Organelle evolution: Paulinella breaks a paradigm

It is commonly assumed that transformations of endosymbionts into organelles are exceptionally rare evolutionary events because of hypothetical difficulties in the origin of an import apparatus for nuclear-encoded, organelle-targeted proteins along with their targeting signals. A challenge to this view comes from recent studies of protein import into the cyanobacterial endosymbionts/organelles of Paulinella chromatophora.     

Paracellular absorption in laboratory mice: Molecule size-dependent but low capacity

Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems lower in nonfliers than in fliers, although that conclusion rests largely on a comparison of relatively larger nonflying mammals (> 155 g) and relatively smaller flying birds (< 155 g). We report on paracellular absorption in laboratory mice, the smallest nonflying mammal species studied to date. Using a standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption = f) of inert carbohydrate probes: l-arabinose (M_r = 150.13 Da) and cellobiose (342.3) that are absorbed exclusively by the paracellular route, and 3-O-methyl d-glucose (3OMD-glucose) (M_r = 194) absorbed both paracellularly and transcellularly. f was measured accurately in urine collection trials of 5–10 h duration. Absorption of 3OMD-glucose by mice was essentially complete (f = 0.95 ± 0.07) and much higher than that for l-arabinose (f = 0.21 ± 0.02), indicating that in mice, like other nonflying mammals, > 80% of glucose is absorbed by mediated process(es) rather than the passive, paracellular route. As in all other vertebrates, absorption of cellobiose (f = 0.13 ± 0.02) was even lower than that for l-arabinose, suggesting an equivalent molecular size cut-off for flying and nonflying animals and thus a comparable effective TJ aperture. An important ecological implication is that smaller water-soluble plant secondary metabolites that have been shown to be absorbed by the paracellular path in cell culture, such as phenolics and alkaloids, might be absorbed in substantial amounts by bats and small birds relative to nonflying mammals such as mice.     

Paracellular nutrient absorption in a gum-feeding new world primate, the common marmoset Callithrix jacchus

The common marmoset is one of the few callitrichid species that is not threatened or endangered in the wild, and is widely used in biomedical research, yet relatively little is understood about its digestive physiology. Dietary specialization on plant exudates has lead to relatively reduced small intestines, yet the common marmoset has exceptional dietary breadth, allowing it to successfully utilize a variety of habitats. We predicted that passive, paracellular nutrient absorption would be used by the common marmoset to a greater extent than in other non-flying mammals. We measured the bioavailability and rates of absorption of two metabolically inert carbohydrates not transported by mediated pathways (L-rhamnose and cellobiose, molecular masses of 164 and 342, respectively) to measure paracellular uptake, and of a non-metabolized D-glucose analog (3-O-methyl-D-glucose) to measure total uptake by both mediated and paracellular pathways. We found high bioavailability of 3-O-methyl-D-glucose (83+/-5%), and much higher bioavailability of the paracellular probes than in similarly sized non-flying mammals (30+/-3% and 19+/-2% for L-rhamnose and cellobiose, respectively). Passive, paracellular nutrient absorption accounts for around 30% of total glucose absorption in common marmosets and intestinal permeability is significantly higher than in humans, the only other species of primate measured to date. This may allow the common marmoset to maintain high digestive efficiency when feeding on higher quality foods (fruit, arthropods, gums with higher proportions of simple sugars), in spite of relatively reduced small intestines correlated with adaptations for fermentative digestion of plant gums. We find no evidence to support, in primates, the hypothesis that reliance on paracellular nutrient absorption should increase with body size in mammals, but suggest instead that it may be associated with small body size and/or taxon-specific adaptations to diet.     

Paracellular absorption of D-glucose by rat small intestine in vivo

D-glucose diffusion in both jejunum and ileum using a perfusion system in vivo was determined. 2,4,6-triaminopyrimidine (20 mM) induced an inhibition on D-glucose diffusion of 32% in the two segments of the small intestine studied. Glucose net efflux from the jejunum into the lumen was higher than that from the ileum. Phlorizin increased the sugar efflux in both areas.     

Thermoregulation in the Angolan free-tailed bat Mops condylurus: A small mammal that uses hot roosts.

