Implications of Below-Ground Allelopathic Interactions of Camelina sativa and Microorganisms for Phosphate Availability and Habitat Maintenance

Toxic breakdown products of young Camelina sativa (L.) Crantz, glucosinolates can eliminate microorganisms in the soil. Since microorganisms are essential for phosphate cycling, only insensitive microorganisms with phosphate-solubilizing activity can improve C. sativa's phosphate supply. In this study, 33P-labeled phosphate, inductively coupled plasma mass spectrometry and pot experiments unveiled that not only Trichoderma viride and Pseudomonas laurentiana used as phosphate-solubilizing inoculants, but also intrinsic soil microorganisms, including Penicillium aurantiogriseum, and the assemblies of root-colonizing microorganisms solubilized as well phosphate from apatite, trigger off competitive behavior between the organisms. Driving factors in the competitiveness are plant and microbial secondary metabolites, while glucosinolates of Camelina and their breakdown products are regarded as key compounds that inhibit the pathogen P. aurantiogriseum, but also seem to impede root colonization of T. viride. On the other hand, fungal diketopiperazine combined with glucosinolates is fatal to Camelina. The results may contribute to explain the contradictory effects of phosphate-solubilizing microorganisms when used as biofertilizers. Further studies will elucidate impacts of released secondary metabolites on coexisting microorganisms and plants under different environmental conditions.

Ablation of glucosinolate accumulation in the oil crop Camelina sativa by targeted mutagenesis of genes encoding the transporters GTR1 and GTR2 and regulators of biosynthesis MYB28 and MYB29

Camelina sativa is an oil crop with low input costs and resistance to abiotic and biotic stresses. The presence of glucosinolates, plant metabolites with adverse health effects, restricts the use of camelina for human and animal nutrition. Cas9 endonuclease-based targeted mutagenesis of the three homeologs of each of the glucosinolate transporters CsGTR1 and CsGTR2 caused a strong decrease in glucosinolate amounts, highlighting the power of this approach for inactivating multiple genes in a hexaploid crop. Mutagenesis of the three homeologs of each of the transcription factors CsMYB28 and CsMYB29 resulted in the complete loss of glucosinolates, representing the first glucosinolate-free Brassicaceae crop. The oil and protein contents and the fatty acid composition of the csgtr1csgtr2 and csmyb28csmyb29 mutant seeds were not affected. The decrease and elimination of glucosinolates improves the quality of the oil and press cake of camelina, which thus complies with international standards regulating glucosinolate levels for human consumption and animal feeding.

Polar lipid characterization and description of Chryseobacterium capnotolerans sp. nov., isolated from high CO2-containing atmosphere and emended descriptions of the genus Chryseobacterium, and the species C. balustinum, C. daecheongense, C. formosense, C. gleum, C. indologenes, C. joostei, C. scophthalmum and C. ureilyticum

Modified atmosphere (MA) packaging plays an important role in improving food quality and safety. By using different gas mixtures and packaging materials the shelf life of fresh produce can significantly be increased. A Gram-negative-staining, rod-shaped, orange-pigmented strain DH-B6T, has been isolated from MA packed raw pork sausage (20% CO2, 80% O2). The strain produced biofilms and showed growth at high CO2 levels of up to 40%. Complete 16S rRNA gene and whole-genome sequences revealed that strain DH-B6T belongs to the genus Chryseobacterium , being closely related to strain Chryseobacterium indologenes DSM 16777T (98.4%), followed by Chryseobacterium gleum NCTC11432T (98.3%) and Chryseobacterium lactis KC1864T (98.2%). Average nucleotide identity value between DH-B6T and C. indologenes DSM 16777T was 81.1% and digital DNA–DNA hybridisation was 24.9%, respectively. The DNA G+C content was 35.51 mol%. Chemotaxonomical analysis revealed the presence of the rare glycine lipid cytolipin, the serine-glycine lipid flavolipin and the sulfonolipid sulfobacin A, as well as phosphatidylethanolamine, monohexosyldiacylglycerol and ornithine lipid, including the hydroxylated forms. Major fatty acids were iC15 : 0 (50.7%) and iC17 : 1 cis 9 (28.7%), followed by iC15 : 0 2-OH (7.0%) and iC17 : 0 3-OH (6.2%). The isolated strain contained MK-6 as the only respiratory quinone and flexirubin-like pigments were detected as the major pigments. Based on the phenotypic, chemotaxonomic and phylogenetic characteristics, the strain DH-B6T (=DSM 110542T=LMG 31915T) represents a novel species of the genus Chryseobacterium , for which the name Chryseobacterium capnotolerans sp. nov. is proposed. Emended descriptions of the genus Chryseobacterium and eight species of this genus based on polar lipid characterisation are also proposed.

Synthesis of the unusual lipid bis(monoacylglycero)phosphate in environmental bacteria

The bacterial membrane is constantly remodelled in response to environmental conditions and the external supply of precursor molecules. Some bacteria are able to acquire exogenous lyso-phospholipids and convert them to the corresponding phospholipids. Here, we report that some soil-dwelling bacteria have alternative options to metabolize lyso-phosphatidylglycerol (L-PG). We find that the plant-pathogen Agrobacterium tumefaciens takes up this mono-acylated phospholipid and converts it to two distinct isoforms of the non-canonical lipid bis(monoacylglycero)phosphate (BMP). Chromatographic separation and quadrupole-time-of-flight MS/MS analysis revealed the presence of two possible BMP stereo configurations acylated at either of the free hydroxyl groups of the glycerol head group. BMP accumulated in the inner membrane and did not visibly alter cell morphology and growth behaviour. The plant-associated bacterium Sinorhizobium meliloti was also able to convert externally provided L-PG to BMP. Other bacteria like Pseudomonas fluorescens and Escherichia coli metabolized L-PG after cell disruption, suggesting that BMP production in the natural habitat relies both on dedicated uptake systems and on head-group acylation enzymes. Overall, our study adds two previously overlooked phospholipids to the repertoire of bacterial membrane lipids and provides evidence for the remarkable condition-responsive adaptation of bacterial membranes.

Sphingomonas aliaeris sp. nov., a new species isolated from pork steak packed under modified atmosphere

Species belonging to the genus Sphingomonas have been isolated from environments such as soil, water and plant tissues. Many strains are known for their capability of degrading aromatic molecules and producing extracellular polymers. A Gram-stain-negative, strictly aerobic, motile, red-pigmented, oxidase-negative, catalase-positive, rod-shaped strain, designated DH-S5^T, has been isolated from pork steak packed under CO₂-enriched modified atmosphere. Cell diameters were 1.5×0.9 µm. Growth optima were at 30 °C and at pH 6.0. Phylogenetic analyses based on both complete 16S rRNA gene sequence and whole-genome sequence data revealed that strain DH-S5^T belongs to the genus Sphingomonas, being closely related to Sphingomonas alpina DSM 22537^T (97.4 % gene sequence similarity), followed by Sphingomonas qilianensis X1^T (97.4 %) and Sphingomonas hylomeconis GZJT-2^T (97.3 %). The DNA G+C content was 64.4 mol%. The digital DNA-DNA hybridization value between the isolate strain and S. alpina DSM 22537^T was 21.0 % with an average nucleotide identity value of 77.03 %. Strain DH-S5^T contained Q-10 as the ubiquinone and major fatty acids were C_18 : 1 cis 11 (39.3 %) and C_16 : 1 cis 9 (12.5 %), as well as C_16 : 0 (12.1 %) and C_14 : 0 2-OH (11.4 %). As for polar lipids, phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, dimethylphosphatidylethanolamine and sphingoglycolipid could be detected, alongside traces of monomethylphosphatidylethanolamine. Based on its phenotypic, chemotaxonomic and phylogenetic characteristics, strain DH-S5^T (=DSM 110829^T=LMG 31606^T) is classified as a representative of the genus Sphingomonas, for which the name Sphingomonas aliaeris sp. nov. is proposed.

