Tissue flow regulates planar cell polarity independently of the Frizzled core pathway

Planar cell polarity (PCP) regulates the orientation of external structures. A core group of proteins that includes Frizzled forms the heart of the PCP regulatory system. Other PCP mechanisms that are independent of the core group likely exist, but their underlying mechanisms are elusive. Here, we show that tissue flow is a mechanism governing core group-independent PCP on the Drosophila notum. Loss of core group function only slightly affects bristle orientation in the adult central notum. This near-normal PCP results from tissue flow-mediated rescue of random bristle orientation during the pupal stage. Manipulation studies suggest that tissue flow can orient bristles in the opposite direction to the flow. This process is independent of the core group and implies that the apical extracellular matrix functions like a “comb” to align bristles. Our results reveal the significance of cooperation between tissue dynamics and extracellular substances in PCP establishment

Diacylglycerol kinase β promotes dendritic outgrowth and spine maturation in developing hippocampal neurons

<p>Abstract</p> <p>Background</p> <p>Diacylglycerol kinase (DGK) is an enzyme that phosphorylates diacylglycerol to phosphatidic acid and comprises multiple isozymes of distinct properties. Of DGKs, mRNA signal for DGKβ is strongly detected in the striatum, and one of the transcripts derived from the human DGKβ locus is annotated in GenBank as being differentially expressed in bipolar disorder patients. Recently, we have reported that DGKβ is expressed in medium spiny neurons of the striatum and is highly concentrated at the perisynapse of dendritic spines. However, it remains elusive how DGKβ is implicated in pathophysiological role in neurons at the cellular level.</p> <p>Results</p> <p>In the present study, we investigated the expression and subcellular localization of DGKβ in the hippocampus, together with its functional implication using transfected hippocampal neurons. DGKβ is expressed not only in projection neurons but also in interneurons and is concentrated at perisynaptic sites of asymmetrical synapses. Overexpression of wild-type DGKβ promotes dendrite outgrowth at 7 d in <it>vitro </it>(DIV) and spine maturation at 14 DIV in transfected hippocampal neurons, although its kinase-dead mutant has no effect.</p> <p>Conclusion</p> <p>In the hippocampus, DGKβ is expressed in both projection neurons and interneurons and is accumulated at the perisynapse of dendritic spines in asymmetrical synapses. Transfection experiments suggest that DGKβ may be involved in the molecular machineries of dendrite outgrowth and spinogenesis through its kinase activity.</p

Signaling Cascade of Diacylglycerol Kinase β in the Pituitary Intermediate Lobe: Dopamine D2 Receptor/Phospholipase Cβ4/Diacylglycerol Kinase β/Protein Kinase Cα

The pituitary gland dynamically changes its hormone output under various pathophysiological conditions. One of the pathways implicated in the regulatory mechanism of this gland is a dopaminergic system that operates the phosphoinositide (PI) cycle to transmit downstream signal through second messengers. We have previously shown that diacylglycerol kinase β (DGKβ) is coexpressed with dopamine D1 and D2 receptors in medium spiny neurons of the striatum, suggesting a plausible implication of DGKβ in dopaminergic transmission. However, it remains elusive whether DGKβ is involved in the dopaminergic system in the pituitary gland. The aim of this study is to investigate the expression and localization of DGK in the pituitary gland, together with the molecular components involved in the PI signaling cascade, including dopamine receptors, phospholipase C (PLC), and a major downstream molecule, protein kinase C (PKC). Here we show that DGKβ and the dopamine D2 receptor are coexpressed in the intermediate lobe and localize to the plasma membrane side by side. In addition, we reveal that PLCβ4 and PKCα are the subtypes expressed in the intermediate lobe among those families. These findings will substantiate and further extend our understanding of the molecular-anatomical pathway of PI signaling and the functional roles of DGK in the pituitary intermediate lobe. (J Histochem Cytochem 58:119–129, 2010

Nuclear relocation of DGKζ in cardiomyocytes under conditions of ischemia/reperfusion

