Phagocytosis of bacteria by polymorphonuclear leukocytes: a freeze-fracture, scanning electron microscope, and thin-section investigation of membrane structure

The changes in membrane structure of rabbit polymorphonuclear (PMN) leukocytes during bacterial phagocytosis was investigated with scanning electron microscope (SEM), thin-section, and freeze-fracture techniques. SEM observations of bacterial attachment sites showed the involvement of limited areas of PMN membrane surface (0.01-0.25μm(2)). Frequently, these areas of attachment were located on membrane extensions. The membrane extensions were present before, during, and after the engulfment of bacteria, but were diminished in size after bacterial engulfment. In general, the results obtained with SEM and thin-section techniques aided in the interpretation of the three-dimensional freeze-fracture replicas. Freeze-fracture results revealed the PMN leukocytes had two fracture faces as determined by the relative density of intramembranous particles (IMP). Membranous extensions of the plasma membrane, lysosomes, and phagocytic vacuoles contained IMP's with a distribution and density similar to those of the plasma membrane. During phagocytosis, IMPs within the plasma membrane did not undergo a massive aggregation. In fact, structural changes within the membranes were infrequent and localized to regions such as the attachment sites of bacteria, the fusion sites on the plasma membrane, and small scale changes in the phagocytic vacuole membrane during membrane fusion. During the formation of the phagocytic vacuole, the IMPs of the plasma membrane appeared to move in with the lipid bilayer while maintaining a distribution and density of IMPs similar to those of the plasma membranes. Occasionally, IMPs were aligned to linear arrays within phagocytic vacuole membranes. This alignment might be due to an interaction with linearly arranged motile structures on the side of the phagocytic vacuole membranes. IMP-free regions were observed after fusion of lysosomes with the phagocytic vacuoles or plasma membrane. These IMP-free areas probably represent sites where membrane fusion occurred between lysosomal membrane and phagocytic vacuole membrane or plasma membrane. Highly symmetrical patterns of IMPs were not observed during lysosomal membrane fusion.     

17beta-Estradiol responsiveness of MCF-7 laboratory strains is dependent on an autocrine signal activating the IGF type I receptor

BACKGROUND: Human MCF-7 cells have been studied extensively as a model for breast cancer cell growth. Many reports have established that serum-starved MCF-7 cells can be induced to proliferate upon the sole addition of 17beta-estradiol (E2). However, the extent of the mitogenic response to E2 varies in different MCF-7 strains and may even be absent. In this study we compared the E2-sensitivity of three MCF-7 laboratory strains. RESULTS: The MCF-7S line is non-responsive to E2, the MCF-7 ATCC has an intermediate response to E2, while the MCF-7 NKI is highly E2-sensitive, although the levels and activities of the estrogen receptor (ER) are not significantly different. Both suramin and IGF type I receptor blocking antibodies are able to inhibit the mitogenic response to E2-treatment in MCF-7 ATCC and MCF-7 NKI cells. From this we conclude that E2-induced proliferation is dependent on IGF type I receptor activation in all three MCF-7 strains. CONCLUSIONS: The results presented in this article suggest that E2-responsiveness of MCF-7 cells is dependent on the secretion of an autocrine factor activating the IGF-IR. All three strains of MCF-7 breast cancer cells investigated do not respond to E2 if the IGF-RI-pathway is blocked. Generally, breast cancer therapy is targeted at inhibiting estrogen action. This study suggests that inhibition of IGF-action in combination with anti-estrogen-treatment may provide a more effective way in treatment or even prevention of breast cancer.     

Demographics and landscape features determine intrariver population structure in Atlantic salmon (Salmo salar L.): the case of the River Moy in Ireland

Contemporary genetic structure of Atlantic salmon (Salmo salar L.) in the River Moy in Ireland is shown here to be strongly related to landscape features and population demographics, with populations being defined largely by their degree of physical isolation and their size. Samples of juvenile salmon were collected from the 17 major spawning areas on the river Moy and from one spawning area in each of five smaller nearby rivers. No temporal allele frequency differences were observed within locations for 12 microsatellite loci, whereas nearly all spatial samples differed significantly, suggesting that each was a separate population. Bayesian clustering and landscape genetic analyses suggest that these populations can be combined hierarchically into five genetically informative larger groupings. Lakes were found to be the single most important determinant of the observed population structure. Spawning area size was also an important factor. The salmon population of the closest nearby river resembled genetically the largest Moy population grouping. In addition, we showed that anthropogenic influences on spawning habitats, in this case arterial drainage, can affect relationships between populations. Our results show that Atlantic salmon biodiversity can be largely defined by geography, and thus, knowledge of landscape features (for example, as characterized within Geographical Information Systems) has the potential to predict population structure in other rivers without an intensive genetic survey, or at least to help direct sampling. This approach of combining genetics and geography, for sampling and in subsequent statistical analyses, has wider application to the investigation of population structure in other freshwater/anadromous fish species and possibly in marine fish and other organisms.     

Variants of Myxococcus virescens Exhibiting Dispersed Growth. Growth and Production of Extracellular Enzymes and Slime

The growth of two strains of Myxococcus virescens exhibiting dispersed growth was followed in casamino acids (N III-C) media and casitone media. The changes in optical density, pH, pigmentation as well as the secretion of bacteriolytic and proteolytic enzymes, DNA and polysaccharides during growth were recorded. In both media the bacteria grew exponentially with a generation time of 4 (casitone) and 20 hours (N III-C) respectively. The maximal cell mass was about 4 times higher in casitone than in casamino acids media. The amounts of bacteriolytic enzymes produced by the two strains in N III-C medium were different but in casitone medium they were about equal and considerably higher. The maximal values of proteolytic enzymes were about the same in both media and always occurred later than the bacteriolytic maxima. Both activity peaks appeared before the phase of decline. The polysaccharide production reached a maximum during the stationary growth phase in both media. A higher value was reached during growth in casitone medium than in N III-C medium. During the phase of decline a second increase of polysaccharide in the medium appeared. No DNA could be detected in the cell-free solutions until the beginning of the phase of decline.