Expulsion of Symbiotic Algae during Feeding by the Green Hydra – a Mechanism for Regulating Symbiont Density?

Background

Algal-cnidarian symbiosis is one of the main factors contributing to the success of cnidarians, and is crucial for the maintenance of coral reefs. While loss of the symbionts (such as in coral bleaching) may cause the death of the cnidarian host, over-proliferation of the algae may also harm the host. Thus, there is a need for the host to regulate the population density of its symbionts. In the green hydra, Chlorohydra viridissima, the density of symbiotic algae may be controlled through host modulation of the algal cell cycle. Alternatively, Chlorohydra may actively expel their endosymbionts, although this phenomenon has only been observed under experimentally contrived stress conditions.

Principal Findings

We show, using light and electron microscopy, that Chlorohydra actively expel endosymbiotic algal cells during predatory feeding on Artemia. This expulsion occurs as part of the apocrine mode of secretion from the endodermal digestive cells, but may also occur via an independent exocytotic mechanism.

Significance

Our results demonstrate, for the first time, active expulsion of endosymbiotic algae from cnidarians under natural conditions. We suggest this phenomenon may represent a mechanism whereby cnidarians can expel excess symbiotic algae when an alternative form of nutrition is available in the form of prey.     

Endocytosis of G Protein-Coupled Receptors and Their Ligands: Is There a Role in Metal Trafficking?

The prevalence of metal dysregulation in many neurodegenerative and neurocognitive disorders has compelled many studying such diseases to investigate the mechanisms underlying metal regulation in the central nervous system. Metal homoeostasis is often complex, with sophisticated, multilayered pathways in operation. G protein-coupled receptors are omnipresent on cell membranes and have intriguing mechanisms of endocytosis and trafficking that may be useful in metal homoeostasis. Indeed, many receptors and/or their cognate ligands are able to bind metals, and in many cases metals are considered to have neuromodulatory roles as a result of receptor binding. In this mini-review, we outline the structural and functional aspects of G protein-coupled receptors with a focus on the mechanisms leading to endocytosis and cellular trafficking. We further highlight how this may help in the trafficking of metal ions, notably copper.     

Mechanism of Fe uptake by the leaf symplast: Is Fe inactivation in leaf a cause of Fe deficiency chlorosis?

The mechanism of iron (Fe) uptake from the leaf apoplast into leaf mesophyll cells was studied to evaluate the putative Fe inactivation as a possible cause of Fe deficiency chlorosis. For this purpose, sunflower (Helianthus annuus L.) and faba bean plants (Vicia faba L.) were precultured with varied Fe and bicarbonate (HCO ₃ ^- ) supply in nutrient solution. After 2–3 weeks preculture, Fe^III reduction and ⁵⁹Fe uptake by leaf discs were measured in solutions with Fe supplied as citrate or synthetic chelates in darkness. The data clearly indicate that Fe^III reduction is a prerequisite for Fe uptake into leaf cells and that the Fe nutritional status of plants does not affect either process. In addition, varied supply of Fe and HCO ₃ ^- to the root medium during preculture had no effect on pH of the xylem sap and leaf apoplastic fluid. A varied pH of the incubation solution had no significant effect on Fe^III reduction and Fe uptake by leaf discs in the physiologically relevant pH range of 5.0–6.0 as measured in the apoplastic leaf fluid. It is concluded that Fe inactivation in the leaf apoplast is not a primary cause of Fe deficiency chlorosis induced by bicarbonate. This revised version was published online in June 2006 with corrections to the Cover Date.     

The regulation of CD47-SIRPα signaling axis by microRNAs in combination with conventional cytotoxic drugs together with the help of nano-delivery: a choice for therapy?

Molecular Biology Reports - CD47, a member of the immunoglobulin superfamily, is an important “Don’t Eat-Me” signal in phagocytosis process [clearance of apoptotic cells] as well...     

The formation of symplasmic domains by plugging of plasmodesmata: a general event in plant morphogenesis?

Summary The plasmodesmal network was examined in multicellular protoplast-derived calluses of the dicotyledonSolanum nigrum which had not yet formed any visible adventitious organs and in globular proembryogenic structures developed from scutellar calluses of the monocotyledonMolinia caerulea. Electron microscopical analyses revealed that both calluses and proembryos consisted of small, undifferentiated cells. The interconnecting plasmodesmata at many cell interfaces were structurally inconspicuous in both systems; in particular cell walls, however, all plasmodesmata were occluded with an osmiophilic, dense material. As the blocking material was obviously located in the microchannels of the plasmodesmal cytoplasmic sleeves, the plugged plasmodesmata can be assumed to be nonfunctional. Thus, selective occlusion of all the plasmodesmata in specific cell walls resulted in the symplasmic disconnection of particular adjacent cells. Complex patterns of symplasmic continuity and discontinuity were established within the developing tissues. Some cells or groups of cells were entirely symplasmically disconnected from the surrounding cells by plugged plasmodesmata and might function as independent domains. However, blockage of plasmodesmata was achieved by the surrounding cells rather than by those cells belonging to the isolated domains. The demarcation of symplasmic domains might be a general prerequisite for differential morphogenesis, since they were found to be established very early in the course of morphogenetic processes.     

