Mutator transposase is widespread in the grasses

Although the Mutator (Mu) system is well characterized in maize (Zea mays), very little is known about this highly mutagenic system of transposons in other grasses. Mutator is regulated by the MuDR class of elements, which encodes two genes, one of which, mudrA, has similarity to a number of bacterial transposases. Experiments in our laboratory, as well as database searches, demonstrate that mudrA sequences are ubiquitous and diverse in the grasses. In several species it is clear that multiple paralogous elements can be present in a single genome. In some species such as wheat (Triticum aestivum) and rice (Oryza sativa), mudrA-similar sequences are represented in cDNA databases, suggesting the presence of active Mu transposon systems in these species. Further, in rice and in sorghum, mudrA-like genes are flanked by long terminal inverted repeats, as well as the short host sequence direct repeats diagnostic of insertion. Thus, there is ample evidence that systems related to Mu in maize are at least potentially active in a wide variety of grasses. However, the mudrB gene, though important for Mu activity in maize, is not necessarily a component of Mu elements in other grasses.

Efficient, rapid and reliable establishment of human trophoblast cell lines using poly-L-ornithine

OBJECTIVE

Human trophoblast cells in primary culture are difficult to use for the rigorous study of trophoblast function because of contamination with other cell types, paucity of numbers, poor viability and inter-experiment variation engendered by the need to prepare fresh cells for each experiment. DNA-transfection to produce immortalized cells, or cells with extended life-span, has been the obvious approach to solve this problem. Although there have been a few reports in the literature describing trophoblast cell lines generated in this way, it is clear that to date the methods are difficult and few lines have been generated. The basic problem is that transfection efficiencies of different methods are cell type-specific. The objectives of this study were therefore to compare the transfection efficiencies of three commonly used techniques, to use the best technique to generate trophoblast cell lines, and to conduct preliminary characterization studies.

METHODS

We have compared calcium phosphate co-precipitation, DEAE-dextran and poly-L-ornithine (PLO) DNA transfection protocols. We then used the most efficient to transfect human extravillous trophoblast with pSV3neo.

RESULTS

Our modification of the PLO method has a transfection efficiency greater than 30 times that of the next best method. Several cell lines were established which had an extended life span and displayed an invasive phenotype, including the expression of MHC Class I framework antigens, human placental lactogen and human chorionic gonadotrophin, and thus have characteristics of extravillous trophoblast. In addition these cells express the integrin subunits b1, a1, and a3, all of which are known to be expressed in human trophoblast, and respond to IL-1alpha by increased secretion of GM-CSF.

CONCLUSIONS

PLO is a highly efficient, rapid, reliable, simple and low-cost technique for the procurement of human trophoblast cell lines which retain most, if not all, the phenotype of the parental cell. These lines are potentially powerful tools in the rigorous study of trophoblast function.

Collagen phagocytosis by human extravillous trophoblast: potential role in trophoblastic invasion

OBJECTIVES

To study collagen phagocytosis by human extravillous trophoblast.

METHODS

First-trimester extravillous trophoblastic cell lines and primary trophoblast cell preparations were cultured in vitro with collagen-coated fluorescent latex beads and fluorescent-labeled collagen. Confocal microscopy was used to demonstrate internalization of collagen and beads. The effect of cytochalasin B, temperature, metabolic inhibitors, and cytokines was studied by culturing trophoblast cells with tritiated collagen. Acridine orange was used to stain for lysosomal compartments, and histochemical methods were used to demonstrate acid phosphatase in trophoblast cells.

RESULTS

Both cell lines and primary culture cells internalize collagen and beads. Confocal microscopy unequivocally localized the phagocytosed material to the intracellular compartment. Inhibition by cytochalasin B and culture at 4C of uptake of [3H] collagen suggested that the process was phagocytosis. Cytokines and growth factors did not affect phagocytosis. Lysosomal compartments and acid phosphatase appear to colocalize.

