Versatile transformation system that is applicable to both multiple transgene expression and gene targeting for Thraustochytrids

A versatile transformation system for thraustochytrids, a promising producer for polyunsaturated fatty acids and fatty acid-derived fuels, was established. G418, hygromycin B, blasticidin, and zeocin inhibited the growth of thraustochytrids, indicating that multiple selectable marker genes could be used in the transformation system. A neomycin resistance gene (neo(r)), driven with an ubiquitin or an EF-1α promoter-terminator from Thraustochytrium aureum ATCC 34304, was introduced into representatives of two thraustochytrid genera, Aurantiochytrium and Thraustochytrium. The neo(r) marker was integrated into the chromosomal DNA by random recombination and then functionally translated into neo(r) mRNA. Additionally, we confirmed that another two genera, Parietichytrium and Schizochytrium, could be transformed by the same method. By this method, the enhanced green fluorescent protein was functionally expressed in thraustochytrids. Meanwhile, T. aureum ATCC 34304 could be transformed by two 18S ribosomal DNA-targeting vectors, designed to cause single- or double-crossover homologous recombination. Finally, the fatty acid Δ5 desaturase gene was disrupted by double-crossover homologous recombination in T. aureum ATCC 34304, resulting in an increase of dihomo-γ-linolenic acid (C(20:3n-6)) and eicosatetraenoic acid (C(20:4n-3)), substrates for Δ5 desaturase, and a decrease of arachidonic acid (C(20:4n-6)) and eicosapentaenoic acid (C(20:5n-3)), products for the enzyme. These results clearly indicate that a versatile transformation system which could be applicable to both multiple transgene expression and gene targeting was established for thraustochytrids.     

Coffee polyphenol caffeic acid but not chlorogenic acid increases 5'AMP-activated protein kinase and insulin-independent glucose transport in rat skeletal muscle

Chlorogenic acid is an ester of caffeic and quinic acids, and is one of the most widely consumed polyphenols because it is abundant in foods, especially coffee. We explored whether chlorogenic acid and its metabolite, caffeic acid, act directly on skeletal muscle to stimulate 5'-adenosine monophosphate-activated protein kinase (AMPK). Incubation of rat epitrochlearis muscles with Krebs buffer containing caffeic acid (≥0.1 mM, ≥30 min) but not chlorogenic acid increased the phosphorylation of AMPKα Thr(172), an essential step for kinase activation, and acetyl CoA carboxylase Ser(79), a downstream target of AMPK, in a dose- and time-dependent manner. Analysis of isoform-specific AMPK activity revealed that AMPKα2 activity increased significantly, whereas AMPKα1 activity did not change. This enzyme activation was associated with a reduction in phosphocreatine content and an increased rate of 3-O-methyl-d-glucose transport activity in the absence of insulin. These results suggest that caffeic acid but not chlorogenic acid acutely stimulates skeletal muscle AMPK activity and insulin-independent glucose transport with a reduction of the intracellular energy status.     

The suppressive function of the rice DELLA protein SLR1 is dependent on its transcriptional activation activity

When the gibberellin (GA) receptor GIBBERELLIN INSENSITIVE DWARF 1 (GID1) binds to GA, GID1 interacts with DELLA proteins, repressors of GA signaling. This interaction inhibits the suppressive function of DELLA protein and thereby activates the GA response. However, how DELLA proteins exert their suppressive function and how GID1s inhibit suppressive function of DELLA proteins is unclear. By yeast one-hybrid experiments and transient expression of the N-terminal region of rice DELLA protein (SLR1) in rice callus, we established that the N-terminal DELLA/TVHYNP motif of SLR1 possesses transactivation activity. When SLR1 proteins with various deletions were over-expressed in rice, the severity of dwarfism correlated with the transactivation activity observed in yeast, indicating that SLR1 suppresses plant growth through transactivation activity. This activity was suppressed by the GA-dependent GID1-SLR1 interaction, which may explain why GA responses are induced in the presence of GA. The C-terminal GRAS domain of SLR1 also exhibits a suppressive function on plant growth, possibly by directly or indirectly interacting with the promoter region of target genes. Our results indicate that the N-terminal region of SLR1 has two roles in GA signaling: interaction with GID1 and transactivation activity.     

