values of sensitivity and specificity. 21% of DPTs were identified as requiring a supplementary radiograph to clarify the image of the anterior maxilla.

CONCLUSIONS

A DPT machine with an adjustable focal trough has significantly reduced the need for supplementary AO radiographs. The AO is indicated when there is abnormality in the premaxilla or where dental malocclusion prevents ideal positioning of the patient in the machine.

Are anterior occlusal radiographs indicated to supplement panoramic radiography during an orthodontic assessment?

Five hundred pairs of dental panoramic tomographs (DPT) and maxillary anterior occlusal radiographs (AO) from patients referred to the orthodontic department of a dental teaching hospital were examined to assess the diagnostic yield from a panoramic radiograph of the premaxillary region alone and then assess the additional yield when this view was supplemented by a maxillary anterior occlusal radiograph. Of the 500 DPTs assessed, 208 (42%) lacked clarity of the premaxillary region when the labial segments were used to locate the patient in the DPT machine. An association was found between patients who had abnormal incisor relationships and poor clarity in the premaxillary region of the DPT. Overall 165 (33%) of the supplementary AO views were used to support or refute findings identified on the DPT. It was concluded that in patients referred for an orthodontic assessment, supplementary radiography of the premaxilla may be justified in the following situations: 1. unsatisfactory image quality which may frequently be the case where there are abnormal incisor relationships, 2. localisation of tooth position by vertical parallax and 3. where a reasonable expectation that pathology exists on clinical grounds.

Lateral thinking: the management of missing upper lateral incisors

Absence of the maxillary lateral incisor creates an aesthetic problem which can be managed in various ways. The condition requires careful treatment planning and a consideration of the options and outcomes following either space closure or prosthetic replacement. Recent developments in restorative dentistry have warranted a re-evaluation of the approach to this clinical situation. Factors relating both to the patient and to the teeth, including the presenting malocclusion and the effect on the occlusion, are considered. This review considers the possible options: no treatment; orthodontic space closure with canine modification; space maintenance and replacement of the missing tooth with denture, bridge (adhesive and conventional), or implant.

I-Cell disease: an unusual cause of gingival enlargement

Dentists have specialised knowledge of the orofacial region and are well placed to identify the signs of general disease which occur in their child patients. A case report is presented in which a patient was diagnosed as suffering from I-Cell disease (mucolipidosis II). The provisional diagnosis of this genetic abnormality was initially made from the presenting gingival appearance. The identification of the oral abnormalities made an important contribution to the diagnosis of this fatal condition.

Orthodontics in The Netherlands

In October 1992 I visited the Netherlands and spent time at both university training centres and a number of selected specialist orthodontic practices. Holland has a population of nearly 15 million and the highest population density of any European country. There are about 6,000 GDPs in Holland and about 300 dentists who have undergone specialty training in orthodontics.

The reliability of positioning pre-adjusted brackets: an in vitro study

To investigate the reliability of bracket positioning, twelve operators, familiar with the straight-wire appliance, placed 0.022" straight-wire brackets on the anterior teeth of a typodont study model, on three different occasions. Bracket position was assessed using a Magiscan image analyser. Angular judgements by the operators were found to be less consistently identified than linear assessments. Slot angulation showed the largest variability and vertical bracket placement the least. The clinical implications of bracket misplacement are discussed.

Resorption of the crown of an unerupted permanent molar

This case report describes an unusual phenomenon where resorption occurred in the crown of an unerupted permanent molar. It was an incidental radiological finding. After eruption the tooth was extracted. Histological examination revealed resorption of enamel and dentine, and partial replacement by calcific material. The possible aetiology of the condition is discussed.

Frictional resistance between orthodontic brackets and archwires in the buccal segments

Orthodontic sliding mechanics using preadjusted brackets is a popular approach for achieving incisor retraction. A distally directed force slides the archwire through brackets and tubes in the buccal segments. Friction in the buccal segments contributes resistance to the force required to achieve tooth movement, and techniques to reduce friction reduce the potential for anchorage loss. This in vitro study used an Instron testing machine to assess frictional forces for three types of 0.022 x 0.028 inch brackets: preadjusted stainless steel premolar brackets (Standard Straight Wire, "A" Company, Inc, San Diego, Calif), Activa brackets ("A" Company Inc, San Diego, Calif), and Speed brackets (Strite Industries Ltd), combined with five wire sizes (0.018, 0.020, 0.016 x 0.022, 0.018 x 0.025 and 0.019 x 0.025 inch). A model with one attached molar bracket and one or two premolar brackets simulated the buccal segments. Activa brackets produced the least friction for all wires tested. Speed brackets with round wires showed little frictional force while rectangular wires gave rise to higher forces, at levels similar to those recorded with two Standard Straight Wire brackets. Static friction for round wires in standard brackets was found to be 178-275 gm-force. The ratio of static to dynamic friction was remarkably consistent in all tests. Different methods of ligation were compared for their effect on static friction. Ligation with loosely placed ligatures or stretched modules reduced frictional forces in Standard Straight Wire brackets, the reduction being greatest for round archwires. Frictional forces recorded from archwires secured with elastomeric modules showed a steady reduction over a 3-week period, depending on how long the module had been in position on the bracket.