Unequal cleavage in the early Tubifex embryo

Unequal cleavage that produces two blastomeres of different size is a cleavage pattern that many animals in a variety of phyla, particularly in Spiralia, adopt during early development. This cleavage pattern is apparently instrumental for asymmetric segregation of developmental potential, but it is also indispensable for normal embryogenesis in many animals. Mechanically, unequal cleavage is achieved by either simple unequal cytokinesis or by forming a polar lobe at the egg's vegetal pole. In the present paper, the mechanisms for unequal cytokinesis involved in the first three cleavages in the oligochaete annelid Tubifex are reviewed. The three unequal cleavages are all brought about by an asymmetrically organized mitotic apparatus (MA). The MA of the first cleavage is monastral in that an aster is present at one pole of a bipolar spindle but not at the other. This monastral form, which arises as a result of the involvement of a single centrosome in the MA assembly, is both necessary and sufficient for unequal first cleavage. The egg cortex during the first mitosis is devoid of the ability to remodel spindle poles. In contrast to the non-cortical mechanisms for the first cleavage, asymmetry in the MA organization at the second and third cleavages depends solely on specialized properties of the cell cortex, to which one spindle pole is physically connected. A cortical attachment site for the second cleavage spindle is generated de novo at the cleavage membrane resulting from the first cleavage; it is an actin-based, cell contact-dependent structure. The cortical microtubule attachment site for the third cleavage, which functions independently of contact with other cells, is not generated at the cleavage membrane resulting from the second cleavage, but is located at the animal pole; it may originate from the second polar body formation and become functional at the 4-cell stage.     

Measurement of early pregnancy factor activity for monitoring the viability of the equine embryo

The viability of embryos before flushing from donor mares (n = 5) and after transfer to recipient mares (n = 7) was monitored in mare serum by detecting early pregnancy factor (EPF) using the rosette inhibition test (RIT). The EPF activity was measured in donor mares before and after natural mating at natural estrus; after ovulation on Days 2, 5 and 8; and after embryo flushing (Day 8) on Days 8, 9, 10 and 13 after ovulation. The collected embryos were transferred immediately after flushing. The EPF activity in recipient mares were measured on the day of transfer and after embryo transfer on Days 1, 2, 3 and 5. Pregnancy was confirmed on Day 12 to 14 after embryo transfer. The mean EPF activity of donor mares was increased to the pregnant level (> an RI titer score of 10) on Day 2 after ovulation. Two days after flushing the embryos, the EPF activity of donor mares had decreased to the nonpregnant level. Among the 7 recipient mares, 3 mares were diagnosed pregnant on Day 12 after embryo transfer with ultrasound. The EPF activity of the pregnant recipient mares was increased above the minimum level observed in pregnant mares on Days 2 to 3 after transfer. However, among the nonpregnant recipient mares after embryo transfer, the EPF activity of 3 mares remained at the pregnant level only 2 to 3 d and then declined to the nonpregnant level. In one recipient mare, EPF activity did not reach the pregnant level throughout the sample collection. The results of this study indicated that equine EPF can be detected in serum of pregnant mares as early as Day 2 after ovulation. From our observation, we conclude that the measurement of EPF activity is useful for monitoring the in vivo viability of equine embryos and early detection of embryonic death.     

Purification and Characterization of Exo-beta-d-Glucosaminidase from a Cellulolytic Fungus, Trichoderma reesei PC-3-7