Functional evolution of duplicated odorant-binding protein genes, Obp57d and Obp57e, in Drosophila

Odorant-binding proteins (OBPs) are extracellular proteins found in insect chemosensilla, where they participate in the sensing of odors, tastes, and pheromones. Although a large number of OBP genes have been identified in insect genomes, their molecular functions and biological roles have been clarified in limited cases. Two OBP genes, Obp57d and Obp57e, were involved in the evolution of host-plant preference in Drosophila sechellia. Comparative analyses of the Obp57d/e genomic sequences from 27 closely related species suggested that the two genes arose by tandem gene duplication and functionally diverged from each other. In this study, the functional evolution of Obp57d and Obp57e was examined by in vitro binding assays using recombinant proteins synthesized in a bacterial system. Compared to the ancestral Dpse\OBP57de, Dmel\OBP57d was more specialized to tridecanoic acid while Dmel\OBP57e was generalized regarding their binding affinity, suggesting that the two OBP genes underwent subfunctionalization and neofunctionalization. A behavioral analysis using knockout flies supported that the biological role is different between OBP57d and OBP57e in vivo. Site-directed mutagenesis of the evolutionarily conserved amino acids revealed that these residues play an important role in protein folding. These findings provide a clue to understanding how the repertoire of OBP genes is maintained in a genome under natural selection.     

Different effects on cell proliferation and migration abilities of endothelial cells by LPA₁ and LPA₃ in mammary tumor FM3A cells

Lysophosphatidic acid (LPA) receptors belong to G protein-coupled transmembrane receptors and mediate a variety of cellular responses through the binding of LPA. So far, six types of LPA receptors (LPA receptor-1 (LPA?) to LPA?) have been identified. Recently, it has been demonstrated that each LPA receptor has opposite effects on malignant property of cancer cells. In this study, to evaluate an involvement of LPA receptors on angiogenic process in mammary tumor cells, we generated Lpar1- and Lpar3-expressing (FM3A-a1 and FM3A-a3A9, respectively) cells from FM3A cells, and investigated the effects on cell proliferation and migration abilities of endothelial F-2 cells by those cells. In Vegf-A and Vegf-C genes, FM3A-a1 cells indicated high expression and FM3A-a3A9 cells showed low expression, compared with control cells. When F-2 cells were cultured with a supernatant from FM3A-a1 cells, the cell growth rate and migration ability of F-2 cells was significantly higher than control cells. By contrast, a supernatant from FM3A-a3A9 cells significantly inhibited those abilities of F-2 cells. These results suggest that LPA? and LPA? may play opposite roles on the regulation of endothelial cells in mouse mammary tumor FM3A cells.     

Epigenetic silencing of core histone genes by HERS in Drosophila

Cell cycle-dependent expression of canonical histone proteins enables newly synthesized DNA to be integrated into chromatin in replicating cells. However, the molecular basis of cell cycle-dependency in the switching of histone gene regulation remains to be uncovered. Here, we report the identification and biochemical characterization of a molecular switcher, HERS (histone gene-specific epigenetic repressor in late S phase), for nucleosomal core histone gene inactivation in Drosophila. HERS protein is phosphorylated by a cyclin-dependent kinase (Cdk) at the end of S-phase. Phosphorylated HERS binds to histone gene regulatory regions and anchors HP1 and Su(var)3-9 to induce chromatin inactivation through histone H3 lysine 9 methylation. These findings illustrate a salient molecular switch linking epigenetic gene silencing to cell cycle-dependent histone production.     

Identification of Tympanic Border Cells as Slow-Cycling Cells in the Cochlea

Mammalian cochlear sensory epithelial cells are believed to possess minimal regenerative potential because they halt proliferation during late stage of embryogenesis and never regenerate after birth. This means that sensorineural hearing loss caused by the death of cochlear sensory epithelial cells is a permanent condition. However, stem cells were recently identified in neonatal mice following dissociation of their inner ear organs. This suggests that regenerative therapy for sensorineural hearing loss may be possible. Unfortunately, dissociation distorts the microanatomy of the inner ear, making it difficult to determine the precise location of stem cells in unaltered specimens. To develop new therapeutic approaches based on sensory epithelial cell regeneration, the location of these stem cells must be elucidated. Stem cells normally proliferate at a slow rate in adult organs. In fact, so-called label-retaining cells, or slow-cycling cells, of the brain and skin are recognized as stem cells. In this study, using the exogenous proliferation marker, 5′-bromo-2′-deoxyuridine (BrdU) in combination with the endogenous proliferation marker Ki-67, we identified tympanic border cells. These cells, which are located beneath the basilar membrane in vivo, represent slow-cycling cells of the murine cochlea. Immunohistochemically, these cells stained positive for the immature cell marker Nestin. But it will be difficult to achieve regeneration of the cochlear function because these slow-cycling cells disappear in the mature murine cochlea.