The advancing timberline on Mt. Fuji: natural recovery or climate change?

The alpine timberline on Mt. Fuji (central Japan) is at 2,400-2,500 m above sea level. Over a 21-year period (1978-1999), we tracked changes in this vegetation boundary on a transect at a site impacted by the 1707 volcanic eruption. The timberline advanced rapidly upwards during this time period. Dominant tree species at the timberline (Alnus maximowiczii, Salix reinii, and Larix kaempferi) colonized sites that were initially largely free of vegetation at higher altitudes. Seedlings of L. kaempferi were particularly abundant at the border of advancing vegetation. According to tree age, we found that this was the first canopy species in the colonized areas. L. kaempferi is drought resistant, and this probably contributes to its establishment capability in the high-altitude climate. Most seedlings of Abies veitchii invaded patches of herbs and shrubs. These vegetation patches in the upper kampfzone provide important shelter for seedlings of invading tree species. We predict that the upward advance of the alpine timberline is a recovery process following the volcanic eruption, and that climate change may accelerate this advance.     

IL-15 up-regulates iNOS expression and NO production by gingival epithelial cells

To investigate the biological activity of epithelial cells in view of host defense, we analyzed the mRNA expression of inducible NOS (iNOS) as well as NO production by human gingival epithelial cells (HGEC) stimulated with IL-15. RT-PCR analysis revealed that HGEC expressed IL-15 receptor alpha-chain mRNA. In addition, stimulation with IL-15 enhanced iNOS expression by HGEC through an increase of both mRNA and protein levels. Moreover, IL-15 up-regulated the production of NO(2)(-)/NO(3)(-), a NO-derived stable end product, from HGEC. The enhanced NO production by IL-15 was inhibited by AMT, an iNOS-specific inhibitor. These results suggest that IL-15 is a potent regulator of iNOS expression by HGEC and involved in innate immunity in the mucosal epithelium.     

Zygospore formation between homothallic and heterothallic strains of Closterium

Zygospore formation in different strains of the Closterium peracerosum-strigosum-littorale complex was examined in this unicellular isogamous charophycean alga to shed light on gametic mating strains in this taxon, which is believed to share a close phylogenetic relationship with land plants. Zygospores typically form as a result of conjugation between mating-type plus (mt⁺) and mating-type minus (mt⁻) cells during sexual reproduction in the heterothallic strain, similar to Chlamydomonas. However, within clonal cells, zygospores are formed within homothallic strains, and the majority of these zygospores originate as a result of conjugation of two recently divided sister gametangial cells derived from one vegetative cell. In this study, we analyzed conjugation of homothallic cells in the presence of phylogenetically closely related heterothallic cells to characterize the reproductive function of homothallic sister gametangial cells. The relative ratio of non-sister zygospores to sister zygospores increased in the presence of heterothallic mt⁺ cells, compared with that in the homothallic strain alone and in a coculture with mt⁻ cells. Heterothallic cells were surface labeled with calcofluor white, permitting fusions with homothallic cells to be identified and confirming the formation of hybrid zygospores between the homothallic cells and heterothallic mt⁺ cells. These results show that at least some of the homothallic gametangial cells possess heterothallic mt⁻-like characters. This finding supports speculation that division of one vegetative cell into two sister gametangial cells is a segregative process capable of producing complementary mating types.     

Purification and properties of NADH oxidase from Bacillus megaterium

NADH oxidase, which catalyzes the oxidation of NADH, with the consumption of a stoichiometric amount of oxygen, to NAD+ and hydrogen peroxide was purified from Bacillus megaterium by 5'-AMP Sepharose affinity chromatography to homogeneity. The enzyme is a dimeric protein containing 1 mol of FAD per mol of subunit, Mr = 52,000. The absorption maxima of the native enzyme (oxidized form) were found at 270, 383, and 450 with a shoulder at 475 nm in 50 mM KPi buffer, pH 7.0. The visible absorption bands at 383 and 450 nm disappeared on the addition of NADH under anaerobic conditions and reappeared upon the introduction of air. Thus, the non-covalently bound FAD functioned as a prosthetic group for the enzyme. We tentatively named this new enzyme NADH oxidase (NADH:oxygen oxidoreductase, hydrogen peroxide forming). This enzyme stereospecifically oxidizes the pro-S hydrogen at C-4 of the pyridine ring of NADH.     

Skp2 controls adipocyte proliferation during the development of obesity

The increase in the mass of adipose tissue during the development of obesity can arise through an increase in cell size, an increase in cell number, or both. Here we show that long term maintenance of C57BL/6 mice on a high fat diet (for approximately 25 weeks) induces an initial increase in adipocyte size followed by an increase in adipocyte number in white adipose tissue. The latter effect was found to be accompanied by up-regulation of expression of the gene for the F-box protein Skp2 as well as by downregulation of the cyclin-dependent kinase inhibitor p27(Kip1), a principal target of the SCF(Skp2) ubiquitin ligase, in white adipose tissue. Ablation of Skp2 protected mice from the development of obesity induced either by a high fat diet or by the lethal yellow agouti (A(y)) mutation, and this protective action was due to inhibition of the increase in adipocyte number without an effect on adipocyte hypertrophy. The reduction in the number of adipocyte caused by Skp2 ablation also inhibited the development of obesity-related insulin resistance in the A(y) mutant mice, although the reduced number of beta cells and reduced level of insulin secretion in Skp2-deficient mice resulted in glucose intolerance. Our observations thus indicate that Skp2 controls adipocyte proliferation during the development of obesity.     

Uncertainty of knee joint muscle activity during knee joint torque exertion: the significance of controlling adjacent joint torque.