Diacylglycerol (DG) and phosphatidic acid (PA) are generated under various conditions, such as ligand stimulation and several stresses. They serve as second messengers to respond to pathophysiological conditions. DG kinase (DGK) catalyzes DG to produce PA. It is regarded as a regulator of these lipid messengers. Previous studies show that DGKζ, a nuclear isozyme, translocates from the nucleus to the cytoplasm in hippocampal neurons under transient ischemia and never relocates to the nucleus after reperfusion. This study examined whether a similar phenomenon is observed in cardiomyocytes, which represent another type of postmitotic, terminally differentiated cell. We performed immunostaining on ischemic hearts induced by occlusion of the left anterior descending coronary artery and on primary cultured cardiomyocytes under oxygen-glucose deprivation (OGD). In the animal model, 10 min ischemia is sufficient to cause DGKζ to disappear from the nucleus in cardiomyocytes. However, DGKζ is observed again in the nucleus at 10 min following reperfusion after 10 min ischemia, which contrasts sharply with ischemic hippocampal neurons. Similar results were obtained from experiments using primary cultured cardiomyocytes under OGD conditions, except that DGKζ relocates autonomously, if at all, to the nucleus, even under continuous OGD conditions. Results suggest that DGKζ is involved in the acute phase of cellular response to ischemic stress in cardiomyocytes in a similar, but not identical, manner to that of neurons

Arachidonoyl-Specific Diacylglycerol Kinase ε and the Endoplasmic Reticulum

The endoplasmic reticulum (ER) comprises an interconnected membrane network, which is made up of lipid bilayer and associated proteins. This organelle plays a central role in the protein synthesis and sorting. In addition, it represents the synthetic machinery of phospholipids, the major constituents of the biological membrane. In this process, phosphatidic acid (PA) serves as a precursor of all phospholipids, suggesting that PA synthetic activity is closely associated with the ER function. One enzyme responsible for PA synthesis is diacylglycerol kinase (DGK) that phosphorylates diacylglycerol (DG) to PA. DGK is composed of a family of enzymes with distinct features assigned to each isozyme in terms of structure, enzymology and subcellular localization. Of DGKs, DGKε uniquely exhibits substrate specificity toward arachidonate-containing DG and is shown to reside in the ER. Arachidonic acid, a precursor of bioactive eicosanoids, is usually acylated at the sn-2 position of phospholipids, being especially enriched in phosphoinositide. In this review, we focus on arachidonoyl-specific DGKε with respect to the historical context, molecular basis of the substrate specificity and ER-targeting, and functional implications in the ER

Expression of mRNAs for the diacylglycerol kinase family in immune cells during an inflammatory reaction.

Phosphoinositide metabolism is intimately involved in cellular signal transduction. In response to extracellular stimuli, it generates diacylglycerol (DG), which serves as a lipid second messenger molecule to activate various proteins in various organs under pathophysiological conditions. Diacylglycerolkinase (DGK) constitutes an enzyme family that catalyzes conversion of DG to phosphatidic acid. It is therefore regarded as a regulator of the DG signal. Previous studies have revealed the critical role of α and ζ types of DGK in T cell functions. Nevertheless, little is known about the expression patterns of the DGK family in immune cells of various kinds. After examination of the expression profile of DGK isozymes in immune cells that are isolated from human blood, we investigated whether their mRNA expression levels would be changed during an inflammatory reaction. Results showed that DGK isozyme mRNAs are widely expressed in immune cells, except for DGKβ and DGKι. During an inflammatory reaction, DGKε mRNA was increased transiently in the initial phase (20-40 min) of stimulation with both LPS and IL-2 in T cell-derived HUT-102 cells and macrophage-derived RAW264 cells. At the organismal level, an intraperitoneal injection of LPS also induced upregulation of DGKε mRNA in the spleen in a similar,but not identical, manner. These results suggest that DGKε is involved in inflammatory processes of the cellular immune system