Contrasting Geographical Distributions as a Result of Thermal Tolerance and Long-Distance Dispersal in Two Allegedly Widespread Tropical Brown Algae

BackgroundMany tropical marine macroalgae are reported from all three ocean basins, though these very wide distributions may simply be an artifact resulting from inadequate taxonomy that fails to take into account cryptic diversity. Alternatively, pantropical distributions challenge the belief of limited intrinsic dispersal capacity of marine seaweeds and the effectiveness of the north-south oriented continents as dispersal barriers. We aimed to re-assess the distribution of two allegedly circumtropical brown algae, Dictyota ciliolata and D. crenulata, and interpret the realized geographical range of the respective species in relation to their thermal tolerance and major tectonic and climatic events during the Cenozoic.Methodology/Principal FindingsSpecies delimitation was based on 184 chloroplast encoded psbA sequences, using a Generalized Mixed Yule Coalescent method. Phylogenetic relationships were inferred by analyzing a six-gene dataset. Divergence times were estimated using relaxed molecular clock methods and published calibration data. Distribution ranges of the species were inferred from DNA-confirmed records, complemented with credible literature data and herbarium vouchers. Temperature tolerances of the species were determined by correlating distribution records with local SST values. We found considerable conflict between traditional and DNA-based species definitions. Dictyota crenulata consists of several pseudocryptic species, which have restricted distributions in the Atlantic Ocean and Pacific Central America. In contrast, the pantropical distribution of D. ciliolata is confirmed and linked to its significantly wider temperature tolerance.Conclusions/SignificanceTectonically driven rearrangements of physical barriers left an unequivocal imprint on the current diversity patterns of marine macroalgae, as witnessed by the D. crenulata–complex. The nearly circumglobal tropical distribution of D. ciliolata, however, demonstrates that the north-south oriented continents do not present absolute dispersal barriers for species characterized by wide temperature tolerances

Possible role of ubiquitin in silica biomineralization in diatoms:identification of a homologue with high silica affinity

In diatom silicon biomineralization peptides are believed to play a role in silica precipitation and the consequent structure direction of the cell wall. Characterization of such peptides should reveal the nature of this organic-inorganic interaction, knowledge that may eventually well be used to expand the existing range of artificial silicas ("biomimicking"). Biochemical studies on Navicula pelliculosa revealed a set of proteins, which have a high affinity for a solid silica matrix; some were only eluted from the matrix when SDS-denaturation was applied. One of the proteins with an affinity for silica, about 8.5 kDa, is shown to be a homologue of ubiquitin on the basis of its N-terminal amino acid sequence; ubiquitin itself is a highly conserved 8.6 kDa protein that is involved in protein degradation. This finding is in line with a model of silica biomineralization in diatoms that implies the removal of templating polypeptides when pores in the growing cell wall develop. Western blotting with specific anti-ubiquitin antibodies confirmed cross-reactivity. Immunocytochemical localization of ubiquitin indicates that it is present along the diatom cell wall and inside pores during different stages of valve formation. (C) 2003 Elsevier Science B.V. All rights reserved

Within-island differentiation and between-island homogeneity: Non-equilibrium population structure in the seaweed Cladophoropsis membranacea (Chlorophyta) in the Canary Islands

The seaweed Cladophoropsis membranacea forms extensive mats of coalesced thalli on coral reefs and along rocky coastlines throughout the tropics and subtropics. In a previous study on Gran Canaria, small-scale dispersal distances were found to be limited to <5 m and significant differentiation (F-ST) was detectable at distances as small as 5 km. Such strong, small-scale differentiation led to the prediction that strong isolation by distance (IBD) would be found under a stepping stone model at larger spatial scales. In the present survey, 23 sites were sampled in the Canary Islands and one in the Cape Verde Islands. Using eight microsatellite loci analysed in an AMOVA framework, we determined that approximately 75% of the variation occurred within sites and approximately 25% between sites separated by 1-125 km. In a three-level AMOVA, only 6% of the variation was accounted for between islands (&AP; 100-300 km). Moderately strong IBD was found within islands and Mantel tests revealed significant correlation for Gran Canaria and Tenerife but not for Fuerteventura. In contrast, there was no detectable IBD among the Canary Islands regardless of how geographic distances were computed. Only when the Canary Islands were compared with the Cape Verde Islands was strong IBD detected. Our seemingly paradoxical results of strong differentiation and IBD at small distances and weak to absent IBD at large distances reflect non-equilibrium conditions. In addition, the wide scatter of points we observed over all degrees of geographic separation is consistent with isolation in which drift dominates over gene flow. The lack of equilibrium in present-day populations of C. membranacea is probably mainly due to the fact that they are only thousands or even hundreds of years old. Therefore, population structure should be interpreted in terms of history rather than gene flow

Scavenger receptor A: a new route for adenovirus 5.

