Nuclear matrix localization and specific matrix DNA binding by receptor binding factor 1 of the avian oviduct progesterone receptor

A chromatin acceptor protein for the avian oviduct progesterone receptor (PR), termed receptor binding factor 1 (RBF-1), has recently been shown to (1) be a component of the nuclear binding sites (acceptor sites) for PR and (2) generate high-affinity binding sites (termed the RBF-1 class of sites) on avian genomic DNA [Schuchard et al. (1991) Biochemistry 30, 4535-4542]. A second class of sites and its associated protein (termed RBF-2) were also identified. This paper demonstrates that RBF-1 and also the PR nuclear binding sites are localized in the oviduct nuclear matrix. RBF-1 is found in abundance in the nuclear matrix of liver but only in traces in the nuclear matrix of spleen. Extraction of the nuclear matrix with 4.0 M Gdn-HCl results in the complete removal of RBF-1 as occurs with whole chromatin. Interestingly, a second class of specific PR binding, termed RBF-2, remains on the nuclear matrix after the removal of all RBF-1. Southern blot analysis indicates that the nuclear matrix DNA contains sequences homologous with the 5'-flanking domains of the rapidly steroid regulated c-myc and c-jun protooncogenes and the beta-actin gene, but not genomic sequences of the late sex steroid regulated gene, ovalbumin, or the alpha-actin gene. A specific, small region in the 5'-flanking domain of the c-myc gene appears to be associated with the nuclear matrix. Southwestern blot analysis using partially purified RBF-1 shows a marked affinity and specificity of the RBF-1 for the nuclear matrix DNA.(ABSTRACT TRUNCATED AT 250 WORDS)     

The oligomerization of a family of four genetically clustered human gastrointestinal mucins

Mucins are synthesized and secreted by many epithelia. They are complex glycoproteins that offer cytoprotection. In their functional configuration, mucins form oligomers by a biosynthetic process that is poorly understood. A family of four human gastrointestinal mucin genes (MUC2, MUC5AC, MUC5B, and MUC6) is clustered to chromosome 11p15.5. To study oligomerization of these related mucins, we performed metabolic labeling experiments with [35S]amino acids in LS174T cells, and isolated mucin precursors by specific immunoprecipitations that were analyzed on SDS-PAGE. Each of the precursors of MUC2, MUC5AC, MUC5B, and MUC6 formed a single species of disulfide-linked homo-oligomer within 1 h after pulse labeling. Based on apparent molecular masses, these oligomeric precursors were most likely dimers. Inhibition of vesicular RER-to-Golgi transport, with brefeldin A and CCCP, did not affect the dimerization of MUC2 precursors, localizing dimerization to the RER. O-Glycosylation of MUC2 followed dimerization. Inhibition of N- glycosylation by tunicamycin retarded, but did not inhibit, dimerization, indicating that N-glycans play a role in efficient dimerization of MUC2 precursors. Based on sequence homology, the ability of MUC2, MUC5AC, MUC5B and MUC6 to dimerize most likely resides in their C-terminal domains. Thus, the RER-localized dimerization of secretory mucins likely proceeds by similar mechanisms, which is an essential step in the formation of the human gastrointestinal mucus- gels.      

Osmotic Behavior of Oat Coleoptile Tissue in Relation to Growth

Efforts were made to estimate the water potential difference that is required, between rapidly growing oat coleoptile cylinders and dilute medium, to support the rate of water uptake involved in elongation, (a) by the traditional method of determining the concentration of mannitol in which the tissue neither gains nor loses water, and (b) by measuring the rates of osmotic exchanges induced by treating the tissue with different hypotonic mannitol concentrations. Both methods indicated large water potential differences (3 to 10 atm), in some cases approaching the osmotic pressure of the cells. However, indication was obtained that the rates of osmotic exchanges induced by mannitol solutions, and presumably also the equilibrium response sought in (a), are governed by the rate of diffusional exchange of mannitol with the free space rather than by the permeability of the tissue to water. Osmotic swelling of the tissue measured by immersing it in water after its turgor pressure had been reduced by evaporation, was at least two to four times more rapid than when mannitol was involved. The permeability to water estimated by the evaporation-immersion method indicated that rapidly elongating cylinders have water potentials between -0.8 and -2.5 atm, or between 10 and 25 per cent of their osmotic pressure.     

Bacterial abundance and aerobic microbial activity across natural and oyster aquaculture habitats during summer conditions in a northeastern Pacific estuary

We measured sediment properties and the abundance and aerobic metabolism of microbes in Willapa Bay, Washington, USA, to test the response of sediment microbes to oyster aquaculture. Sites spanned the estuary gradient (practical salinity units ranged from 24 to 30 under seasonally low river flows) and six different low-intertidal habitat types: eelgrass (Zostera marina), unstructured tideflat, oyster hummocks (reefs of Crassostrea gigas), longline oyster aquaculture, hand-picked on-bottom oyster aquaculture, and dredged on-bottom oyster aquaculture. Aerobic metabolism was assessed by sole-source carbon use (SSCU) of 31 carbon sources on Biolog plates. Sediments generally became siltier and more organically enriched into the estuary, but no consistent differences in sediment properties occurred across habitat types. Bacterial cell density tracked organic content. Across the estuary gradient, overall aerobic SSCU increased less steeply than bacterial cell density, possibly as anaerobic metabolism became more important. Across habitats, aerobic SSCU differed significantly in both overall metabolism and diversity of carbon sources. Aerobic metabolism was generally lower for sediment microbes from intertidal on-bottom oyster aquaculture than from eelgrass. Humans indirectly alter microbial activity through biogenic habitats created during aquaculture, but, as has been shown for bivalves more generally, these changes were relatively small, particularly in comparison to sediment changes along estuarine gradients.     

