New Insight Into the Roles of Membrane Microdomains in Physiological Activities of Fungal Cells.

The organization of biological membranes into structurally and functionally distinct lateral microdomains is generally accepted. From bacteria to mammals, laterally compartmentalized membranes seem to be a vital attribute of life. The crucial fraction of our current knowledge about the membrane microdomains has been gained from studies on fungi. In this review we summarize the evidence of the microdomain organization of membranes from fungal cells, with accent on their enormous diversity in composition, temporal dynamics, modes of formation, and recognized engagement in the cell physiology. A special emphasis is laid on the fact that in addition to their other biological functions, membrane microdomains also mediate the communication among different membranes within a eukaryotic cell and coordinate their functions. Involvement of fungal membrane microdomains in stress sensing, regulation of lipid homeostasis, and cell differentiation is discussed more in detail.

Plants and fungi in the era of heterogeneous plasma membranes.

Examples from yeast and plant cells are described that show that their plasma membrane is laterally compartmented. Distinct lateral domains encompassing both specific lipids and integral proteins coexist within the plane of the plasma membrane. The compartments are either spatially stable and include distinct sets of proteins, or they are transiently formed to accomplish diverse functions. They are not related to lipid rafts or their clusters, as defined for mammalian cells. This review summarises only well-documented compartments of plasma membranes from plants and fungi, which have been recognised using microscopic approaches. In several cases, physiological functions of the membrane compartmentation are revealed.

[Reminiscences on the occasion of the Whipple's disease centenary: a summary paper]. / Reminiscence k stoletému výrocí objevu Whippleovy nemoci: souborný referát.

The disease referred to eponymically as Whipple's disease (WD) in medical literature was thoroughly described by the American physician and pathologist George Hoyot Whipple (1878-1976) in 1907 and given a temporary denomination of "intestinal lipodystrophy". According to literature, WD is rare, but its precise incidence has not yet been established. Familial incidence of the disease is acknowledged, and its immunogenetic pathogenesis is assumed. The incidence ofWD is prevailingly observed in middle-aged men (mean age 55), exceptionally at child age - the ratio being 3 to 6 for men and women, respectively. 1. Clinical diagnosis is based on symptoms in the GIT region and, in rare cases, on extraintestinal symptoms. Clinical symptomatology includes: abdominal pain with persistent diarrhoea (steatorrhoea), symptoms typical of malabsorption connected with weight loss, fevers, polyarthritic symptoms, swollen lymph nodes and, in part of patients, skin hyperpigmentation. Anaemia and hypoalbuminaemia (reduced IgA) are typically detected in laboratory tests. Rarer extraintestinal symptoms of the disease are of a diverse nature: cardiac lesions, cerebral lesions, ocular symptoms, conspicuous or even tumour-like enlargement of lymph nodes, lesions of the hemopoietic system. The clinical course ofWD is of progressive or remittent nature and the disease is fatal without treatment. Long-term therapy with antibiotics, especially a combination oftetracyclines (doxycyclin) and corticoids (dexametazone), or chloramphenicol in case of cerebral lesion, have a significantly positive effect on the course and prognosis of WD. From the point of view of pathology, WD is a multisystem infectious disease (Tropheryma whipplei) primarily affecting the GIT (39, 47, 52, 103) or different extraintestinal locations. Due to the known diversity of clinical symptoms, no clinical-diagnostic standard has been established for WD. Differential diagnosis includes different multisystem diseases, primarily malignant lymphomas (especially Hodgkin's disease). From the pathogenetic point of view, we can either assume the effect of a particular cytokine (or TNFalpha) activating macrophage phagocytosis or, if its production is normal, a disorder or defect of the respective receptor in the macrophage cellular membrane. The identification of "Whipple's bacteria" - Tropheryma whipplei - gen. nov. et sp. nov. was made possible by modern molecular biology research methodologies. Its cultivation allows both for the acquisition of the specific antibody and of detailed knowledge of its genoma (PCR, 16S rRNA sequencing).

NORs and their transcription competence during the cell cycle.

In human cells ribosomal genes are organized as clusters, NORs, situated on the short arms of acrocentric chromosomes. It was found that essential components of the RNA polymerase I transcription machinery, including UBF, can be detected on some NORs, termed "competent" NORs, during mitosis. The competent NORs are believed to be transcriptionally active during interphase. However, since individual NORs were not observed in the cell nucleus, their interphase status remains unclear. To address this problem, we detected the competent NORs by two commonly used methods, UBF immunofluorescence and silver staining, and combined them with FISH for visualization of rDNA and/or specific chromosomes. We found that the numbers of competent NORs on specific chromosomes were largely conserved in the subsequent cell cycles, with certain NOR-bearing homologues displaying a very stable pattern of competence. Importantly, those and only those NORs that were loaded with UBF incorporated bromo-uridine in metaphase after stimulation with roscovitine and in telophase, suggesting that competent and only competent NORs contain ribosomal genes transcriptionally active during interphase. Applying premature chromosome condensation with calyculin A, we visualized individual NORs in interphase cells, and found the same pattern of competence as observed in the mitotic chromosomes.