CONCLUSIONS

The continuous remodeling and turnover of collagen which occur in a wide variety of tissues under both physiologic and pathologic conditions are thought to be mediated by two pathways: one external (involving release of proteolytic enzymes), and the other internal (involving phagocytosis). Similar remodeling events are likely to occur during trophoblast invasion. Although current views emphasize the importance of the extracellular pathway, we postulate, on the basis of our findings, that both pathways are used, with the internal pathway probably being dominant. We hypothesize that the proteolytic enzymes (extracellular pathway) disrupt collagen matrices, thereby facilitating phagocytosis. It is teleologically sound to conceive of a dominant intracellular pathway, as it allows for more precise control of the process of invasion and is economical, as the products of collagen degradation can be used as energy sources or building blocks.

The phagocytic activity of human first trimester extravillous trophoblast

It has been suggested previously that phagocytic activity in the human placenta is confined to cells of the macrophage lineage. However, earlier studies were hampered by the paucity and poor viability of cells inherent in primary trophoblast cell cultures, contamination by other cell types which themselves have phagocytic activity, lack of reliable markers of trophoblasts, and by limitations of methods available to demonstrate unequivocally the internalization of particulate material. We have overcome these limitations by using: (i) DNA transfection to provide unlimited supplies of pure trophoblast cell lines; (ii) human placental lactogen as a marker unique to trophoblast; and (iii) confocal microscopy to demonstrate unequivocally the intracellular locality of phagocytosed material. We found that both untransfected primary culture extravillous trophoblast cells, as well as the cell lines, had the capacity to phagocytose sheep red blood cells, Staphylococcus aureus and baker's yeast cells, and that this activity was inhibited by cytochalasin B and by culture at 4 degrees C. Phagocytic activity in trophoblast cells was less avid than that seen in a professional phagocyte. In physiological and pathological situations where tissue remodelling occurs, such as the rapid turnover in the periodontal ligament or during inflammation, epithelial cells and other cells that are not considered professional phagocytes actively phagocytose components of the extracellular matrix. We postulate that phagocytosis by human trophoblasts may play an important role in the extensive tissue remodelling that occurs during trophoblastic invasion of the decidua.

A role for noradrenaline in pre-eclampsia: towards a unifying hypothesis for the pathophysiology

OBJECTIVE

To compare plasma catecholamine (noradrenaline and adrenaline) levels in pre-eclamptic to normotensive pregnancy, and to study the activity of synthetic enzymes for catecholamines in placental and trophoblastic cell cultures. We postulated that catecholamines might be an important signal secreted by the fetoplacental unit in pre-eclampsia.

METHODS

We recruited 12 women with pre-eclampsia and 12 pregnant women with nonproteinuric hypertension undergoing delivery by caesarean section, 23 normotensive women undergoing elective caesarean section at term, and 26 normotensive primigravid women with ongoing pregnancies at gestations equivalent to those women with pre-eclampsia. We measured venous blood concentrations of catecholamines. Following delivery, we studied tyrosine hydroxylase (the rate limiting enzyme for catecholamine synthesis) activity in placental tissue of these women as well as from four eclamptic women not in the observer study. We used Northern blot analysis to quantify mRNA for tyrosine hydroxylase and dopamine-beta-hydroxylase (D-beta-H, a non-rate-limiting synthetic enzyme for catecholamine) in placental tissue, as well as in trophoblast cells in primary culture and trophoblast cell lines.

RESULTS

Venous blood concentrations of noradrenaline were significantly higher in pre-eclamptic women compared with normotensive women. Tyrosine hydroxylase activity was greater in placental tissue from pre-eclamptic and eclamptic compared with normotensive pregnancies, as were mRNA levels for this enzyme. The mRNA levels for the non-rate-limiting D-beta-H in women with pre-eclampsia were similar to those in normotensive pregnancies. First trimester trophoblast cells in primary culture and trophoblast cell lines transcript mRNA for tyrosine hydroxylase and D-beta-H.

