Cytochemistry and freeze-fracture of membranes isolated from the electrocyte of Electrophorus electricus (L.)

Summary Membranes were isolated from the main electric organ of Electrophorus electricus and studied by means of cytochemistry and freezefracture. The membrane fractions consisted of vesicles inside-in as determined by localization of anionic sites using colloidal iron and cationized ferritin particles. The anionic sites were not homogeneously distributed on the surface of the vesicle. Freeze-fracture showed the presence of intramembranous particles associated with either protoplasmic (P) or extracellular (E) faces of the membrane. Regions of the membrane without particles were observed. The results are discussed in relation to the existence of association between intramembranous particles and membrane receptors.For all correspondence     

An improved method for staining cells of the endocrine polypeptide (APUD) series by masked metachromasia: application of the principle of ''fixation by excluded volume''.

Synopsis Masked metachromasia is demonstrated by staining with a metachromatic basic dye, after acid hydrolysis of suitably fixed tissue. We report that the addition of 20% Carbowax 20M (an inert polymer, mol. wt. about 20000) to the hydrolysis mixture improved the reaction. The improved method gives increased metachromasia, greater tolerance to variations in hydrolysis conditions, and demonstrates a greater proportion of cells — presumably due to a lower threshold of sensitivity. Lower molecular weight polymers (Carbowax 1000, Carbowax 6000) are less effective.     

Different root strategies of perennial native grasses under two contrasting water availability conditions: implications for their spatial distribution in desert dunes

Plant Ecology - The distribution pattern of perennial native grasses in the dune systems of the Monte desert might be determined by the ability of plant roots to acquire water under drought...     

Effect of competition intensity on recruitment of palatable and unpalatable grasses

In this study, we made an attempt to reveal how competition intensity from established plants impacts on palatable and unpalatable grass seedlings recruitment, in a natural mesic grassland of central Argentina. Our objective was to assess the seedling recruitment of a palatable species (Chascolytrum subaristatum) and an unpalatable species (Nassella trichotoma) in microsites differing in competition intensity from established plants. Identity (C. subaristatum and N. trichotoma) and defoliation severity were used as surrogate for competition intensity. In March 2017, we permanently marked established individuals of N. trichotoma and C. subaristatum and placed two circular plots adjacent to each individual. In one plot we added seeds of N. trichotoma and in the other seeds of C. subaristatum. After seeding, established plants were randomly assigned to one of three level of defoliation: without defoliation, low defoliation severity and high defoliation severity. From April to November 2017 (i.e. over a complete annual growing cycle), we measured seedling density, recruitment and growth. Our results supported the hypothesis that seedlings of palatable grasses are more competitive than seedlings of unpalatable grasses. Seedling of the palatable grass C. subaristatum recruited successfully regardless the intensity of competition from established plants, whereas seedlings of the unpalatable grass N. trichotoma recruited better under low competitive pressure from established plants. Our results suggest that the availability of microsites with low competitive pressure from the established vegetation, created by selective grazing of palatable grasses, promotes the recruitment of unpalatable grass seedlings. This mechanism may contribute to the species replacement process commonly observed in heavy grazed grasslands.     

A genomic island in Brucella involved in the adhesion to host cells: Identification of a new adhesin and a translocation factor

Adhesion to host cells is the first step in the virulence cycle of any pathogen. In Gram‐negative bacteria, adhesion is mediated, among other virulence factors such as the lipopolysaccharides, by specific outer‐membrane proteins generally termed adhesins that belong to a wide variety of families and have different evolutionary origins. In Brucella, a widespread zoonotic pathogen of animal and human health concern, adhesion is central as it may determine the intracellular fate of the bacterium, an essential stage in its pathogenesis. In the present paper, we further characterised a genomic locus that we have previously reported encodes an adhesin (BigA) with a bacterial immunoglobulin‐like domain (BIg‐like). We found that this region encodes a second adhesin, which we have named BigB; and PalA, a periplasmic protein necessary for the proper display in the outer membrane of BigA and BigB. Deletion of bigB or palA diminishes the adhesion of the bacterium and overexpression of BigB dramatically increases it. Incubation of cells with the recombinant BIg‐like domain of BigB induced important cytoskeletal rearrangements and affected the focal adhesion sites indicating that the adhesin targets cell–cell or cell–matrix proteins. We additionally show that PalA has a periplasmic localisation and is completely necessary for the proper display of BigA and BigB, probably avoiding their aggregation and facilitating their transport to the outer membrane. Our results indicate that this genomic island is entirely devoted to the adhesion of Brucella to host cells.     

Colony aging affects the reproductive performance of Swiss Webster females used as recipients for embryo transfer

The objective was to evaluate the influence of colony aging in a Swiss Webster (SW) outbred stock used as recipients for embryo transfer. In the first study, a retrospective analysis was performed throughout several generations during a 38-month period in 2,398 embryos transferred to 108 SW recipients. A decrease in the percentage of live pups from transferred embryos was found at the end of the period. Impairment occurred due to the incidence of maternal cannibalism that increased from 0% to 67-100% (P<0.05), while pregnancy rate (pregnant/transferred recipients) and number of pups per delivered female were not affected throughout the period (P=NS). A following study was carried out to compare the reproductive performance of SW stock vs. B6D2F1 hybrid females in a 5-year interval. The study was conducted on a total of 893 embryos transferred to 40 females (20 SW and 20 B6D2F1) in Year #1, and 514 embryos transferred to 30 females (15 SW and 15 B6D2F1) in Year #5. No cases of maternal cannibalism were found on Year #1 in any of the strains (0/10 and 0/10). However, an incidence of 44,4% (4/9) was seen on Year #5 for SW, while for B6D2F1 the incidence was 0% (0/12) (P<0.05). Further examination of the uterus showed endometrial cysts and abnormal implantation sites in SW on Year #5 but not in B6D2F1 females. In conclusion, this study reports an impairment of the reproductive performance of an early aged SW outbred stock colony mainly due to the occurrence of maternal cannibalism. This finding has important implications for embryo transfer programs conducted in mouse facilities.     

An early representation of a gorilla from fifteenth-century Central Asia

Primates - The present work describes the earliest known image of a gorilla (Gorilla sp.) to appear outside Africa. This is found in an Asian miniature painted on silk from the second half of the...     

Development of a multi-excitation fluorescence (MEF) imaging method to improve the information content of benthic coral reef surveys

Benthic surveys are a key component of monitoring and conservation efforts for coral reefs worldwide. While traditional image-based surveys rely on manual annotation of photographs to characterise benthic composition, automatic image annotation based on computer vision is becoming increasingly common. However, accurate classification of some benthic groups from reflectance images presents a challenge to local ecologists and computers alike. Most coral reef organisms produce one or a combination of fluorescent pigments, such as Green Fluorescent Protein (GFP)-like proteins found in corals, chlorophyll-a found in all photosynthetic organisms, and phycobiliproteins found in red macroalgae, crustose coralline algae (CCA) and cyanobacteria. Building on the potential of these pigments as a target for automatic image annotation, we developed a novel imaging method based on off-the-shelf components to improve classification of coral and other biotic substrates using a multi-excitation fluorescence (MEF) imaging system. We used RGB cameras to image the fluorescence emission of coral and algal pigments stimulated by narrow-waveband blue and green light, and then combined the information into three-channel pseudocolour images. Using a set of a priori rules defined by the relative pixel intensity produced in different channels, the method achieved successful classification of organisms into three categories based on the dominant fluorescent pigment expressed, facilitating discrimination of traditionally problematic groups. This work provides a conceptual foundation for future technological developments that will improve the cost, accuracy and speed of coral reef surveys.