Structural Analysis of Glycosylglycerolipids Using NMR Spectroscopy

Glycosylglycerolipids are essential components of plant and bacterial membranes. These lipids exert central roles in physiological processes such as photosynthesis in plants or to maintain membrane stability in bacteria. They are composed of a glycerol backbone esterified with two fatty acids at the sn-1 and sn-2 positions, and carbohydrate moieties connected via a glycosidic bond at the sn-3 position. Nuclear magnetic resonance (NMR) spectroscopy is a state-of-the-art technique to determine the nature of the bound carbohydrates as well as their anomeric configurations. Here we describe the analysis of intact glycosylglycerolipids by NMR spectroscopy to determine structural details of their sugar head groups without the need of chemical derivatization.

Arthrobacter bussei sp. nov., a pink-coloured organism isolated from cheese made of cow's milk

A pink-coloured bacterium (strain KR32^T) was isolated from cheese and assigned to the 'Arthrobacter agilis group'. Members of the 'pink Arthrobacter agilis group' form a stable clade (100 % bootstrap value) and contain the species Arthrobacter agilis, Arthrobacter ruber and Arthrobacter echini, which share ≥99.0 % 16S rRNA gene sequence similarity. Isolate KR32^T showed highest 16S rRNA gene sequence similarity (99.9 %) to A. agilis DSM 20550^T. Additional multilocus sequence comparison confirmed the assignment of strain KR32^T to the clade 'pink A. agilis group'. Average nucleotide identity and digital DNA-DNA hybridization values between isolate KR32^T and A. agilis DSM 20550^T were 82.85 and 26.30 %, respectively. The G+C content of the genomic DNA of isolate KR32^T was 69.14 mol%. Chemotaxonomic analysis determined anteiso-C_15 : 0 as the predominant fatty acid and MK-9(H₂) as the predominant menaquinone. Polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and monoacyldimannosyl-monoacylglycerol. The peptidoglycan type of the isolate was A3α. The carotenoid bacterioruberin was detected as the major pigment. At 10 °C, strain KR32^T grew with increased concentrations of bacterioruberin and production of unsaturated fatty acids. Strain KR32^T was a Gram-stain-positive, catalase-positive, oxidase-positive and coccus-shaped bacterium with optimal growth at 27-30 °C and pH 8. The results of phylogenetic and phenotypic analyses enabled the differentiation of the isolate from other closely related species of the 'pink A. agilis group'. Therefore, strain KR32^T represents a novel species for which the name Arthrobacter bussei sp. nov. is proposed. The type strain is KR32^T (=DSM 109896^T=LMG 31480^T=NCCB 100733^T).

Chloroplast Lipids and Their Biosynthesis

Chloroplasts contain high amounts of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) and low levels of the anionic lipids sulfoquinovosyldiacylglycerol (SQDG), phosphatidylglycerol (PG), and glucuronosyldiacylglycerol (GlcADG). The mostly extraplastidial lipid phosphatidylcholine is found only in the outer envelope. Chloroplasts are the major site for fatty acid synthesis. In Arabidopsis, a certain proportion of glycerolipids is entirely synthesized in the chloroplast (prokaryotic lipids). Fatty acids are also exported to the endoplasmic reticulum and incorporated into lipids that are redistributed to the chloroplast (eukaryotic lipids). MGDG, DGDG, SQDG, and PG establish the thylakoid membranes and are integral constituents of the photosynthetic complexes. Phosphate deprivation induces phospholipid degradation accompanied by the increase in DGDG, SQDG, and GlcADG. During freezing and drought stress, envelope membranes are stabilized by the conversion of MGDG into oligogalactolipids. Senescence and chlorotic stress lead to lipid and chlorophyll degradation and the deposition of acyl and phytyl moieties as fatty acid phytyl esters.

Headgroup hydroxylation by OlsE occurs at the C4 position of ornithine lipid and is widespread in proteobacteria and bacteroidetes

Amino acid-containing acyloxyacyl lipids are composed of a 3-hydroxy fatty acid amide-bound to the α-amino group of an amino acid. A second fatty acid is ester-linked to the 3-hydroxy group of the first fatty acid. Most commonly, ornithine is the headgroup of these lipids, but glycine, serineglycine, glutamine and lysine have also been described in bacteria. Ornithine lipids (OL) can be synthesized by about 50% of the sequenced bacterial species, and several covalent modifications of its basic structure have been described. The OL hydroxylase OlsE is widespread in Rhizobium and Agrobacterium species and is responsible for introducing a hydroxyl group at a hence unknown position within the ornithine headgroup causing the formation of the OL named S2. Using NMR on purified OL S2, we show that the OlsE-mediated hydroxylation takes place at the C-4 position of the ornithine headgroup. Furthermore, we identify a hydroxylase in the genome of Pseudopedobacter saltans, distantly related to OlsE from α-proteobacteria, able to hydroxylate the headgroup of both ornithine lipids and lysine lipids. A homology search with the amino acid sequence of this hydroxylase allows us to predict that OL headgroup hydroxylation is not restricted to a few α-proteobacteria, but is apparently also common in many genera belonging to the Cytophaga-Flavobacterium-Bacteroidetes (CFB) group of bacteria.

Identification and characterization of a plastidial phosphatidylglycerophosphate phosphatase in Arabidopsis thaliana

Phosphatidylglycerol (PG) is the only phospholipid in the thylakoid membranes of chloroplasts of plants, and it is also found in extraplastidial membranes including mitochondria and the endoplasmic reticulum. Previous studies showed that lack of PG in the pgp1-2 mutant of Arabidopsis deficient in phosphatidylglycerophosphate (PGP) synthase strongly affects thylakoid biogenesis and photosynthetic activity. In the present study, the gene encoding the enzyme for the second step of PG synthesis, PGP phosphatase, was isolated based on sequence similarity to the yeast GEP4 and Chlamydomonas PGPP1 genes. The Arabidopsis AtPGPP1 protein localizes to chloroplasts and harbors PGP phosphatase activity with alkaline pH optimum and divalent cation requirement. Arabidopsis pgpp1-1 mutant plants contain reduced amounts of chlorophyll, but photosynthetic quantum yield remains unchanged. The absolute content of plastidial PG (34:4; total number of acyl carbons:number of double bonds) is reduced by about 1/3, demonstrating that AtPGPP1 is involved in the synthesis of plastidial PG. PGP 34:3, PGP 34:2 and PGP 34:1 lacking 16:1 accumulate in pgpp1-1, indicating that the desaturation of 16:0 to 16:1 by the FAD4 desaturase in the chloroplasts only occurs after PGP dephosphorylation.

