Life history stages of Pyramimonas tychotreta (Prasinophyceae, Chlorophyta), a marine flagellate from the Ross Sea, Antarctica

During a summer cruise to the Ross Sea (Antarctica) areas of snow‐covered sea ice were red‐coloured due to high concentrations of the recently described Pyramimonas tychotreta Daugbjerg. Light microscopy of living material revealed that the population was comprised of quadriflagellate motile cells and thick‐walled cysts. The red colour was due to large numbers of secondary carotenoid‐containing granules, positioned in the periphery of motile cells and cysts. Mature cysts also contained numerous starch grains and lipid droplets. Cells from a red‐coloured field sample turned green overnight as the secondary carotenoids disappeared when cells were placed in low light conditions. The sample then exhibited the typical grass‐green colour of motile cells observed in water samples from the area. Under reduced light motile cells showed strong positive phototaxis. The encystment process involved the asexual transformation of quadriflagellate cells into cysts. A single type of square cyst scale, with perforated floors and walls, replaced the body scales of motile cells. A marked extension, often ending in a hook was at each corner of the cyst scales. Germinating cysts produced four motile cells. Electron microscopy showed the cyst wall to be tri‐layered, with a thin, electron‐dense inner layer, a thick middle layer and a thin outer layer. Sea ice samples with dense populations of motile cells and cyst stages also contained elongate uniflagel‐late cells. These cells were covered with box scales, foot‐print scales, an underlayer of pentagonal scales, limuloid scales and flagellar hair scales identical to those present on the quadriflagellate stage. We tentatively suggest that the uniflagellate stage represents a gamete and its presence implies the occurrence of sexual reproduction. Although, fusion of gametes was not observed, a biflagellate cell with a larger volume was seen which may have been a zygote. How this stage fits into of the life history remains to be explained.     

Of Worms and Men: An Evolutionary Perspective on the Fibroblast Growth Factor (FGF) and FGF Receptor Families

FGFs (fibroblast growth factors) play major roles in a number of developmental processes. Recent studies of several human disorders, and concurrent analysis of gene knock-out and properties of the corresponding recombinant proteins have shown that FGFs and their receptors are prominently involved in the development of the skeletal system in mammals. We have compared the sequences of the nine known mammalian FGFs, FGFs from other vertebrates, and three additional sequences that we extracted from existing databases: two human FGF sequences that we tentatively designated FGF10 and FGF11, and an FGF sequence from C?norhabditis elegans. Similarly, we have compared the sequences of the four FGF receptor paralogs found in chordates with four non-chordate FGF receptors, including one recently identified in C. elegans. The comparison of FGF and FGF receptor sequences in vertebrates and nonvertebrates shows that the FGF and FGF receptor families have evolved through phases of gene duplications, one of which may have coincided with the emergence of vertebrates, in relation with their new system of body scaffold. Received: 6 April 1996 / Accepted: 5 July 1996     

MiRNA-21 Expression Decreases from Primary Tumors to Liver Metastases in Colorectal Carcinoma

Objective

Metastasis is the major cause of death in colorectal cancer patients. Expression of certain miRNAs in the primary tumors has been shown to be associated with progression of colorectal cancer and the initiation of metastasis. In this study, we compared miRNA expression in primary colorectal cancer and corresponding liver metastases in order to get an idea of the oncogenic importance of the miRNAs in established metastases.

Methods

We analyzed the expression of miRNA-21, miRNA-31 and miRNA-373 in corresponding formalin-fixed paraffin-embedded (FFPE) tissue samples of primary colorectal cancer, liver metastasis and healthy tissues of 29 patients by quantitative real-time PCR.

Results

All three miRNAs were significantly up-regulated in the primary tumor tissues as compared to healthy colon mucosa of the respective patients (p < 0.01). MiRNA-21 and miRNA-31 were also higher expressed in liver metastases as compared to healthy liver tissues (p < 0.01). No significant difference of expression of miRNA-31 and miRNA-373 was observed between primary tumors and metastases. Of note, miRNA-21 expression was significantly reduced in liver metastases as compared to the primary colorectal tumors (p < 0.01).

Conclusion

In the context of previous studies demonstrating increased miRNA-21 expression in metastatic primary tumors, our findings raise the question whether miRNA-21 might be involved in the initiation but not in the perpetuation and growth of metastases.     