CONCLUSIONS

Trophoblasts have the capacity to secrete catecholamines, and we found increased activity of the rate-limiting synthetic enzyme in placental tissue from pre-eclamptic pregnancies. We postulate that the higher levels of catecholamines we found in the plasma of women with pre-eclampsia might be of placental origin. We hypothesise that in pre-eclampsia ischaemic trophoblast tissue secretes catecholamines as a physiological signal to increase maternal blood flow to the fetoplacental unit, which itself is spared the vasoconstrictor effects of catecholamines (placental vessels are known to be unresponsive to catecholamines). However, since the basic pathology--defective trophoblast invasion--is not corrected, the increased blood flow fails to resolve the ischaemia, and the secretion of catecholamines is therefore sustained or even enhanced. Noradrenaline is known to cause lipolysis. This results in breakdown of triglycerides to free fatty acids, which are oxidized to lipid peroxides. The latter are cytotoxic and cause widespread endothelial cell damage and dysfunction, culminating in the clinical syndrome of pre-eclampsia.

Immunoepidemiology of intestinal helminthic infections. 3. Mucosal macrophages and cytokine production in the colon of children with Trichuris trichiura dysentery

Mucosal macrophages and accessory cells have been studied by immunohistochemistry in the lamina propria of the colon of children with Trichuris trichiura dysentery syndrome (TDS). No difference was found in the numbers of cells recognized by the monoclonal antibodies CD11c, CD68, or RFD7 between TDS children and local controls. However, large numbers of cells were recognized by an antibody against calprotectin (an anti-bacterial glycoprotein found in tissue infiltrating-monocytes) in TDS colonic mucosa, but few in control colon. Large numbers of cells containing tumour necrosis factor alpha (TNF alpha) were also seen in TDS mucosa; cells isolated from TDS mucosa secreted more TNF alpha than cells from control mucosa; and children with TDS had high levels of circulating TNF alpha. Non-specific macrophage-mediated inflammation and local cytokine production may therefore play a role in the pathogenesis of TDS.

Modulation of MHC expression on human endothelial cells by sera from patients with systemic lupus erythematosus

Major histocompatibility complex (MHC) antigen expression on cells is a prerequisite for immune interaction with activated T-cells. This study examined the ability of sera from patients with systemic lupus erythematosus (SLE) to modulate MHC expression on vascular endothelial cells. SLE sera were able to selectively upregulate MHC class I antigen expression on cultured human umbilical venous endothelial (HUVE) cells, without concomitant induction of MHC class II antigen. The stimulation index (SI) for MHC class I expression produced by SLE sera (1.21 +/- 0.23) was significantly higher than those for normal controls (1.01 +/- 0.10) (P < 0.0001) and non-SLE patients (1.12 +/- 0.14) (P < 0.05). Additionally, active SLE patients had higher mean SI than inactive patients (P < 0.001). Preincubation of SLE sera with Protein A-Sepharose beads conjugated with antibodies against tumor necrosis factor-alpha and interferon-alpha was able to significantly reduce their ability to upregulate class I MHC expression by HUVE cells, indicating that these cytokines were responsible for the modulatory effect. This could be an important mechanism for the immune-mediated vascular injury seen in SLE.

T cell receptor V beta expression by mucosal T cells

Immunohistochemistry with monoclonal antibodies to the T cell receptor V beta regions 5, 6, 8 and 12 was used to determine whether normal intestinal lymphocytes that are potentially exposed to many bacterially derived superantigens show any preferential expression of particular V beta regions compared with the blood. No difference between V beta expression in the mucosa and the blood was observed, suggesting that they share a common pool of alpha beta T cells and that there is no expansion of alpha beta T cells in response to bacterial "superantigens" in the gut. The T cell receptor V beta expressed by the activated T cells in the lamina propria of bowel from patients with Crohn's disease was also studied. There was no increase in V beta 8 expression in these cells, suggesting that the increase in V beta 8 observed in the blood and mesenteric nodes of patients with Crohn's disease is not of primary importance in the aetiology of the disease. Finally, V beta expression by mucosal T cells in coeliac disease was studied. There was no difference in V beta use by T cells in coeliac disease and those in the blood and normal jejunum.

