The role of glucose in the Kluyveromyces bulgaricus flocculation phenomenon: transduction by cAMP-dependent protein kinase pathway?

Yeast flocculation appears to be dependent on several culture conditions such as nitrogen or carbon sources. In 0.2% glucose medium Kluyveromyces bulgaricus flocculation intensity is weak (10% at maximum) by comparison with flocculation in 2% glucose medium (85% maximum). Addition of glucose to K. bulgaricus in exponential growth phase in 0.2% glucose medium produced a rapid increase of the flocculation percentage during the 30 min following the addition of glucose. cAMP and 2,4-dinitrophenol showed similar effects while cAMP-dependent protein kinase (PKA) inhibitors exhibited an antagonist effect. Moreover, the induction of flocculation did not seem to imply translation of new proteins: cycloheximide had no effect, although growth was inhibited. The induction of flocculation mainly implies ATP hydrolysis for activation or secretion of galactose-specific receptors as demonstrated by treatment with NaN(3). We propose a hypothesis that involves a PKA transduction signal leading to flocculation.

Solid-phase microextraction of volatile components from natural grassland plants

The volatile components from nine plants growing on natural grasslands in Auvergne, central France, selected for the broad qualitative and quantitative diversity of their terpenoid fractions, were analyzed by high-resolution gas-phase chromatography and mass spectrometry (HRGC-MS) after static headspace solid-phase microextraction (SHS-SPME). SHS-SPME allowed all the plant material to be analyzed under the same conditions despite its wide-ranging composition. This is not always possible with other extraction methods. Using an apolar poly(dimethylsiloxane) (PDMS) phase, numerous terpenoid hydrocarbons, together with alcohols, cyclic ethers, and esters, were extracted. Its ease of use and the high resolution of the chromatographic profiles obtained make SHS-SPME well suited to the rapid characterization of the main components of the volatile fraction of plants. Of the nine plants studied, four (Meum athamanticum, Pimpinella saxifraga, Achillea millefolium, and Thymus pulegioides) exhaled more than 60 different volatile components. Certain terpenes present in large amounts in these plants might help link dairy products to grazing pasture, thus improving food traceability.

Amphotericin B resistance and membrane fluidity in Kluyveromyces lactis strains

The membrane fluidity of reduced-amphotericin B (AmB)-sensitivity Kluyveromyces lactis mutant strain is higher than that of the wild-type K. lactis strain. After culture of the K. lactis and K. lactis mutant cells in the presence of subinhibitory doses of AmB (10 and 125 mg/liter, respectively), the plasma membranes of both yeast strains also showed a higher fluidity than did those of control cells. High membrane fluidity was associated with changes in the structural properties of the membranes. Culture of the K. lactis and K. lactis mutant cells in the presence of AmB induced changes in membrane lipid contents. In particular, phospholipid contents were increased in both strains treated with AmB, compared with their corresponding counterparts. As a result, the sterol/phospholipid ratio decreased. The relative proportion of monounsaturated fatty acids also increased after AmB treatment. The saturated fatty acid/monounsaturated fatty acid ratio decreased in K. lactis and K. lactis mutant cells treated with AmB but also in K. lactis mutant control cells compared to that in the K. lactis wild strain. These changes in lipid composition explain the higher fluidity, which could represent a process of metabolic resistance of the yeasts to AmB.

Permeability of yeast cell envelope to fluorescent galactosylated telomers derived from THAM

The work reported herein deals with the study of cellular recognition and permeability phenomena in yeasts. Various galactosylated organic telomers derived from trishydroxymethyl-aminomethane (THAM) and bearing fluorescent moieties were synthesized in order to measure their ability to cross the yeast cell envelope. Grafting fluorescent probes on the organic telomer backbone allowed us to study their specific behaviors toward the yeasts by fluorescence microscopy. Yeasts belonging to the genera Kluyveromyces and Saccharomyces were used for this study. With Saccharomyces yeast cells bearing mannose-specific lectins or lectin-like proteins, on their outer surface, all the galactosylated or nongalactosylated organic telomers passed through the cell envelope and invaded the cytoplasm. With Kluyveromyces yeast cells bearing galactose-specific lectins, the galactosylated organic telomers were blocked at the outer surface while the nongalactosylated derivatives crossed the cell envelope. Moreover, preincubation of Kluyveromyces yeasts with galactose or methylgalactose inhibited the cell surface anchorage of the organic telomers and allowed their penetration into the cytoplasm. When assays were performed on spheroplasts of both Kluyveromyces and Saccharomyces yeasts, no fixation on the surface could be observed, and all the derivatives went through the membrane and invaded the cytoplasm.

