From Membrane Pores to Aquaporins: 50 Years Measuring Water Fluxes

This review focuses on studies of water movement across biological membranes performed over the last 50 years. Different scientific approaches had tried to elucidate such intriguing mechanism, from hypotheses emphasizing the role of the lipid bilayer to the cloning of aquaporins, the ubiquitous proteins described as specific water channels. Pioneering and clarifying biophysical work are reviewed beside results obtained with the help of recent sophisticated techniques, to conclude that great advances in the subject live together with old questions without definitive answers.     

Mapping QTLs contributing to <Emphasis Type="Italic">Ustilago maydis</Emphasis> resistance in specific plant tissues of maize

Quantitative trait loci (QTL) contributing to the frequency and severity of Ustilago maydis infection in the leaf, ear, stalk, and tassel of maize plants were mapped using an A188 × CMV3 and W23 × CMV3 recombinant inbred (RI) populations. QTLs mapped to genetic bins 2.04 and 9.04–9.05 of the maize genome contributed strongly (R ² = 18–28%) to variation in the frequency and severity of U. maydis infection over the entire plant in both populations and within the majority of environments. QTLs mapped to bins 3.05, 3.08, and 8.00 in the A188 × CMV3 population and bin 4.05 in both populations significantly contributed to the frequency or severity of infection in only the tassel tissue. QTLs mapped to bin 1.07 in the A188 × CMV3 population and bin 7.00 in the W23 × CMV3 population contributed to U. maydis resistance in only the ear tissue. Interestingly, the CMV3 allele of the QTL mapped to bin 1.10 in the A188 × CMV3 population significantly contributed to U. maydis susceptibility in the ear and stalk but significantly increased resistance in the tassel tissue. Digenic epistatic interactions between the QTL mapped to bin 5.08 and four distinct QTLs significantly contributed to the frequency and severity of infection over the entire plant and within the tassel tissue of the A188 × CMV3 population. Several QTLs detected in this study mapped to regions of the maize genome containing previously mapped U. maydis resistance QTLs and genes involved in plant disease resistance. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Morphological analysis of tumor cell/endothelial cell interactions under shear flow

In the process of hematogenous cancer metastasis, tumor cells (TCs) must shed into the blood stream, survive in the blood circulation, migrate through the vascular endothelium (extravasation) and proliferate in the target organs. However, the precise mechanisms by which TCs penetrate the endothelial cell (EC) junctions remain one of the least understood aspects of TC extravasation. This question has generally been addressed under static conditions, despite the important role of flow induced mechanical stress on the circulating cell-endothelium interactions. Moreover, flow studies were generally focused on transient or firm adhesion steps of TC-EC interactions and did not consider TCs spreading or extravasation. In this paper, we used a parallel-plate flow chamber to investigate TC-EC interactions under flow conditions. An EC monolayer was cultured on the lower plate of the flow chamber to model the endothelial barrier. Circulating TCs were introduced into the flow channel under a well-defined flow field and TC cell shape changes on the EC monolayer were followed in vitro with live phase contrast and fluorescence microscopy. Two spreading patterns were observed: radial spreading which corresponds to TC extravasation, and axial spreading where TCs formed a mosaic TC-EC monolayer. By investigating the changes in area and minor/major aspect ratio, we have established a simple quantitative basis for comparing spreading modes under various shear stresses. Contrary to radial spreading, the extent of axial spreading was increased by shear stress.     

On the origin of the sweet-smelling Parma violet cultivars (Violaceae): wide intraspecific hybridization, sterility, and sexual reproduction

Parma violets are reputed for their double, fragrant flowers and have been cultivated for centuries in Europe. However, due to a rather atypical morphology their taxonomic affinity has not been clarified. Authors have proposed an origin from three possible species, Viola alba, V. odorata, or V. suavis, or a hybrid origin. Using both ITS sequence variation and allozyme variation in 14 putative loci, we showed that the Parma violet cultivars have their origin within Viola alba and that they are best included in the Mediterranean subsp. dehnhardtii. There is no trace of interspecific hybridization. However, the cultivars appear to have a single origin in a wide hybrid within V. alba, involving parental plants from the eastern and western Mediterranean region; historical literature sources seem to indicate Turkey and Italy, respectively. The Parma violet cultivars possess high levels of allozyme heterozygosity and to some extent also within-individual ITS sequence variation. Losses of heterozygosity and within-individual ITS sequence variation in some of the cultivars indicate subsequent rare events of sexual reproduction, presumably through cleistogamous seed set. We unambiguously identify the closest wild relative of this group of cultivars, allowing growers to develop new selection procedures, and show a peculiar molecular process associated with human selection.     