In the single-joint torque exertion task, which has been widely used to control muscle activity, only the relevant joint torque is specified. However, the neglect of the neighboring joint could make the procedure unreliable, considering our previous result that even monoarticular muscle activity level is indefinite without specifying the adjacent joint torque. Here we examined the amount of hip joint torque generated with knee joint torque and its influence on the activity of the knee joint muscles. Twelve healthy subjects were requested to exert various levels of isometric knee joint torque. The knee and hip joint torques were obtained by using a custom-made device. Because no information about hip joint torque was provided to the subjects, the hip joint torque measured here was a secondary one associated with the task. The amount of hip joint torque varied among subjects, indicating that they adopted various strategies to achieve the task. In some subjects, there was a considerable internal variability in the hip joint torque. Such variability was not negligible, because the knee joint muscle activity level with respect to the knee joint torque, as quantified by surface electromyography (EMG), changed significantly when the subjects were requested to change the strategy. This change occurred in a very systematic manner: in the case of the knee extension, as the hip flexion torque was larger, the activity of mono- and biarticular knee extensors decreased and increased, respectively. These results indicate that the conventional single knee joint torque exertion has the drawback that the intersubject and/or intertrial variability is inevitable in the relative contribution among mono- and biarticular muscles because of the uncertainty of the hip joint torque. We discuss that the viewpoint that both joint torques need to be considered will bring insights into various controversial problems such as the shape of the EMG-force relationship, neural factors that help determine the effect of muscle strength training, and so on.     

Enhancement of Glossiness Perception by Retinal-Image Motion: Additional Effect of Head-Yoked Motion Parallax

It has been argued that when an observer moves, a contingent retinal-image motion of a stimulus would strengthen the perceived glossiness. This would be attributed to the veridical perception of three-dimensional structure by motion parallax. However, it has not been investigated whether the effect of motion parallax is more than that of retinal-image motion of the stimulus. Using a magnitude estimation method, we examine in this paper whether cross-modal coordination of the stimulus change and the observer''s motion (i.e., motion parallax) is essential or the retinal-image motion alone is sufficient for enhancing the perceived glossiness. Our data show that a retinal-image motion simulating motion parallax without head motion strengthened the perceived glossiness but that its effect was weaker than that of motion parallax with head motion. These results suggest the existence of an additional effect of the cross-modal coordination between vision and proprioception on glossiness perception. That is, motion parallax enhances the perception of glossiness, in addition to retinal-image motions of specular surfaces.     

Phylogeography of Fischer’s blue,Tongeia fischeri,in Japan: Evidence for introgressive hybridization

The widespread lycaenid butterfly Tongeia fischeri is distributed from eastern Europe to northeastern Asia and represented by three geographically isolated populations in Japan. In order to clarify the phylogeographic history of the species, we used sequences of three mitochondrial (COI, Cyt b and ND5) and two nuclear (Rpl5 and Ldh) genes of 207 individuals collected from 55 sites throughout Japan and five sites on the Asian continent. Phylogenetic trees and the median-joining network revealed six evolutionary mitochondrial haplotype clades, which corresponded to the geographic distribution of the species. Common ancestors of Japanese T. fischeri might have come to Japan during the mid-Pleistocene by multiple dispersals of continental populations, probably via a land bridge or narrow channel between western Japan and the Korean Peninsula. The geographical patterns of variation of mitochondrial and nuclear markers are discordant in northeastern Kyushu, possibly as a result of introgressive hybridization during the ancient contact between the Kyushu and Shikoku populations in the last glacial maximum. The phylogeographic pattern of T. fischeri in Japan are probably related to the geological history, Pleistocene climatic oscillations and distribution of the host plant.     

Lipopolysaccharides of Escherichia coli K12 Strains That Express Cloned Genes for the Ogawa and Inaba Antigens of Vibrio cholerae O1: Identification of O-Antigenic Factors

Structural and serological studies were performed with the lipopolysaccharide (LPS) expressed by Escherichia coli K12 strains No. 30 and No. 64, into which cosmid clones derived from Vibrio cholerae O1 NIH 41 (Ogawa) and NIH 35A3 (Inaba) had been introduced, respectively. The two recombinant strains, No. 30 (Ogawa) and No. 64 (Inaba), produced LPS that included, in common, the O-polysaccharide chain composed of an α(1 → 2)-linked N-(3-deoxy-L -glycero-tetronyl)-D -perosamine (4-amino-4,6-dideoxy-D -manno-pyranose) homopolymer attached to the core oligosaccharide of the LPS of E. coli K12. Structural analysis revealed the presence of N-(3-deoxy-L -glycero-tetronyl)-2-O-methyl-D -perosamine at the non-reducing terminus of the O-polysaccharide chain of LPS from No. 30 (Ogawa) but not from No. 64 (Inaba). Serological analysis revealed that No. 30 (Ogawa) and No. 64 (Inaba) LPS were found to share the group antigen factor A of V. cholerae O1. They were distinguished by presence of the Ogawa antigen factor B [co-existing with relatively small amounts of the Inaba antigen factor (c)] in the former LPS and the Inaba antigen factor C in the latter LPS. It appears, therefore, that No. 30 (Ogawa) and No. 64 (Inaba) have O-antigenic structures that are fully consistent with the AB(c) structure for the Ogawa and the AC structure for the Inaba O-forms of V. cholerae O1, respectively. Thus, the present study clearly confirmed our previous finding that the Ogawa antigenic factor B is substantially related to the 2-O-methyl group at the non-reducing terminus of the α(1 → 2)-linked N-(3-deoxy-L -glycero-tetronyl)-D -perosamine homopolymer that forms the O-polysaccharide chain of LPS of V. cholerae O1 (Ogawa).