Evidence for a lectin in Kluyveromyces sp. that is involved in co-flocculation with Schizosaccharomyces pombe

Co-flocculation is the aggregation of yeasts belonging to different genera or species. Kluyveromyces bulgaricus and Kluyveromyces lactis 5c are self-flocculent, but they can also co-flocculate with the non-flocculent yeast Schizosaccharomyces pombe 972 h(-). This co-flocculation is inhibited by D-galactose and galactose derivatives and involves the binding of a galactose-specific proteinic receptor (or lectin) of Kluyveromyces sp. to the cell wall galactomannans of S. pombe. The proteinic receptor is strongly anchored in the cell wall, it was partially purified by affinity chromatography using immobilized S. pombe galactomannans. This galactose-specific proteinic receptor does not appear to interfere in K. bulgaricus or K. lactis self-flocculation, which is mediated by another galactose-specific lectin weakly linked at the cell wall.

Mitochondrial function in cell wall glycoprotein synthesis in Saccharomyces cerevisiae NCYC 625 (Wild type) and [rho(0)] mutants

We studied phosphopeptidomannans (PPMs) of two Saccharomyces cerevisiae NCYC 625 strains (S. diastaticus): a wild type strain grown aerobically, anaerobically, and in the presence of antimycin and a [rho(0)] mutant grown aerobically and anaerobically. The aerobic wild-type cultures were highly flocculent, but all others were weakly flocculent. Ligands implicated in flocculation of mutants or antimycin-treated cells were not aggregated as much by concanavalin A as were those of the wild type. The [rho(0)] mutants and antimycin-treated cells differ from the wild type in PPM composition and invertase, acid phosphatase, and glucoamylase activities. PPMs extracted from different cells differ in the protein but not in the glycosidic moiety. The PPMs were less stable in mitochondrion-deficient cells than in wild-type cells grown aerobically, and this difference may be attributable to defective mitochondrial function during cell wall synthesis. The reduced flocculation of cells grown in the presence of antimycin, under anaerobiosis, or carrying a [rho(0)] mutation may be the consequence of alterations of PPM structures which are the ligands of lectins, both involved in this cell-cell recognition phenomenon. These respiratory chain alterations also affect peripheral, biologically active glycoproteins such as extracellular enzymes and peripheral PPMs.

Molecular identification of Lactobacillus hilgardii and genetic relatedness with Lactobacillus brevis

Conventional phenotypic methods lead to misidentification of the lactic acid bacteria Lactobacillus hilgardii and Lactobacillus brevis. Random amplified polymorphic DNA (RAPD) and repetitive element PCR (REP-PCR) techniques were developed for a molecular study of these two species. The taxonomic relationships were confirmed by analysis of the ribosomal operon. Amplified DNA fragments were chosen to isolate L. hilgardii-specific probes. In addition to rapid molecular methods for identification of L. hilgardii, these results convincingly proved that some strains first identified as L. brevis must be reclassified as L. hilgardii. The data clearly showed that these molecular methods are more efficient than phenotypic or biochemical studies for bacterial identification at the species level.

Neurogenesis during caudal spinal cord regeneration in adult newts

After tail amputation in urodele amphibians, dramatic changes appear in the spinal cord rostral to the amputation level. Transection induces a proliferation response in cells lining the ependymal canal, giving rise to an ependymal tube in which neurogenesis occurs. Using the thymidine analog bromodeoxyuridine (BrdU) in short- and long-term labeling of cells undergoing DNA synthesis (S phase of the cell cycle), specific cell markers, and cell cultures, we show that neurons derive from the proliferative ependymal layer of the ependymal tube.

Cell targeting by glycosidic telomers. Specific recognition of the Kb CWL1 lectin by galactosylated telomers

This work deals with the synthesis and lectinic recognition ability of galactosylated telomers. To investigate if telomeric carriers could exhibit cellular recognition properties, we have synthesized mono- and polygalactosylated tris(hydroxymethyl)acrylamidomethane (THAM) telomers. The affinity of such macromolecular drug carriers toward a receptor, the yeast Kb CWL1 lectin, was defined, and the influence of mono- or polygalactosylation of THAM units on the recognition phenomenon was assessed. The lectinic affinity of the compounds was estimated by measuring the inhibition of yeast aggregation. The average degree of polymerization as well as the hydrophilic-lipophilic balance of such galactosylated telomers affects their recognition ability for the lectin.