Chitosan-degrading activities induced by glucosamine (GlcN) or N-acetylglucosamine (GlcNAc) were found in a culture filtrate of Trichoderma reesei PC-3-7. One of the chitosan-degrading enzymes was purified to homogeneity by precipitation with ammonium sulfate followed by anion-exchange and hydrophobic-interaction chromatographies. The enzyme was monomeric, and its molecular mass was 93 kDa. The optimum pH and temperature of the enzyme were 4.0 and 50 degrees C, respectively. The activity was stable in the pH range 6.0 to 9.0 and at a temperature below 50 degrees C. Reaction product analysis from the viscosimetric assay and thin-layer chromatography and H nuclear magnetic resonance spectroscopy clearly indicated that the enzyme was an exo-type chitosanase, exo-beta-d-glucosaminidase, that releases GlcN from the nonreducing end of the chitosan chain. H nuclear magnetic resonance spectroscopy also showed that the exo-beta-d-glucosaminidase produced a beta-form of GlcN, demonstrating that the enzyme is a retaining glycanase. Time-dependent liberation of the reducing sugar from partially acetylated chitosan with exo-beta-d-glucosaminidase and the partially purified exo-beta-d-N-acetylglucosaminidase from T. reesei PC-3-7 suggested that the exo-beta-d-glucosaminidase cleaves the glycosidic link of either GlcN-beta(1-->4)-GlcN or GlcN-beta(1-->4)-GlcNAc.     

Comparative study of grooming relationships among wild Japanese macaques in Kinkazan A troop and Yakushima M troop

The influences of socionomic sex ratio (SSR; adult males/adult female) and troop size upon male-male, female-female, and male-female grooming relationships were examined and compared between two wild Japanese macaque troops (Kinkazan A and Yakushima M troops) in Japan. The Yakushima M troop was smaller and had a higher-SSR than the Kinkazan A troop. Between the troops, (1) the male-male grooming frequency and number of partners were greater in the Yakushima M troop than in the Kinkazan A troop; (2) the female-female grooming frequency and number of partners were not different; and (3) the male-female grooming frequency and number of partners were not different. Based on these features, the patterns of female-female and male-female grooming relationships appear to be independent of SSR and troop size variations. In contrast, male-male grooming relationships are influenced by both factors, especially SSR. Frequent grooming interactions among males may be useful for the continued coexistence of relatively many males especially in a higher-SSR troop.     

A possible role for actin dots in the formation of the contractile ring in the ultra-micro algaCyanidium caldarium RK-1

Summary In the primitive red algaCyanidium caldarium RK-1, cytokinesis is controlled by a simple contractile ring, as in animal cells. To clarify the mechanism of formation of the contractile ring, we isolated actin genes and performed an immunocytological study.C. caldarium RK-1 has two actin genes encoding proteins with the same sequence of 377 amino acids. The primary structure indicated that the actin molecules ofC. caldarium RK-1 are typical, despite the fact that the organism is considered to be phylogenetically primitive. We prepared antiserum against aC. caldarium RK-1 actin fusion protein and indirect immunofluorescence staining was performed. In interphase cells, many actin dots were observed in the cytoplasm but none at the future cleavage plane. Prior to cytokinesis, some of these dots appeared and became aligned along the equatorial plane. At the same time, a thin immature contractile ring was observed to appear to be formed by connection of the aligned actin dots. This immature contractile ring thickened to nearly its maximum size by the time cytokinesis began. The formation of the contractile ring seemed to be a result of de novo assembly of actin monomers, rather than a result of the accumulation and bundling of pre-existing actin filaments. During the constriction of the contractile ring, no actin dots were observed in the cytoplasm. These observations suggest that actin dots are responsible for the formation of the contractile ring, but are not necessary for its disintegration. Furthermore, immunogold localization specific for actin revealed at electron microscopy level that fine filaments running just beneath the cleavage furrow are, in fact, actin filaments.Abbreviations ORF open reading frame - IPTG isopropyl--D(–)-thiogalactopyranoside - SDS-PAGE sodium dodecyl sulphate-poly-acrylamide gel electrophoresis - DAPI 4,6-diamidino-2-phenylindole     

More than a 600-fold variation in nitrogen dioxide assimilation among 217 plant taxa

