Measurement of DNA and antigen expression of live cells using three fluorochromes and two detectors.

In a multiparameter flow cytometric study, the fluorescence from the two different dyes fluorescein and dansyl-lysine were detected in the same spectral interval on the same photomultiplier tube, using two lasers to excite the fluorochromes at two separate laser foci. The two signals were split by a T-cable at the output of the photomultiplier tube and synchronized by delaying the first signal. Dansyl-lysine binds to the membrane of heat-inactivated cells and was used to distinguish between live and dead cells after a hyperthermic treatment. By gating on the dansyl-lysine signal, the DNA distribution and surface antigen expression of live and dead cells were obtained separately, using Hoechst 33342 and a monoclonal antibody conjugated to fluorescein.     

Temporal variation in trophic relationships among three congeneric penguin species breeding in sympatry

Penguins are a monophyletic group in which many species are found breeding sympatrically, raising questions regarding how these species coexist successfully. Here, the isotopic niche of three sympatric pygoscelid penguin species was investigated at Powell Island, South Orkney Islands, during two breeding seasons (austral summers 2013–2014 and 2015–2016). Measurements of carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios were obtained from blood (adults) or feather (chicks) samples collected from Adélie Pygoscelis adeliae, chinstrap P. antarctica, and gentoo P. papua penguins. Isotopic niche regions (a proxy for the realized trophic niches) were computed to provide estimates of the trophic niche width of the studied species during the breeding season. The isotopic niche regions of adults of all three species were similar, but gentoo chicks had noticeably wider isotopic niches than the chicks of the other two species. Moderate to strong overlap in isotopic niche among species was found during each breeding season and for both age groups, suggesting that the potential for competition for shared food sources was similar during the two study years, although the actual level of competition could not be determined owing to the lack of data on resource abundance. Clear interannual shifts in isotopic niche were seen in all three species, though of lower amplitude for adult chinstrap penguins. These shifts were due to variation in carbon, but not nitrogen, isotopic ratios, which could indicate either a change in isotopic signature of their prey or a switch to an alternative food web. The main conclusions of this study are that (1) there is a partial overlap in the isotopic niches of these three congeneric species and that (2) they responded similarly to changes that likely occurred at the base of their food chain between the 2 years of the study.     

Scaling marine fish movement behavior from individuals to populations

Understanding how, where, and when animals move is a central problem in marine ecology and conservation. Key to improving our knowledge about what drives animal movement is the rising deployment of telemetry devices on a range of free‐roaming species. An increasingly popular way of gaining meaningful inference from an animal's recorded movements is the application of hidden Markov models (HMMs), which allow for the identification of latent behavioral states in the movement paths of individuals. However, the use of HMMs to explore the population‐level consequences of movement is often limited by model complexity and insufficient sample sizes. Here, we introduce an alternative approach to current practices and provide evidence of how the inclusion of prior information in model structure can simplify the application of HMMs to multiple animal movement paths with two clear benefits: (a) consistent state allocation and (b) increases in effective sample size. To demonstrate the utility of our approach, we apply HMMs and adapted HMMs to over 100 multivariate movement paths consisting of conditionally dependent daily horizontal and vertical movements in two species of demersal fish: Atlantic cod (Gadus morhua; n = 46) and European plaice (Pleuronectes platessa; n = 61). We identify latent states corresponding to two main underlying behaviors: resident and migrating. As our analysis considers a relatively large sample size and states are allocated consistently, we use collective model output to investigate state‐dependent spatiotemporal trends at the individual and population levels. In particular, we show how both species shift their movement behaviors on a seasonal basis and demonstrate population space use patterns that are consistent with previous individual‐level studies. Tagging studies are increasingly being used to inform stock assessment models, spatial management strategies, and monitoring of marine fish populations. Our approach provides a promising way of adding value to tagging studies because inferences about movement behavior can be gained from a larger proportion of datasets, making tagging studies more relevant to management and more cost‐effective.     

Tracking plant preference for higher‐quality mycorrhizal symbionts under varying CO2 conditions over multiple generations

The symbiosis between plants and root‐colonizing arbuscular mycorrhizal (AM) fungi is one of the most ecologically important examples of interspecific cooperation in the world. AM fungi provide benefits to plants; in return plants allocate carbon resources to fungi, preferentially allocating more resources to higher‐quality fungi. However, preferential allocations from plants to symbionts may vary with environmental context, particularly when resource availability affects the relative value of symbiotic services. We ask how differences in atmospheric CO₂‐levels influence root colonization dynamics between AMF species that differ in their quality as symbiotic partners. We find that with increasing CO₂‐conditions and over multiple plant generations, the more beneficial fungal species is able to achieve a relatively higher abundance. This suggests that increasing atmospheric carbon supply enables plants to more effectively allocate carbon to higher‐quality mutualists, and over time helps reduce lower‐quality AM abundance. Our results illustrate how environmental context may affect the extent to which organisms structure interactions with their mutualistic partners and have potential implications for mutualism stability and persistence under global change.     

