http://hdl.handle.net/10061/6332 Wed, 22 May 2013 15:13:57 GMT 2013-05-22T15:13:57Z http://hdl.handle.net/10061/8622 Title: Synthesis of Very-Long-Chain Fatty Acids in the Epidermis Controls Plant Organ Growth by Restricting Cell Proliferation Authors: Takashi Nobusawa; Yoko Okushima; Noriko Nagata; Mikiko Kojima; Hitoshi Sakakibara; Masaaki Umeda Abstract: Plant organ growth is controlled by inter-cell-layer communication, which thus determines the overall size of the organism. The epidermal layer interfaces with the environment and participates in both driving and restricting growth via inter-cell-layer communication. However, it remains unknown whether the epidermis can send signals to internal tissue to limit cell proliferation in determinate growth. Very-long-chain fatty acids (VLCFAs) are synthesized in the epidermis and used in the formation of cuticular wax. Here we found that VLCFA synthesis in the epidermis is essential for proper development of Arabidopsis thaliana. Wild-type plants treated with a VLCFA synthesis inhibitor and pasticcino mutants with defects in VLCFA synthesis exhibited overproliferation of cells in the vasculature or in the rib zone of shoot apices. The decrease of VLCFA content increased the expression of IPT3, a key determinant of cytokinin biosynthesis in the vasculature, and, indeed, elevated cytokinin levels. These phenotypes were suppressed in ipt3;5;7 triple mutants, and also by vasculature-specific expression of cytokinin oxidase, which degrades active forms of cytokinin. Our results imply that VLCFA synthesis in the epidermis is required to suppress cytokinin biosynthesis in the vasculature, thus fine-tuning cell division activity in internal tissue, and therefore that shoot growth is controlled by the interaction between the surface (epidermis) and the axis (vasculature) of the plant body. Wed, 10 Apr 2013 00:00:00 GMT http://hdl.handle.net/10061/8622 2013-04-10T00:00:00Z http://hdl.handle.net/10061/8621 Title: Conversion of a Signal into Forces for Axon Outgrowth through Pak1-Mediated Shootin1 Phosphorylation Authors: Michinori Toriyama; Satoshi Kozawa; Yuichi Sakumura; Naoyuki Inagaki Abstract: Soluble guidance cues can direct cellular protrusion and migration by modulating adhesion and cytoskeletal dynamics. Actin filaments (F-actins) polymerize at the leading edge of motile cells and depolymerize proximally [1 and 2]; this, together with myosin II activity, induces retrograde flow of F-actins [3, 4 and 5]. It has been proposed that the traction forces underlying cellular motility may be regulated by the modulation of coupling efficiency between F-actin flow and the extracellular substrate via “clutch” molecules [6, 7, 8, 9 and 10]. However, how cell signaling controls the coupling efficiency remains unknown. Shootin1 functions as a linker molecule that couples F-actin retrograde flow and the substrate at neuronal growth cones to promote axon outgrowth [11]. Here we show that shootin1 is located at a critical interface, transducing a chemical signal into traction forces for axon outgrowth. We found that a chemoattractant, netrin-1, positively regulates traction forces at axonal growth cones via Pak1-mediated shootin1 phosphorylation. This phosphorylation enhanced the interaction between shootin1 and F-actin retrograde flow, thereby promoting F-actin-substrate coupling, force generation, and concomitant filopodium extension and axon outgrowth. These results suggest that dynamic actin-substrate coupling can transduce chemical signals into mechanical forces to control cellular motility and provide a molecular-level description of how this transduction may occur. Thu, 28 Feb 2013 00:00:00 GMT http://hdl.handle.net/10061/8621 2013-02-28T00:00:00Z http://hdl.handle.net/10061/8612 Title: Negative feedback by IRE1β optimizes mucin production in goblet cells Authors: Akio Tsuru; Naoko Fujimoto; Satsuki Takahashi; Michiko Saito; Daisuke Nakamura; Megumi Iwano; Takao Iwawaki; Hiroshi Kadokura; David Ron; Kenji Kohno Abstract: In mammals, the prototypical endoplasmic reticulum (ER) stress sensor inositol-requiring enzyme 1 (IRE1) has diverged into two paralogs. IRE1α is broadly expressed and mediates the unconventional splicing of X-box binding protein 1 (XBP1) mRNA during ER stress. By contrast, IRE1β is expressed selectively in the digestive tract, and its function remains unclear. Here, we report that IRE1β plays a distinctive role in mucin-secreting goblet cells. In IRE1β-/- mice, aberrant mucin 2 (MUC2) accumulated in the ER of goblet cells, accompanied by ER distension and elevated ER stress signaling such as increased XBP1 mRNA splicing. In contrast, conditional IRE1α-/- mice showed no such ER distension but a marked decrease in spliced XBP1 mRNA. mRNA stability assay revealed that MUC2 mRNA was greatly stabilized in IRE1β-/- mice. These findings suggest that in goblet cells, IRE1β, but not IRE1α, promotes efficient protein folding and secretion in the ER by optimizing the level of mRNA encoding their major secretory product, MUC2. Fri, 01 Feb 2013 00:00:00 GMT http://hdl.handle.net/10061/8612 2013-02-01T00:00:00Z http://hdl.handle.net/10061/8565 Title: Astrocyte-Specific Genes Are Generally Demethylated in Neural Precursor Cells Prior to Astrocytic Differentiation Authors: Izuho Hatada; Masakazu Namihira; Sumiyo Morita; Mika Kimura; Takuro Horii; Kinichi Nakashima Abstract: Epigenetic changes are thought to lead to alterations in the property of cells, such as differentiation potential. Neural precursor cells (NPCs) differentiate only into neurons in the midgestational brain, yet they become able to generate astrocytes in the late stage of development. This differentiation-potential switch could be explained by epigenetic changes, since the promoters of astrocyte-specific marker genes, glial fibrillary acidic protein (Gfap) and S100b, have been shown to become demethylated in late-stage NPCs prior to the onset of astrocyte differentiation; however, whether demethylation occurs generally in other astrocyctic genes remains unknown. Here we analyzed DNA methylation changes in mouse NPCs between the mid-(E11.5) and late (E14.5) stage of development by a genome-wide DNA methylation profiling method using microarrays and found that many astrocytic genes are demethylated in late-stage NPCs, enabling the cell to become competent to express these genes. Although these genes are already demethylated in late-stage NPCs, they are not expressed until cells differentiate into astrocytes. Thus, late-stage NPCs have epigenetic potential which can be realized in their expression after astrocyte differentiation. Thu, 11 Sep 2008 00:00:00 GMT http://hdl.handle.net/10061/8565 2008-09-11T00:00:00Z