Assimilation of nitrogen dioxide in response to fumigation with ¹⁵N-labelled nitrogen dioxide was studied in 217 plant taxa. The taxa included 50 wild herbaceous plants collected from roadsides (42 genera, 15 families), 60 cultivated herbaceous plants (55 genera, 30 families) and 107 cultivated woody plants (74 genera, 45 families). Two parameters, the 'NO₂-N content', or NO₂-derived reduced nitrogen content in fumigated plant leaves (mg N g^–1 dry weight), and the 'NO₂-utilization index', or percentage of the NO₂-derived reduced nitrogen in the total reduced nitrogen, were determined. The NO₂-N content differed 657-fold between the highest ( Eucalyptus viminalis ; 6·57) and lowest ( Tillandsia ionantha and T. caput-medusae ; 0·01) values in the 217 taxa; 62-fold in a family (Theaceae) and 26-fold in a species ( Solidago altissima ). Nine species had NO₂-utilization indices greater than 10%, of which Magnolia kobus , Eucalyptus viminalis , Populus nigra , Nicotiana tabacum and Erechtites hieracifolia had NO₂-N contents > 4·9. These plants can be considered 'NO₂-philic' because in them NO₂-nitrogen has an important function(s). The Compositae and Myrtaceae had high values for both parameters, whereas the monocots and gymnosperms had low ones. These findings suggest that the metabolic pathway of NO₂-nitrogen differs among plant species. The information presented here will be useful for creating a novel vegetation technology to reduce the atmospheric concentration of nitrogen dioxide.     

Relationship between vascular endothelial growth factor and angiogenesis in spontaneous and indomethacin-delayed healing of acetic acid-induced gastric ulcers in rats.

Angiogenesis is an important event for gastric ulcer healing. Vascular endothelial growth factor (VEGF) is known to be a potent stimulator of angiogenesis. This study consequently examined VEGF production, VEGF mRNA expression and angiogenesis during the spontaneous and indomethacin-delayed healing of acetic acid-induced ulcers in rats. The production of VEGF, taking place in the normal mucosa, was significantly elevated by ulceration. The mRNA expression of three isoforms of VEGF (VEGF188, VEGF164 and VEGF120) was also detected. Following the increase in VEGF production, angiogenesis was significantly promoted in the ulcer base. VEGF-immunoreactivity was observed in granulocytes, fibroblasts and regenerated epithelial cells. Indomethacin markedly inhibited prostaglandin E2 synthesis in the ulcer base, resulting in the prevention of ulcer healing. Angiogenesis was also significantly inhibited by indomethacin, but neither VEGF production nor VEGF mRNA expression was reduced. Such results suggest that VEGF might play a role in angiogenesis in the spontaneous healing of gastric ulcers in rats. However, the inhibition of angiogenesis in indomethacin-delayed ulcer healing is not explainable on VEGF expression.     

Spatial pattern changes in aboveground plant biomass in a grazing pasture

Using gamma distribution and spatial autocorrelation, it was demonstrated that plant biomass per unit area of a pasture grazed by cattle exhibited two kinds of spatial heterogeneity: small-scale heterogeneity caused by grazing and large-scale heterogeneity caused by topography, land aspect, etc. For each of the 10 measurement times from May to August, 100 quadrats 50cm × 50cm were arranged along a straight line 50m long in a pasture, and the plants within the quadrats were harvested at the height of 3cm above the ground surface to measure the dry weight. The data were aggregated into frequency distributions, and gamma distribution and the parameter values were estimated. This analysis showed that with the progression of grazing the amount of biomass decreased and the degree of spatial heterogeneity in biomass, measured per 0.25m², increased, and due to plant regrowth the trends were reversed. By rearranging the 100 biomass data in order of weight, it was suggested that plots with an extremely large biomass were not grazed by cattle and remained in the pasture. For the same data, variations of biomass along the straight line were divided into two parts based on the moving average: the spatial trend and the residuals which cannot be explained by the trend. In this analysis, 48–75% of the total spatial variation was explained by the trend along the straight line. Analysis using spatial autocorrelation for the actual biomass changes showed that the biomass changes within a range of about 10m on the straight line gave a positive correlation, which indicates a topographical trend in biomass. Spatial autocorrelation for residuals suggested that the spatial changes in biomass along the straight line followed a wave-like or checker-board pattern. Small-scale spatial heterogeneity in plant biomass may be caused by the uneven deposition of excreta by grazing animals, uneven use of the grassland by grazing animals, and uneven dispersal of plant seeds through faeces over the grassland. The possibility that such unevenness might accelerate energy flow in the grassland ecosystem and contribute to grassland sustainability is discussed.