The Angolan free-tailed bat (Mops condylurus) uses roosts that often exceed 40 degrees C, an ambient temperature (Ta) that is lethal to many microchiropterans. We measured the physiological responses of this species at Ta's from 15 degrees to 45 degrees C. Torpor was commonly employed during the day at the lower Ta, but the bats generally remained euthermic at night, with a mean body temperature (Tb) of 35.2 degrees C. Metabolic rate reflected the pattern of Tb, increasing with falling Ta at night but decreasing during the day. Metabolic rate and evaporative losses were lower in torpid than in euthermic bats. Body temperature increased at each Ta >35 degrees C and was 43 degrees C at Ta of 45 degrees C. At Ta of 40 degrees C bats increased dry thermal conductance and evaporative heat loss compared to lower Ta. At 45 degrees C dry thermal conductance was lower than at 40 degrees C and evaporative heat loss was 132% of metabolic heat production. At high Ta there was only a slight increase in metabolic rate despite the employment of evaporative cooling mechanisms and an increase in Tb. Collectively our results suggest that M. condylurus is well suited to tolerate high Ta, and this may enable it to exploit thermally challenging roost sites and to colonise habitats and exploit food sources where less stressful roosts are limiting.     

The capacity for paracellular absorption in the insectivorous bat Tadarida brasiliensis

Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems greater in fliers than in nonfliers, although that conclusion rests mainly on a comparison of flying birds and nonflying mammals because only two frugivorous bat species have been studied. Furthermore, the bats studied so far were relatively large (>85 g, compared with most bat species which are <20 g) and were not insectivores (like about 70 % of bat species). We studied the small (11 g) insectivorous bat Tadarida brasiliensis and tested the prediction that the capacity for paracellular absorption would be as high as in the other bat and avian species studied so far, well above that in terrestrial, nonflying mammals. Using standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption = f) of inert carbohydrate probes: L-arabinose (MM = 150.13) absorbed exclusively by paracellular route and 3OMD-glucose (MM = 194) absorbed both paracellularly and transcellularly. As predicted, the capacity of paracellular absorption in this insectivorous bat was high (L-arabinose f = 1.03 ± 0.14) as in other frugivorous bats and small birds. Absorption of 3OMD-glucose was also complete (f = 1.09 ± 0.17), but >80 % was accounted for by paracellular absorption. We conclude that passive paracellular absorption of molecules of the size of amino acids and glucose is extensive in this bat and, generally in bats, significantly higher than that in nonflying mammals, although the exact extent can be somewhat lower or higher depending on molecule size, polarity and charge.     

Curiosity killed the bat: Domestic cats as bat predators

Domestic cats are suspected to have an impact on wild populations of birds and small mammals, but published reports of predation on bats are either rare or anecdotal. We based our study on 1012 records of bats admitted at four wildlife rescue centres in peninsular Italy in 2009–2011. We hypothesized that (1) cats prevalently prey on bats emerging from roosts, so newborns or non volant juveniles should be less exposed to predation; (2) because cats occur in human settlements, the bat species most frequently involved are house-roosting (3) predation is season-biased, most events being more likely to take place in summer when females congregate in roosts to reproduce; (4) predation events concentrate in sparse-urban and rural areas, where free-ranging cats occur more frequently; and (5) some individual cats may specialize in capturing bats. We found that predation by cats was the first cause of rescue for bats in the study area, accounting for 28.7% of records of adult bats admitted to rehabilitation centres. Although most bats caught by cats belonged to house-roosting species, at least 3 of the 11 species affected were tree- or cave-roosting. Predation affected more frequently adult females in summer and thus threatened reproductive colonies, which were often subjected to repeated predations. As predicted, predation events were associated with land cover, being more abundant in rural and sparse urban areas, where cats are more often allowed to stay outdoor, as confirmed by the results of a cat owner survey we carried out. Cats are explorative mammals, so they may be easily attracted at bat roosts by sensory cues involving sound, smell and vision. Our analysis covered a broad geographical area over a relatively long period and suggests that the threat posed to bats by cats may be significant and should be carefully considered in conservation plans. Strategies to mitigate this impact should encompass the control of feral cat populations and indoor restriction of owned cats at least where predation on bats is probable.     

In situ feeding tactics of short-nosed fruit bat (Cynopterus sphinx) on mango fruits: evidence of extractive foraging in a flying mammal

We report a sequence of behaviors exhibited by the short-nosed fruit bat Cynopterus sphinx while feeding on fruits of Mangifera indica. They peel off the outer skin to form a feeding area of about 3–6 cm diameter. Such food preparatory behaviors were more pronounced on larger mangoes. Bats competed among themselves to feed on the mangoes that had such feeding areas exposed. Individuals that spent a considerable amount of time on food preparatory behaviors actively secured the fruits. Altogether, these behaviors indicate that Cynopterus bats might have learnt, over evolutionary time, and developed behaviors that facilitate efficient processing and feeding of fruits such as mangoes. It appears that actions exhibited by C. sphinx in peeling off the outer skin of mangoes exemplify “extractive foraging”, a behavior that is prominently known in large-brained mammals. Thus, our findings will have implications on the distribution and evolution of extractive foraging and “technical intelligence” among mammalian lineages.     