Comparing residence time and natural enemies between low- and high- density invasions

Ecological and historical factors influence the probability that a known invader will experience success in new locations. Using field and laboratory studies, we investigated how residence time and natural enemies (co-evolved castrating parasite, and native crabs) differ between two introduced populations of the intertidal snail, Batillaria attramentaria. The populations have substantially different invasion histories (~?10 vs.?>?80 years) and exhibit markedly different densities and tidal distributions. The less-dense, vertically-restricted population was recently introduced, and thus has potentially had less opportunity to fill the fundamental niche at that site. However, no increase in density or intertidal range occurred in this population over 10 years, suggesting that it had reached its realized niche. The newer population experienced much greater effects of native cancrid crabs than the older, high-density population, particularly below the minimum tidal elevation of observed snail distribution, where crabs were found in the greatest densities. Prevalence of parasite infection did not differ between populations. This is the first study documenting effects of predators on this invasive snail, which is widespread along coastlines of the northeast Pacific, whereas previous studies have suggested that the primary restriction on population growth rate was likely to be parasitic castration. Further, this study supports the general understanding that, while novel predators can reduce the impacts or population growth rates of invasive species, such top-down effects are not likely to preclude persistence at a given site.     

Congener comparison of native (Zostera marina) and introduced (Z. japonica) eelgrass at multiple scales within a Pacific Northwest estuary

A congener comparison of native (Zostera marina) and introduced (Zostera japonica) eelgrasses was conducted in Willapa Bay, Washington, USA. Along intertidal transects, Z. japonica (0.1–1.5 m above mean lower low water [MLLW]) occurred above Z. marina (<0.6 m MLLW). Both species declined in shoot length at higher elevation, but Z. japonica was always shorter (20 vs. 100 cm) and occurred at higher shoot density (>3,800 vs. <360 m^?2 in Z. marina). Z. japonica exhibited greater seasonal variation in biomass, with increases supported by both sustained asexual reproduction (rhizome branching) and recruitment from seeds (30 vs. <5% in Z. marina). Z. japonica’s successful invasion appears related to small size and high reproductive output, allowing it to spread quickly in a variable and stressful intertidal environment where competitive effects are low. Based on interannual changes in abundance, the native eelgrass has also recently increased in Willapa Bay, and one hypothesis involves “engineering” of suitable habitat at higher tidal elevations by Z. japonica.     

Mass-Balance Analyses of Boreal Forest Population Cycles: Merging Demographic and Ecosystem Approaches

UsingEcopath, a trophic mass-balance modeling framework, we developed six models of a Canadian boreal forest food web centered around snowshoe hares, which have conspicuous 10-year population cycles. Detailed models of four phases of the cycle were parameterized with long-term population data for 12 vertebrate taxa. We also developed five other models that, instead of observed data, used parameter values derived from standard assumptions. Specifically, in the basic model, production was assumed to equal adult mortality, feeding rates were assumed to be allometric, and biomass was assumed to be constant. In the actual production, functional response, and biomass change models, each of these assumed values from the basic model was replaced individually by field data. Finally, constant biomass models included actual production by all species and functional responses of mammalian predators and revealed the proportion of herbivore production used by species at higher trophic levels. By comparing these models, we show that detailed information on densities and demographics was crucial to constructing models that captured dynamic aspects of the food web. These detailed models reinforced an emerging picture of the causes and consequences of the snowshoe hare cycle. The snowshoe hare decline and low phases were coincident with times when per capita production was relatively low and predation pressure high. At these times, ecotrophic efficiencies (EE) suggest there was little production that remained unconsumed by predators. The importance of both production and consumption implies that bottom–up and top–down factors interacted to cause the cycle. EEs of other herbivores (ground squirrels, red squirrels, small mammals, small birds, grouse) were generally low, suggesting weak top–down effects. Predation rates on these “alternative” prey, except ground squirrels, were highest when predators were abundant, not when hares were rare; consequently, any top–down effects reflected predator biomass and were not a function of diet composition or functional responses. Finally, several predators (lynx, coyotes, great-horned owls) showed clear bottom–up regulation, reproducing only when prey exceeded threshold densities. Taken altogether, these results demonstrate that ecosystem models parameterized by population data can describe the dynamics of nonequilibrial systems, but only when detailed information is available for the species modeled. Received 30 November 2000; Accepted 6 September 2001.     

Daily changes in the sensitivity of wax-moth larvae, Galleria mellonella, to cooling stress

ABSTRACT. Sensitivity to cooling stress in the last instar larvae of Galleria mellonella was measured as (a) the number of extra larval moults, (b) the number of larvae retaining the ability to secrete silk, and (c) the number showing arrested development. With respect to (a) and (b) there were considerable differences in sensitivity across the day. A relationship was observed between the number of additional larval moults induced by chilling and the ability of prepupal larvae to spin silk: the periods during the 24 h when the most larvae passed through additional larval moults were periods characterized by the smallest number of larvae capable of spinning, and vice versa. These daily changes were apparently partly independent of developmental age. Daily variations in sensitivity also occurred when larvae of the same age were cooled at different times of day. It is suggested that these rhythms in cold-sensitivity are related to a cold-sensitive rhythm in juvenile hormone secretion, or hormone sensitivity in the tissues.