Adenoviruses are common pathogens associated with respiratory diseases, gastrointestinal illnesses and/or conjunctivitis. Currently, this virus is used as a vector in gene therapy trials. The promise of viral gene therapy applications is substantially reduced because the virus is cleared by liver macrophages upon systemic administration. The mechanism underlying adenoviral tropism to and degradation in macrophages is poorly understood. We identified a new adenoviral receptor, the scavenger receptor A (SR-A), responsible for uptake of the virus in macrophages. CHO cells expressing SR-A showed increased viral transgene expression when compared with wild type cells. Preincubation of J774 macrophage cells with SR-A ligands decreased significantly adenoviral uptake. Electron-microscopy analysis of infected J774 cells showed activation of a viral degradation pathway. Infection of mice with adenovirus resulted in a substantial decrease of the virus in liver macrophages when SR-A was blocked. Our data provide a basis for understanding of the adenoviral uptake and degradation mechanism in macrophages in vitro and in vivo. Inhibition of adenoviral SR-A uptake can be utilized in gene therapy applications to increase its efficiency and efficacy

Compartmental Analysis Suggests Macropinocytosis at the Onset of Diatom Valve Formation

During valve formation of the siliceous frustules of diatoms, bulk uptake of silicic acid and its subsequent transport through the cell is required before it can be deposited in the silica deposition vesicle (SDV). It has been assumed that transport takes place via silicon transporters (SITs), but if that were the case a control mechanism would have to exist for stabilization of the large amounts of reactive silicon species during their passage through the cell on the way to the SDV. There is, however, no reason to assume that classical silica chemistry does not apply at elevated levels of silicic acid, and therefore autopolymerization could reasonably be expected to occur. In order to find alternative ways of Si transport that correspond with the high speed of valve formation at the earliest stages of cell division we followed 31Si(OH)4 uptake in synchronously dividing cells of the diatoms Coscinodiscus wailesii, Navicula pelliculosa, N. salinarum, and Pleurosira laevis. The results were related to systematically derived mathematical models for a compartmental analysis of 5 possible uptake/transport pathways, including one involving SITs and one involving (macro)pinocytosis-mediated uptake from the extracellular environment. Our study indicates that the uptake of radioactive silicic acid matches best with the model that describes macropinocytosis-mediated silicon uptake. This process is well in line with the observed ‘surge uptake’ at the start of valve formation when the demand for silicon is high; it infers that in diatoms a pathway of uptake and transport exists in which SITs are not involved.Radiation, Radionuclides and ReactorsApplied Science

Regulation of inducible BALT formation and contribution to immunity and pathology

Inducible bronchus-associated lymphoid tissue (iBALT) is an organized tertiary lymphoid structure that is not preprogrammed but develops in response to infection or under chronic inflammatory conditions. Emerging research has shown that iBALT provides a niche for T-cell priming and B-cell education to assist in the clearance of infectious agents, highlighting the prospect that iBALT may be engineered and harnessed to enhance protective immunity against respiratory pathogens. Although iBALT formation is associated with several canonical factors of secondary lymphoid organogenesis such as lymphotoxin-α and the homeostatic chemokines, CXCL13, CCL19, and CCL21, these cytokines are not mandatory for its formation, even though they influence its organization and function. Similarly, lymphoid tissue inducer cells are not a requisite of iBALT formation. In contrast, dendritic cells are emerging as pivotal players required to form and sustain the presence of iBALT. Regulatory T cells appear to be able to attenuate the development of iBALT, although the underlying mechanisms remain ill-defined. In this review, we discuss facets unique to iBALT induction, the cellular subsets, and molecular cues that govern this process, and the contribution of this ectopic structure toward the generation of immune responses in the pulmonary compartment