Paracellular ion channel at the tight junction

The tight junction of epithelial cells excludes macromolecules but allows permeation of ions. However, it is not clear whether this ion-conducting property is mediated by aqueous pores or by ion channels. To investigate the permeability properties of the tight junction, we have developed paracellular ion flux assays for four major extracellular ions, Na(+), Cl(-), Ca(2+), and Mg(2+). We found that the tight junction shares biophysical properties with conventional ion channels, including size and charge selectivity, dependency of permeability on ion concentration, competition between permeant molecules, anomalous mole-fraction effects, and sensitivity to pH. Our results support the hypothesis that discrete ion channels are present at the tight junction. Unlike conventional ion channels, which mediate ion transport across lipid bilayers, the tight junction channels must orient parallel to the plane of the plasma membranes to support paracellular ion movements. This new class of paracellular-tight junction channels (PTJC) facilitates the transport of ions between separate extracellular compartments.     

Proteomics: a paradigm shift

Proteome--the protein complement of a genome--has become the protein renaissance and a key research tool in the post-genomic era. The basic technology involves the routine usage of gel electrophoresis and spectrometry procedures for deciphering the primary protein sequence/structure as well as knowing certain unique post-translational modifications that a particular protein has undergone to perform a specific function in the cell. However, the recent advancements in protein analysis have ushered this science to provide deeper, bigger and more valuable perspectives regarding performance of subtle protein-protein interactions. Applications of this branch of molecular biology are as vast as the subject is and include clinical diagnostics, pharmaceutical and biotechnological industries. The 21st century hails the use of products, procedures and advancements of this science as finer touches required for the grooming of fast-paced technology.     

Holocene mammal extinctions in the Carpathian Basin: a review

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Chew-track-cards: a multiple-species small mammal detection device

New Zealand's protected natural areas are being increasingly threatened by weeds as the natural landscape is fragmented and surrounding land use intensifies. To assist in designing management to reduce the threat, we attempted to determine the most important reserve characteristics influencing the presence of problem weeds in forest and scrub reserves. Data on 15 reserve characteristics were derived from surveys of 234 reserves. From correlation analysis, analysis of variance and consideration of several multivariate models, it appears that the most important characteristics influencing the number of problem weeds in reserves are proximity to towns, distance from roads and railway lines, human use, reserve shape, and habitat diversity. These factors reflect principally increased proximity to source of propagules associated with intensifying land use, including urbanisation. Reserves with the most weeds are narrow remnants on fertile soils with clearings and a history of modification, and those close to towns or sites of high human activity. If these reserves are to continue to protect natural values, they will require regular attention to prevent the establishment of further weeds. Accidental spread of weeds and disturbance in reserves should be minimised.     

cGAMP：一种新的哺乳动物第二信使

在细菌中已发现多种环二核苷酸如c-di-GMP、c-di-AMP和cGAMP等可作第二信使,但在哺乳动物中一直未鉴定成功。最新研究发现cGAMP在哺乳动物天然免疫信号通路中也发挥着第二信使作用。在DNA结合条件下cGAMP可由cGAMP合成酶（cGAS）催化生成,随后结合干扰素基因激活蛋白（STING）而诱导Ⅰ型干扰素依赖的天然免疫。这些研究为天然免疫信号通路提供了新的视野,有益于免疫治疗药物的开发。     

Specific local induction of DNA strand breaks by infrared multi-photon absorption

Highly confined DNA damage by femtosecond laser irradiation currently arises as a powerful tool to understand DNA repair in live cells as a function of space and time. However, the specificity with respect to damage type is limited. Here, we present an irradiation procedure based on a widely tunable Er/Yb : fiber femtosecond laser source that favors the formation of DNA strand breaks over that of UV photoproducts by more than one order of magnitude. We explain this selectivity with the different power dependence of the reactions generating strand breaks, mainly involving reactive radical intermediates, and the direct photochemical process leading to UV-photoproducts. Thus, localized multi-photon excitation with a wavelength longer than 1 µm allows for the selective production of DNA strand breaks at sub-micrometer spatial resolution in the absence of photosensitizers.     