Implication of cell wall constituents in the sensitivity of Kluyveromyces lactis strains to amphotericin B

In Kluyveromyces lactis, the cell wall compositions of Kl (ATCC 96897), a wild sensitive strain, and Klm (ATCC 96896), a strain resistant to amphotericin B (AmB), were shown to be very different, since the walls in the latter were significantly enriched in hexosamine, but had a reduced content in phosphate and amino acid. In both strains, the cell walls limited their sensitivity to this antifungal agent. The absence of cell wall increased the sensitivity of the cells to this polyene by 5 to 10-fold. When the cells were treated with enzymes such as pronase and chitinase in order to change the cell wall structure just before inoculation, the yeasts appeared more resistant to the antibiotic. However, treatments with chymopapain and phospholipase C did not significantly change the sensitivity of the two strains to this agent. Cells treated with acid phosphatase displayed a longer lag phase than the control cells. In addition, when cultured in the presence of AmB, the cells were less sensitive to this agent. The present results reveal that both a change in the ionic charges of the cell wall and an alteration in the cell wall structure modified the sensitivity of these yeast strains to AmB.

Comparative extraction procedures for a galactose-specific lectin involved in flocculation of Kluyveromyces lactis strains

The extraction of a lectinic factor involved in yeast flocculation, from two Kluyveromyces lactis strains (a flocculent K. lactis 5c and a non-flocculent K. lactis 5a strain) was performed using EDTA and two surfactants, Hecameg and HTAC. The properties of the different extracts were tested by haemagglutination and reflocculation of deflocculated K. lactis 5c cells. Hecameg gave the highest yields of active lectinic extract but the extraction with EDTA seemed more specific. HTAC extracts showed a very low activity. The possibilities of extraction of the agglutinating factor, either by an ion chelator or by surfactants, suggest that this factor may be anchored in the cell envelope, i.e. the cell wall and the membrane, by different mechanisms. All the assays revealed a galactose-specific lectinic activity was present that in the flocculent as well as in the non-flocculent strain. This indicates that the absence of flocculation with K. lactis 5a is mainly due to a defect in the ligands of the lectin rather than to a loss of the lectinic factor itself.

Neural crest-like cells originate from the spinal cord during tail regeneration in adult amphibian urodeles

Using in vitro cell-marking experiments and transplantation in tail regenerates, we have recently shown (Benraiss et al., 1996) that clonal cells derived from adult newt spinal cord (SC) cultures could find suitable cues in blastemal mesenchyme to enable them to differentiate into melanocytes or Schwann cells. This led to the question of whether neural crest-like cell derivatives might emerge from the ependymal tube as tail regeneration proceeded. To address this question we used the biolistic method for in situ transfection of caudal SC cells. These cells were transfected with an alkaline phosphatase marker gene. The potentialities of transfected cell derivatives in tail regenerates were analyzed using histochemistry or immunohistochemistry. As early as eight days after transfection, labeled cells were detected in the regenerating SC and around its "terminal vesicle" (TV). Two to four weeks following transfection, most of the labeled cell derivatives could be identified either by dark granules as melanocytes or by galactocerebroside staining as Schwann cells. Electron microscopic investigations revealed the incompletely organized cytoarchitecture of the TV, suggesting that an exit of cells was possible at this level, at least from its "open" dorsal part. Furthermore, the localization of ciliated cells in the blastemal mesenchyme, especially around the TV, supported this view by suggesting that they might be ependymal cells detached from it. Our findings therefore led us to believe that in the newt, during tail regeneration, neural crest-like cells emerging from the TV could participate in the formation of the peripheral nervous system, especially by providing Schwann cells and melanocytes.

The function of type IV collagen during Drosophila muscle development

Type IV collagen forms a network that provides the major structural support for basement membranes. Basement membranes are specialized forms of extracellular matrix with important functions in development. One collagen gene (Dcg1) was characterized in Drosophila melanogaster and shown to encode a collagen chain related to vertebrate basement membrane type IV collagen chains. Therefore, to access the functional importance of type IV collagen during Drosophila myogenesis, we adopted two different approaches to decrease the Dcg1 gene expression in Drosophila embryos. We describe, here, that the decrease in Dcg1 gene expression causes, in particular, defective muscle attachments. These mutant phenotypes suggest that type IV collagen acts to stabilize cell-matrix interactions.

