Ultrastructural visualization of the internalization of low density lipoprotein by human placental cells

Low density lipoproteins (LDL) were conjugated to colloidal gold to visualize the route for internalization of LDL in the cultured cells of human term placenta. Cells were obtained from placental villi (caesarian section) by a standard trypsin-DNase dispersion method followed in some cases by a Percoll gradient centrifugation step. Employing electron microscopy it was observed that after 3 days of culture, cells obtained by trypsin-DNase dispersion were a mixture of macrophages, mononucleated cells and large multinucleated cells. When the cells were incubated for 3 days after the Percoll purification, essentially multinucleated cells identical to the syncytiotrophoblast were present. The number of LDL receptor was increased by preincubation in medium with lipoprotein depleted serum. In binding experiments cells incubated at 4 degrees C for 2 h with medium containing gold LDL conjugates showed gold LDL attached to the plasma membrane without characteristic localization. After incubation with gold LDL at 37 degrees C for various times, the three cellular types showed ligand internalization. Gold LDL endocytosis involved first coated pits but also uncoated plasmalemmal invaginations. Then gold LDL was further observed in coated and non coated vesicles, smooth walled endosomes, multivesicular bodies and tubular vesicles. Lastly free gold particles were observed in lysosome like dense bodies. These results prove the internalization of gold LDL conjugates by human cultured placental cells, particularly by syncytiotrophoblast like multinucleated cells. This accumulation of LDL (the major cholesterol carrying protein in humans) is recognised to be responsible for the exogenous cholesterol supply indispensable to the progesterone biosynthesis and cellular growth of the placenta.     

Protoplast fusion ofCatharanthus roseus cells by electrofusion of chemically-agglutinated protoplasts

Mesophyll derived protoplasts ofCatharanthus roseus cv. Little pinkie were fused with protoplasts derived from an habituated cell line ofC. roseus. Polyethylene glycol was used as agglutinating agent while fusions were induced by square pulses. Best results were obtained by fusing protoplasts from primary leaves with those from three-day-old cell cultures. Adding calcium ions considerably enhanced heterofusion rate. Good cell viabilities indicated that this fusion process was not cytotoxic. The heterofusion frequency was up to 10% or more. Most of the heterokaryons were able to regenerate their cell walls and underwent division. Communicated by J. TUPY     

MIAH: automatic alignment of eukaryotic SSU rRNAs.

SUMMARY: MIAH is a WWW server for the automatic alignment of new eukaryotic SSU rRNA sequences to an existing alignment of 1500 sequences. AVAILABILITY: http://chah.ucc.ie/MIAH Contact :     

Ultrastructure d'une cyanophycée aérienne calcifiée cavernicole: Geitleria calcarea Friedmann

Résumé L'ultrastructure de Geitleria calcarea Friedmann, cyanophycée filamenteuse aérienne, calcifiée et cavernicole, rarement signalée, est étudiée ici pour la première fois. La cytologie de cet organisme présente des originalités. Huit enveloppes cellulaires concentriques sont dénombrées: membrane plasmique, L I, L II, L III, L IV, enveloppe pariétale, gaine fibreuse et gaine carbonatée. La dernière est décrite à l'aide du M.E.B. Les thylacoïdes très nombreux ont une forme extrêmement contournée. Ils supportent des phycobilisomes cylindriques alternant avec des polysaccharides de même allure. L'organisation des synapses est détaillée. L'élongation est apicale et le mode de ramification est soit latéral, soit dichotomique.

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The ultrastructure of the atmophytic lime-encrusted filamentous blue-green alga Geitleria calcarea Friedmann, which grows in caves, is studied here for the first time. The cytology of this organism presents original features concerning the cellular sheath, envelopes, wall, thylacoïds and pit connections. Its filament growth is apical and its type of branching is lateral and dichotomous.

