The brain consists of various types of neurons that are generated from neural stem cells; however, the mechanisms underlying neuronal diversity remain uncertain. A recent study demonstrated that the medulla, the largest component of the Drosophila optic lobe, is a suitable model system for brain development because it shares structural features with the mammalian brain and consists of a moderate number and various types of neurons. The concentric zones in the medulla primordium that are characterized by the expression of four transcription factors, including Homothorax (Hth), Brain-specific homeobox (Bsh), Runt (Run) and Drifter (Drf), correspond to types of medulla neurons. Here, we examine the mechanisms that temporally determine the neuronal types in the medulla primordium. For this purpose, we searched for transcription factors that are transiently expressed in a subset of medulla neuroblasts (NBs, neuronal stem cell-like neural precursor cells) and identified five candidates (Hth, Klumpfuss (Klu), Eyeless (Ey), Sloppy paired (Slp) and Dichaete (D)). The results of genetic experiments at least explain the temporal transition of the transcription factor expression in NBs in the order of Ey, Slp and D. Our results also suggest that expression of Hth, Klu and Ey in NBs trigger the production of Hth/Bsh-, Run- and Drf-positive neurons, respectively. These results suggest that medulla neuron types are specified in a birth order-dependent manner by the action of temporal transcription factors that are sequentially expressed in NBs.

Sequential progression of differentiation in a tissue or in multiple tissues in a synchronized manner plays important roles in development. Such waves of differentiation are especially important in the development of the Drosophila visual system, which is composed of the retina and the optic lobe of the brain. All of the components of the fly visual system are topographically connected, and each ommatidial unit in the retina corresponds to a columnar unit in the optic lobe, which is composed of lamina, medulla, lobula and lobula plate. In the developing retina, the wave of differentiation follows the morphogenetic furrow, which progresses in a posterior-to-anterior direction. At the same time, differentiation of the lamina progresses in the same direction, behind the lamina furrow. This is not just a coincidence: differentiated photoreceptor neurons in the retina sequentially send axons to the developing lamina and trigger differentiation of lamina neurons to ensure the progression of the lamina furrow just like the furrow in the retina. Similarly, development of the medulla accompanies a wave of differentiation called the proneural wave. Thus, the waves of differentiation play important roles in establishing topographic connections throughout the fly visual system. In this article, we review how neuronal differentiation and connectivity are orchestrated in the fly visual system by multiple waves of differentiation.

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A chiral organic base catalyst with halogen-bonding-donor functionality has been developed. This quinidine-derived acid/base catalyst smoothly promoted the asymmetric Mannich reaction of malononitrile and various N-Boc imines with up to 98% ee. The cooperative interaction with both substrates was responsible for the high activity that allowed a reduction of the catalyst amount to 0.5 mol%.

Homo-and cross-[4+ +2] cycloadditions of 2-alkenylindoles,c atalyzedb yc ationic halogen-bond donors,w ere developed. Under mild reaction conditions,3 -indolyl-substituted tetrahydrocarbazole derivatives were obtained in good to excellent yields.Experimental and quantum calculation studies revealed that the electrophilic activation of 2-alkenylindoles was achieved by C À I···p halogen bonds.

A wide variety of neurons, including populations derived from different origins, are precisely arranged and correctly connected with their partner to establish a functional neural circuit during brain development. The molecular mechanisms that orchestrate the production and arrangement of these neurons have been obscure. Here, we demonstrate that cell-cell interactions play an important role in establishing the arrangement of neurons of different origins in the Drosophila visual center. Specific types of neurons born outside the medulla primordium migrate tangentially into the developing medulla cortex. During their tangential migration, these neurons express the repellent ligand Slit, and the two layers that the neurons intercalate between express the receptors Robo2 and Robo3. Genetic analysis suggests that Slit-Robo signaling may control the positioning of the layer cells or their processes to form a path for migration. Our results suggest that conserved axon guidance signaling is involved in the interactions between neurons of different origins during brain development.

It usuallytakes a few weeks to analyze dioxin concentrations and dioxin-TEQ (toxicity equivalency quantity) in fluegases from municipal solid waste (MSW) incinerators by a standard method provided by Japanese industrial standard (JIS 0311). To reduce the required time for analysis, we have developed a new on-line measuring system for furans homologues. This system is composed of a sensitive and robust vacuum ultraviolet (VUV) single-photon ionization (SPI) ion trap (IT) time-of-flight mass spectrometer (VUV-SPI-IT-TOFMS) and automatic sampling/concentrating process. In this work, pentachloro-dibenzofuran (P5CDF) was selected as an index homologue in chlorinated dibenzo-p-dioxin/ furan homologues (DXNs) because its concentration and I-TEF (international toxicity equivalency factor), which are 2,3,4,7,8-P5CDF is 0.5 and 1,2,3,7,8-P5CDF is 0.05, are high and the concentration correlates closely with the total amount of dioxin-TEQ. The lowest detectable limit, 1 pg (0.001 ng-TEQ/m3 N) was demonstrated by laboratory tests. This system underwent a field test at several actual MSW plants and the tests revealed the following: (a) This system is applicable for dioxin-TEQ evaluation from actual MSW incinerators. (b) It can continuously monitor P5CDF in a fluegas for 7 months. (c) The frequency of the measurements is once every 2-6 h, depending on the concentration of P5-CDF.

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