[Immigration of a pregnant female in an alpine marmot family group: behavioural and genetic data]

The acceptance of a pregnant female by the dominant male of a family group of alpine marmots (Marmota marmota) (population of La Grande Sassière, Parc national de la Vanoise, French Alps) was revealed by the combined results from microsatellite polymorphism analysis and behavioural studies. These first results seem to indicate that the mating system of the alpine marmot is more complex than previously thought, that polygyny cannot be excluded, and that adult females can join neighbouring groups. This acceptance would have been interpreted as an extra-pair fertilization if complete field data had not been available.

Clonal cell cultures from adult spinal cord of the amphibian urodele Pleurodeles waltl to study the identity and potentialities of cells during tail regeneration

The urodele amphibians are nearly the only adult vertebrates able to regenerate their missing or amputated tail. The most striking feature of this model lies in the ability of the spinal cord (SC) to differentiate, within the regenerating tail, a new ependymal tube from which the SC and the peripheral nervous system originate. A fundamental question is whether, in response to tail excision, the ependymoglia of the old SC stump behaves as an embryonic neuroepithelium. To evaluate this possibility, cell lines from primary cell cultures of adult SC were established for the first time in newts, and two cell clones, immunochemically characterized as ependymoglial cell populations, could be obtained. To analyze the potentialities of these clonal cells, after transplantation in tail regenerates, cell-marking experiments, using either in vitro transfection with lacZ gene or the lineage tracer lysinated rhodamine dextran (LRD), were performed. One to 2 weeks postimplantation, most of labeled derivatives were identified as melanocytes. Interestingly, labeled cells were also seen integrated in the ependymoglia of the regenerating SC. Two to 6 weeks after implantation in young regenerates, we also observed LRD-labeled elongated cells close to nerves or myofibers which were unambiguously identified as Schwann cells by galactocerebroside staining. Taken together, these findings showed that clonal cells derived from adult newt SC cultures could largely find, in regenerate mesenchyme, suitable environmental conditions to differentiate into melanocytes or Schwann cells. Because these two cells types arise from neural crest cells during embryo-genesis, this supports the interesting view that multipotent cells are still present in the SC of adult urodeles.

Identification of 24-methylene-24,25-dihydrolanosterol as a precursor of ergosterol in the yeasts Schizosaccharomyces pombe and Schizosaccharomyces octosporus

Study of the plasma membrane sterol composition in the yeasts Schizosaccharomyces pombe and Schizosaccharomyces octosporus revealed the presence of ergosterol, lanosterol, dehydroergosterol, fecosterol, episterol and 24-methylene-24,25-dihydrolanosterol (eburicol), a C-31 derivative. The growth of both yeasts in the presence of ketoconazole led to a decrease by 85% of the ergosterol content while the levels of lanosterol and eburicol increased. This suggests that in the biosynthetic pathway of ergosterol in Schizosaccharomyces species, the transmethylation process on the C-24 may occur directly on lanosterol and not only on zymosterol. On the other hand, it cannot be excluded that in the genus Schizosaccharomyces two routes exist from lanosterol to ergosterol: the classical one via a direct C-14, C-4 demethylation of lanosterol and the second one via the formation of a C-31 derivative followed by demethylations.

Changes in cell wall composition of deformed ras1- cells of Schizosaccharomyces pombe

Disruption of the Schizosaccharomyces pombe ras1 gene results in a morphological transformation to large spheres, in contrast to wild-type cells which grow as rods. Chemical analysis of isolated cell walls showed no significant changes in saccharide content but an increase in protein and phosphate contents in ras1- walls relative to parent walls. Polymers tightly bound to the cell wall were solubilized by SDS treatment. Several compounds with molar mass ranging from 22 to 130 kDa and more were resolved by gel filtration and SDS-PAGE. Among low-molar-mass species, a component moving as a band at 31 kDa was conspicuous in ras1- cell walls. It was solubilized by heating in Tris-HCl buffer and shown to have a beta-1,3-glucanase activity against laminarin. The level of the enzyme was by 30% higher in the ras1- cell wall than in the wild-type cell wall. This enzyme may participate in the remodelling of the rigid glucan network and account (at least partially) for the aberrant cell shape. The ras1- cell wall contained a high level of charged polymers, especially phosphoproteins, raising the appealing possibility that ras1- is involved in a putative kinase cascade required to sense and respond to external stimuli destined for the cell wall. Although the present study shows that ras1 loss of function and altered cell wall composition are closely linked defects, it has still to be shown that the ras1 protein is directly involved in alterations found in the mutant cell walls.

