Regulation of sister chromatid cohesion between chromosome arms

Sister chromatid separation in anaphase depends on the removal of cohesin complexes from chromosomes. In vertebrates, the bulk of cohesin is already removed from chromosome arms during prophase and prometaphase, whereas cohesin remains at centromeres until metaphase, when cohesin is cleaved by the protease separase. In unperturbed mitoses, arm cohesion nevertheless persists throughout metaphase and is principally sufficient to maintain sister chromatid cohesion. How arm cohesion is maintained until metaphase is unknown. Here we show that small amounts of cohesin can be detected in the interchromatid region of metaphase chromosome arms. If prometaphase is prolonged by treatment of cells with microtubule poisons, these cohesin complexes dissociate from chromosome arms, and arm cohesion is dissolved. If cohesin dissociation in prometaphase-arrested cells is prevented by depletion of Plk1 or inhibition of Aurora B, arm cohesion is maintained. These observations imply that, in unperturbed mitoses, small amounts of cohesin maintain arm cohesion until metaphase. When cells lacking Plk1 and Aurora B activity enter anaphase, chromatids lose cohesin. This loss is prevented by proteasome inhibitors, implying that it depends on separase activation. Separase may therefore be able to cleave cohesin at centromeres and on chromosome arms.     

Identification of a subunit of a novel Kleisin-beta/SMC complex as a potential substrate of protein phosphatase 2A

Protein phosphatase 2A (PP2A) holoenzymes consist of a catalytic C subunit, a scaffolding A subunit, and one of several regulatory B subunits that recruit the AC dimer to substrates. PP2A is required for chromosome segregation, but PP2A's substrates in this process remain unknown. To identify PP2A substrates, we carried out a two-hybrid screen with the regulatory B/PR55 subunit. We isolated a human homolog of C. elegans HCP6, a protein distantly related to the condensin subunit hCAP-D2, and we named this homolog hHCP-6. Both C. elegans HCP-6 and condensin are required for chromosome organization and segregation. HCP-6 binding partners are unknown, whereas condensin is composed of the structural maintenance of chromosomes proteins SMC2 and SMC4 and of three non-SMC subunits. Here we show that hHCP-6 becomes phosphorylated during mitosis and that its dephosphorylation by PP2A in vitro depends on B/PR55, suggesting that hHCP-6 is a B/PR55-specific substrate of PP2A. Unlike condensin, hHCP-6 is localized in the nucleus in interphase, but similar to condensin, hHCP-6 associates with chromosomes during mitosis. hHCP-6 is part of a complex that contains SMC2, SMC4, kleisin-beta, and the previously uncharacterized HEAT repeat protein FLJ20311. hHCP-6 is therefore part of a condensin-related complex that associates with chromosomes in mitosis and may be regulated by PP2A.     

Synthesis and structure-activity relationships of 2-amino-8-hydroxyadenines as orally active interferon inducing agents

Recently, we have reported the 8-hydroxyadenine derivatives (2–4) as a novel class of interferon (IFN) inducing agents. In the present study, a series of 8-hydroxyadenines, which possess various amino moieties at the adenine C(2)-position, were synthesized and evaluated for their ability to induce endogenous IFN in comparison to the known active agent, Imiquimod. Among the compounds prepared, compound 9o possessing a 2-methoxyethylamino group at C(2)-position of adenine was found to exhibit potent IFN inducing activity in vivo. Compound 9o induced IFN from the dosage of 0.1 mg/kg, which was 30-fold potent than that of Imiquimod, and showed a good oral bioavailability (F=81%).     

Antipsychotic action of selective group II metabotropic glutamate receptor agonist MGS0008 and MGS0028 on conditioned avoidance responses in the rat

The present study was designed to investigate the antipsychotic-like effects of selective group II metabotropic glutamate receptor (mGluR) agonists, 5-[2-[4-(6-fluoro-1H-indole-3-yl) piperidin-1-yl]ethyl]-4-(4-fluorophenyl)thiazole-2-carboxylic acid amide (MGS0008) and (1R, 2S, 5S, 6S)-2-amino-6-fluoro-4-oxobicyclo[3.1.0]hexane-2,6-dicarboxylic acid monohydrate (MGS0028) on conditioned avoidance responses in rats. MGS0008 (1, 3 and 10 mg/kg, p.o.) and MGS0028 (0.3, 1 and 3 mg/kg, p.o.) significantly and reduced conditioned avoidance responses in a dose-dependent fashion. Similar effects were seen with LY418426 (0.3, 1 and 3 mg/kg, p.o.), but not with LY354740 (3, 10 and 30 mg/kg, p.o.), both of which are selective agonists for group II mGluR. Since this effect is seen with a wide range of antipsychotics, such as haloperidol and clozapine [Life Sciences 71 (2002) 947], group II mGluR agonists deserve further attention for possible antipsychotic activity.     

