Chromophyte algae differ fundamentally from plants in possessing chloroplasts that contain chlorophyll c and that have a more complex bounding-membrane topology. Although chromophytes are known to be evolutionary chimaeras of a red alga and a non-photosynthetic host, which gave rise to their exceptional membrane complexity, their cell biology is poorly understood. Cryptomonads are the only chromophytes that still retain the enslaved red algal nucleus as a minute nucleomorph. Here we report complete sequences for all three nucleomorph chromosomes from the cryptomonad Guillardia theta. This tiny 551-kilobase eukaryotic genome is the most gene-dense known, with only 17 diminutive spliceosomal introns and 44 overlapping genes. Marked evolutionary compaction hundreds of millions of years ago eliminated nearly all the nucleomorph genes for metabolic functions, but left 30 for chloroplast-located proteins. To allow expression of these proteins, nucleomorphs retain hundreds of genetic-housekeeping genes. Nucleomorph DNA replication and periplastid protein synthesis require the import of many nuclear gene products across endoplasmic reticulum and periplastid membranes. The chromosomes have centromeres, but possibly only one loop domain, offering a means for studying eukaryotic chromosome replication, segregation and evolution.

The plastid genome of the cryptophyte alga Guillardia theta (121,524 bp) has been completely sequenced. The genome is 33% G+C and contains a short, nonidentical inverted repeat (4.9 kb) encoding the two rRNA cistrons. The large and small single-copy regions are 96.3 and 15.4 kb, respectively. Forty-six genes encoding proteins for photosynthesis, 5 genes for biosynthetic function, 5 genes involved in replication and division, 30 tRNA genes, 44 ribosomal protein genes (26 large subunit and 18 small subunit), 3 translation factors, 8 genes encoding components of the transcriptional machinery including 3 ycfs (hypothetical chloroplast frames), and 26 additional ycfs have been identified. There are eight ORFs larger than 50 amino acids, 3 of which have homologues on the plastid genome of the rhodophyte, Porphyra purpurea (Reith and Munholland 1995) and/or the Synechocystis genome (Kaneko et al. 1996) and can be designated new ycfs. Intergenic spacers are very short, no introns have been detected, and several genes overlap, all resulting in a very compact genome. In addition, large clusters of genes (such as those for the ribosomal proteins) are organized into single transcriptional units (Wang et al. 1997), again resulting in an economically organized genome. The cryptophyte plastid genome is almost completely comprised of clusters of genes that are found on the rhodophyte Porphyra purpurea, confirming its common ancestry with red algae. Furthermore, recombination events involving both tRNA genes and the rRNA cistrons appear to have been responsible for the structure of the cryptophyte plastid genome, including the formation of the inverted repeat.

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Although it is widely accepted that the plastids of plants and algae originated as endosymbionts, the details of this evolutionary process are unclear. It has been proposed that in organisms whose plastids are surrounded by more than two membranes, the endosymbiont was a eukaryotic alga rather than a photosynthetic prokaryote. The DNA-containing nucleomorph of cryptomonad algae appears to be the vestigial nucleus of such an algal endosymbiont. Eukaryotic-type ribosomal RNA sequences have been localized to a nucleolus-like structure in the nucleomorph. In support of the hypothesis that cryptomonads are evolutionary chimaeras of two distinct eukaryotic cells, we show here that Cryptomonas phi contains two phylogenetically separate, nuclear-type small-subunit rRNA genes, both of which are transcriptionally active. We incorporate our rRNA sequence data into phylogenetic trees, from which we infer the evolutionary ancestry of the host and symbiont components of Cryptomonas phi. Such trees do not support the thesis that chromophyte algae evolved directly from a cryptomonad-like ancestor.

IntroductionCationic antimicrobial peptides (CAPs) defend against microbial pathogens; however, certain CAPs also exhibit anticancer activity. The purpose of this investigation was to determine the effect of the pleurocidin-family CAPs, NRC-03 and NRC-07, on breast cancer cells.MethodsMTT (3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide) and acid phosphatase cell-viability assays were used to assess NRC-03- and NRC-07-mediated killing of breast carcinoma cells. Erythrocyte lysis was determined with hemolysis assay. NRC-03 and NRC-07 binding to breast cancer cells and normal fibroblasts was assessed with fluorescence microscopy by using biotinylated-NRC-03 and -NRC-07. Lactate dehydrogenase-release assays and scanning electron microscopy were used to evaluate the effect of NRC-03 and NRC-07 on the cell membrane. Flow-cytometric analysis of 3,3'-dihexyloxacarbocyanine iodide- and dihydroethidium-stained breast cancer cells was used to evaluate the effects of NRC-03 and NRC-07 on mitochondrial membrane integrity and reactive oxygen species (ROS) production, respectively. Tumoricidal activity of NRC-03 and NRC-07 was evaluated in NOD SCID mice bearing breast cancer xenografts.ResultsNRC-03 and NRC-07 killed breast cancer cells, including drug-resistant variants, and human mammary epithelial cells but showed little or no lysis of human dermal fibroblasts, umbilical vein endothelial cells, or erythrocytes. Sublethal doses of NRC-03 and, to a lesser extent, NRC-07 significantly reduced the median effective concentration (EC50) of cisplatin for breast cancer cells. NRC-03 and NRC-07 bound to breast cancer cells but not fibroblasts, suggesting that killing required peptide binding to target cells. NRC-03- and NRC-07-mediated killing of breast cancer cells correlated with expression of several different anionic cell-surface molecules, suggesting that NRC-03 and NRC-07 bind to a variety of negatively-charged cell-surface molecules. NRC-03 and NRC-07 also caused significant and irreversible cell-membrane damage in breast cancer cells but not in fibroblasts. NRC-03- and NRC-07-mediated cell death involved, but did not require, mitochondrial membrane damage and ROS production. Importantly, intratumoral administration of NRC-03 and NRC-07 killed breast cancer cells grown as xenografts in NOD SCID mice.ConclusionsThese findings warrant the development of stable and targeted forms of NRC-03 and/or NRC-07 that might be used alone or in combination with conventional chemotherapeutic drugs for the treatment of breast cancer.

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Natural products are leads for new antibiotics as a result of their structural complexity and diversity. We have isolated a series of structurally related polyketide-derived natural products from Streptomyces venezuelae ISP5230. The most active of these jadomycin analogues showed good activity against a variety of staphylococci, including methicillin-resistant Staphylococcus aureus.

Supplies of marine fish oils (FO) are limited, and sustainable production in aquaculture dictates that alternatives that do not compromise fish health and product quality, such as vegetable oils, must be found. Nutrigenomics will increase our understanding of how nutrition influences metabolic pathways and homeostatic control, and may be used to measure and validate subtle changes in organ-specific, metabolic gene expression signatures. We compared 2 groups of Atlantic salmon fed diets containing 100% FO or 75% rapeseed oil (RO) for 42 wk. A small-scale cDNA microarray was constructed to screen for changes in the expression of lipid metabolism genes in the liver resulting from this partial substitution of RO for FO. Delta5 fatty acid desaturase gene expression was significantly greater in fish fed 75% RO than in fish fed the control diet; this was confirmed by quantitative real time PCR analysis. In addition, several genes, among these mitochondrial proteins, peroxisome proliferator-activated receptor gamma, as well as other transcription factors, coactivators, and signal transducers, showed significant differential regulation. This partially validated microarray may be used for further gene expression profiling using other dietary comparisons, and for further characterization of selected genes.