Morphology and ultrastructure of the swimming larvae of Crambe crambe (Demospongiae, Poecilosclerida)

Abstract. We describe the morphology and ultrastructure of the free-swimming larvae of the sponge Crambe crambe , one of the most abundant encrusting sponges on shallow rocky bottoms of the western Mediterranean. Larvae of C. crambe are released in July and August. The larva is uniformly flagellated except at the posterior zone. Flagellated cells are extraordinarily slender, elongate, and sinuous and form a pseudo-stratified layer. Their distal zone contains abundant mitochondria, some small vesicles, a Golgi complex, and the basal apparatus of the flagellum. Abundant lipid droplets are present throughout the cell. The nucleus is most often in a basal position. The flagellum projects from the bottom of an asymmetrical socket formed by cytoplasmic expansions. The basal body extends in a conical tuft and a laminar rootlet in close association with the Golgi system. The cells at the posterior pole are flat and polygonal on the surface, with long overlapping pseudopodia in the typical shape of a pinacoderm. Sparse collagen is present throughout the whole larva including the flagellated layer. Archeocytes and sclerocytes are abundant in the posterior region. Typical collencytes and spherulous cells seem to be absent. Intracellular and extracellular rod-like bacteria with conspicuous fimbria occur exclusively in the posterior region of the larva. The asymmetrical cytoplasmic prolongations, which surround the flagellum, and the basal apparatus of the flagellum are suggested as the sites of stimulus reception and triggering of locomotor responses, respectively. This ultrastructural study of the larva of C. crambe has shown features directly linked to its behavior and ecology.     

Construction of a bacterial artificial chromosome (BAC) library of Lycopersicon esculentum cv. Stevens and its application to physically map the Sw-5 locus

The Sw-5 gene is a dominantly inherited resistance gene in tomato and functional against a number of tospovirus species. The gene has been mapped on chromosome 9, tightly linked to RFLP markers CT220 and SCAR421. To analyse the Sw-5 locus, a BAC genomic library was constructed of tomato cv. Stevens, homozygous for the Sw-5 gene. The library comprised 18 816 clones with an average insert size of 100 kb, corresponding to two genome equivalents. The library was screened by PCR using primers designed for the CT220 and SCAR421 sequences, resulting in a 250 kb contig of known orientation on the long arm of chromosome 9. Using degenerate primers based on homologous sequences in the nucleotide binding site of resistance gene sequences, three discrete PCR fragments obtained from this contig were cloned and sequenced. Analysis of these fragments revealed a high similarity with numerous resistance genes or resistance gene like sequences. The present data indicate that at least three different resistance gene candidate (RGC) sequences are present in the vicinity of marker CT220, supporting the view that a resistance gene family may be responsible for the unusually broad resistance to tospoviruses conferred by the Sw-5 locus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of heavy resistance training on maximal and explosive force production, endurance and serum hormones in adolescent handball players

To determine the effects of 6-weeks of heavy-resistance training on physical fitness and serum hormone status in adolescents (range 14-16 years old) 19 male handball players were divided into two different groups: a handball training group (NST, n = 10), and a handball and heavy-resistance strength training group (ST, n = 9). A third group of 4 handball goalkeepers of similar age served as a control group (C, n = 4). After the 6-week training period, the ST group showed an improvement in maximal dynamic strength of the leg extensors (12.2%; P < 0.01) and the upper extremity muscles (23%; P < 0.01), while no changes were observed in the NST and C groups. Similar differences were observed in the maximal isometric unilateral leg extension forces. The height of the vertical jump increased in the NST group from 29.5 (SD 4) cm to 31.4 (SD 5) cm (P < 0.05) while no changes were observed in the ST and C groups. A significant increase was observed in the ST group in the velocity of the throwing test [from 71.7 (SD 7) km x h(-1) to 74.0 (SD 7) km x h(-1); P < 0.001] during the 6-week period while no changes were observed in the NST and C groups. During a submaximal endurance test running at 11 km x h(-1), a significant decrease in blood lactate concentration occurred in the NST group [from 3.3 (SD 0.9) mmol x l(-1) to 2.4 (SD 0.8) mmol x l(-1); P < 0.01] during the experiment, while no change was observed in the ST or C groups. Finally, a significant increase (P < 0.01) was noted in the testosterone:cortisol ratio in the C group, while the increase in the NST group approached statistical significance (P < 0.08) and no changes in this ratio occurred in the ST group. The present findings suggested that the addition of 6-weeks of heavy resistance training to the handball training resulted in gains in maximal strength and throwing velocity but it compromised gains in leg explosive force production and endurance running. The tendency for a compromised testosterone:cortisol ratio observed in the ST group could have been associated with a state of overreaching or overtraining.     