DGDG and Glycolipids in Plants and Algae

Photosynthetic organelles in plants and algae are characterized by the high abundance of glycolipids, including the galactolipids mono- and digalactosyldiacylglycerol (MGDG, DGDG) and the sulfolipid sulfoquinovosyldiacylglycerol (SQDG). Glycolipids are crucial to maintain an optimal efficiency of photosynthesis. During phosphate limitation, the amounts of DGDG and SQDG increase in the plastids of plants, and DGDG is exported to extraplastidial membranes to replace phospholipids. Algae often use betaine lipids as surrogate for phospholipids. Glucuronosyldiacylglycerol (GlcADG) is a further glycolipid that accumulates under phosphate deprived conditions. In contrast to plants, a number of eukaryotic algae contain very long chain polyunsaturated fatty acids of 20 or more carbon atoms in their glycolipids. The pathways and genes for galactolipid and sulfolipid synthesis are largely conserved between plants, Chlorophyta, Rhodophyta and algae with complex plastids derived from secondary or tertiary endosymbiosis. However, the relative contribution of the endoplasmic reticulum- and plastid-derived lipid pathways for glycolipid synthesis varies between plants and algae. The genes for glycolipid synthesis encode precursor proteins imported into the photosynthetic organelles. While most eukaryotic algae contain the plant-like galactolipid (MGD1, DGD1) and sulfolipid (SQD1, SQD2) synthases, the red alga Cyanidioschyzon harbors a cyanobacterium-type DGDG synthase (DgdA), and the amoeba Paulinella, derived from a more recent endosymbiosis event, contains cyanobacterium-type enzymes for MGDG and DGDG synthesis (MgdA, MgdE, DgdA).

DGDG and Glycolipids in Plants and Algae

Photosynthetic organelles in plants and algae are characterized by the high abundance of glycolipids, including the galactolipids mono- and digalactosyldiacylglycerol (MGDG, DGDG) and the sulfolipid sulfoquinovosyldiacylglycerol (SQDG). Glycolipids are crucial to maintain an optimal efficiency of photosynthesis. During phosphate limitation, the amounts of DGDG and SQDG increase in the plastids of plants, and DGDG is exported to extraplastidial membranes to replace phospholipids. Algae often use betaine lipids as surrogate for phospholipids. Glucuronosyldiacylglycerol (GlcADG) is a further glycolipid that accumulates under phosphate deprived conditions. In contrast to plants, a number of eukaryotic algae contain very long chain polyunsaturated fatty acids of 20 or more carbon atoms in their glycolipids. The pathways and genes for galactolipid and sulfolipid synthesis are largely conserved between plants, Chlorophyta, Rhodophyta and algae with complex plastids derived from secondary or tertiary endosymbiosis. However, the relative contribution of the endoplasmic reticulum- and plastid-derived lipid pathways for glycolipid synthesis varies between plants and algae. The genes for glycolipid synthesis encode precursor proteins imported into the photosynthetic organelles. While most eukaryotic algae contain the plant-like galactolipid (MGD1, DGD1) and sulfolipid (SQD1, SQD2) synthases, the red alga Cyanidioschyzon harbors a cyanobacterium-type DGDG synthase (DgdA), and the amoeba Paulinella, derived from a more recent endosymbiosis event, contains cyanobacterium-type enzymes for MGDG and DGDG synthesis (MgdA, MgdE, DgdA).

Remobilization of Phytol from Chlorophyll Degradation Is Essential for Tocopherol Synthesis and Growth of Arabidopsis

Phytol from chlorophyll degradation can be phosphorylated to phytyl-phosphate and phytyl-diphosphate, the substrate for tocopherol (vitamin E) synthesis. A candidate for the phytyl-phosphate kinase from Arabidopsis thaliana (At1g78620) was identified via a phylogeny-based approach. This gene was designated VITAMIN E DEFICIENT6 (VTE6) because the leaves of the Arabidopsis vte6 mutants are tocopherol deficient. The vte6 mutant plants are incapable of photoautotrophic growth. Phytol and phytyl-phosphate accumulate, and the phytyl-diphosphate content is strongly decreased in vte6 leaves. Phytol feeding and enzyme assays with Arabidopsis and recombinant Escherichia coli cells demonstrated that VTE6 has phytyl-P kinase activity. Overexpression of VTE6 resulted in increased phytyl-diphosphate and tocopherol contents in seeds, indicating that VTE6 encodes phytyl-phosphate kinase. The severe growth retardation of vte6 mutants was partially rescued by introducing the phytol kinase mutation vte5. Double mutant plants (vte5 vte6) are tocopherol deficient and contain more chlorophyll, but reduced amounts of phytol and phytyl-phosphate compared with vte6 mutants, suggesting that phytol or phytyl-phosphate are detrimental to plant growth. Therefore, VTE6 represents the missing phytyl-phosphate kinase, linking phytol release from chlorophyll with tocopherol synthesis. Moreover, tocopherol synthesis in leaves depends on phytol derived from chlorophyll, not on de novo synthesis of phytyl-diphosphate from geranylgeranyl-diphosphate.

A bifunctional glycosyltransferase from Agrobacterium tumefaciens synthesizes monoglucosyl and glucuronosyl diacylglycerol under phosphate deprivation

Glycolipids are mainly found in phototrophic organisms (like plants and cyanobacteria), in Gram-positive bacteria, and a few other bacterial phyla. Besides the function as bulk membrane lipids, they often play a role under phosphate deprivation as surrogates for phospholipids. The Gram-negative Agrobacterium tumefaciens accumulates four different glycolipids under phosphate deficiency, including digalactosyl diacylglycerol and glucosylgalactosyl diacylglycerol synthesized by a processive glycosyltransferase. The other two glycolipids have now been identified by mass spectrometry and nuclear magnetic resonance spectroscopy as monoglucosyl diacylglycerol and glucuronosyl diacylglycerol. These two lipids are synthesized by a single promiscuous glycosyltransferase encoded by the ORF atu2297, with UDP-glucose or UDP-glucuronic acid as sugar donors. The transfer of sugars differing in their chemistry is a novel feature not observed before for lipid glycosyltransferases. Furthermore, this enzyme is the first glucuronosyl diacylglycerol synthase isolated. Deletion mutants of Agrobacterium lacking monoglucosyl diacylglycerol and glucuronosyl diacylglycerol or all glycolipids are not impaired in growth or virulence during infection of tobacco leaf discs. Our data suggest that the four glycolipids and the nonphospholipid diacylglyceryl trimethylhomoserine can mutually replace each other during phosphate deprivation. This redundancy of different nonphospholipids may represent an adaptation mechanism to enhance the competitiveness in nature.

