Two-photon laser-generated microtracks in 3D collagen lattices: principles of MMP-dependent and -independent collective cancer cell invasion

Cancer invasion into an extracellular matrix (ECM) results from a biophysical reciprocal interplay between the expanding cancer lesion and tissue barriers imposed by the adjacent microenvironment. In vivo, connective tissue provides both densely packed ECM barriers adjacent to channel/track-like spaces and loosely organized zones, both of which may impact cancer invasion mode and efficiency; however little is known about how three-dimensional (3D) spaces and aligned tracks present in interstitial tissue guide cell invasion. We here describe a two-photon laser ablation procedure to generate 3D microtracks in dense 3D collagen matrices that support and guide collective cancer cell invasion. Whereas collective invasion of mammary tumor (MMT) breast cancer cells into randomly organized collagen networks required matrix metalloproteinase (MMP) activity for cell-derived collagen breakdown, re-alignment and track generation, preformed tracks supported MMP-independent collective invasion down to a track caliber of 3 μm. Besides contact guidance along the track of least resistance and initial cell deformation (squeezing), MMP-independent collective cell strands led to secondary track expansion by a pushing mechanism. Thus, two-photon laser ablation is useful to generate barrier-free microtracks in a 3D ECM which guide collective invasion independently of pericellular proteolysis.     

The hypothalamic neuropeptide oxytocin is required for formation of the neurovascular interface of the pituitary

The hypothalamo-neurohypophyseal system (HNS) is?the neurovascular structure through which the hypothalamic neuropeptides oxytocin and arginine-vasopressin exit the brain into the bloodstream, where they go on to affect peripheral physiology. Here, we investigate the molecular cues that regulate the neurovascular contact between hypothalamic axons and neurohypophyseal capillaries of the zebrafish. We developed a transgenic system in which both hypothalamic axons and neurohypophyseal vasculature can be analyzed in?vivo. We identified the cellular organization of the zebrafish HNS as well as the dynamic processes that contribute to formation of the HNS neurovascular interface. We show that formation of this interface is regulated during development by local release of oxytocin, which affects endothelial morphogenesis. This cell communication process is essential for the establishment of a tight axovasal interface between the neurons and blood vessels of the HNS. We present a unique example of axons affecting endothelial morphogenesis through secretion of a neuropeptide.     

Phylogenetic relationships in Interfilum and Klebsormidium (Klebsormidiophyceae, Streptophyta)

Members of the genus Klebsormidium have cosmopolitan distribution and occur in a very wide range of freshwater and terrestrial habitats. Due to its simple filamentous morphology, this genus represents a taxonomically and systematically complex taxon in which phylogenetic relationships are still poorly understood. The phylogeny of Klebsormidium and closely related taxa was investigated using new ITS rRNA and rbcL sequences generated from 75 strains (isolated from field samples or obtained from culture collections). These sequences were analyzed both as single-marker datasets and in a concatenated dataset. Seven main superclades were observed in the analyses, which included sixteen well-supported clades. Some species of Klebsormidium, including the type species Klebsormidium flaccidum, were polyphyletic. Interfilum was recovered with high statistical support as sister taxon to a clade of Klebsormidium formed mainly by strains identified as K. flaccidum. Whereas some clades could be easily associated with described species, this was not possible for other clades. A new lineage of Klebsormidium, isolated from arid soils in southern Africa and comprising undescribed species, was discovered. Several morphological characters traditionally used for taxonomic purposes were found to have no phylogenetic significance and in some cases showed intra-clade variation. The capacity to form packet-like aggregates (typical of Interfilum), features of the morphology of the chloroplast and the type of habitat were the main phylogenetically relevant characters. Overall, Klebsormidium and Interfilum formed a more diverse algal group than was previously appreciated, with some lineages apparently undergoing active evolutionary radiation; in these lineages the genetic variation observed did not match the morphological and ecological diversity.     