Ultrastructure of motor nerve terminals on different types of muscle fibers in the atlantic hagfish (Myxine glutinosa,L.)

Summary White and intermediate parietal muscle fibers of Myxine are innervated focally at one end. Most synaptic vesicles are empty. These terminals also contain 1–2% large 800–1.100 Å dense-core vesicles. Red fibers of parietal and craniovelar muscle are innervated in a distributed fashion, and the presynaptic profiles contain a higher number of large dense-core vesicles (averaging 9% and 15%, respectively; up to 37%). For all terminals the synaptic gap is 450–600 Å wide, and postsynaptic folds are absent.Empty synaptic vesicles exist as round or elongated profiles. The proportion of elongated profiles increases by formation from round ones when increasing the molarity of the buffer in the aldehyde fixative. Furthermore, the proportion of elongated vesicle profiles in terminals on Myxine white fibers at different buffer molarities, is identical with that in mammalian motor terminals at similar molarities. On this basis the significance and mode of formation of elongated vesicle profiles is discussed. The conclusion is made that the susceptibility of flattening depends on the osmotic pressure of the vesicle contents once the aldehyde has influenced the vesicle membrane.The different vesicle populations in terminals on different types of muscle fibers are significant. Terminals on red fibers probably contain serotonin (5-HT) either as sole transmitter or in addition to acetylcholine.The author is indebted to Dr. Finn Walvig, Biological Station, University of Oslo, Drøbak, for supply of hagfishes, and to Mrs. Jorunn Line Vaaland for expert technical assistance.     

Der Ganzheitsbegriff in der Systematik

Summary Kleinschmidt's definition of the Weltformenkreis as the smallest systematical unit of affinity removes any danger of obliterating the type and at the same time opens a way for judging the superior taxonomic groups on principle differently from the subspecies of a Formenkreis.It is demonstrated that the characters of geographical subspecies (Rassen) are characters of apparent shaping, those of the species however are characters of construction and qualitative and autonomic ones. It is the type differentiating in quality that justifies the definition of species. As the characters of type do not necessarily appear gradual and quantitative, but are qualitative, the types cannot be derived from one another, unless they are conceived by the common superordinate idea of the superior systematical category next in order.The distinct division of species is opposed to the hypothetical continuity of the pedigree, which cannot be explained by a consanguinity nor by an affinity based on reproduction. The pedigree, however, is an expression of the spiritual order of nature, in which the types appear as units hierarchically graduated and determined by entelechy, not by dead matter.Within the systematical units there is a creative evolution, steadily pursuing its aim and leading from the primitive stage to the differentiated one, beginning with a juvenile phase, which is followed by orthogenetic maturity and, finally, by the aged stage with its detypification. The adaptation to the environment (biotope) may be also proved for the primitive forms and is an organic part of the whole design of the world for them as well as for the specialized and differentiated forms. — The formation of new types cannot be explained in a merely mechanical way; everywhere, even in the gens and genoms, we state ingenious modifications, which do not only bring about a reaction of a single modification to the whole, but operate from the whole. Since the origin of man, since the tertiary formation, the creation of species has completely ceased. There are only alterations of subspecific character.After a digressive treatise on the fundamental difference of man and animal in order to explain the type the superior systematical categories are characterized as spiritual realities. It is especially for the genus that a revision is necessary. The reality of the common origin of certain species within the genus is not based on reproduction (as it is the case in the Formenkreis), but on the superior totality comprising the species. Individuals can be conceived by the character of the species, species by the character of genus only. This is an evidence for the methodicalness of creative nature. It excludes any evolution of the genus from bottom to top, which is irregular, accidental or immediately formed by environment. From this we derive the comprehensive right of a natural system which now is more than mere classification.