Analysis and quantification of plant membrane lipids by thin-layer chromatography and gas chromatography

Galactolipids represent the predominant membrane lipid class in plants. In general, galactolipids are restricted to plastids, but during phosphate deficiency, they also accumulate in extraplastidial membranes. Two groups of plants can be distinguished based on the presence of a specific fatty acid, hexadecatrienoic acid (16:3), in chloroplast lipids. Plants that contain galactolipids with 16:3 acids are designated "16:3-plants"; the other group of plants which lack 16:3 contain mostly 18:3 in their galactolipids ("18:3-plants"). The methods in this chapter describe the extraction of membrane lipids from whole leaves, or from subcellular fractions, and their analysis via thin-layer chromatography (TLC) with different staining methods. Furthermore, a protocol for membrane lipid quantification is presented starting with the separation via TLC, transmethylation of the isolated lipids to fatty acid methyl esters, and their quantitative analysis via gas chromatography (GC).

Accumulation of glycolipids and other non-phosphorous lipids in Agrobacterium tumefaciens grown under phosphate deprivation

Phosphate deficiency is characteristic for many natural habitats, resulting in different physiological responses in plants and bacteria including the replacement of phospholipids by glycolipids and other phosphorous-free lipids. The plant pathogenic bacterium Agrobacterium tumefaciens, which is free of glycolipids under full nutrition, harbors an open reading frame (ORF) coding for a processive glycosyltransferase (named as Pgt). This glycosyltransferase was previously shown to synthesize glucosylgalactosyldiacylglycerol (GGD) and digalactosyldiacylglycerol (DGD) after heterologous expression. The native function of this enzyme and the conditions for its activation remained unknown. We show here that Pgt is active under phosphate deprivation synthesizing GGD and DGD in Agrobacterium. A corresponding deletion mutant (Δpgt) is free of these two glycolipids. Glycolipid accumulation is mainly regulated by substrate (diacylglycerol) availability. Diacylglycerol and the total fatty acid pool are characterized by an altered acyl composition in dependence of the phosphate status with a strong decrease of 18:1 and concomitant increase of 19:0 cyclo during phosphate deprivation. Furthermore, Agrobacterium accumulates two additional unknown glycolipids and diacylglycerol trimethylhomoserine (DGTS) during phosphate deprivation. Accumulation of all these lipids is accompanied by a reduction in phospholipids from 75 to 45% in the wild type. A further non-phosphorous lipid, ornithine lipid, was not increased but its degree of hydroxylation was elevated under phosphate deprivation. The lack of GGD and DGD in the Δpgt mutant has no effect on growth and virulence of Agrobacterium, suggesting that these two lipids are functionally replaced by DGTS and the two unknown glycolipids under phosphate deprivation.

Fatty acid phytyl ester synthesis in chloroplasts of Arabidopsis

During stress or senescence, thylakoid membranes in chloroplasts are disintegrated, and chlorophyll and galactolipid are broken down, resulting in the accumulation of toxic intermediates, i.e., tetrapyrroles, free phytol, and free fatty acids. Chlorophyll degradation has been studied in detail, but the catabolic pathways for phytol and fatty acids remain unclear. A large proportion of phytol and fatty acids is converted into fatty acid phytyl esters and triacylglycerol during stress or senescence in chloroplasts. We isolated two genes (PHYTYL ESTER SYNTHASE1 [PES1] and PES2) of the esterase/lipase/thioesterase family of acyltransferases from Arabidopsis thaliana that are involved in fatty acid phytyl ester synthesis in chloroplasts. The two proteins are highly expressed during senescence and nitrogen deprivation. Heterologous expression in yeast revealed that PES1 and PES2 have phytyl ester synthesis and diacylglycerol acyltransferase activities. The enzymes show broad substrate specificities and can employ acyl-CoAs, acyl carrier proteins, and galactolipids as acyl donors. Double mutant plants (pes1 pes2) grow normally but show reduced phytyl ester and triacylglycerol accumulation. These results demonstrate that PES1 and PES2 are involved in the deposition of free phytol and free fatty acids in the form of phytyl esters in chloroplasts, a process involved in maintaining the integrity of the photosynthetic membrane during abiotic stress and senescence.

Analysis of lipid content and quality in Arabidopsis plastids

Chloroplasts of plants contain an intricate membrane system, the thylakoids, which harbor the complexes of the photosynthetic machinery. Chloroplasts are confined by two membranes, the inner and outer envelope. The major glycerolipids of chloroplasts are the glycolipids monogalactosyl diacylglycerol (MGD), digalactosyl diacylglycerol (DGD), and sulfoquinovosyl diacylglycerol (SQD). Furthermore, two phospholipids, phosphatidyl glycerol (PG) and phosphatidyl choline (PC), are found in chloroplast membranes. The photosystems and light-harvesting complexes in the thylakoids are rich in photosynthetic pigments (chlorophyll, carotenoids, and xanthophylls) and contain a unique set of prenylquinol lipids (tocochromanol/vitamin E, plastoquinol, and phylloquinol/vitamin K1). In this chapter, methods for the isolation and quantification of chloroplast and leaf glycerolipids and prenylquinol lipids are presented. Glycerolipids are separated by thin-layer chromatography prior to conversion of the fatty acids into methyl esters. Fatty acid methyl esters are subsequently quantified by gas chromatography. Prenylquinol lipids are separated by HPLC and quantified by UV absorption (plastoquinol) or fluorescence (tocochromanol, phylloquinol).

The role of diglycosyl lipids in photosynthesis and membrane lipid homeostasis in Arabidopsis

The galactolipid digalactosyldiacylglycerol (DGD) is an abundant thylakoid lipid in chloroplasts. The introduction of the bacterial lipid glucosylgalactosyldiacylglycerol (GGD) from Chloroflexus aurantiacus into the DGD-deficient Arabidopsis (Arabidopsis thaliana) dgd1 mutant was previously shown to result in complementation of growth, but photosynthetic efficiency was only partially restored. Here, we demonstrate that GGD accumulation in the double mutant dgd1dgd2, which is totally devoid of DGD, also complements growth at normal and high-light conditions, but photosynthetic efficiency in the GGD-containing dgd1dgd2 line remains decreased. This is attributable to an increased susceptibility of photosystem II to photodamage, resulting in reduced photosystem II accumulation already at normal light intensities. The chloroplasts of dgd1 and dgd1dgd2 show alterations in thylakoid ultrastructure, a phenotype that is restored in the GGD-containing lines. These data suggest that the strong growth retardation of the DGD-deficient lines dgd1 and dgd1dgd2 can be primarily attributed to a decreased capacity for chloroplast membrane assembly and proliferation and, to a smaller extent, to photosynthetic deficiency. During phosphate limitation, GGD increases in plastidial and extraplastidial membranes of the transgenic lines to an extent similar to that of DGD in the wild type, indicating that synthesis and transport of the bacterial lipid (GGD) and of the authentic plant lipid (DGD) are subject to the same mechanisms of regulation.

