A putative GDP–GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans

The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities.     

Aggregatibacter actinomycetemcomitans induces detachment and death of human gingival epithelial cells and fibroblasts via elastase release following leukotoxin‐dependent neutrophil lysis

Aggregatibacter actinomycetemcomitans is considered to be associated with periodontitis. Leukotoxin (LtxA), which destroys leukocytes in humans, is one of this bacterium's major virulence factors. Amounts of neutrophil elastase (NE), which is normally localized in the cytoplasm of neutrophils, are reportedly increased in the saliva of patients with periodontitis. However, the mechanism by which NE is released from human neutrophils and the role of NE in periodontitis is unclear. In the present study, it was hypothesized that LtxA induces NE release from human neutrophils, which subsequently causes the breakdown of periodontal tissues. LtxA‐treatment did not induce significant cytotoxicity against human gingival epithelial cells (HGECs) or human gingival fibroblasts (HGFs). However, it did induce significant cytotoxicity against human neutrophils, leading to NE release. Furthermore, NE and the supernatant from LtxA‐treated human neutrophils induced detachment and death of HGECs and HGFs, these effects being inhibited by administration of an NE inhibitor, sivelestat. The present results suggest that LtxA mediates human neutrophil lysis and induces the subsequent release of NE, which eventually results in detachment and death of HGECs and HGFs. Thus, LtxA‐induced release of NE could cause breakdown of periodontal tissue and thereby exacerbate periodontitis.     

Pathogenesis of persistent truncus arteriosus induced by nimustine hydrochloride in chick embryos

Nimustine hydrochloride (ACNU) is a nitrosourea derivative anticancer agent which has been shown to cause persistent truncus arteriosus in chick embryos. The objective of this study was to confirm the teratogenic effects of ACNU on the cardiovascular system of chick embryos and to determine whether ACNU induces persistent truncus arteriosus by interfering with neural crest cells. Various doses of ACNU ranging from 10 to 200 micrograms were injected under the chorioallantoic membrane of chick embryos on the third day of incubation. Saline solution was used as the control. After 10 to 11 days of incubation, 242 (46%) survivors of the 524 treated eggs were obtained. The survival rates of the embryos and the frequencies of cardiovascular anomalies were dose dependent. Of 146 embryos with cardiovascular anomalies, 104 (71%) had persistent truncus arteriosus. Ventricular septal defect and double-outlet right ventricle were seen in 37 (25%) and one (1%), respectively. Aortic arch anomalies were seen in 116 embryos (79%). Quail-chick chimeras (chick embryos with quail cardiac neural crest) were treated with 50 micrograms of ACNU and examined histologically 24 hours later. These chimeras showed dying neural crest cells in the pharyngeal arches. Dying cells were also noted in the neural tube, cranial ganglia, retina, and otocyst. These results suggest that persistent truncus arteriosus in chick embryos treated with ACNU is induced by neural crest cell death.     

A toxic substance produced by Nocardia otitidiscaviarum isolated from cutaneous nocardiosis

During our studies on toxic substances from clinically isolated Nocarida, a new isolate identified as Nocardia otitidiscaviarum from cutaneous nocardiosis was found to produce a toxic substance called HS-6 that had strong in vitro as well as in vivo toxicity. The mouse intraperitoneal LD₅₀ value was 1.25 mg/kg and the ED₅₀ value for L1210 cultured cells was 0.3 ng/ml. The structure of HS-6 was determined and found to belong to the 16-membered macrocyclic group with a molecular formula of C₄₃H₆₈O₁₂. HS-6 also showed activity against pathogenic fungi such as Cryptococcus neoformans.     

Germination traits and seed-bank dynamics of a biennial plant,Oenothera glazioviana Micheli

A study was conducted on the germination traits and seed-bank dynamics ofOenothera glazioviana (=O. erythrosepala), which sets seed in August in sand-dune systems in Japan. More than 90% of freshly matured seeds germinated over a wide range of temperature in light, but less than 10% did so in continuous darkness. Stratification (chilling under moist conditions) was ineffective in diminishing the light-requirement for germination. When fresh seeds were imbibed for 24 h including a 12-h light period, followed by 7-day air-drying, 94% of them became germinable in the dark at 25°C, but remained dormant at less than 15°C. of seeds collected in March from capsules of dead plants, 58% germinated in the dark at 25°C. After four cycles of alternatc 1-day wetting followed by 2-day drying or 1.5-day wetting followed by 1.5-day drying under a 12-h photoperiod, the fraction of viable seeds declined from 76% to 40% and 22%, respectively, due to germination during the wet periods. Seed-bag experiments were conducted in the field, using seeds given and not given a light-stimulus. Forty percent of the light-stimulated seeds germinated in the soil, whereas the seeds without a light-stimulus remained dormant throughout the experiment. When seeds were placed on the soil surface or at a depth of 0.5-1 cm, the proportion of germinable seeds declined during late spring and autumn, but not during winter and early spring. The seed-bank size of a natural population just prior to current seed dispersal was 2–3% of the seed production in the previous year, suggesting a high turnover rate of the seed-bank.     