Filamentous Aggregation of Sequestosome-1/p62 in Brain Neurons and Neuroepithelial Cells upon <Emphasis Type="Italic">Tyr-Cre</Emphasis>-Mediated Deletion of the Autophagy Gene <Emphasis Type="Italic">Atg7</Emphasis>

Defects in autophagy and the resulting deposition of protein aggregates have been implicated in aging and neurodegenerative diseases. While gene targeting in the mouse has facilitated the characterization of these processes in different types of neurons, potential roles of autophagy and accumulation of protein substrates in neuroepithelial cells have remained elusive. Here we report that Atg7^f/f Tyr-Cre mice, in which autophagy-related 7 (Atg7) is conditionally deleted under the control of the tyrosinase promoter, are a model for accumulations of the autophagy adapter and substrate sequestosome-1/p62 in both neuronal and neuroepithelial cells. In the brain of Atg7^f/f Tyr-Cre but not of fully autophagy competent control mice, p62 aggregates were present in sporadic neurons in the cortex and other brain regions as well in epithelial cells of the choroid plexus and the ependyma. Western blot analysis confirmed a dramatic increase of p62 abundance and formation of high-molecular weight species of p62 in the brain of Atg7^f/f Tyr-Cre mice relative to Atg7^f/f controls. Immuno-electron microscopy showed that p62 formed filamentous aggregates in neurons and ependymal cells. p62 aggregates were also highly abundant in the ciliary body in the eye. Atg7^f/f Tyr-Cre mice reached an age of more than 2 years although neurological defects manifesting in abnormal hindlimb clasping reflexes were evident in old mice. These results show that p62 filaments form in response to impaired autophagy in vivo and suggest that Atg7^f/f Tyr-Cre mice are a model useful to study the long-term effects of autophagy deficiency on the homeostasis of different neuroectoderm-derived cells.     

Determination of PS I oligomerisation in various cyanobacterial strains and mutants by non-invasive methods

Photosynthetica - PSI trimer to monomer ratio in intact cyanobacterial cells and isolated thylakoids was analysed by two noninvasive, in vivo methods; low-temperature fluorescence emission and...     

Patterns of association in the human metaphase complement: Ring analysis and estimation of associativity of specific chromosome regions

Summary The pattern of metaphase chromosome association in the human complement was studied by two methods of statistical analysis of interchromosomal distances. Those methods included ring analysis in which a characteristic position of the centromere of each chromosome relative to the center of a two-dimensional representation of a metaphase complement was defined, and estimation of the capacity for associativity of each of three regions of each chromosome: the centromere (c) and the ends of each arm (p,q).The following information was obtained: 1. In general, the distance from the center is directly related to chromosome size. 2. The most notable deviation from that size-related progression is displayed by the X chromosomes. The markedly peripheral position of the X is characteristic of both X's of the female and the single X of the male. 3. The relative associativity of each chromosome of the complement is, in general, inversely related to size with an additional preferential capacity of associativity displayed by the acrocentric chromosomes. Analyses of the different inter-regional classes established that the supplementary associativity factor of the acrocentric chromosomes was inherent in their pericentromeric and p-arm regions and excluded the ends of the q arms from participation in that factor. 4. Those analyses demonstrated that the specific morphology or geometry of the acrocentric chromosomes contributes little to their high relative associativity. In addition to the tendency for the c/p regions of the acrocentric chromosomes to associate with each other, presumably because of their common function in nucleolar organization, those regions also displayed a propensity to associate with the distal regions of the arms of other chromosomes. A molecular basis for that propensity other than that of ribosomal DNA is postulated to be that of other fractions of highly reiterated DNA sequences. 5. Analysis of the relative associativities of each of the three regions of the Y chromosome revealed that the Yq displays a much stronger capacity to associate with the c's of other chromosomes than does the Yc or Yp.     

NITRATE REDUCTASE MUTANTS IN EUDORINA ELEGANS (CHLOROPHYCEAE)1

Three nitrate reductase mutants were independently isolated and characterized in the colonial alga, Eudorina elegans Ehrenberg. nar-1 is a leaky mutant, deficient in the production of nitrate reductase. nar-2 and nar-3 both lack the ability to produce nitrate reductase. However, nar-2 grows and nar-3 does not grow when hypoxanthine is the sole nitrogen source. The specific activity of the next enzyme, in the pathway, nitrite reductase is increased in nar-3 when compared to wild-type, nar-1 and nar-2.     

Pore Formation by S. aureus α-toxin in Liposomes and Planar Lipid Bilayers: Effects of Nonelectrolytes

Nonelectrolytes such as polyethylene glycols (PEG) and dextrans (i) promote the association of S. aureus α-toxin with liposomes (shown by Coomassie staining) and (ii) enhance the rate and extent of calcein leakage from calcein-loaded liposomes; such leakage is inhibited by H⁺, Zn²⁺ and Ca²⁺ to the same extent as that of nonPEG-treated liposomes. Incubation of liposomes treated with α-toxin in the presence of PEG with the hydrophobic photo-affinity probe 3-(trifluoromethyl)-3-m-[¹²⁵I]iodophenyl)diazirine(¹²⁵I-TID) labels monomeric and—predominantly—hexameric forms of liposome-associated α-toxin; in the absence of PEG little labeling is apparent. At high concentrations of H⁺ and Zn²⁺ but not of Ca²⁺—all of which inhibit calcein leakage—the distribution of label between hexamer and monomer is perturbed in favor of the latter. In α-toxin-treated planar lipid bilayers from which excess toxin has been washed away, PEGs and dextrans strongly promote the appearance of ion-conducting pores. The properties of such pores are similar in most regards to pores induced in the absence of nonelectrolytes; they differ only in being more sensitive to ``closure' by voltage (as are pores induced in cells). In both systems, the stimulation by nonelectrolytes increases with concentration and with molecular mass up to a maximum around 2,000 Da. We conclude (i) that most of the α toxin that becomes associated with liposome or planar lipid bilayers does not form active pores and (ii) that the properties of α-toxin-induced pores in lipid bilayers can be modulated to resemble those in cells. Received: 2 October 1995/Revised: 3 November 1995