Type III Cu mutants of Myrothecium verrucaria bilirubin oxidase

Type III Cu ligand, His456 and His458, of Myrothecium verrucaria (MT-1) bilirubin oxidases (BO) [EC 1.3.3.5] were doubly mutated as to Lys, Asp, and Val. In spite of perturbation of the type III Cu centers, these mutants were pale blue or colourless when isolated. However, they became intense blue on reaction with reducing agents such as dithionite, ascorbate, hexacyanoferrate(II), and octacyanotangstate(IV) under air, or with an oxidizing agent such as hexacyanoferrate(III), indicating that they are in mixed forms when expressed in Aspergillus oryzae. His456.458Lys and His456.458Asp mutated as to potential coordinating groups showed weak BO and ferroxidase activities, while His 456.458Val mutated as to non-coordinating groups showed no enzyme activity at all.     

Two-state conformational changes in inositol 1,4,5-trisphosphate receptor regulated by calcium

Inositol 1,4,5-trisphosphate receptor (IP3R) is a highly controlled calcium (Ca2+) channel gated by inositol 1,4,5-trisphosphate (IP3). Multiple regulators modulate IP3-triggered pore opening by binding to discrete allosteric sites within IP3R. Accordingly we have postulated that these regulators structurally control ligand gating behavior; however, no structural evidence has been available. Here we show that Ca2+, the most pivotal regulator, induced marked structural changes in the tetrameric IP3R purified from mouse cerebella. Electron microscopy of the IP3R particles revealed two distinct structures with 4-fold symmetry: a windmill structure and a square structure. Ca2+ reversibly promoted a transition from the square to the windmill with relocations of four peripheral IP3-binding domains, assigned by binding to heparin-gold. Ca2+-dependent susceptibilities to limited digestion strongly support the notion that these alterations exist. Thus, Ca2+ appeared to regulate IP3 gating activity through the rearrangement of functional domains.     

Pupal commitment and its hormonal control in wing imaginal discs

The timing of pupal commitment of the forewing imaginal discs of the silkworm, Bombyx mori, was determined by a transplantation assay using fourth instar larvae. The wing discs were not pupally committed at the time of ecdysis to the fifth instar. Pupal commitment began shortly after the ecdysis and was completed in 14 h. When the discs of newly molted larvae (0-h discs) were cultured in medium containing no hormone, they were pupally committed in 26 h. In vitro exposure of 0-h discs to 20-hydroxyecdysone accelerated the progression of pupal commitment. Methoprene, a juvenile hormone analog (JHA), did not suppress the change in commitment in vitro at physiological concentrations. Thus the wing discs at the time of the molt have lost their sensitivity to JH, and 20E is not a prerequisite for completion of pupal commitment. These results suggest that the change in commitment in the forewing discs may begin before the last larval molt.     

Geraniol-inducible glutathione S-transferase in cultured soybean cells

When the cultured cells of Glycine max (soybean) were treated with 5 mM geraniol as a chemical stress, an mRNA level was elevated in a rapid but transient increase. The mRNA was cloned and sequenced, and found to correspond to the mRNA encoding glutathione S-transferase (GST). The GST mRNA level and GST activity were elevated to maxima at 4-6 h and 8 h, respectively, after treatment of the cultures with geraniol. These indicate that GST is one of the geraniol-responsive factors in soybean cells.     

Effect of postprandial posture on digestion and absorption of dietary carbohydrate

The effect of postprandial body posture on digestion and absorption of dietary carbohydrate were examined through breath hydrogen test on 6 female subjects. During the experiment, the participants either sat on a chair or lay on their backs for the first 4 hr (from 08:00 to 12:00) after eating the test breakfast meal. They then remained sedentary on a sofa for 6 hr (12:00 to 18:00). Participants' end alveolar breath samples were collected for 10 hr (every 15 min from 08:00 to 12:30, and then every 30 min until 18:00). The experiment was conducted on two consecutive days using a randomized, crossover study design. The results demonstrated that in the supine position orocecal transit time of the test meal was significantly slower than in the sitting position (260 +/- 21 min and 238 +/- 20 min, respectively, p < 0.01). In addition, afternoon breath hydrogen excretion due to a partial malabsorption of dietary carbohydrate and its fermentation in the colon was significantly larger in the sitting position (144.0 +/- 24.1 ppm.hr) than in the supine position (110.0 +/- 26.1 ppm.hr, p < 0.05). These results support the hypothesis that there was a marked effect of postprandial body posture on the function of the digestive system. The present findings suggest that the postprandial supine position is preferable to the sitting position for the digestion and absorption of dietary carbohydrate.