The scaling of colony size with nest volume in termites: a role in population dynamics?

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Similar Endothelial Glycocalyx Structures in Microvessels from a Range of Mammalian Tissues: Evidence for a Common Filtering Mechanism?

The glycocalyx or endocapillary layer on the luminal surface of microvessels has a major role in the exclusion of macromolecules from the underlying endothelial cells. Current structural evidence in the capillaries of frog mesentery indicates a regularity in the structure of the glycocalyx, with a center-to-center fiber spacing of 20 nm and a fiber width of 12 nm, which might explain the observed macromolecular filtering properties. In this study, we used electron micrographs of tissues prepared using perfusion fixation and tannic acid treatment. The digitized images were analyzed using autocorrelation to find common spacings and to establish whether similar structures, hence mechanisms, are present in the microvessel glycocalyces of a variety of mammalian tissues. Continuous glycocalyx layers in mammalian microvessels of choroid, renal tubules, glomerulus, and psoas muscle all showed similar lateral spacings at ∼19.5 nm (possibly in a quasitetragonal lattice) and longer spacings above 100 nm. Individual glycocalyx tufts above fenestrations in the first three of these tissues and also in stomach fundus and jejunum showed evidence for similar short-range structural regularity, but with more disorder. The fiber diameter was estimated as 18.8 (± 0.2) nm, but we believe this is an overestimate because of the staining method used. The implications of these findings are discussed.     

The roots of Evo-Devo in Russia: Is there a characteristic “Russian Tradition”?

This paper raises the general question of whether there are any national peculiarities that characterize the scientific and philosophical roots of Russian-language evolutionary developmental biology. The researchers and theories are surveyed which, with hindsight, have been crucial for the Russian tradition when it comes to general methodological principles and constituting concepts. Based on published works and archival documents the main concepts of the “founding fathers” of the Russian tradition with their “Western analogues” are compared. The focus is on A. O. Kowalevsky (1840–1901), I. I. Metschnikov (1945–1916), A. N. Sewertzoff (1866–1936), I. I. Schmalhausen (1884–1963) and the parallelisms between them and E. Haeckel (1834–1919), V. Franz (1883–1950), and C. H. Waddington (1905–1977). In addition, the problem of specific influences constituting the Russian-language context of the Modern Synthesis is addressed. The major thesis of this paper is that the very character of the Russian developmental biology and its intellectual environment predisposed a strong bias towards environmentalist interpretations and thus anticipated what we now call “ecological developmental biology”. This paper is an extended version of my talk delivered to the First and founding meeting of the European Society for Evolutionary Developmental Biology (EDD), 16–19 August (Prague, Czech Republic). I thank Scott Gilbert for inviting me to this meeting

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The exploratory behaviour of rats in the hole-board apparatus: Is head-dipping a valid measure of neophilia?

The exploratory behaviour of laboratory rodents is of interest within a number of areas of behavioural pharmacology. However, how best to measure exploratory behaviour in rodents remains a contentious issue. Many unconditioned tests, such as the open field, potentially confound general locomotor activity with exploration. The hole-board apparatus appears to avoid this confound, as head-dipping into holes in the floor is assumed to be a valid measure of the subject's attraction towards novelty (neophilia). This study aimed to investigate whether head-dipping should be considered a valid measure of neophilia by comparing performance of adult male and female Lister hooded rats on the hole-board task (a) over repeated sessions and (b) when novel objects were absent or present underneath the holes. The results show that head-dipping initially decreased across repeated exposures, while time spent in the aversive central area increased. No change in head-dipping was seen in response to objects being placed underneath the holes. Rather than being a measure of neophilia, these results support the hypothesis that head-dipping represents an escape response, which declines as the subject becomes less fearful. These results are compared with previous studies of repeated exposure to other novel environments.     