Structure and function of glycoglycerolipids in plants and bacteria

Phosphoglycerolipids are abundant membrane constituents in prokaryotic and eukaryotic cells. However, glycoglycerolipids are the predominant lipids in chloroplasts of plants and eukaryotic algae and in cyanobacteria. Membrane composition in chloroplasts and cyanobacteria is highly conserved, with monogalactosyldiacylglycerol (MGD) and digalactosyldiacylglycerol (DGD) representing the most abundant lipids. The genes encoding enzymes of galactolipid biosynthesis have been isolated from Arabidopsis. Galactolipids are crucial for growth under normal and phosphate limiting conditions. Furthermore, they are indispensable for maximal efficiency of photosynthesis. A wide variety of glycoglycerolipids is found in different bacteria. These lipids contain glucose or galactose, in some cases also mannose or other sugars with different glycosidic linkages in their head group. Some bacterial species produce unusual glycoglycerolipids, such as glycophospholipids or glycoglycerolipids carrying sugar head groups esterified with acyl residues. A number of genes coding for bacterial glycoglycerolipid synthases have been cloned and the enzymes characterized. In contrast to the breadth of information available on their structural diversity, much less is known about functional aspects of bacterial glycoglycerolipids. In some bacteria, glycoglycerolipids are required for membrane bilayer stability, they serve as precursors for the formation of complex membrane components, or they are crucial to support anoxygenic photosynthesis or growth during phosphate deficiency.

Allelic loss analysis by denaturing high-performance liquid chromatography and electrospray ionization mass spectrometry

Analysis of allelic imbalance is of great importance for understanding tumorigenesis and the clinical management of malignant disease. Fluorescent-based capillary electrophoresis (CE) of highly polymorphic short tandem repeats (STRs) has become the main method used to detect the loss/gain of alleles. However, there is continued interest in the development of techniques that require no fluorescence and allow the rapid analysis of individual samples. One promising alternative is ion-pair reversed-phase high-performance liquid chromatography (IP-RP-HPLC), which is widely available because of its use in denaturing HPLC. Its applicability in combination with ultraviolet (UV) absorbance detection to the efficient separation of di- and tetranucleotide repeats on the short arm of chromosome 11 was tested using 25 matched pairs of normal and ovarian cancer tissues. Loss of heterozygosity (LOH) could be readily identified for all 13 loci tested, based on changes in the ratios between either the alleles or homo- and heteroduplex signals. However, discrimination between noninformative homo- or hemizygous and heterozygous samples was difficult or impossible when HPLC failed to resolve the alleles. Hyphenation of HPLC with electrospray ionization (ESI) quadrupole ion trap (IT) mass spectrometry (MS) not only allowed the identification of coeluting alleles, but also the reliable detection of a 40% reduction of one allele. The size range of DNA fragments amenable to mass spectrometric analysis was effectively tripled to >300 bp by the use of a linear IT and a Taq DNA polymerase cocktail lacking detergents that otherwise adversely affect ESI.

Analysis of biological and synthetic ribonucleic acids by liquid chromatography-mass spectrometry using monolithic capillary columns

Ion-pair reversed-phase high-performance liquid chromatography (IP-RP-HPLC) has been evaluated as a method for the fractionation and desalting of ribonucleic acids prior to their characterization by electrospray ionization mass spectrometry. Monolithic, poly(styrene-divinylbenzene)-based capillary columns allowed the rapid and highly efficient fractionation of both synthetic and biological ribonucleic acids. The common problem of gas-phase cation adduction that is particularly prevalent in the mass spectrometric analysis of ribonucleic acids was tackled through a combination of chromatographic purification and the addition of ethylenediaminetetraacetic acid to the sample at a concentration of 25 mmol/L shortly before on-line analysis. For RNA molecules ranging in size from 10 to 120 nucleotides, the mass accuracies were typically better than 0.02%, which allowed the characterization and identification of failure sequences and byproducts with high confidence. Following injection of a 500 nL sample onto a 60 x 0.2 mm column, the limit of detection for a 120-nucleotide ribosomal RNA transcript from Escherichia coli was in the 50-80 fmol range. The method was applied to the analysis of synthetic oligoribonucleotides, transfer RNAs, and ribosomal RNA. Finally, sequence information was derived for low picomole amounts of a 32-mer RNA upon chromatographic purification and tandem mass spectrometric investigation in an ion trap mass spectrometer. Complete series of fragment ions of the c- and y-types could be assigned in the tandem mass spectrum. In conclusion, IP-RP-HPLC using monolithic capillary columns represents a very useful tool for the structural investigation and quantitative determination of RNAs of synthetic and biological origin.

Functional differences between galactolipids and glucolipids revealed in photosynthesis of higher plants

Galactolipids represent the most abundant lipid class in thylakoid membranes, where oxygenic photosynthesis is performed. The identification of galactolipids at specific sites within photosynthetic complexes by x-ray crystallography implies specific roles for galactolipids during photosynthetic electron transport. The preference for galactose and not for the more abundant sugar glucose in thylakoid lipids and their specific roles in photosynthesis are not understood. Introduction of a bacterial glucosyltransferase from Chloroflexus aurantiacus into the galactolipid-deficient dgd1 mutant of Arabidopsis thaliana resulted in the accumulation of a glucose-containing lipid in the thylakoids. At the same time, the growth defect of the dgd1 mutant was complemented. However, the degree of trimerization of light-harvesting complex II and the photosynthetic quantum yield of transformed dgd1 plants were only partially restored. These results indicate that specific interactions of the galactolipid head group with photosynthetic protein complexes might explain the preference for galactose in thylakoid lipids of higher plants. Therefore, galactose in thylakoid lipids can be exchanged with glucose without severe effects on growth, but the presence of galactose is crucial to maintain maximal photosynthetic efficiency.

Glycoengineering of cyanobacterial thylakoid membranes for future studies on the role of glycolipids in photosynthesis

The lipid composition of thylakoid membranes is conserved from cyanobacteria to angiosperms. The predominating components are monogalactosyl- and digalactosyldiacylglycerol. In cyanobacteria, thylakoid membrane biosynthesis starts with the formation of monoglucosyldiacylglycerol which is C4-epimerized to the corresponding galactolipid, whereas in plastids monogalactosyldiacylglycerol is formed at the beginning. This suggests that galactolipids have specific functions in thylakoids. We wanted to investigate whether galactolipids can be replaced by glycosyldiacylglycerols with headgroups differing in their epimeric and anomeric details as well as the attachment point of the terminal hexose in diglycosyldiacylglycerols. For this purpose putative glycosyltransferase sequences were identified in databases to be used for functional expression in various host organisms. From 18 newly identified sequences, four turned out to encode glycosyltransferases catalyzing final steps in glycolipid biosynthesis: two alpha-glucosyltransferases, one beta-galactosyltransferase and one beta-glucosyltransferase. Their functional annotation was based on detailed structural characterization of the new glycolipids formed in the transformant hosts as well as on in vitro enzymatic assays. The expression of alpha-glucosyltransferases in the cyanobacterium Synechococcus resulted in the accumulation of the new alpha-galactosyldiacylglycerol which is ascribed to epimerization of the corresponding glucolipid. The expression of the beta-glucosyltransferase led to a high proportion of new beta-glucosyl-(1-->6)-beta-galactosyldiacylglycerol almost entirely replacing the native digalactosyldiacylglycerol. These results demonstrate that modifications of the glycolipid pattern in thylakoids are possible.