Histopathology and immunohistochemistry of the caecum in children with the Trichuris dysentery syndrome

Caecal biopsy specimens from Jamaican children with the Trichuris dysentery syndrome (TDS) and age matched Jamaican controls were investigated by immunohistochemistry and by light microscopy. Biopsy specimens from all children (with TDS and controls) showed a mild to moderate increase in inflammatory cells. Except in the vicinity of the worm, where the epithelium was flattened, there was no other epithelial abnormality. Compared with controls, children with TDS had increased IgM lamina propria plasma cells and decreased intraepithelial T cells. There was also an increase in crypt epithelial cell proliferation. Lamina propria T cells (both activated and non-activated) were no more common in children with the Trichuris syndrome than controls. Epithelial cell HLA-DR and VLA-1 expression (which are increased in other colitides) were the same in both groups. Despite the presence of large worm burdens and chronic dysentery, therefore, only minor changes were seen in the caecal mucosa of children with TDS.

Differential expression of CD25 (interleukin-2 receptor) on lamina propria T cells and macrophages in the intestinal lesions in Crohn's disease and ulcerative colitis

Many interleukin-2 receptor (CD25) bearing cells can be identified by alkaline phosphatase immunohistochemistry in the diseased intestinal lamina propria of children with Crohn's disease or ulcerative colitis, but rarely in normal intestine. In both diseases, the CD25+ cells are present as aggregates in the lamina propria below the epithelium, and constitute a large proportion of the lamina propria mononuclear cells. In Crohn's disease, but not ulcerative colitis, CD25+ cells are abundant in the submucosa. The CD25+ cells in Crohn's disease are 58-88% CD3+, CD4+, CD8-, indicating that they are T cells, whereas in ulcerative colitis the CD25+ cells are greater than 80% CD3-, CD4+, HLA-DR+, indicating that they are macrophages. Thus, differential expression of CD25 on T cells and macrophages serves to distinguish the immunologic lesions in ulcerative colitis and Crohn's disease.

Tumour necrosis factor-alpha and interferon-gamma production measured at the single cell level in normal and inflamed human intestine

The spot-ELISA technique has been used to enumerate the frequency of cells secreting tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), isolated from biopsies of normal intestine and from biopsies of children with inflammatory bowel disease. TNF-alpha production was undetectable in six out of 12 biopsies from normal intestine and in the other six biopsies it ranged from 60 to 580 TNF-alpha-secreting cells/10(6) isolated intestinal cells. In contrast, cells isolated from biopsies of children with Crohn's disease (n = 9) all showed elevated frequencies of TNF-alpha-secreting cells (500-12,000 secreting cells/10(6) cells). In ulcerative colitis, four out of eight children had increased production of TNF-alpha and in children with indeterminate colitis two out of three had elevated levels. There was no correlation between plasma TNF-alpha levels and the number of intestinal cells secreting TNF-alpha. In controls and all groups of patients IFN-gamma-secreting cells were uncommon. These results suggest that TNF-alpha is an important mediator of inflammation in the human gut, and, furthermore, may play a role in the growth failure frequently seen in children with inflammatory bowel disease.

Increased expression of laminin/collagen receptor (VLA-1) on epithelium of inflamed human intestine

Immunohistochemical techniques were used to investigate the epithelial expression of VLA-1 in inflammatory bowel disease in six patients with Crohn's disease, in four patients with ulcerative colitis, and in one patient with indeterminate colitis, and compared with that in the small intestine and colons of 10 normal controls. In normal small bowel VLA-1 was expressed on crypt epithelial cells and only weakly or not at all on surface epithelium. VLA-1 was again expressed weakly in normal colon, except in one case, a 1 year old child with diarrhoea but no histological abnormalities. In small and large intestine affected with Crohn's disease, ulcerative colitis, or indeterminate colitis, there was increased expression of VLA-1 on the basolateral aspects of crypt cells and de novo expression on surface epithelium. It is suggested that this is an adaptive response to prevent epithelial cell loss as a result of inflammation in the underlying lamina propria.