Guanine Nucleotide-binding Protein (Gα) Endocytosis by a Cascade of Ubiquitin Binding Domain Proteins Is Required for Sustained Morphogenesis and Proper Mating in Yeast

Heterotrimeric G proteins are well known to transmit signals from cell surface receptors to intracellular effector proteins. There is growing appreciation that G proteins are also present at endomembrane compartments, where they can potentially interact with a distinct set of signaling proteins. Here, we examine the cellular trafficking function of the G protein α subunit in yeast, Gpa1. Gpa1 contains a unique 109-amino acid insert within the α-helical domain that undergoes a variety of posttranslational modifications. Among these is monoubiquitination, catalyzed by the NEDD4 family ubiquitin ligase Rsp5. Using a newly optimized method for G protein purification together with biophysical measures of structure and function, we show that the ubiquitination domain does not influence enzyme activity. By screening a panel of 39 gene deletion mutants, each lacking a different ubiquitin binding domain protein, we identify seven that are necessary to deliver Gpa1 to the vacuole compartment including four proteins (Ede1, Bul1, Ddi1, and Rup1) previously not known to be involved in this process. Finally, we show that proper endocytosis of the G protein is needed for sustained cellular morphogenesis and mating in response to pheromone stimulation. We conclude that a cascade of ubiquitin-binding proteins serves to deliver the G protein to its final destination within the cell. In this instance and in contrast to the previously characterized visual system, endocytosis from the plasma membrane is needed for proper signal transduction rather than for signal desensitization.     

Biosynthesis of Firefly Luciferin in Adult Lantern: Decarboxylation of ?-Cysteine is a Key Step for Benzothiazole Ring Formation in Firefly Luciferin Synthesis

Background

Bioluminescence in fireflies and click beetles is produced by a luciferase-luciferin reaction. The luminescence property and protein structure of firefly luciferase have been investigated, and its cDNA has been used for various assay systems. The chemical structure of firefly luciferin was identified as the ᴅ-form in 1963 and studies on the biosynthesis of firefly luciferin began early in the 1970’s. Incorporation experiments using ¹⁴C-labeled compounds were performed, and cysteine and benzoquinone/hydroquinone were proposed to be biosynthetic component for firefly luciferin. However, there have been no clear conclusions regarding the biosynthetic components of firefly luciferin over 30 years.

Methodology/Principal Findings

Incorporation studies were performed by injecting stable isotope-labeled compounds, including ʟ-[U-¹³C₃]-cysteine, ʟ-[1-¹³C]-cysteine, ʟ-[3-¹³C]-cysteine, 1,4-[D₆]-hydroquinone, and p-[2,3,5,6-D]-benzoquinone, into the adult lantern of the living Japanese firefly Luciola lateralis. After extracting firefly luciferin from the lantern, the incorporation of stable isotope-labeled compounds into firefly luciferin was identified by LC/ESI-TOF-MS. The positions of the stable isotope atoms in firefly luciferin were determined by the mass fragmentation of firefly luciferin.

Conclusions

We demonstrated for the first time that ᴅ- and ʟ-firefly luciferins are biosynthesized in the lantern of the adult firefly from two ʟ-cysteine molecules with p-benzoquinone/1,4-hydroquinone, accompanied by the decarboxylation of ʟ-cysteine.     

The Potential Distribution of Invading Helicoverpa armigera in North America: Is It Just a Matter of Time?

Helicoverpa armigera has recently invaded South and Central America, and appears to be spreading rapidly. We update a previously developed potential distribution model to highlight the global invasion threat, with emphasis on the risks to the United States. The continued range expansion of H. armigera in Central America is likely to change the invasion threat it poses to North America qualitatively, making natural dispersal from either the Caribbean islands or Mexico feasible. To characterise the threat posed by H. armigera, we collated the value of the major host crops in the United States growing within its modelled potential range, including that area where it could expand its range during favourable seasons. We found that the annual value of crops that would be exposed to H. armigera totalled approximately US$78 billion p.a., with US$843 million p.a. worth growing in climates that are optimal for the pest. Elsewhere, H. armigera has developed broad-spectrum pesticide resistance; meaning that if it invades the United States, protecting these crops from significant production impacts could be challenging. It may be cost-effective to undertake pre-emptive biosecurity activities such as slowing the spread of H. armigera throughout the Americas, improving the system for detecting H. armigera, and methods for rapid identification, especially distinguishing between H. armigera, H. zea and potential H. armigera x H. zea hybrids. Developing biological control programs, especially using inundative techniques with entomopathogens and parasitoids could slow the spread of H. armigera, and reduce selective pressure for pesticide resistance. The rapid spread of H. armigera through South America into Central America suggests that its spread into North America is a matter of time. The likely natural dispersal routes preclude aggressive incursion responses, emphasizing the value of preparatory communication with agricultural producers in areas suitable for invasion by H. armigera.