Effect of C-reactive protein on peritoneal macrophages. II. Human C-reactive protein activates peritoneal macrophages of guinea pigs to release superoxide anion in vitro

The effect of human C-reactive protein (CRP) on macrophage function was studied in an assay of superoxide anion (O2-) production. Peritoneal exudate macrophages (PEM) of guinea pigs exposed in vitro to various doses of CRP for 72 hr resulted in the development of O2- production dose-dependently, measured by increases in superoxide dismutase-inhibitable nitro blue tetrazolium reduction. The O2--producing activity of PEM cultured without CRP, used as a control, decreased markedly in proportion to incubation time. The O2- production by PEM exposed to CRP for 18 hr when control PEM were still high in O2- production, was decreased by larger doses of CRP, while PEM cultured without CRP for 72 hr, when O2- production by control PEM was very low, followed by incubation with CRP for another 18 hr, produced O2- CRP-dose-dependently as in the case of that observed after 72-hr incubation with CRP. These results indicate that CRP is capable of activating macrophages and acts on macrophage function as a modulator. CRP possesses migration inhibitory factor (MIF)-like activity (as reported in the preceding paper) and also macrophage-activating factor (MAF)-like activity, indicating that CRP may play a functional role at the site of inflammation and tissue damage by accumulating and activating macrophages.     

Water Potential and Mechanical Properties of the Cell Wall of Hypocotyls of Dark-Grown Squash (Cucurbita maxima Duch.) under Water-Stress Conditions

Hypocotyl growth of seedlings of dark-grown squash (Cucurbitamaxima Duch.) was greatly reduced by the addition of 60mM polyethyleneglycol (PEG) to hydroponic solution (water stress). Apoplastic solution (A) and cell sap (C) were separately collectedfrom the hypocotyl segments by a centrifugation method. Theosmotic potentials of A (_A) and C (_c), and (=_c–_A) ofstressed hypocotyls were always lower than those of unstressedhypocotyls. Suction force was measured by immersing the segments into solutionsof different concentrations of mannitol. Suction force was significantlycorrelated with _C (r= –0.99). The mechanical properties of the cell wall of hypocotyl segmentswere measured by stressrelaxation technique. Minimum stressrelaxation time (T_o), relaxation rate (R) and residual stressof unstressed hypocotyls were low during the growth period andincreased when the growth ceased. T_o and R of stressed hypocotylsdecreased one day after the stress treatment, but the residualstress was not decreased by the water stress throughout theexperiment. These results suggest that the suppressed growth of dark-grownsquash hypocotyls under water stress was due neither to thereduction of the osmotic potential difference between innerand outer space of the cell, nor to the decrease in suctionforce, but was partly due to the unchanged mechanical propertiesof the cell wall, as represented by one stress-relaxation parameter,residual stress. (Received February 5, 1988; Accepted September 8, 1988)     

Studies on hst, a transforming gene which belongs to a new superfamily of growth factors

The hst gene was originally identified in surgically obtained human gastric mucosae as a transforming gene which could transform NIH3T3 cells morphologically. The hst cDNA clone was synthesized from mRNA of one of the NIH3T3 transformants. A human leukocyte genomic library was screened with this cDNA clone, and an hst genomic fragment was obtained. This genomic fragment itself had transforming activity, and the protein coding sequences were proved to be completely identical to those of the cDNA clone prepared from mRNA of the NIH3T3 transformant. This fact suggests that rearrangement or other structural alterations in the coding sequence are not required for the activation of the hst gene. The predicted hst protein consists of 206 amino acids and has a significant homology (40-50%) to fibroblast growth factors and int-2 protein. They together make up a new superfamily of growth factors and transforming genes.     

Germination ecology of coastal plants in relation to salt environment

Responses of seed germination to salinity were examined using 37 species collected from salt marshes, cliffs, and fore (unstable) and hind (stable) sand dunes along Japanese coasts. For comparison, seed germination of nine inland species was also examined. The soil salinities in salt marshes ranged from 150 to 300 mmol/L NaCl, whereas those in fore and hind dunes ranged from 0 to 150 mmol/L NaCl, with a few exceptions. Cliff soils showed relatively high salinities up to 300 mmol/L NaCl. Ciff and foredune soils that encountered a typhoon and storm showed high salinities >300 mmol/L NaCl. Salt tolerance in seed germination of coastal plants was ordered by comparing the responses of percentage and rate of germination to salinity conditions up to 200 mmol/L NaCl, being in the order of salt marsh>cliff>foredune≅hind dune≅inland. Thse results indicate that salt tolerance in seed germination of coastal plants is closely related to the salinity conditions of their habitats. Germination experiments under favorable conditions showed that a high percentage of the seeds of salt marsh species germinate rapidly, those of diff species germinate slowly and those of foredune species exhibit a low percentage and low rate of germination. It seems that these germination characteristics contribute to the success of germination at the ‘safe site’ and the subsequent survivorship of emerged plants in their natural habitats.