Role of cell death in the formation of sexual dimorphism in the Drosophila central nervous system

Currently, sex differences in behavior are believed to result from sexually dimorphic neural circuits in the central nervous system (CNS). Drosophila melanogaster is a common model organism for studying the relationship between brain structure, behavior, and genes. Recent studies of sex‐specific reproductive behaviors in D. melanogaster have addressed the contribution of sexual differences in the CNS to the control of sex‐specific behaviors and the development of sexual dimorphism. For example, sexually dimorphic regions of the CNS are involved in the initiation of male courtship behavior, the generation of the courtship song, and the induction of male‐specific muscles in D. melanogaster. In this review, I discuss recent findings about the contribution of cell death to the formation of sexually dimorphic neural circuitry and the regulation of sex‐specific cell death by two sex determination factors, Fruitless and Doublesex, in Drosophila.     

Asp- and Glu-specific novel dipeptidyl peptidase 11 of Porphyromonas gingivalis ensures utilization of proteinaceous energy sources

Porphyromonas gingivalis and Porphyromonas endodontalis, asaccharolytic black-pigmented anaerobes, are predominant pathogens of human chronic and periapical periodontitis, respectively. They incorporate di- and tripeptides from the environment as carbon and energy sources. In the present study we cloned a novel dipeptidyl peptidase (DPP) gene of P. endodontalis ATCC 35406, designated as DPP11. The DPP11 gene encoded 717 amino acids with a molecular mass of 81,090 Da and was present as a 75-kDa form with an N terminus of Asp(22). A homology search revealed the presence of a P. gingivalis orthologue, PGN0607, that has been categorized as an isoform of authentic DPP7. P. gingivalis DPP11 was exclusively cell-associated as a truncated 60-kDa form, and the gene ablation retarded cell growth. DPP11 specifically removed dipeptides from oligopeptides with the penultimate N-terminal Asp and Glu and has a P2-position preference to hydrophobic residues. Optimum pH was 7.0, and the k(cat)/K(m) value was higher for Asp than Glu. Those activities were lost by substitution of Ser(652) in P. endodontalis and Ser(655) in P. gingivalis DPP11 to Ala, and they were consistently decreased with increasing NaCl concentration. Arg(670) is a unique amino acid completely conserved in all DPP11 members distributed in the genera Porphyromonas, Bacteroides, and Parabacteroides, whereas this residue is converted to Gly in all authentic DPP7 members. Substitution analysis suggested that Arg(670) interacts with an acidic residue of the substrate. Considered to preferentially utilize acidic amino acids, DPP11 ensures efficient degradation of oligopeptide substrates in these Gram-negative anaerobic rods.     

Truncation of N- and C-terminal regions of <Emphasis Type="Italic">Streptococcus mutans</Emphasis> dextranase enhances catalytic activity

Multiple forms of native and recombinant endo-dextranases (Dexs) of the glycoside hydrolase family (GH) 66 exist. The GH 66 Dex gene from Streptococcus mutans ATCC 25175 (SmDex) was expressed in Escherichia coli. The recombinant full-size (95.4 kDa) SmDex protein was digested to form an 89.8 kDa isoform (SmDex90). The purified SmDex90 was proteolytically degraded to more than seven polypeptides (23–70 kDa) during long storage. The protease-insensitive protein was desirable for the biochemical analysis and utilization of SmDex. GH 66 Dex was predicted to comprise four regions from the N- to C-termini: N-terminal variable region (N-VR), conserved region (CR), glucan-binding site (GBS), and C-terminal variable region (C-VR). Five truncated SmDexs were generated by deleting N-VR, GBS, and/or C-VR. Two truncation-mutant enzymes devoid of C-VR (TM-NCGΔ) or N-VR/C-VR (TM-ΔCGΔ) were catalytically active, thereby indicating that N-VR and C-VR were not essential for the catalytic activity. TM-ΔCGΔ did not accept any further protease-degradation during long storage. TM-NCGΔ and TM-ΔCGΔ enhanced substrate hydrolysis, suggesting that N-VR and C-VR induce hindered substrate binding to the active site.     