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Résumé Kleinschmidt qui donne une définition du Weltformenkreis comme la plus petite unité d'affinité systématique, déjoue le danger d'oblitérer le type et offre, en même temps, la possibilité de juger les groupes taxonomiques supérieurs par principe différemment de la souspèce d'un Formenkreis.Nous démontrons que les caractères des souspèces géographiques sont des caractères du façonnement extérieur, tandis que ceux de l'espèce sont des caractères de la construction d'une manière qualitative et autonome. Le type différent en qualité justifie seulement la définition de l'espèce. Comme les caractères du type n'apparaissent pas nécessairement graduels et quantitatifs, mais sont au contraire, qualitatifs, les types ne se dérivent pas l'un de l'autre, à moins qu'ils ne soient compris par la commune idée supérieure du plus sublime groupe systématique.La division distincte des espèces s'oppose à la continuité hypothétique de la généalogie, qui ne s'explique pas par une consanguinité ni par une affinité se fondant sur la reproduction, mais qui est plutôt une expression du régime spirituel de la nature, dans lequel les types se présentent comme des unités rangées hiérarchiquement et réglées par l'entéléchie et non par la matière.Dans les unités systématiques il y a une évolution créatrice qui tend continuellement à son but et mène de la phase primitive à la phase différentiée commençant par un état juvénile, qui est succédé par la maturité orthogénétique et enfin par l'âge avec sa détypification. L'adaptation au milieu est démontrée pour les formes primitives et représente un élément organique du grand projet mondial pour elles aussi bien que pour les formes spécialisées et différentiées. — La formation de types nouveaux ne s'explique pas seulement d'une manière mécanique; partout, même dans les genes et les genomes, nous observons des transformations ingénieuses, qui ne sont pas seulement une réaction d'une modification particulière à l'ensemble, mais un effet de l'ensemble. Depuis l'origine de l'homme, depuis la période tertiaire la formation d'espèces est complètement finie. À présent il n'y a plus que des variations d'un caractère souspécifique. Après un traité digressif sur la différence essentielle de l'homme et de l'animal pour expliquer le type les groupes systématiques supérieurs sont caractérisés comme des réalités spirituelles. C'est surtout pour le genre (genus) qu'une révision est nécessaire. La réalité de la racine commune de certaines espèces dans le genre (genus) ne se fonde pas sur la reproduction (comme cela est juste pour le Formenkreis), mais sur la totalité supérieure qui implique toutes les espèces. Des individus sont compris par le caractère d'espèce, des espèces seulement par le caractère de genre. C'est une preuve de la méthode de la nature créatrice. Elle exclut une évolution de genre du bas en haut, qui est irrégulière, faite par hasard ou formée directement par le milieu. De là nous dérivons le droit compréhensible d'un système naturel, qui est désormais plus qu'une simple classification.

     

Toward FRP-Based Brain-Machine Interfaces—Single-Trial Classification of Fixation-Related Potentials

The co-registration of eye tracking and electroencephalography provides a holistic measure of ongoing cognitive processes. Recently, fixation-related potentials have been introduced to quantify the neural activity in such bi-modal recordings. Fixation-related potentials are time-locked to fixation onsets, just like event-related potentials are locked to stimulus onsets. Compared to existing electroencephalography-based brain-machine interfaces that depend on visual stimuli, fixation-related potentials have the advantages that they can be used in free, unconstrained viewing conditions and can also be classified on a single-trial level. Thus, fixation-related potentials have the potential to allow for conceptually different brain-machine interfaces that directly interpret cortical activity related to the visual processing of specific objects. However, existing research has investigated fixation-related potentials only with very restricted and highly unnatural stimuli in simple search tasks while participant’s body movements were restricted. We present a study where we relieved many of these restrictions while retaining some control by using a gaze-contingent visual search task. In our study, participants had to find a target object out of 12 complex and everyday objects presented on a screen while the electrical activity of the brain and eye movements were recorded simultaneously. Our results show that our proposed method for the classification of fixation-related potentials can clearly discriminate between fixations on relevant, non-relevant and background areas. Furthermore, we show that our classification approach generalizes not only to different test sets from the same participant, but also across participants. These results promise to open novel avenues for exploiting fixation-related potentials in electroencephalography-based brain-machine interfaces and thus providing a novel means for intuitive human-machine interaction.     

Revealing Compartmentalized Diffusion in Living Cells with Interferometric Scattering Microscopy

The spatiotemporal organization and dynamics of the plasma membrane and its constituents are central to cellular function. Fluorescence-based single-particle tracking has emerged as a powerful approach for studying the single molecule behavior of plasma-membrane-associated events because of its excellent background suppression, at the expense of imaging speed and observation time. Here, we show that interferometric scattering microscopy combined with 40 nm gold nanoparticle labeling can be used to follow the motion of membrane proteins in the plasma membrane of live cultured mammalian cell lines and hippocampal neurons with up to 3 nm precision and 25 μs temporal resolution. The achievable spatiotemporal precision enabled us to reveal signatures of compartmentalization in neurons likely caused by the actin cytoskeleton.