Processive lipid galactosyl/glucosyltransferases from Agrobacterium tumefaciens and Mesorhizobium loti display multiple specificities

The glycosyltransferase family 21 (GT21) includes both enzymes of eukaryotic and prokaryotic organisms. Many of the eukaryotic enzymes from animal, plant, and fungal origin have been characterized as uridine diphosphoglucose (UDP-Glc):ceramide glucosyltransferases (glucosylceramide synthases [Gcs], EC 2.4.1.80). As the acceptor molecule ceramide is not present in most bacteria, the enzymatic specificities and functions of the corresponding bacterial glycosyltransferases remain elusive. In this study, we investigated the homologous and heterologous expression of GT21 enzymes from Agrobacterium tumefaciens and Mesorhizobium loti in A. tumefaciens, Escherichia coli, and the yeast Pichia pastoris. Glycolipid analyses of the transgenic organisms revealed that the bacterial glycosyltransferases are involved in the synthesis of mono-, di- and even tri-glycosylated glycolipids. As products resulting from their activity, we identified 1,2-diacyl-3-(O-beta-D-galacto-pyranosyl)-sn-glycerol, 1,2-diacyl-3-(O-beta-D-gluco-pyranosyl)-sn-glycerol as well as higher glycosylated lipids such as 1,2-diacyl-3-[O-beta-D-galacto-pyranosyl-(1-->6)-O-beta-D-galacto-pyranosyl]-sn-glycerol, 1,2-diacyl-3-[O-beta-D-gluco-pyranosyl-(1-->6)-O-beta-D-galacto-pyranosyl]-sn-glycerol, 1,2-diacyl-3-[O-beta-D-gluco-pyranosyl-(1-->6)-O-beta-D-gluco-pyranosyl]-sn-glycerol, and the deviatingly linked diglycosyldiacylglycerol 1,2-diacyl-3-[O-beta-D-gluco-pyranosyl-(1-->3)-O-beta-D-galacto-pyranosyl]-sn-glycerol. From a mixture of triglycosyldiacylglycerols, 1,2-diacyl-3-[O-beta-D-galacto-pyranosyl-(1-->6)-O-beta-D-galacto-pyranosyl-(1-->6)-O-beta-D-galacto-pyranosyl]-sn-glycerol could be separated in a pure form. In vitro enzyme assays showed that the glycosyltransferase from A. tumefaciens favours uridine diphosphogalactose (UDP-Gal) over UDP-Glc. In conclusion, the bacterial GT21 enzymes differ from the eukaryotic ceramide glucosyltransferases by the successive transfer of up to three galactosyl and glucosyl moieties to diacylglycerol.

Optimized suppression of adducts in polymerase chain reaction products for semi-quantitative SNP genotyping by liquid chromatography-mass spectrometry

While electrospray ionization mass spectrometry has shown great potential for the identification of genotypes in DNA sequences amplified by polymerase chain reaction (PCR), the quantitative determination of allele frequencies remains challenging because of the presence of cationic adducts in the mass spectra which severely impairs accuracy of quantitation. We report here on the elaboration of an optimized desalting protocol for ion-pair reversed-phase high-performance liquid chromatography-electrospray ionization mass spectrometry (ICEMS) of PCR amplicons which facilitates the genotyping of single nucleotide polymorphisms (SNPs). Chromatographic purification at temperatures between 50 and 70 degrees C using monolithic reversed-phase columns and acetonitrile gradients in aqueous, 20-30 mmol/l butyldimethylammonium bicarbonate enabled the mass spectrometric analysis of nucleic acid solutions containing up to 1.7 mol/l sodium chloride. A further improvement in removal of metal cations was achieved upon the addition of 5-10 mmol/l ethylenediaminetetraacetic acid (EDTA) to the sample solution prior to liquid chromatography. ICEMS was used for the semi-quantitative genotyping of SNPs amplified from the tetraploid genome of potato cultivars. Using a quadrupole ion trap mass spectrometer, allele frequencies were determined with an accuracy of 2-9% by measuring the relative intensities of the signals corresponding to the molecular mass of each of the alleles in the deconvoluted mass spectra. ICEMS results correlated well with those obtained by pyrosequencing, single nucleotide primer extension, and conventional dideoxy sequencing.

Single nucleotide polymorphism genotyping by on-line liquid chromatography-mass spectrometry in forensic science of the Y-chromosomal locus M9

A method is described for genotyping alleles of the Y-chromosomal locus M9, incorporating DNA extraction, amplification by polymerase chain reaction (PCR), sample purification by ion-pair reversed-phase high-performance liquid chromatography (IP-RP-HPLC), and allele identification by on-line hyphenation to electrospray ionization mass spectrometry (ESI-MS). The alleles G and C were differentiated in 114 base pair amplicons on the basis of intact molecular mass measurements with a mass accuracy between 0.007 and 0.017%. The accuracy of mass determination was significantly reduced to less than 0.0036% upon amplification of a short, 61 bp fragment. The application of steep gradients of acetonitrile in 25 mM butyldimethylammonium bicarbonate not only enabled the efficient separation of non-target components from the PCR product in a monolithic, poly-(styrene-divinylbenzene)-based capillary column, but also allowed the high-throughput analysis of the PCR products with cycle times of 2 min. The new method was compared to a conventional restriction fragment length polymorphism assay with capillary gel electrophoretic analysis. In a blind study, 90 samples of unrelated individuals were genotyped. The high accuracy (<0.004%) and small relative standard deviation (<0.007%, n=20) of mass measurements, which enables even the differentiation of A and T alleles with a mass difference of 9 mass units, make IP-RP-HPLC-ESI-MS a potent tool for the routine characterization of SNPs in forensic science.

Monolithic capillary columns for liquid chromatography-electrospray ionization mass spectrometry in proteomic and genomic research

Peptides, proteins, single-stranded oligonucleotides, and double-stranded DNA fragments were separated with high resolution in micropellicular, monolithic capillary columns prepared by in situ radical copolymerization of styrene and divinylbenzene. Miniaturized chromatography both in the reversed-phase and the ion-pair reversed-phase mode could be realized in the same capillary column because of the nonpolar character of the poly-(styrene/divinylbenzene) stationary phase. The high chromatographic performance of the monolithic stationary phase facilitated the generation of peak capacities for the biopolymers in the range of 50-140 within 10 min under gradient elution conditions. Employing volatile mobile phase components, separations in the two chromatographic separation modes were on-line hyphenated to electrospray ionization (tandem) mass spectrometry, which yielded intact accurate molecular masses as well as sequence information derived from collision-induced fragmentation. The inaccuracy of mass determination in a quadrupole ion trap mass spectrometer was in the range of 0.01-0.02% for proteins up to a molecular mass of 20000, and 0.02-0.12% for DNA fragments up to a molecular mass of 310000. High-performance liquid chromatography-electrospray ionization mass spectrometry utilizing monolithic capillary columns was applied to the identification of proteins by peptide mass fingerprinting, tandem mass spectrometric sequencing, or intact molecular mass determination, as well as to the accurate sizing of double-stranded DNA fragments ranging in size from 50 to 500 base pairs, and to the detection of sequence variations in DNA fragments amplified by the polymerase chain reaction.

