Gogo Receptor Contributes to Retinotopic Map Formation and Prevents R1-6 Photoreceptor Axon Bundling

<div><p>Background</p><p>Topographic maps form the basis of neural processing in sensory systems of both vertebrate and invertebrate species. In the Drosophila visual system, neighboring R1–R6 photoreceptor axons innervate adjacent positions in the first optic ganglion, the lamina, and thereby represent visual space as a continuous map in the brain. The mechanisms responsible for the establishment of retinotopic maps remain incompletely understood.</p><p>Results</p><p>Here, we show that the receptor Golden goal (Gogo) is required for R axon lamina targeting and cartridge elongation in a partially redundant fashion with local guidance cues provided by neighboring axons. Loss of function of Gogo in large clones of R axons results in aberrant R1–R6 fascicle spacing. Gogo affects target cartridge selection only indirectly as a consequence of the disordered lamina map. Interestingly, small clones of <i>gogo</i> deficient R axons perfectly integrate into a proper retinotopic map suggesting that surrounding R axons of the same or neighboring fascicles provide complementary spatial guidance. Using single photoreceptor type rescue, we show that Gogo expression exclusively in R8 cells is sufficient to mediate targeting of all photoreceptor types in the lamina. Upon lamina targeting and cartridge selection, R axons elongate within their individual cartridges. Interestingly, here Gogo prevents bundling of extending R1-6 axons.</p><p>Conclusion</p><p>Taken together, we propose that Gogo contributes to retinotopic map formation in the Drosophila lamina by controlling the distribution of R1–R6 axon fascicles. In a later developmental step, the regular position of R1–R6 axons along the lamina plexus is crucial for target cartridge selection. During cartridge elongation, Gogo allows R1–R6 axons to extend centrally in the lamina cartridge.</p></div

Effects of 5’-UTR of MTP-A and MTP-C on translation efficiency.

<p>CHO cells were transfected with Renilla luciferase and 5’-UTR constructs of either MTP-C (top) or MTP-A (bottom). The cells were lysed and assayed for luciferase activity. Data are expressed as mean ± s.d. (n = 3/group). a, significantly different from Control, p < .001; b, significantly different from C-UTR, p < .05.</p

Nucleotide sequence for exons 1B and 1A.

<p>Start (boxes with solid lines) and stop (boxes with dashed lines) codons in the 5’-UTR of MTP-C are highlighted. Start sites ATG-1, -2, and -6 are in frame with a TGA-2; ATG-3 is in frame with TAG-1; ATG-4, -5, and -7 are in frame with TGA-3. ATG* denotes translation initiation site for MTP-A. Note that this start site codon overlaps a potential stop codon.</p

Retinotopic map formation and target cartridge selection is disrupted in the absence of Gogo.

<p>(A–B) Schematics of cartridge assembly. (A) Within each fascicle, the R8 axon extends first to the lamina plexus during larval development, followed by a sequential outgrowth of R1–R7. R1-6 axon fascicles reach the lamina plexus in a precise spatial pattern, forming the initial topographic map (30 hr APF), whereas R8 projects through the lamina to innervate the medulla. (B) Subsequently, R1-6 fascicles separate and project to different specific cartridges. Six R1–R6 axons from six different ommatidia in turn converge with one set of lamina neurons (not shown) to a single target cartridge. (C–D’’’) Confocal images and schematics of retinotopic mapping of R1–R6 fascicles in wild-type and <i>eyflp;gogo</i> background at 30 hr APF. (C–C’’’) In wild-type FRT80 controls R1–R6 fascicles terminate at the lamina plexus maintaining their equal spacing and the spatial order of their ommatidia. (D–D’’’) In <i>gogo</i> mutant background, R1–R6 fascicles fail to arrange in the correct order to neighboring axons. (E–F’’’) Sections of midpupal lamina at the onset of target cartridge selection at 42 hr APF in control and in <i>gogo</i> mutant background. Arrowheads (E–E’’’, F–F’’’) and dots (E’’’, F’’’) mark the start points and asterisks (E–E’’’, F–F’’’) the end of R4 extensions. (E–E’’’) In control animals, R4 projection pattern (green) is uniform in direction and length and the overall pattern (magenta) displays orderly distributed and uniformly sized cartridges. (F–F’’’) When Gogo is removed from the majority of R cells R4 extensions (green) are not parallel and the overall pattern of the lamina (magenta) is highly disrupted. R4 cells sometimes form long growth cones (orange arrow) or two axons converge to a single target (red arrow). (G, J) Polar plots visualize orientation vectors of R4 axons in wild-type control and mutant. (H, I) DeLaunay (green strokes) and Voronoi diagrams (grey strokes) display the uniform and irregular retinotopic mapping in wild-type (E–E’’’) and mutant (F–F’’’), respectively. Scale bars: 10 µm.</p

One-year time variations of anthropogenic radionuclides in aerosols in Tokyo after the Fukushima Dai-ichi Nuclear Power Plant reactor failures