Bacterial symbionts of the giant jewel stinkbug Eucorysses grandis (Hemiptera: Scutelleridae)

Microbiological characterization of gut symbiotic bacteria in a limited number of stinkbugs of the families Acanthosomatidae, Plataspidae, Pentatomidae, Scutelleridae, Parastrachiidae, Alydidae and Pyrrhocoridae has shown symbiotic association with midgut bacteria to be common in phytophagous taxa of these heteropteran insects. Here we investigated the midgut bacterial symbiont of Eucorysses grandis, a stinkbug of the family Scutelleridae. A specific gammaproteobacterium was consistently identified in insects from five different geographic origins. The bacterium was detected in 64 of 64 insects sampled from three host populations. Phylogenetic analyses revealed that the bacterium constitutes a distinct lineage in the Gammaproteobacteria, neither closely related to the gut symbiont of another scutellerid stinkbug, Cantao ocellatus, nor to gut symbionts of other stinkbugs. Diagnostic PCR, in situ hybridization and electron microscopy demonstrated that the bacterium is located extracelluarly, in the midgut fourth section, which possesses crypts. These results indicate that the primary gut symbionts have multiple evolutionary origins in the Scutelleridae. A Sodalis-allied facultative symbiont was also identified in some insects from natural populations. Biological aspects of the primary gut symbiont and the secondary Sodalis-allied symbiont are discussed.     

Suitable top concentration for tests with mammalian cells: mouse lymphoma assay workgroup

The Mouse Lymphoma Expert Workgroup of the International Workshop for Genotoxicity Tests (IWGT) met in Basel, Switzerland in August of 2009. The Workgroup (WG) was tasked with discussing the appropriate top concentration for non-pharmaceuticals that would be required for the conduct of the mouse lymphoma assay (MLA) when sufficient cytotoxicity [to between 10 and 20% relative total growth (RTG)] has not been attained. The WG approached this task by (1) enumerating the various regulatory decisions/use for MLA data, (2) discussing the appropriate assays to which MLA data and assay performance should be compared and (3) discussing all the proposals put forth concerning the top concentration for non-pharmaceuticals. In addition, one of the members presented a summary of a re-evaluation of the National Toxicology Program MLA data using the IWGT harmonized guidance that was underway as a separate (non IWGT) activity, being conducted by two members of the Expert WG. The WG was asked to vote on each of the various proposals for top concentration for when cytotoxicity is not concentration limiting. While there was general agreement that the top concentration for non-pharmaceuticals should be re-evaluated and likely lowered from the current recommended levels, there was no agreement on a specific new recommendation.     

Hydrogen sulfide protects the retina from light-induced degeneration by the modulation of Ca2+ influx

Hydrogen sulfide (H(2)S) has recently been recognized as a signaling molecule as well as a cytoprotectant. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are well-known as H(2)S-producing enzymes. We recently demonstrated that 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase (CAT) produces H(2)S in the brain and in vascular endothelium. However, the cellular distribution and regulation of these enzymes are not well understood. Here we show that 3MST and CAT are localized to retinal neurons and that the production of H(2)S is regulated by Ca(2+); H(2)S, in turn, regulates Ca(2+) influx into photoreceptor cells by activating vacuolar type H(+)-ATPase (V-ATPase). We also show that H(2)S protects retinal neurons from light-induced degeneration. The excessive levels of light exposure deteriorated photoreceptor cells and increased the number of TUNEL- and 8-hydroxy-2'-deoxyguanosine (8-OHdG)-positive cells. Degeneration was greatly suppressed in the retina of mice administered with NaHS, a donor of H(2)S. The present study provides a new insight into the regulation of H(2)S production and the modulation of the retinal transmission by H(2)S. It also shows a cytoprotective effect of H(2)S on retinal neurons and provides a basis for the therapeutic target for retinal degeneration.     

Enhanced epithelial-mesenchymal transition-like phenotype in N-acetylglucosaminyltransferase V transgenic mouse skin promotes wound healing

N-Acetylglucosaminyltransferase V (GnT-V) catalyzes the β1,6 branching of N-acetylglucosamine on N-glycans. GnT-V expression is elevated during malignant transformation in various types of cancer. However, the mechanism by which GnT-V promotes cancer progression is unclear. To characterize the biological significance of GnT-V, we established GnT-V transgenic (Tg) mice, in which GnT-V is regulated by a β-actin promoter. No spontaneous cancer was detected in any organs of the GnT-V Tg mice. However, GnT-V expression was up-regulated in GnT-V Tg mouse skin, and cultured keratinocytes derived from these mice showed enhanced migration, which was associated with changes in E-cadherin localization and epithelial-mesenchymal transition (EMT). Further, EMT-associated factors snail, twist, and N-cadherin were up-regulated, and cutaneous wound healing was accelerated in vivo. We further investigated the detailed mechanisms of EMT by assessing EGF signaling and found up-regulated EGF receptor signaling in GnT-V Tg mouse keratinocytes. These findings indicate that GnT-V overexpression promotes EMT and keratinocyte migration in part through enhanced EGF receptor signaling.