Hydrophobic, pellicular, monolithic capillary columns based on cross-linked polynorbornene for biopolymer separations

Monolithic capillary columns were prepared by transition metal-catalyzed ring-opening metathesis copolymerization of norborn-2-ene and 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene inside a silanized 200-microm-i.d. fused-silica capillary using a mixture of toluene and 2-propanol as porogen and Cl2(PCy3)2Ru(=CHPh) as initiator. The synthesized columns allowed the rapid and highly efficient separation of single- and double-stranded nucleic acids by ion-pair reversed-phase high-performance liquid chromatography and of proteins by reversed-phase high-performance liquid chromatography. Compared to 3-mm-i.d. analytical columns synthesized from an identical polymerization mixture, a considerable improvement in the peak widths at half-height of oligonucleotides in the order of 60-80% was obtained. Significant differences in morphology between the capillary column, where the surface of the monolith was rather soft and rugulose, and the analytical column, where the surface was very sharp and smooth, were observed, most probably due to differences in polymerization kinetics. The synthesized monoliths were successfully applied to the separation of the diastereomers of phosphorothioate oligodeoxynucleotides. To confirm the identity of the eluting compounds on the basis of their intact molecular masses, the chromatographic separation system was on-line hyphenated to electrospray ionization mass spectrometry.

[Algorithm for extrication and medical care in vehicular trauma]

The rescue and treatment of trapped persons in car accidents requires a close cooperation and coordination between firefighters and medical personnel. Priorities of medical care as well as aspects of extrication should be considered equally. Procedures on scene should follow a sequence securing life support and careful rescue of the trapped patient.The developed algorithm allows for prioritized and coordinated management and represents a transparent guide for both teams, during training as well as practical application. The concept incorporates the ABC priorities for polytrauma management and also the structure of the ATLS((R))-programme. The algorithm was validated in simulated scenarios and was by affirmed by the German Trauma Surgeons Task Force on Emergency Care under the regulations of a nominal group process via resolution.

Re-sequencing of multiple single nucleotide polymorphisms by liquid chromatography-electrospray ionization mass spectrometry

Allelic discrimination of single nucleotide polymorphisms (SNPs) and, particularly, determination of the phase of multiple variations are of utmost importance in genetics. The physicochemical separation of alleles by completely denaturing ion-pair reversed-phase high-performance liquid chromatography and their on-line sequence determination by electrospray ionization mass spectrometry is demonstrated. Simultaneous genotyping of two and three simple sequence polymorphisms contained within 73-114 bp was accomplished with low femtomolar amounts of unpurified amplicons from polymerase chain reaction. Determination of allelic composition is enabled by the high accuracy (better than 0.019%) of intact mass measurements or by comparative sequencing using gas-phase fragmentation and tandem mass spectrometry in combination with fully automated, computer-aided data interpretation.

Different regulation of c-Myc- and E2F-1-induced apoptosis during the ongoing cell cycle

The transcription factors c-Myc and E2F-1 have been shown to harbour both mitogenic and apoptotic properties. Both factors have been implicated in the regulation of the transition from the G1 phase to the S phase in the mammalian cell cycle. However, whether cell death triggered by these molecules is dependent on the cell's position in the ongoing cell cycle remained elusive. Using centrifugal elutriation we here show for the first time that c-Myc induces apoptosis in G1 and in G2 phase, whereas E2F-1-induced apoptosis specifically occurs in G1. S phase cells are resistant to cell death triggered by these factors. We demonstrate that this is not a general phenomenon, since S phase cells are susceptible to apoptosis induced by treatment with actinomycin D and to the anti-apoptotic activity of Bcl-2. Our data indicate that S phase cells harbour specific protective activities against c-Myc- and E2F-1-induced apoptosis. Our results demonstrate that these transcription factors, although probably sharing specific apoptotic pathways, also take distinct routes to induce cell death and that apoptosis can occur at different phases of the cell cycle depending on the apoptotic stimulus. In this report we present the usefulness of a new approach to determine the regulation of apoptosis in the ongoing unperturbated cell cycle. This approach has clear implications for the identification of target genes involved in the regulation of cell death.

Activation of the human anaphase-promoting complex by proteins of the CDC20/Fizzy family

The initiation of anaphase and exit from mitosis depend on the activation of the cyclosome/anaphase-promoting complex (APC) that ubiquitinates regulatory proteins such as anaphase inhibitors and mitotic cyclins [1-4]. Genetic experiments have demonstrated that two related WD40-repeat proteins--called Cdc20p and Hct1p/Cdh1p in budding yeast and Fizzy and Fizzy-related in Drosophila--are essential for APC--dependent proteolysis [5-11]. Human orthologs of these proteins--hCDC20/p55CDC [12] and hCDH1--have recently been found to associate with APC in a cell-cycle-dependent manner [13,14]. Here, we show that the amount of hCDC20 and hCDH1 bound to APC correlates with a high ubiquitination activity of APC and that binding of recombinant hCDC20 and hCDH1 can activate APC in vitro. Our results suggest that the association between hCDH1 and APC is regulated by post-translational mechanisms, whereas the amount of hCDC20 bound to APC may in addition be controlled by hCDC20 synthesis and destruction [15]. The temporally distinct association of hCDC20 and hCDH1 with APC suggests that these proteins are, respectively, mitosis-specific and G1-specific activating subunits of APC.

Investigation of the cell cycle regulation of cdk3-associated kinase activity and the role of cdk3 in proliferation and transformation

The G1-S transition in mammalian cells has been demonstrated to require the cyclin-dependent kinases cdk2, cdk3 and cdk4/6. Here we show that a novel kinase activity associated with cdk3 fluctuates throughout the cell cycle differently from the expression of cyclin D1-, E- and A-associated kinase activities. Cdk3 kinase activity is neither affected by p16 (in contrast to cdk4/6) nor by E2F-1 (in contrast to cdk2), but is downregulated upon transient p27 expression. We found cdk3 to bind to p21 and p27. We provide evidence that p27 could be involved in the regulation of the cell cycle fluctuation of cdk3 activity: cdk3 protein does not fluctuate and interaction of cdk3 with p27, but not with p21, is lost when cdk3 kinase becomes active during the cell cycle. In Myc-overexpressing cells, but not in normal Ratl cells, constitutive ectopic expression of cdk3 induces specific upregulation of cdk3-associated kinase activity that is still cell cycle phase dependent. Ectopic cdk3, but not cdk2, enhances Myc-induced proliferation and anchorage-independent growth associated with Myc activation, without effects on cyclin D1, E and A protein expression or kinase activities. High levels of cdk3 in Myc-overexpressing cells trigger up- and deregulation of E2F-dependent transcription without inducing the E2F-DNA binding capacity. In contrast to all other studied positive G regulators, cdk3 is unable to cooperate with ras in fibroblast transformation suggesting a function of cdk3 in G1 progression that is different from cyclin D- or E-associated kinase activities. Our data provide first insights into the regulation of cdk3-associated kinase activity and suggest a model how cdk3 participates in the regulation of the G1-S transition.