Dead reckoning in a small mammal: the evaluation of distance

When hoarding food under infra-red light, golden hamsters Mesocricetus auratus W. return fairly directly from a feeding place to their nest site by evaluating and updating internal signals that they have generated during the previous outward journey to the feeding place. To test more specifically the animals' capacity to evaluate the linear components of the outward journey, the subjects were led from their (cone-shaped) nest to a feeding place along a detour which comprised either 2 (experiment 1) or 5 (experiment 2) segments; adjoining segments were at right angles to each other. In these conditions, the subjects remained significantly oriented towards the nest and therefore were capable of assessing translations as well as rotations during the outward journey. In experiment 3, the nest was removed after the hamsters had started the direct outward journey to the feeding place and the hamsters were rotated during the food uptake. The animals were no longer oriented towards the starting point of their journey, but nonetheless covered, along a fairly straight path, the correct homing distance, and then changed over to a circular search path. These results confirm that mammals can derive the linear components of an outward journey from self-generated signals and therefore are able to judge the homing distance without relying on cues from the environment. For a number of detour outward journeys, our data yield an unexpectedly good fit to Müller and Wehner's (1988) model of dead reckoning in ants. However, this is no longer the case when the outward journey contains an initial loop which brings the subject back to the starting point. These findings are discussed in terms of the biological significance and limitations of an approximate form of path integration.     

Paracellular pathway in the shell epithelium of Anodonta cygnea

Ultrastructural study of cell-cell connections in the outer mantle epithelium (OME) on high-pressure-frozen specimens revealed zonula adherens, septate junctions and gap junctions in Anodonta cygnea. In order to evaluate the permeability of the paracellular pathway, the OME was incubated under gradients of lanthanum and calcium. After lanthanum incubation (4 mM) from the basal side, the septate junctions were penetrated completely by this tracer. When applied from the apical side, lanthanum deposits were located similarly over the entire length of the septate junctions up to the first dilatations of the intercellular space. Calcium deposits were also present in paracellular areas only when OME had been incubated simultaneously with calcium (6 mM) and lanthanum (4 mM) gradients. Lanthanum and calcium deposits were detected with ESI (Electron Spectroscopic Imaging) and identified with EELS (Electron Energy Loss Spectroscopy). On the other hand, electrophysiological observations showed a 48% reduction of conductance when the OME was bathed on both sides with solutions containing lanthanum (4 mM) and calcium (6 mM), compared to bathing with lanthanum-free solution (control). The conductance reduction was 52% when calcium was removed from the control solution. Supported by morphological and physiological evidence, it appears that, under in vivo conditions, calcium ions may diffuse paracellularly from the haemolymph towards the extrapallial fluid and vice-versa across the septate junctions in the OME of A. cygnea. Permeability of the septate junctions depended proportionally on the calcium concentration in fluids.     

Caribbean ciguatera: a changing paradigm

Analyses of ciguatoxicity in the great barracuda Sphyraena barracuda and quantity of toxic benthic dinoflagellates on coastal reefs (correlated with the number of cases of human ciguatera intoxications in Puerto Rico) were used to construct a model formulated on data obtained during the period of 1985-1988. The validity of the proposed model has been questioned by recent data obtained during the period of 1990-2000. Barracuda ciguatoxicity no longer showed a prominent seasonality while the fraction of randomly caught barracuda that were ciguatoxic significantly increased during this period. These two changes, accompanied by the discovery that ciguatoxic fish contained a variety of multiple toxins, appear to be correlated with the steadily increasing periods of elevated sea surface temperatures in this region.     

Claudin-21 Has a Paracellular Channel Role at Tight Junctions

Claudin protein family members, of which there are at least 27 in humans and mice, polymerize to form tight junctions (TJs) between epithelial cells, in a tissue- and developmental stage-specific manner. Claudins have a paracellular barrier function. In addition, certain claudins function as paracellular channels for small ions and/or solutes by forming selective pores at the TJs, although the specific claudins involved and their functional mechanisms are still in question. Here we show for the first time that claudin-21, which is more highly expressed in the embryonic than the postnatal stages, acts as a paracellular channel for small cations, such as Na⁺, similar to the typical channel-type claudins claudin-2 and -15. Claudin-21 also allows the paracellular passage of larger solutes. Our findings suggest that claudin-21-based TJs allow the passage of small and larger solutes by both paracellular channel-based and some additional mechanisms.