Mitochondrial respiratory control and early defects of oxidative phosphorylation in the failing human heart

Heart failure is a consequence of progressive deterioration of cardiac performance. Little is known about the role of impaired oxidative phosphorylation in the progression of the disease, since previous studies of mitochondrial injuries are restricted to end-stage chronic heart failure. The present study aimed at evaluating the involvement of mitochondrial dysfunction in the development of human heart failure. We measured the control of oxidative phosphorylation with high-resolution respirometry in permeabilized myocardial fibres from donor hearts (controls), and patients with no or mild heart failure but presenting with heart disease, or chronic heart failure due to dilated or ischemic cardiomyopathy. The capacity of the phosphorylation system exerted a strong limitation on oxidative phosphorylation in the human heart, estimated at 121 pmol O(2)s(-1)mg(-1) in the healthy left ventricle. In heart disease, a specific defect of the phosphorylation system, Complex I-linked respiration, and mass-specific fatty acid oxidation were identified. These early defects were also significant in chronic heart failure, where the capacities of the oxidative phosphorylation and electron transfer systems per cardiac tissue mass were decreased with all tested substrate combinations, suggesting a decline of mitochondrial density. Oxidative phosphorylation and electron transfer system capacities were higher in ventricles compared to atria, but the impaired mitochondrial quality was identical in the four cardiac chambers of chronic heart failure patients. Coupling was preserved in heart disease and chronic heart failure, in contrast to the mitochondrial dysfunction observed after prolonged cold storage of cardiac tissue. Mitochondrial defects in the phosphorylation system, Complex I respiration and mass-specific fatty acid oxidation occurred early in the development of heart failure. Targeting these mitochondrial injuries with metabolic therapy may offer a promising approach to delay the progression of heart disease.     

High local substrate availability stabilizes a cooperative trait

Cooperative behavior is widely spread in microbial populations. An example is the expression of an extracellular protease by the lactic acid bacterium Lactococcus lactis, which degrades milk proteins into free utilizable peptides that are essential to allow growth to high cell densities in milk. Cheating, protease-negative strains can invade the population and drive the protease-positive strain to extinction. By using multiple experimental approaches, as well as modeling population dynamics, we demonstrate that the persistence of the proteolytic trait is determined by the fraction of the generated peptides that can be captured by the cell before diffusing away from it. The mechanism described is likely to be relevant for the evolutionary stability of many extracellular substrate-degrading enzymes.     

The self in social interactions: sensory attenuation of auditory action effects is stronger in interactions with others

The experience of oneself as an agent not only results from interactions with the inanimate environment, but often takes place in a social context. Interactions with other people have been suggested to play a key role in the construal of self-agency. Here, we investigated the influence of social interactions on sensory attenuation of action effects as a marker of pre-reflective self-agency. To this end, we compared the attenuation of the perceived loudness intensity of auditory action effects generated either by oneself or another person in either an individual, non-interactive or interactive action context. In line with previous research, the perceived loudness of self-generated sounds was attenuated compared to sounds generated by another person. Most importantly, this effect was strongly modulated by social interactions between self and other. Sensory attenuation of self- and other-generated sounds was increased in interactive as compared to the respective individual action contexts. This is the first experimental evidence suggesting that pre-reflective self-agency can extend to and is shaped by interactions between individuals.     

Copepod and microzooplankton grazing in mesocosms fertilised with different Si:N ratios: no overlap between food spectra and Si:N influence on zooplankton trophic level

We hypothesized that the trophic level of marine copepods should depend on the composition of the protist community. To test this hypothesis, we manipulated the phytoplankton composition in mesocosms and measured grazing rates of copepods and mesozooplankton in those mesocosms. Twelve mesocosms with Northeast Atlantic phytoplankton were fertilised with different Si:N ratios from 0:1 to 1:1. After 1 week, ten of the mesocosms were filled with natural densities of mesozooplankton, mainly calanoid copepods, while two remained as mesozooplankton-free controls. Both before and after the addition of copepods there was a positive correlation of diatom dominance with Si:N ratios. During the second phase of the experiment, copepod and microzooplankton grazing rates on different phytoplankton species were assessed by a modification of the Landry-Hassett dilution technique, where the bottles containing the different dilution treatments were replaced by dialysis bags incubated in situ. The results indicated no overlap in the food spectrum of microzooplankton (mainly ciliates) and copepods. Ciliates fed on nanoplankton, while copepods fed on large or chain-forming diatoms, naked dinoflagellates, and ciliates. The calculated trophic level of copepods showed a significantly negative but weak correlation with Si:N ratios. The strength of this response was strongly dependent on the trophic levels assumed for ciliates and mixotrophic dinoflagellates.