PIGMENT SUITES AND TAXONOMIC GROUPS IN PRASINOPHYCEAE1

Pigment analysis performed on 30 Prasinophyceae strains revealed two main groups: the prasinoxanthin‐containing and prasinoxanthin‐less Prasinophyceae. Prasinoxanthin‐containing Prasinophyceae comprised the orders Mamiellales, Pseudoscourfieldiales (Pycnococcaceae), and Prasinococcales. For this group, classification with pigment composition showed a good agreement with molecular phylogeny. Mamiellales, except Crustomastix stigmatica, accumulated uriolide, micromonal, dihydrolutein, and the pigment Unidentified M1 as characteristic pigments. Prasinococcales and Pseudoscourfieldiales (Pycnococcaceae) lacked micromonal and Unidentified M1. In addition, Pseudoscourfieldiales (Pycnococcaceae) lacked uriolide. A chl c₃‐like pigment was present in prasinoxanthin‐containing strains isolated from the deep sea. Common green algae pigments, a loroxanthin derivative, and siphonaxanthin plus derivatives were found in the prasinoxanthin‐less Prasinophyceae, which included strains from Pyramimonadales, Pseudoscourfieldiales (Nephroselmidiaceae), Chlorodendrales, and a new order. Although some associations could be observed, the correspondence between pigments and molecular taxonomy was less clear for this group.     

The effect of dynamic light regimes on Chlorella

The patterns of diurnal variations in pigmentation and optical cross-section were compared for two cyclostat cultures of Chlorella pyrenoidosa, where the dynamics of the photoperiod differed. Populations were light-limited, nutrient rich and growing on an 8:16 light-dark (LD) cycle. One light regime was an 8 h sine function of the light period (sinusoidal culture), while the second had an 1 h sine function super-imposed on the 8 hour sine function (oscillating sinusoidal culture). Hourly samples were taken throughout a 12 h period including the light period. Determinations were made of chlorophyll (Chl) a and b abundance, in vivo absorption spectra, cell number and volume and used to derive both cell-specific (cell) and optical chlorophyll specific (chl) cross sections, as well as the absorption efficiency, Q, of the cells. The results indicate that C. pyrenoidosa is capable of adapting to dynamics in light intensity within an 8 h photoperiod. The sinusoidal culture showed a constant decrease in the Chl a/b ratio of 28% while the total Chl content per cell increased slightly and chl and Q remained constant, suggesting coordinated changes in reaction centers and light harvesting complexes. Over the oscillating photoperiod, however, the second culture displayed a diurnal variation in Chl a/b ratio, a 20% increase in chl and an apparent oscillation in Q. These observations suggest that an oscillating photoperiod promoted the capability of Chl molecules to collect light and that the fractional area of all Chl molecules exposed to the photon flux is inversely related to the photon flux.     

Absolute DNA values from Feulgen microspectrophotometric measurements and quantitative electron microscopy. A comparison of two species

Quantitative electron microscopy (QEM) and microspectrophotometry were used to correlate the Feulgen stain absorption values to the calculated picograms of DNA. Measurements were made in human lymphocytes, rainbow trout lymphocytes and nuclei of trout erythrocytes. The median dry weight of the nucleus, as determined by QEM, was 35.9 pg for a human lymphocyte and 30.5 pg for a trout lymphocyte. Using Salzman's value of 20% DNA per chromosome (i.e., chromatin), a human lymphocyte nucleus thus contains 7.18 pg of DNA and a trout lymphocyte nucleus 6.1 pg of DNA. The mean Feulgen absorption value of the nucleus, given in arbitrary units (AU), was 14.5 for a human lymphocyte, 12.7 for a trout lymphocyte and 12.0 for a trout erythrocyte. From these values, it was derived that each picogram of DNA of a human lymphocyte nucleus is represented by 2.02 arbitrary Feulgen units while the values for trout nuclei were 2.08 AU and 1.97 AU. On the average, we find that each picogram of DNA is represented by two arbitrary Feulgen units in our microspectrophotometric measurements.     

Double-stranded RNA bending by AU-tract sequences

Sequence-dependent structural deformations of the DNA double helix (dsDNA) have been extensively studied, where adenine tracts (A-tracts) provide a striking example for global bending in the molecule. However, in contrast to dsDNA, sequence-dependent structural features of dsRNA have received little attention. In this work, we demonstrate that the nucleotide sequence can induce a bend in a canonical Watson-Crick base-paired dsRNA helix. Using all-atom molecular dynamics simulations, we identified a sequence motif consisting of alternating adenines and uracils, or AU-tracts, that strongly bend the RNA double-helix. This finding was experimentally validated using atomic force microscopy imaging of dsRNA molecules designed to display macroscopic curvature via repetitions of phased AU-tract motifs. At the atomic level, this novel phenomenon originates from a localized compression of the dsRNA major groove and a large propeller twist at the position of the AU-tract. Moreover, the magnitude of the bending can be modulated by changing the length of the AU-tract. Altogether, our results demonstrate the possibility of modifying the dsRNA curvature by means of its nucleotide sequence, which may be exploited in the emerging field of RNA nanotechnology and might also constitute a natural mechanism for proteins to achieve recognition of specific dsRNA sequences.     

