The size of the synaptic cleft and distinct distributions of filamentous actin,ezrin, CD43, and CD45 at activating and inhibitory human NK cell immune synapses

In this study, we report the organization of cytoskeletal and large transmembrane proteins at the inhibitory and activating NK cell immunological or immune synapse (IS). Filamentous actin accumulates at the activating, but not the inhibitory, NK cell IS. However, surprisingly, ezrin and the associated protein CD43 are excluded from the inhibitory, but not the activating, NK cell IS. This distribution of ezrin and CD43 at the inhibitory NK cell IS is similar to that previously seen at the activating T cell IS. CD45 is also excluded from the inhibitory, but not activating, NK cell IS. In addition, electron microscopy reveals wide and narrow domains across the synaptic cleft. Target cell HLA-C, located by immunogold labeling, clusters where the synaptic cleft spans the size of HLA-C bound to the inhibitory killer Ig-like receptor. These data are consistent with assembly of the NK cell IS involving a combination of cytoskeletal-driven mechanisms and thermodynamics favoring the organization of receptor/ligand pairs according to the size of their extracellular domains.     

Food web stability: the influence of trophic flows across habitats

In nature, fluxes across habitats often bring both nutrient and energetic resources into areas of low productivity from areas of higher productivity. These inputs can alter consumption rates of consumer and predator species in the recipient food webs, thereby influencing food web stability. Starting from a well-studied tritrophic food chain model, we investigated the impact of allochthonous inputs on the stability of a simple food web model. We considered the effects of allochthonous inputs on stability of the model using four sets of biologically plausible parameters that represent different dynamical outcomes. We found that low levels of allochthonous inputs stabilize food web dynamics when species preferentially feed on the autochthonous sources, while either increasing the input level or changing the feeding preference to favor allochthonous inputs, or both, led to a decoupling of the food chain that could result in the loss of one or all species. We argue that allochthonous inputs are important sources of productivity in many food webs and their influence needs to be studied further. This is especially important in the various systems, such as caves, headwater streams, and some small marine islands, in which more energy enters the food web from allochthonous inputs than from autochthonous inputs.     

Trophic cascades and trophic trickles in pelagic food webs

Prey-dependent models, with the predation rate (per predator) a function of prey numbers alone, predict the existence of a trophic cascade. In a trophic cascade, the addition of a top predator to a two-level food chain to make a three-level food chain will lead to increases in the population size of the primary producers, and the addition of nutrients to three-level chains will lead to increases in the population numbers at only the first and third trophic levels. In contrast, ratio-dependent models, with the predation rate (per predator) dependent on the ratio of predator numbers to prey, predict that additions of top predators will not increase the population sizes of the primary producers, and that the addition of nutrients to a three-level food chain will lead to increases in population numbers at all trophic levels. Surprisingly, recent meta-analyses show that freshwater pelagic food web patterns match neither prey-dependent models (in pelagic webs, ''prey'' are phytoplankton, and ''predators'' are zooplankton), nor ratio-dependent models. In this paper we use a modification of the prey-dependent model, incorporating strong interference within the zooplankton trophic level, that does yield patterns matching those found in nature. This zooplankton interference model corresponds to a more reticulate food web than in the linear, prey-dependent model, which lacks zooplankton interference. We thus reconcile data with a new model, and make the testable prediction that the strength of trophic cascades will depend on the degree of heterogeneity in the zooplankton level of the food chain.     

Australian genetics: A brief history

Although Australia has a productive history in plant and animal breeding, fundamental genetics was late in becoming established. Before the 1950s there was no separate department of genetics in any university in the country. Reasons for the delay include geographical isolation, Australian and British colonial science policy, and the lack of a critical mass of researchers. Through the efforts of Ian Clunies Ross and the CSIR several prominent scientists were induced to come from overseas to set up the framework for an Australian-based genetics community. Since that time fundamental genetics in Australia has flourished with high quality graduates in genetics being produced at a number of universities, and many local research programs being initiated. This period has seen the gradual internationalisation of Australian genetics and increased collaboration with overseas researchers taking place. This paper provides an historical overview of the origins and progress of genetics in Australia beginning with plant breeding in the first decades of this century to the present era of molecular genetics. Significant personalities, institutions, policies, reports and publications are discussed in order to make sense of the current structures.     