Deregulated expression of CDK2- or CDK3-associated kinase activities enhances c-Myc-induced apoptosis

Activation of high ectopic levels of c-Myc in serum-deprived Rat1-MycER cells by 4-hydroxytamoxifen induces both proliferation and apoptosis. To further elucidate the role of G1 cyclin-dependent kinases (CDKs) in the process of Myc-induced apoptosis, we generated Rat1-MycER cells stably overexpressing CDK2 or CDK3. Ectopic expression of these CDKs in Myc-overexpressing cells was accompanied by upregulation of the specific kinase activities. Whereas neither high ectopic CDK2 nor CDK3 alone induced apoptosis in serum-deprived Rat1 cells, both CDKs markedly elevated the incidence of Myc-induced apoptosis. It was shown earlier that in Rat1-MycER cells, which are resistant to tumor necrosis factor-alpha (TNF) when grown in high serum concentrations, the addition of TNF with the concomitant activation of Myc resulted in apoptotic cell death. Here, we show that neither CDK2 nor CDK3 induces susceptibility to the cytotoxic action of TNF in Rat1 cells. However, both molecules heavily elevated the incidence of apoptosis induced by TNF together with Myc. It has earlier been reported that Myc-induced apoptosis in serum-deprived Rat1 fibroblasts is inhibited by specific cytokines, such as platelet-derived growth factor (PDGF). Here, we demonstrate that PDGF-mediated protection from Myc-induced apoptosis is almost lost in Rat1 cells overexpressing CDK2 or CDK3. These apoptotic effects of CDK2 or CDK3 are not accompanied by alterations of proliferation parameters, such as DNA distribution, time the cells spend in each phase of the cell cycle, thymidine incorporation into DNA, or cell size analyzed during Myc-induced apoptosis. However, we found CDK3 to deregulate E2F-dependent transcription. In this report, we provide evidence for a not yet described property of CDK2 or CDK3 besides their activity in promoting proliferation: these G1-CDKs can promote apoptosis by interfering with the cell's response to survival factors.

A role of the tuberous sclerosis gene-2 product during neuronal differentiation

Tuberous sclerosis is an autosomal dominant disorder. Besides the development of benign growths (hamartomas) in different tissues, one hallmark of this disease is the presence of highly epileptogenic dysplastic lesions in the cerebral cortex (tubers) composed of abnormal shaped neurones. Patients often show evidence of severe mental retardation. Linkage analysis revealed two disease-determining genes on chromosome 9 and chromosome 16. The TSC2 gene on chromosome 16 encodes a 1784-amino acid putative tumour suppressor protein, tuberin, that functions as a GTPase-activating protein. Here we show that tuberin expression is upregulated upon induction of neuronal differentiation in the neuroblastoma cell lines SK-N-SH and LAN-1. This upregulation occurs at post-transcriptional level and is independent of the proliferation status. TSC2 expression is unaffected during differentiation of C2C12 myoblasts into myotubes and of F9 embryonal carcinoma cells into cells resembling parietal endoderm. Antisense inhibition of tuberin expression in SK-N-SH or LAN-1 cells inhibits neuronal differentiation, but does not affect the differentiation of F9 cells. Ectopic overexpression of TSC2 not only reverts the antisense-associated phenotype but furthermore accelerates the neuronal differentiation process. Our data show for the first time that tuberin plays a critical role in neuronal differentiation. Such role is consistent with the phenotype of tuberous sclerosis patients, who inherit one defective TSC2 allele, and frequently lose the remaining normal allele in many of the tubers/hamartomas which develop in the central nervous system of these patients.

Influence of neuroleptics on the metabolism of tricyclic antidepressants--in vitro experiments with rat liver microsomes

The influence of two neuroleptics--the phenothiazine perazine and the butyrophenone haloperidol--on the metabolism of the tricyclic antidepressants amitriptyline (AMI), imipramine (IMI), and chlorimipramine (CMI) was studied in vitro in isolated liver microsomes of female Sprague-Dawley rats. The rats were pretreated over 10 days with either NaCl solutions or with 1, 3, and 10 mg/kg haloperidol or 5 and 15 mg/kg perazine, respectively. The microsomal fraction was incubated with various concentrations of antidepressants. The drugs and their metabolites were analyzed by high-performance liquid chromatography (HPLC). Neither pretreatment with haloperidol nor perazine had any significant influence on the demethylation and N-oxidation activity of the microsomes. Benzylic 10-hydroxylation of AMI or IMI or 10- and 11-hydroxylation of CMI was inhibited significantly by pretreatment with perazine, as was 2-hydroxylation of IMI and CMI, whereas 8-hydroxylation of CMI was not influenced. The inhibition was dose dependent. With haloperidol, only the high dose of 10 mg/kg caused a significant inhibition of benzylic 10-hydroxylation, whereas phenolic hydroxylation was not influenced. The inhibition was much lower than for perazine. Comparing the results with pharmacokinetic studies in humans revealed a good agreement in metabolic pathways. The study could therefore be important in the choice of neuroleptic drugs in combination therapy.

Comparison of the metabolism of the three antidepressants amitriptyline, imipramine, and chlorimipramine in vitro in rat liver microsomes

The metabolism of the tricyclic antidepressants amitriptyline (AMI), imipramine (IMI), chlorimipramine (CMI) and some of their metabolites was studied in vitro in isolated liver microsomes of female Spraque-Dawley rats. Nine metabolites of AMI, seven metabolites of IMI, and 11 metabolites of CMI were quantitatively determined with high-performance liquid chromatography. The main metabolic reactions, mediated by an NADPH generating system, were hydroxylation, demethylation, and N-oxidation. The ratio of these reactions was different for the three drugs. AMI was hydroxylated more than CMI and CMI more than IMI. The order for demethylation was CMI greater than AMI = IMI, the order for N-oxidation IMI greater than CMI less than or equal to AMI. The substrate dependence of metabolism was investigated. Demethylation and N-oxidation increased proportionally to increasing substrate concentrations, whereas formation of hydroxylated metabolites became saturated (in the concentration range of 10(-6)-10(-5) M). The in vitro metabolism was compared with the in vivo metabolism in humans, reflected by the plasma concentrations of these drugs and their metabolites. A good agreement in metabolic pathways was found.