Dynamics of replication foci in early S phase as visualized by cross-correlation function.

To monitor gradual changes in the replication foci distribution during early S phase, different segments of newly synthesized DNA were visualized by immunocytochemical mapping of two consecutively incorporated deoxythymidine analogs in pulse-chase-pulse experiments in HeLa cells. The resulting dual-labeled fluorescence images were evaluated using cross-correlation function (CCF) analysis. General changes of CCF shape due to image deterioration caused by blur, noise, and lateral sampling (pixel size) were also discussed. Using CCF analysis of model images simulating either random initiation of new replication foci, or the firing of new foci in close proximity to completed ones, we were able to ascribe the changes in the early S replication foci distribution to the latter mechanism. In contrast to the data published previously, we monitored the dynamics of all replication foci for up to 3 h. In addition, we showed that the replication foci dynamics is well described by random walk model, so that the average de-localization of individual foci is proportional to square root of the applied chase.

Pseudo real-time method for monitoring of the limiting anisotropy in membranes.

Data acquisition and analysis of the time-resolved fluorescence anisotropy is typically a time consuming process preventing usage of this experimental method for monitoring of time-dependent phenomena. We describe a method for pseudo real-time monitoring of the limiting fluorescence anisotropy r(infinity) allowing to track changes of the membrane order occurring on the time scale of minutes. Principle and performance of the method is demonstrated in the time domain with the time-correlated single photon counting detection. DMPC liposomes stained with 1,6-diphenyl-1,3,5-hexatriene (DPH) have been used to test influence of the diffusion membrane potential on the membrane order during the temperature-induced phase transition in DMPC membranes. It has been found that the transmembrane field of the order of -70 mV increases the phase transition temperature by about 1.5 degrees C-2 degrees C. It is proposed that the full advantage of the method can be utilized with a gated detection, which besides a faster data acquisition brings additional advantage of excitation light suppression. The method can be also used for imaging.

The supply of exogenous deoxyribonucleotides accelerates the speed of the replication fork in early S-phase.

Earlier studies have established that the average speed of a replication fork is two to three times slower in early S-phase than in late S-phase and that the intracellular 2'-deoxyribonucleoside 5'-triphosphate pools grow during S-phase. In this study, the effect of the exogenous 2'-deoxyribonucleoside 5'-triphosphate (dNTP) supply on the average replication speed in a synchronised population of human HeLa cells was tested. The speed of replication fork movement was measured on extended DNA fibers labelled with 2'-deoxythymidine analogues 5-chloro-2'-deoxyuridine and 5-iodo-2'-deoxyuridine. We show that the introduction of exogenous dNTPs accelerates the replication process at the beginning of DNA synthesis only. In late S-phase, the administration of additional dNTPs has no effect on the speed of replication forks. The availability of 2'-deoxynucleotides seems to be a rate-limiting factor for DNA replication during early S-phase.

Non-isotopic mapping of ribosomal RNA synthesis and processing in the nucleolus.

The precise location of ribosomal RNA (rRNA) synthesis within the nucleolus is the subject of recent controversy; some investigators have detected nascent RNA in the dense fibrillar components (DFCs) while others have localized transcription to the fibrillar centers (FCs). We endeavored to resolve this controversy by applying a new technique for non-isotopic labeling of RNA and examined the synthesis and movement of non-isotopically labeled rRNA within the nucleolus. We found that rRNA is synthesized only in a restricted area of DFCs, also involving the boundary region with FCs. We traced a movement of RNA from transcription sites through DFCs to granular components. Our results indicate functional compartmentalization of DFCs with respect to the synthesis and processing of precursor rRNA. In situ mapping of the 5' leader sequence of the 5' external transcribed spacer together with transcription labeling indicated that transcription and the first steps in processing of precursor rRNA are spatially separated. Surprisingly, the results also pointed to a partially extended conformation of newly synthesized precursor rRNA transcripts.

In situ fluorescence visualization of bromouridine incorporated into newly transcribed nucleolar RNA.

Bromouridine-triphosphate is commonly used for in situ immunocytochemical labeling of newly synthesized RNA in living cells. While extranucleolar transcripts do not require special conditions for visualization, special treatment prior to fixation (e.g. incubation with alpha-amanitine) is necessary for immunofluorescence detection of bromouridine-labeled nucleolar RNA in previous studies. We show in the present investigation that bromouridine-triphosphate is efficiently used by both extranucleolar and nucleolar RNA polymerases in living cultured cells. The failure to detect incorporated bromouridine within nucleoli is entirely due to improper treatment of cells after bromouridine incorporation. When methanol/acetone fixation is used, fluorescence signals within nucleoli can be routinely found.