A Novel Hydroxyproline-Deficient Arabinogalactan Protein Secreted by Suspension-Cultured Cells of Daucus carota (Purification and Partial Characterization)

Arabinogalactan proteins (AGPs) are secreted or membrane-associated glycoproteins that have been operationally defined as binding to [beta]-glucosyl Yariv artificial antigen, being rich in arabinose and galactose, and containing high levels of alanine, serine, and hydroxyproline. Using an anti-AGP monoclonal antibody (MAC 207) bound to cyanogen bromide-activated Sepharose 4B, we have purified by immunoaffinity chromatography an extracellular AGP from the culture medium of suspension-cultured cells of carrot (Daucus carota). The apparent molecular mass of this highly glycosylated proteoglycan is 70 to 100 kD as judged by sodium dodecyl sulfate-polyacrylamide gels. Although its sugar analysis, [beta]-glucosyl Yariv binding, and high alanine, serine, and proline content are consistent with it being an AGP, the amino acid composition unexpectedly revealed this molecule to have no detectable hydroxyproline. This suggests that this glycoprotein is not a "classical" AGP, but represents the first example of a new class of hydroxyproline-poor AGPs. Deglycosylation of the AGP with anhydrous hydrogen fluoride revealed that the purified proteoglycan contains probably a single core protein with an apparent molecular mass of 30 kD. Direct visualization of the native AGP in the electron microscope showed ellipsoidal putative AGP monomers, approximately 25 nm by 15 nm, that showed a strong tendency to self assemble into higher-order structures. Upon desiccation, the glycosylated AGP formed paracrystalline arrays visible in the light microscope. Polarized Fourier transform infrared microspectroscopy of these arrays demonstrated a high degree of polarization of the sugar moieties under these conditions. These results put possible constraints on current models of AGP structure; a putative role for these novel AGPs as pectin-binding proteins is discussed.     

Simultaneous loss of multiple differentiated functions in aerial mycelium-negative isolates of streptomycetes.

Germination and outgrowth of spores of Streptomyces alboniger, Streptomyces scabies, and Streptomyces violaceus-ruber in the presence of intercalating dyes resulted in a high frequency (2 to 20%) of occurrence of aerial mycelium-negative (Amy-) isolates. Coincident with the appearance of the Amy- trait was the loss of several differentiated functions, including the characteristic pigments and earthy odor of the wild types. All S. alboniger, 27% of S. scabies, and 39% of the S. violaceus-ruber Amy- isolates were arginine auxotrophs. The missing enzyme step was identified as argininosuccinate synthetase by using a sensitive microassay for estimation of enzyme activity. The remainder of the S. scabies and S. violaceus-ruber isolates were prototrophs. In addition, S. alboniger Amy- isolates failed to produce or respond to the stimulator of aerial mycelium formation isolated from the wild type. The Amy- isolates did not revert to either Amy+ of Arg+. The lack of any detectable reversion, coupled with the high frequency of curing, supports the idea that a deletion of genetic material, possibly a plasmid, has occurred.     

Two distinct mechanisms for ornithine decarboxylase regulation by polyamines in rat hepatoma cells.

Exogenous diamines and polyamines added to rat hepatoma (HTC) cells in culture rapidly decrease ornithine decarboxylase (ODC) activity. Previous evidence has suggested that these amines set either at the level of blocking new enzyme synthesis or by the induction of a non-competitive protein inhibitor, termed antizyme, which complexes with ODC to form an inactive complex. Wth the use of HMOA cells, a recently cloned rat hepatoma cell line that has a greatly stabilized ODC, it has been possible to demonstrate that 10(-5) M of exogenous putrescine blocks the increase in ODC activity, but unlike in the parent HTC cell line, without induction of the antizyme or formation of any inactive ODC-antizyme complex. However, complete blockade of ODC at 10(-2) M putrescine is effected by induction of antizyme and formation of the ODC-antizyme complex, as now evidenced by the isolation of the active enzyme and antizyme components after Sephadex column chromatography in the presence of 250 mM NaCl. These findings indicate clearly that two polyamine-regulatory mechanisms for ODC exist and are separable in this cell line.     

Effects of a dopaminergic stimulant,amfonelic acid,on anterior pituitary hormone release in conscious rats

The response of plasma LH, Prolactin, GH and TSH levels to systematic administration of a specific central dopaminergic stimulant, amfonelic acid (AFA), by intravenous pulse injection in ovariectomized (OVX) and OVX estrogen-progesterone primed conscious rats has been evaluated. Intravenous injection of 0.2 mg/kg of AFA had no influence on plasma LH concentration until 60 min after injection when it was significantly elevated. Increasing the dose to 1 mg/kg reduced LH titers at 15 and 30 min with a return to preinjection levels by 60 min. AFA produced a dose-dependent decrease in plasma prolactin levels; the decrease occurred as early as 5 min after injection. AFA, both at 0.2 and 1 mg/kg doses, was effective in producing a sharp, dose-related rise in plasma GH levels. By contrast, TSH levels were significantly suppressed by both doses of AFA. Injection of the 1 mg/kg dose of AFA did not modify plasma LH levels in OVX-steroid-primed animals, white producing a comparable effect on plasma prolactin, GH and TSH levels to that observed in OVX animals. The present results indicate that endogenously released DA can have profound effects on pituitary hormone release, inhibiting PRL and TSH discharge, stimulating GH release and either inhibiting or stimulating LH release.