Expression of the VLA family of integrins in human intestine

The distribution of cells expressing the integrins VLA-1 to 6 in human intestine was examined by alkaline phosphatase immunohistochemistry using monoclonal antibodies specific for the individual alpha-chains of the VLA heterodimer. VLA-2,3, and 6 were expressed on all epithelial cells in the small and large bowel. VLA-1 was expressed on crypt cells in the small and large bowel, but was only weakly expressed or was absent on villus epithelial cells in the small bowel and colonic surface epithelial cells. All epithelia were negative for VLA-4 and VLA-5. Intraepithelial lymphocytes were VLA-1+ and VLA-4+. VLA-1,3, and 5 were expressed uniformly by muscularis propria, muscularis mucosae, pericrypt cells, and smooth muscle fibres within the villi. By contrast, VLA-2 and 4 were present only in pericrypt cells and fibres within the villi; they were absent from the muscularis mucosae. VLA-1,3,5, and 6 were expressed by endothelium. Staining of muscle fibres and endothelium in the lamina propria made it difficult to determine the extent of VLA expression on lamina propria lymphocytes. However, VLA-1+ cells with lymphoid morphology were only rarely seen. All mononuclear cells in the lamina propria were VLA-4+.

Purification and reconstitution studies of the nucleoside transporter from pig erythrocytes

The pig erythrocyte nucleoside transporter has been identified as a band 4.5 polypeptide (Mr 64,000) on the basis of photoaffinity labelling experiments with the nucleoside transport inhibitor nitrobenzylthioinosine (NBMPR). This protein was purified 140-fold by treatment of haemoglobin-free erythrocytes 'ghosts' with EDTA (pH 11.2) to remove extrinsic proteins, extraction of the protein-depleted membranes with n-octyl-glucoside and subsequent gradient-elution ion-exchange chromatography on DEAE-cellulose. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the purified material revealed the presence of only two detectable protein bands, one which co-migrated with the radiolabelled NBMPR-binding protein, and a lower molecular weight species with an Mr of 43,000. The latter protein may be a degradation product of the band 3 anion-exchange transporter. The overall purification of the NBMPR-binding protein with respect to the Mr 64,000 band was 350-fold. Reversible NBMPR-binding to the partially-purified band 4.5 preparation was saturable (apparent Kd 7.2 nM). Adjustment of the chromatography conditions to allow elution of the NBMPR-binding protein along with the majority of solubilised membrane phospholipid reduced the apparent Kd value to 3.0 nM. Purification of reversible NBMPR-binding activity during ion-exchange chromatography was paralleled by an increase in the specific activity of nitrobenzylthioguanosine (NBTGR) -sensitive uridine transport as assayed in proteoliposomes reconstituted by a freeze-thaw-sonication procedure.

Erythrocyte nucleoside and sugar transport. Endo-beta-galactosidase and endoglycosidase-F digestion of partially purified human and pig transporter proteins

Nucleoside- and glucose-transport proteins isolated from human erythrocyte membranes were photoaffinity-labelled with [3H]nitrobenzylthioinosine and [3H]cytochalasin B, respectively, and subjected to endo-beta-galactosidase or endoglycosidase-F digestion. Without enzyme treatment the two radiolabelled transporters migrated on SDS/polyacrylamide gels with the same apparent Mr (average) of 55,000. Apparent Mr (average) values after endo-beta-galactosidase digestion were 47,000 and 48,000 for the nucleoside and glucose transporters respectively, and 44,000 and 45,000 respectively after endoglycosidase-F digestion. In contrast, endo-beta-galactosidase had no effect on the electrophoretic mobility of the nucleoside transporter isolated from pig erythrocytes. This transport system exhibited a higher Mr than the human protein, endoglycosidase-F treatment decreasing its apparent Mr (average) from 64,000 to 57,000. It is concluded that the human and pig erythrocyte nucleoside transporters are glycoproteins containing N-linked oligosaccharide. The data provide evidence of substantial carbohydrate and polypeptide differences between the human and pig erythrocyte nucleoside transporters, but evidence of molecular similarities between the human erythrocyte nucleoside and glucose transporters.