A new species of yunnanozoan with implications for deuterostome evolution

Yunnanozoans are a distinctive clade of Lower Cambrian metazoans. Although widely accepted as deuterostomes, their exact placement within this superphylum is controversial. Here we describe a new species of Haikouella (H. jianshanensis) from the Chengjiang Lagerst?tte (Yunnan, China) with exceptional preservation of a number of features. These include external gills, which suggest that the origin of the pharyngeal clefts was independent of the gills. The diagnostic branchial arches of chordates may, therefore, be composite structures. No evidence was found for the chordate-like structures that have been described in other yunnanozoans. We propose that yunnanozoans are stem-group deuterostomes, allied to the vetulicolians.     

The changing morphology and increasing deceleration of supernova 1993J in M81

Twenty consecutive Very Long Baseline Interferometry images of supernova 1993J from the time of explosion to the present show the dynamic evolution of the expanding radio shell of an exploded star. High-precision astrometry reveals that the supernova expands isotropically from its explosion center. Systematic changes in the images may reflect a pattern of anisotropies and inhomogeneities in the material left over from the progenitor star. As the shock front sweeps up the material in the surrounding medium, it is increasingly decelerated and influenced by the material. After 5 years, the supernova has slowed to half of its original expansion velocity and may have entered the early stages of the adiabatic phase common in much older supernova remnants in the Milky Way Galaxy.     

Quantification of serpulid biogenic reef coverage of the sea bed (Polychaeta: Serpulidae) using a video transect technique

• 1. The large size, patchiness and fragility of serpulid reefs present difficulties for the measurement of reef coverage for mapping and monitoring studies. Video transect measures of cover are assessed in terms of accuracy and sensitivity of the method for the identification of spatial or temporal changes.
• 2. By comparison with direct in situ measurement of reef cover, it was found that still photography was capable of providing an accurate means for the measurement of the seabed coverage by individual reefs.
• 3. By comparison of video and still photographic measurement of reef cover, it was found that video transects were capable of providing cover estimates of sufficient accuracy for conservation purposes, differing from still photographic estimates by 0.3% cover.
• 4. Power analysis was employed on replicate video estimates of reef cover in order to determine the degree of replication required to identify different levels of spatial or temporal change in cover using video transects of different lengths. The modest level of replication required to identify changes in coverage as small as 25% of the initial value suggests that the use of video transects offers great potential in monitoring and mapping studies.

Copyright © 2002 John Wiley & Sons, Ltd.     

Senescence of nickel-transformed cells by an X chromosome: possible epigenetic control

Transfer of a normal Chinese hamster X chromosome (carried in a mouse A9 donor cell line) to a nickel-transformed Chinese hamster cell line with an Xq chromosome deletion resulted in senescense of these previously immortal cells. At early passages of the A9/CX donor cells, the hamster X chromosome was highly active, inducing senescence in 100% of the colonies obtained after its transfer into the nickel-transformed cells. However, senescence was reduced to 50% when Chinese hamster X chromosomes were transferred from later passage A9 cells. Full senescing activity of the intact hamster X chromosome was restored by treatment of the donor mouse cells with 5-azacytidine, which induced demethylation of DNA. These results suggest that a senescence gene or genes, which may be located on the Chinese hamster X chromosome, can be regulated by DNA methylation, and that escape from senescence and possibly loss of tumor suppressor gene activity can occur by epigenetic mechanisms.     

Physicochemical properties and bioactivity of fungal chitin and chitosan

Chitinous material was extracted from mycelia of Aspergillus niger and Mucor rouxii grown in yeast peptone dextrose broth for 15 and 21 days, respectively. The extracted material was characterized for purity, degree of acetylation, and crystallinity and tested for antibacterial and eliciting properties. The maximum glucosamine level determined in the mycelium of A. niger was 11.10% dw and in the mycelium of M. rouxii was 20.13% dw. On the basis of the stepwise extraction of freeze-dried mycelia, it appeared that M. rouxii mycelia contained both chitin and chitosan, whereas A. niger contained only chitin. The yields of crude chitin from A. niger and M. rouxii were 24.01 and 13.25%, respectively, and the yield of chitosan from M. rouxii was 12.49%. Significant amounts (7.42-39.81%) of glucan were associated with chitinous compounds from both species and could not be eliminated by the extraction method used. The degrees of acetylation were determined to be 76.53 and 50.07% for chitin from A. niger and M. rouxii, respectively, and 19.5% for M. rouxii chitosan. The crystallinity of fungal chitin and chitosan was estimated to be less intense than in corresponding materials from shrimp shells. The extracted chitin and chitosan in a concentration of 0.1% reduced Salmonella Typhimurium DT104 2576 counts by 0.5-1.5 logs during a 4 day incubation in tryptic soy broth at 25 degrees C. Furthermore, all tested chitinous materials from fungal sources significantly reduced lesions caused by Botrytis cinerea and Penicillium expansum in harvested apples.