Role of the cytoskeleton in choanoflagellate lorica assembly

ABSTRACT. Cell division in Acanthoeca spectabilis produces a "naked" motile daughter cell (juvenile) that settles onto a surface and deposits siliceous costal strips that are stored extracellularly in bundles. When complete, the bundles of strips are assembled in a single continuous movement to form a basket-like lorica. Assembly can be divided into four overlapping stages. Stage 1 entails the left-handed rotation of strips at the anterior end while the posterior end remains stationary. Stage 2 includes the posterior protrusion of the cell to form a stalk. Stage 3 involves the anterior extension of the spines, and Stage 4 the dilation of the lorica chamber and deposition of the organic investment. Scanning electron microscopic images reveal a one-to-one association between the moving bundles of strips and the anterior ring of lorica-assembling tentacles. Treatment with microtubule inhibitors produces "dwarf" cells that lack stalks, have their spines extended, and possess collars but lack flagella. Treatment with microfilament (actin) inhibitors prevents extension of the anterior spines. These experiments demonstrate that posterior cell extension is primarily mediated by microtubules whereas extension of the spines is controlled by the actin cytoskeleton. The processes of cytoskeletal rotation and extracellular costal strip movement are compared, respectively, with rotation of nuclei in animal embryos and movement of mammalian cells over surfaces.     

Nitric oxide synthase mediates regulation of cell polarity and movement during <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> morphogenesis

The effect of expression of the enzyme producing nitric oxide on Drosophila melanogaster morphogenesis was studied using ectopic expression of a truncated splice form of the enzyme that has a dominant negative effect on the full-length enzyme form. The suppressed enzyme expression was shown to affect the cell polarity and movement as well as the structural pattern of organs during Drosophila development. The effect of nitric oxide production on the intercellular distribution of significant factors of cell polarity, protein products of the Strabismus and Prospero genes, has been revealed.     

Influence of abiotic factors on the structure of the population of the brown alga <Emphasis Type="Italic">Fucus vesiculosus</Emphasis> in East Murman (Barents Sea)

The peculiarities of the structure of the population of the brown alga Fucus vesiculosus in East Murman at different combinations of abiotic factors were studied. Salinity below 10‰ and high surf activity reduced the average life span of the plants (to 1 year) and caused a significant predominance of female specimens (60–90% of the fertile specimens). The proportion of female specimens increased with age. The greatest average age (3 branchings) and the highest survival of F. vesiculosus occurred in the wave-protected parts of bays. The distribution of F. vesiculosus was related to water movement intensity, salinity, and substrate type. The size-weight characteristics of F. vesiculosus thalli were decreased during maximum salinity fluctuations. The optimal conditions for this species were those existing on a weakly protected shore with short-term fluctuations of salinity (24–25‰).     

Epidemiology and vector efficiency during a dengue fever outbreak in Cixi,Zhejiang Province,China

An emigrant worker returning from Southeast Asia triggered the outbreak of a DF epidemic in Zhejiang province, China, in October, 2004. Eighty‐three cases, mainly young and middle‐aged people between 20 and 50 (78.3%), were reported in the area of Cixi. There were no obvious occupational patterns. The majority of cases were female, with a sex ratio of 1:1.86 (m:f). The dengue virus (DENV) strains from the epidemic area were isolated and identified as DENV‐1, which belongs to Asian strain 1. According to the epidemiological investigation, the incidence of DF had no relationship to temperature, humidity, or precipitation, and the Breteau index of larvae showed a clear relationship only with the House Index and Container Index. Recent dengue problems in the town have been associated with the complex social factors and hygienic conditions for endemic villagers and immigrant workers. Some hygienic measures should be taken by the local government to reduce the risk of mosquito‐borne disease. These measures should aim to eliminate the breeding sites of the vector Aedes albopictus in indoor and outdoor containers filled with rainwater and thus reducing the risk of DF transmission.