     

Simulation methods with extended stability for stiff biochemical Kinetics

Background  

With increasing computer power, simulating the dynamics of complex systems in chemistry and biology is becoming increasingly routine. The modelling of individual reactions in (bio)chemical systems involves a large number of random events that can be simulated by the stochastic simulation algorithm (SSA). The key quantity is the step size, or waiting time, τ, whose value inversely depends on the size of the propensities of the different channel reactions and which needs to be re-evaluated after every firing event. Such a discrete event simulation may be extremely expensive, in particular for stiff systems where τ can be very short due to the fast kinetics of some of the channel reactions. Several alternative methods have been put forward to increase the integration step size. The so-called τ-leap approach takes a larger step size by allowing all the reactions to fire, from a Poisson or Binomial distribution, within that step. Although the expected value for the different species in the reactive system is maintained with respect to more precise methods, the variance at steady state can suffer from large errors as τ grows.     

Ontogeny of the proventitious epicormic buds in Quercus petraea.

In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia. The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk, but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when epicormic buds develop into shoots. Received: 30 March 1999 / Accepted: 09 June 1999     

EAAT expression by macrophages and microglia: still more questions than answers

Glutamate is the main excitatory amino acid, but its presence in the extracellular milieu has deleterious consequences. It may induce excitotoxicity and also compete with cystine for the use of the cystine–glutamate exchanger, blocking glutathione neosynthesis and inducing an oxidative stress-induced cell death. Both mechanisms are critical in the brain where up to 20% of total body oxygen consumption occurs. In normal conditions, the astrocytes ensure that extracellular concentration of glutamate is kept in the micromolar range, thanks to their coexpression of high-affinity glutamate transporters (EAATs) and glutamine synthetase (GS). Their protective function is nevertheless sensitive to situations such as oxidative stress or inflammatory processes. On the other hand, macrophages and microglia do not express EAATs and GS in physiological conditions and are the principal effector cells of brain inflammation. Since the late 1990s, a number of studies have now shown that both microglia and macrophages display inducible EAAT and GS expression, but the precise significance of this still remains poorly understood. Brain macrophages and microglia are sister cells but yet display differences. Both are highly sensitive to their microenvironment and can perform a variety of functions that may oppose each other. However, in the very particular environment of the healthy brain, they are maintained in a repressed state. The aim of this review is to present the current state of knowledge on brain macrophages and microglial cells activation, in order to help clarify their role in the regulation of glutamate under pathological conditions as well as its outcome.     

Ribosomal subunits and ribosomal proteins of Tetrahymena thermophila. Effect of the presence of iodoacetamide during ribosome extraction on the properties of the subunits

Proteolytic degradation of ribosomal proteins occurs during the preparation of subunits of the cytoplasmic ribosomes of the protozoa Tetrahymena thermophila and the isolated subunits are inactive. Addition of 5 mM iodoacetamide to cell suspensions before extraction inhibits proteolytic activity and permits isolation of active subunits. The protein complements of these subunits have been characterized in two different two-dimensional electrophoretic systems, and their molecular weights have been determined.     

Impaired beta-cell regeneration in perinatally malnourished rats: a study with STZ.

We investigated the mechanisms implicated in beta-cell mass reduction observed during late fetal and early postnatal malnutrition in the rat. Beta-cell regeneration, including proliferation and neogenesis, was studied after neonatal beta-cell destruction by streptozotocin (STZ). STZ was injected at birth and maternal food restriction was continued until weaning. Beta-cell mass, proliferation, and islet number were quantified by morphometrical measurements on pancreatic sections in STZ-injected normal (C-STZ) and malnourished (R-STZ) rats, with noninjected C and R rats as controls. At day 4, only 20% of the beta cell-mass remained in C-STZ rats. It regenerated to 50% that of noninjected controls, mainly through active neogenesis, as shown by the entire recovery of islet number/cm(2), and also through moderately increased beta-cell proliferation. In contrast, beta-cell mass from R-STZ animals poorly regenerated, despite a dramatic increase of beta-cell proliferation, because islet number/cm(2) recovered insufficiently. In conclusion, perinatal malnutrition impairs neogenesis and the capacity of beta-cell regeneration by neogenesis but preserves beta-cell proliferation, which remains the elective choice to increase beta-cell mass. These results provide an explanation for the impaired capacity of malnourished animals to adapt their beta-cell mass during aging or pregnancy, which aggravate glucose tolerance.