Mice Lacking Endoglin in Macrophages Show an Impaired Immune Response

Endoglin is an auxiliary receptor for members of the TGF-β superfamily and plays an important role in the homeostasis of the vessel wall. Mutations in endoglin gene (ENG) or in the closely related TGF-β receptor type I ACVRL1/ALK1 are responsible for a rare dominant vascular dysplasia, the Hereditary Hemorrhagic Telangiectasia (HHT), or Rendu-Osler-Weber syndrome. Endoglin is also expressed in human macrophages, but its role in macrophage function remains unknown. In this work, we show that endoglin expression is triggered during the monocyte-macrophage differentiation process, both in vitro and during the in vivo differentiation of blood monocytes recruited to foci of inflammation in wild-type C57BL/6 mice. To analyze the role of endoglin in macrophages in vivo, an endoglin myeloid lineage specific knock-out mouse line (Eng^fl/flLysMCre) was generated. These mice show a predisposition to develop spontaneous infections by opportunistic bacteria. Eng^fl/flLysMCre mice also display increased survival following LPS-induced peritonitis, suggesting a delayed immune response. Phagocytic activity is impaired in peritoneal macrophages, altering one of the main functions of macrophages which contributes to the initiation of the immune response. We also observed altered expression of TGF-β1 target genes in endoglin deficient peritoneal macrophages. Overall, the altered immune activity of endoglin deficient macrophages could help to explain the higher rate of infectious diseases seen in HHT1 patients.     

Small-scale spatial heterogeneity and seasonal variation in a population of a cave-dwelling Mediterranean mysid

Seasonal changes in small-scale spatial distribution patternsof abundance and composition of Hemimysis speluncola Ledoyer(1963) (Crustacea, Mysidacea) were studied in a population ofcave-dwelling mysids off the Medes Islands (NW MediterraneanSea). The distribution pattern was characterized all year roundby marked spatial segregation of juveniles, which occupied areascloser to the cave entrance, while adults were concentratedmainly in the innermost part of the cave. The small-scale spatialheterogeneity observed appears to be regulated by biologicalfactors, particularly social and reproductive behaviour. Nevertheless,a certain adaptation of the distribution of the swarms to hydrodynamicfactors suggests that physical factors may also play a role.The heterogeneous aggregation pattern recorded would clearlyappear to be an adaptive strategy by the population to enableit to thrive within its habitat. That adaptation is designedto reduce predation mortality, enhance mating efficiency andregulate the population generally. Marked seasonal fluctuationsin the density and composition of the population were recorded,with high density levels in winter and throughout the spring.Two methods were employed to quantify the population: haulswith plankton nets towed by divers and collection of faecalpellets. The patterns observed using both these methods weresimilar, although the latter method yielded total density valuesthat were an order of magnitude greater.     

A Highlights from MBoC Selection: A Gαi–GIV Molecular Complex Binds Epidermal Growth Factor Receptor and Determines Whether Cells Migrate or Proliferate

Cells respond to growth factors by either migrating or proliferating, but not both at the same time, a phenomenon termed migration-proliferation dichotomy. The underlying mechanism of this phenomenon has remained unknown. We demonstrate here that Gα_i protein and GIV, its nonreceptor guanine nucleotide exchange factor (GEF), program EGF receptor (EGFR) signaling and orchestrate this dichotomy. GIV directly interacts with EGFR, and when its GEF function is intact, a Gα_i–GIV–EGFR signaling complex assembles, EGFR autophosphorylation is enhanced, and the receptor''s association with the plasma membrane (PM) is prolonged. Accordingly, PM-based motogenic signals (PI3-kinase-Akt and PLCγ1) are amplified, and cell migration is triggered. In cells expressing a GEF-deficient mutant, the Gαi–GIV-EGFR signaling complex is not assembled, EGFR autophosphorylation is reduced, the receptor''s association with endosomes is prolonged, mitogenic signals (ERK 1/2, Src, and STAT5) are amplified, and cell proliferation is triggered. In rapidly growing, poorly motile breast and colon cancer cells and in noninvasive colorectal carcinomas in situ in which EGFR signaling favors mitosis over motility, a GEF-deficient splice variant of GIV was identified. In slow growing, highly motile cancer cells and late invasive carcinomas, GIV is highly expressed and has an intact GEF motif. Thus, inclusion or exclusion of GIV''s GEF motif, which activates Gαi, modulates EGFR signaling, generates migration-proliferation dichotomy, and most likely influences cancer progression.