pH modulation of transport properties of alamethicin oligomers inserted in zwitterionic-based artificial lipid membranes

Electric features of biological membranes are major determinants of the function and physiological manifestation of membrane-penetrating peptides, and such features are prone to be modulated by the properties of the surrounding aqueous medium. In this work, we demonstrate that pH plays crucial roles in modulating electric characteristics of zwitterionic-based artificial lipid membranes. The effect of pH on electrical properties of such membranes was probed by evaluating the transport properties of embedded alamethicin oligomers over a wide range of pH values (i.e., 0.65, 2.08, 2.94, 7 and 10.1). Our data strongly support the paradigm of a pH-dependent variation of the surface and membrane dipole potential which, in conjunction with possible lateral pressure effects within the lipid membrane, lead to a non-monotonic modulation of the electrical conductance of alamethicin oligomers. As expected, pH modulation of transport properties through the alamethicin oligomer is more visible for narrower pores (that is, the 1st conductive state) with slightly better cation selectivity as compared to larger oligomers.     

Male reproductive senescence: the price of immune-induced oxidative damage on sexual attractiveness in the blue-footed booby

In animals, male reproduction is commonly a function of sexual attractiveness, based on the expression of sexually dimorphic traits that advertise genuinely the male's quality. Male performance may decline with age because physiological functions underlying sexual attractiveness may be affected by senescence. Here we show that a sexual signal (foot colour) declines with age, due probably to the deleterious effects of oxidative damage. We found that in the blue-footed booby Sula nebouxii foot colour during courtship was less attractive in senescent than in middle-aged males. In addition, we increased reactive oxygen species experimentally by immunizing males with lipopolysaccharide, a bacterial cell wall component that induces marked oxidative stress in animals. The immune system activation induced greater lipid peroxidation and invoked changes on colour expression (less attractive), particularly in senescent males. These results support the idea that oxidative stress affects reproductive senescence, and suggest that oxidative damage might be a proximal mechanism underlying age-reproductive patterns in long-lived animals.     

The role of vitellogenin during gestation of Girardinichthys viviparus and Ameca splendens; two goodeid fish with matrotrophic viviparity

Goodeid fish have matrotrophic viviparity, and unlike lecitotrophic fish, yolk loss forces the female to provide the nutritional requirements for embryonic development. Vitellogenin (VTG) is the yolk precursor protein synthesized in the maternal liver, but there is only circumstantial evidence regarding VTG supply during the ontogenesis of bony fish with matrotrophic viviparity. Therefore, the goal of the present study was to identify and quantify VTG during gestation of the black fin goodeid Girardinichthys viviparus and the butterfly split-fin goodeid Ameca splendens. Females at different gonadic developmental stages were selected in order to evaluate VTG mRNA expression in the maternal liver using RT-PCR; VTG quantification in maternal muscle and liver, as well as in the embryos, was done using ELISA, and immunohistochemical detection of VTG was done in the black fin goodeid. The results suggest that VTG supplies nutrients during embryonic development of both species, which have different life histories. It is possible that the transition from lecitotrophy to matrotrophic viviparity in bony fish with intraluminal gestation involved adaptive transition strategies that included changes in the relationship between oocytes and follicular cells, as well as a gradual loss of VTG synthesis during embryonic development.     

Biodegradation of phytane (2,6,10,14-tetramethylhexadecane) and accumulation of related isoprenoid wax esters by Mycobacterium ratisbonense strain SD4 under nitrogen-starved conditions

The accumulation of storage lipids during the biodegradation of 2,6,10,14-tetramethylhexadecane (phytane) by Mycobacterium ratisbonense strain SD4 grown under nitrogen-starved conditions was investigated. Detailed chemical analysis of intracellular metabolites revealed the existence of (at least) three different pathways for the catabolism of phytane, and the accumulation of significant proportions (39% of the total lipids) of several isoprenoid wax esters formed by condensation of oxidation products of the hydrocarbon. In contrast, triacylglycerols but no wax esters were accumulated by strain SD4 grown on hexadecane, the unbranched homologue of phytane.