Nuclear pre-mRNA compartmentalization: trafficking of released transcripts to splicing factor reservoirs.

In the present study, the spatial organization of intron-containing pre-mRNAs of Epstein-Barr virus (EBV) genes relative to location of splicing factors is investigated. The intranuclear position of transcriptionally active EBV genes, as well as of nascent transcripts, is found to be random with respect to the speckled accumulations of splicing factors (SC35 domains) in Namalwa cells, arguing against the concept of the locus-specific organization of mRNA genes with respect to the speckles. Microclusters of splicing factors are, however, frequently superimposed on nascent transcript sites. The transcript environment is a dynamic structure consisting of both nascent and released transcripts, i.e., the track-like transcript environment. Both EBV sequences of the chromosome 1 homologue are usually associated with the track, are transcriptionally active, and exhibit in most cases a polar orientation. In contrast to nascent transcripts (in the form of spots), the association of a post-transcriptional pool of viral pre-mRNA (in the form of tracks) with speckles is not random and is further enhanced in transcriptionally silent cells when splicing factors are sequestered in enlarged accumulations. The transcript environment reflects the intranuclear transport of RNA from the sites of transcription to SC35 domains, as shown by concomitant mapping of DNA, RNA, and splicing factors. No clear vectorial intranuclear trafficking of transcripts from the site of synthesis toward the nuclear envelope for export into the cytoplasm is observed. Using Namalwa and Raji cell lines, a correlation between the level of viral gene transcription and splicing factor accumulation within the viral transcript environment has been observed. This supports a concept that the level of transcription can alter the spatial relationship among intron-containing genes, their transcripts, and speckles attributable to various levels of splicing factors recruited from splicing factor reservoirs. Electron microscopic in situ hybridization studies reveal that the released transcripts are directed toward reservoirs of splicing factors organized in clusters of interchromatin granules. Our results point to the bidirectional intranuclear movement of macromolecular complexes between intron-containing genes and splicing factor reservoirs: the recruitment of splicing factors to transcription sites and movement of released transcripts from DNA loci to reservoirs of splicing factors.

Ultrastructure of synapses in the supraoptic nucleus of the cat after induced hypothermia.

Ultrastructure of axosomatic (AS) and axodendritic (AD) synapses in the supraoptic nucleus (NSO) was investigated in a group of normothermic cats and compared with another group of cats after short-term induced hypothermia. Quantitative analysis demonstrated a significant decrease of number of AS synapses, smaller size of AD synaptic knobs, shorter length of the synaptic contact and an increase of the active zone. Evaluation of the shape of the synaptic cleft demonstrated an increase of both positive (P) and negative (N) types in hypothermic animals. The observed morphological changes can be ascribed to the decreased synaptic activity in a greater part of the synaptic population and to the increased activity in a smaller portion of synapses.

Nuclear organization studied with the help of a hypotonic shift: its use permits hydrophilic molecules to enter into living cells.

A new procedure for introduction of hydrophilic molecules into living cells based on efficient uptake of these molecules into the cells during hypotonic treatment is presented and its use is demonstrated by a variety of applications. Experiments with cultured vertebrate and Drosophila cells and various animal tissues demonstrated that the increase in cell membrane permeability under hypotonic conditions is a general phenomenon in all animal cells tested. The efficiency of the method depends on the composition and temperature of the hypotonic buffer, the duration of the hypotonic treatment and the molecular weight of the molecules introduced into living cells. The versatility of this approach is demonstrated with various types of molecules such as modified nucleotides, nucleotides with conjugated fluorochrome, peptides, phosphatase substrates and fluorescent dyes. The method opens new possibilities for the direct investigation of a variety of biological problems as documented here with data on the functional organization of the cell nucleus.

An ultrastructural study of the biostimulative effect of He-Ne laser radiation on the early postnatal differentiation of the rat submandibular gland.

Submandibular gland of the rat during the first week of postnatal development was used for the study of the ultrastructural changes after the He-Ne laser radiation. In the experimental group we observed an increase of the dark cells with greater quantity of the granular endoplasmic reticulum and an increased number of specific secretory granules. These changes show positive biostimulative effect of He-Ne laser radiation on the morphologic differentiation of the submandibular gland of the rat in the early postnatal period.

Nuclear channel system (NCS) in normal endometrium and after hormonal stimulation.