<div><p>We report on the results of monitoring of environmental radiation for one year (13 March 2011 to 12 March 2012), including air dose rates and the concentrations of radionuclides in aerosols in Tokyo, after the reactor failures at the Fukushima Dai-ichi Nuclear Power Plant. The air dose rates began to increase at 4:00–5:00 JST on 15 March 2011, and the maximum rate was observed at 10:00–11:00 JST. Two peaks were observed before 23 March 2011, and then the air dose rates decreased until March 2012. The time variations of concentrations of radionuclides in aerosols showed tendencies similar to those of air dose rates. Short-lived radionuclides (⁹⁹Mo (^99mTc), ^129mTe (¹²⁹Te), ^131mTe, ¹³²Te (¹³²I), ¹³³I and ¹³⁶Cs) were under the detection limit during April 2011. Iodine-131 was detected until early June 2011, and long-lived radionuclides (¹³⁴Cs and ¹³⁷Cs) were detected intermittently for one year. Based on our results, gamma doses and committed effective doses resulting from inhalation were estimated.</p></div

Roles of Raft-Anchored Adaptor Cbp/PAG1 in Spatial Regulation of c-Src Kinase

<div><p>The tyrosine kinase c-Src is upregulated in numerous human cancers, implying a role for c-Src in cancer progression. Previously, we have shown that sequestration of activated c-Src into lipid rafts via a transmembrane adaptor, Cbp/PAG1, efficiently suppresses c-Src-induced cell transformation in Csk-deficient cells, suggesting that the transforming activity of c-Src is spatially regulated via Cbp in lipid rafts. To dissect the molecular mechanisms of the Cbp-mediated regulation of c-Src, a combined analysis was performed that included mathematical modeling and <i>in vitro</i> experiments in a c-Src- or Cbp-inducible system. c-Src activity was first determined as a function of c-Src or Cbp levels, using focal adhesion kinase (FAK) as a crucial c-Src substrate. Based on these experimental data, two mathematical models were constructed, the sequestration model and the ternary model. The computational analysis showed that both models supported our proposal that raft localization of Cbp is crucial for the suppression of c-Src function, but the ternary model, which includes a ternary complex consisting of Cbp, c-Src, and FAK, also predicted that c-Src function is dependent on the lipid-raft volume. Experimental analysis revealed that c-Src activity is elevated when lipid rafts are disrupted and the ternary complex forms in non-raft membranes, indicating that the ternary model accurately represents the system. Moreover, the ternary model predicted that, if Cbp enhances the interaction between c-Src and FAK, Cbp could promote c-Src function when lipid rafts are disrupted. These findings underscore the crucial role of lipid rafts in the Cbp-mediated negative regulation of c-Src-transforming activity, and explain the positive role of Cbp in c-Src regulation under particular conditions where lipid rafts are perturbed.</p></div

Identification of MTP-C in mouse tissue.

<p>RNA was extracted from mouse tissues, and RT-PCR was run using forward primers in exons 1A and 1B and a reverse primer in exon 2. Specific fragments were generated for MTP-A and MTP-B in all tissues examined. Note the extra product in brain tissue (X) when using primers for MTP-B. IM, intestinal mucosa; WF, white fat; BF, brown fat.</p

Comparison of mouse MTP splice variants.

<p>The mouse <i>Mttp</i> gene consists of 19 exons spanning 40 kB. Exon 1B is located 8.7 kB upstream of exon 2 and 2.7 kB upstream of exon 1A, which contains the initiator codon for MTP-A. MTP-B arises through a novel mechanism in which exon 1B is spliced directly to exon 2. The MTP-C transcript arises when exon 1A is not spliced out of the MTP-B transcript; thus, it contains both exons 1B and 1A. Black areas in exons represent open reading frames; white areas represent 5’-untranslated regions (5’-UTR).</p

Mutations in NA That Induced Low pH-Stability and Enhanced the Replication of Pandemic (H1N1) 2009 Influenza A Virus at an Early Stage of the Pandemic

<div><p>An influenza A virus that originated in pigs caused a pandemic in 2009. The sialidase activity of the neuraminidase (NA) of previous pandemic influenza A viruses are stable at low pH (≤5). Here, we identified the amino acids responsible for this property. We found differences in low-pH stability at pH 5.0 among pandemic (H1N1) 2009 viruses, which enhanced the replication of these viruses. Low-pH-stable NA enhancement of virus replication may have contributed to the rapid worldwide spread and adaptation to humans of pandemic (H1N1) 2009 viruses during the early stages of the 2009 pandemic.</p></div

Preparation of Au Nanowire Films by Electrodeposition Using Mesoporous Silica Films as a Template: Vital Effect of Vertically Oriented Mesopores on a Substrate

Films consisting of polycrystalline Au nanowires were prepared by electrodeposition using mesoporous silica films with vertically oriented mesochannels as a template. The importance of the mesostructure near the surface of the substrate is emphasized by the comparison of films possessing vertically aligned mesochannels to the substrate with those having parallel aligned mesochannels from the viewpoints of Au deposition in the films and the presence or absence of the resulting cracking. When all mesopores lie parallel to the substrate, the mesoporous film was cleaved by the deposition of Au, which is in clear contrast to the case of Pt deposition. Fabricated Au nanowires are not interconnected with each other unlike Pt, irrespective of the presence of interconnected micropores