Tenascin expression in developing, adult and regenerating caudal spinal cord in the urodele amphibians

Tenascin (Tn) protein and transcripts were analyzed in developing, adult and regenerating caudal spinal cord (SC) of Pleurodeles waltl. A polyclonal antibody (PAb) against Xenopus Tn and a newt Tn cDNA probe were used. In Western blots, anti-Tn PAb recognized Tn polypeptides of 200-220 kDa in tail regenerate extracts, but also the homolog of Tn/Cytotactin/J1 in brain and SC of adult newt. Immunofluorescence studies showed some reactivity around ependymoglial cells and strong labeling in the nervous tracts, in the developing as well as in the regenerating SC or adult SC. Immunogold electron microscopy revealed the presence of Tn throughout the ependymoglial cells, particularly near and along the plasma membrane of radial processes surrounding axons, especially growth cones. Tn could be more precisely found within rough endoplasmic reticulum and Golgi structures, or again in the surrounding extracellular space. This suggested that Tn was at least produced by radial glial profiles forming axonal compartments in which axons grew. Using the DNA probe for Tn, expression of Tn mRNA was also examined by Northern blot and RNAase protection analyses and by in situ hybridization, respectively. The levels of transcripts, barely detectable in adult tail, increased in regenerates from 3 days through 4-8 weeks post-amputation. In situ Tn mRNA were mainly localized in the mesenchyme, especially at the epithelial-mesenchymal interface, and in the developing cartilage, at the early regeneration stages, whereas high amounts of transcripts were seen not only at these stages, but also later, in the regenerating SC. Our main results supported the view that, in the caudal SC of newts, Tn, synthesized by radial ependymoglial cells, was similarly expressed during regeneration as well as larval development, and exhibited a sustained high accumulation level in the adult SC. On the basis of the multifunctional properties of Tn, the putative roles played by Tn as a substrate for neuronal pathfinding and boundary shaping were discussed.

Membrane phospholipid composition in Saccharomyces uvarum cells grown in the presence of subinhibitory doses of amphotericin B and desertomycin

In Saccharomyces uvarum cultures, subinhibitory doses of amphotericin B and desertomycin induced alterations in the plasma membrane phospholipid composition. Amphotericin B increased the lipid content in the plasma membrane. It showed a pronounced effect on fatty acyl constituents by raising the amounts of mono- and polyunsaturated derivatives in phospholipids. On the other hand, desertomycin had no apparent effect on fatty acid synthesis but altered the relative composition of phospholipids in the membrane. Phosphatidyl choline and phosphatidyl ethanolamine contents decreased, while their precursors, phosphatidyl serine and phosphatidic acid, increased. On the other hand, the rates of phosphatidyl inositol were not significantly affected by the action of either antifungal agent.

Formation of the extracellular matrix during the epimorphic anterior regeneration of Owenia fusiformis: autoradiographical and in situ hybridization studies

During post-traumatic regeneration of the polychaete annelid Owenia fusiformis, the extracellular matrix (ECM) formation was studied by light and electron microscopy and by histoautoradiography after incorporation of tritiated proline as marker for collagenic proteins. Three days after amputation, a new basement membrane was reformed in the blastema between the ectoderm and the mesoderm. At the same time, the cytoskeleton and the anchoring structures (hemidesmosomes) were differentiated in the basal part of the ectodermal cells. Four days after amputation, collagen fibers appeared in the extracellular matrix newly reformed between the ectodermal and mesodermal layers. The existence of a proximo-distal gradient in the organization of the new extracellular matrix and the accumulation of molecules labeled by 3H-proline was shown. This accumulation started at the level of the injured segment of the stump. Differences in labeling intensity were seen in the regenerate. Within specific organogenetic zones, i.e. the epidermal gland analagen, the branchial buds and the stomodeal invagination, the labeling between the ectodermal and mesodermal layers was less intense than in other parts of the regenerate. In the mesodermal connective septa (dissepiments), located between consecutive segments, the labeling and the accumulation of extracellular material occurred later than the formation of the ectodermal basement membrane. In situ hybridization of a DNA molecular probe corresponding partially to the coding region of the collagen-like gene Ocg8, showed a spatio-temporal expression of this gene. Northern blot analysis showed a single transcript of 6.6 kb. Four days after amputation the accumulation of this transcript was exclusively localized at the level of the ectodermal layer during differentiation of the regenerate. The ectoderm was thus shown to play a dynamic role during the first stages of traumatic regeneration, although it did not seem to be directly involved in the early events of the metameric process.