The ultrastructure of NCS was investigated in two groups of patients (15 in each) during the secretory phase of the normal menstrual cycle and after the hormonal stimulation performed in the IVF programme by GnRH-a, FSH and hCG. Three developmental stages of the NCS were classified. The most numerous were the NCS in the mature stage (type 2), less in the early developmental stage (type 1) and least in the regression stage (type 3). The simultaneous occurrence of all three types does not conform the statement of Spornitz. The proportions of the three types were identical in both investigated groups of patients. The number of NCS (per 100 of nuclei) was higher in the group after hormonal stimulation than in the normal cycle. The quantitative measurement of the NCS showed its larger size in the group after hormonal stimulation than in the normal cycle, but the differences in the shape were not significant. In the serial ultrathin sections we demonstrated the relation of NCS to the nucleolus and to the invaginations of the nuclear envelope, the formation of the electron lucent center and the spiral arrangement of the tubules. In the early regression stage we described the relation of the internal row of tubules to the formed myelin figures. We suppose that the higher number and larger size of NCS can be taken as a sign of the increased activity of the endometrium during the early secretory phase after the hormonal stimulation.

Ultrastructure of endometrial surface relief in normal menstrual cycle and after hormonal stimulation.

Ultrastructure of the superficial relief of the endometrial epithelium was investigated under the scanning (SEM) and transmission electron microscopes (TEM) in a group of patients after the hormonal stimulation, performed in the program of in vitro fertilization and embryotransfer. The results were compared with those obtained in a group of patients studied during the secretory phase of normal menstrual cycle. Total 26 bioptic samples were subjected to the investigation, 13 in each group. Different types of the epithelial surface were classified in TEM and SEM and their relative amount was evaluated quantitatively in TEM. Special attention was paid to the pinopodes, considered as specific markers of the nidation window. Differences in the number of pinopodes were observed under the SEM in two groups of patients after different schemes of the hormonal treatment. These differences were not manifested under the TEM due to the small frequency of pinopodes in the ultrathin sections. The ultrastructural changes observed in the two groups of patients after different schemes of hormonal stimulation can be considered as signs of the changed metabolic activity of the endometrial epithelium and they can reflect the different endometrial receptivity for nidation.

Fluorescent probing of membrane potential in walled cells: diS-C3(3) assay in Saccharomyces cerevisiae.

Membrane-potential-dependent accumulation of diS-C3(3) in intact yeast cells in suspension is accompanied by a red shift of the maximum of its fluorescence emission spectrum, lambda max, caused by a readily reversible probe binding to cell constituents. Membrane depolarization by external KCl (with or without valinomycin) or by ionophores causes a fast and reproducible blue shift. As the potential-reporting parameter, the lambda max shift is less affected by probe binding to cuvette walls and possible photobleaching than, for example, fluorescence intensity. The magnitude of the potential-dependent red lambda max shift depends on relative cell-to-probe concentration ratio, a maximum shift (572-->582 nm) being found in very thick suspensions and in cell lysates. The potential therefore has to be assessed at reasonably low cell (< or = 5 x 10(6) cells/ml) and probe (10(-7)M) concentrations at which a clearly defined relationship exists between the lambda max shift and the potential-dependent accumulation of the dye in the cells. The redistribution of the probe between the medium and yeast protoplasts takes about 5 min, but in intact cells it takes 10-30 min because the cell wall acts as a barrier, hampering probe penetration into the cells. The barrier properties of the cell wall correlate with its thickness: cells grown in 0.2% glucose (cell wall thickness 0.175 +/- 0.015 micron, n = 30) are stained much faster and the lambda max is more red-shifted than in cells grown in 2% glucose (cell wall thickness 0.260 +/- 0.043 micron, n = 44). At a suitable cell and probe concentration and under standard conditions, the lambda max shift of diS-C3(3) fluorescence provides reliable information on even fast changes in membrane potential in Saccharomyces cerevisiae.

Effect of the new fluorescent brightener Rylux BSU on morphology and biosynthesis of cell walls in Saccharomyces cerevisiae.

Rylux BSU, a new fluorescent brightener from the family of 4,4'-diaminostilbene-2,2'disulfonic acid derivatives, inhibited growth and cytokinesis of the yeast Saccharomyces cerevisiae. In the presence of 0.1-1 mg/ml Rylux BSU the cells grew in clumps, had irregular shape and were larger than controls. They formed apparently normal primary septa but their secondary septa and lateral cell walls, especially those in older cells, were abnormally thick with large deposits of amorphous wall material in the periplasmic spaces all over the cell surface. Chitin content in the cell walls of cells grown in the presence of Rylux BSU was increased 2 to 5 times in comparison to that of the controls and glucan content was reduced by up to 30%. In the in vitro assays with particulate membrane fractions, Rylux BSU acted as a non-competitive inhibitor of beta-1,3-glucan synthase with inhibitory constant Ki = 1.75 mg/ml whereas the chitin synthase was inhibited to a much lesser extent. From the difference of the effects of Rylux BSU on the synthesis of chitin in vivo and in vitro it is concluded that the brightener interacts with chitin synthase only indirectly, possibly by influencing the properties of integral plasma membrane.