Architecture and material properties of diatom shells provide effective mechanical protection

Diatoms are the major contributors to phytoplankton blooms in lakes and in the sea and hence are central in aquatic ecosystems and the global carbon cycle. All free-living diatoms differ from other phytoplankton groups in having silicified cell walls in the form of two 'shells' (the frustule) of manifold shape and intricate architecture whose function and role, if any, in contributing to the evolutionary success of diatoms is under debate. We explored the defence potential of the frustules as armour against predators by measuring their strength. Real and virtual loading tests (using calibrated glass microneedles and finite element analysis) were performed on centric and pennate diatom cells. Here we show that the frustules are remarkably strong by virtue of their architecture and the material properties of the diatom silica. We conclude that diatom frustules have evolved as mechanical protection for the cells because exceptional force is required to break them. The evolutionary arms race between diatoms and their specialized predators will have had considerable influence in structuring pelagic food webs and biogeochemical cycles.     

The cognition-knowledge distinction in Kant and Dilthey and the implications for psychology and self-understanding

Both Kant and Dilthey distinguish between cognition and knowledge, but they do so differently in accordance with their respective theoretical interests. Kant’s primary cognitive interest is in the natural sciences, and from this perspective the status of psychology is questioned because its phenomena are not mathematically measurable. Dilthey, by contrast, reconceives psychology as a human science.For Kant, knowledge is conceptual cognition that has attained certainty by being part of a rational system. Dilthey also links knowledge with certainty; however, he derives the latter from life-experience rather than from reason. Dilthey’s psychology begins with the self-certainty of lived experience and life-knowledge, but this turns out to fall short of cognitive understanding. In the final analysis, both Kant and Dilthey move beyond psychology to arrive at self-understanding. Because of his doubts about introspection, Kant replaces psychology with a pragmatic anthropology to provide a communal framework for self-understanding. Dilthey supplements psychology with other human sciences as part of a project of anthropological reflection.     

DGCR8 is essential for microRNA biogenesis and silencing of embryonic stem cell self-renewal

The molecular controls that govern the differentiation of embryonic stem (ES) cells remain poorly understood. DGCR8 is an RNA-binding protein that assists the RNase III enzyme Drosha in the processing of microRNAs (miRNAs), a subclass of small RNAs. Here we study the role of miRNAs in ES cell differentiation by generating a Dgcr8 knockout model. Analysis of mouse knockout ES cells shows that DGCR8 is essential for biogenesis of miRNAs. On the induction of differentiation, DGCR8-deficient ES cells do not fully downregulate pluripotency markers and retain the ability to produce ES cell colonies; however, they do express some markers of differentiation. This phenotype differs from that reported for Dicer1 knockout cells, suggesting that Dicer has miRNA-independent roles in ES cell function. Our findings indicate that miRNAs function in the silencing of ES cell self-renewal that normally occurs with the induction of differentiation.     

The conserved protein DCN-1/Dcn1p is required for cullin neddylation in C. elegans and S. cerevisiae

SCF-type E3 ubiquitin ligases are multi-protein complexes required for polyubiquitination and subsequent degradation of target proteins by the 26S proteasome. Cullins, together with the RING-finger protein Rbx1, form the catalytic core of the ligase, and recruit the substrate-recognition module. Cycles of covalent modification of cullins by the ubiquitin-like molecule Nedd8 (neddylation) and removal of Nedd8 by the COP9 signalosome (deneddylation) positively regulate E3 ligase activity. Here we report the identification and analysis of a widely conserved protein that is required for cullin neddylation in the nematode Caenorhabditis elegans and the yeast Saccharomyces cerevisiae. C. elegans DCN-1 and S. cerevisiae Dcn1p (defective in cullin neddylation) are characterized by a novel UBA-like ubiquitin-binding domain and a DUF298 domain of unknown function. Consistent with their requirements for neddylation, DCN-1 and Dcn1p directly bind Nedd8 and physically associate with cullins in both species. Moreover, overexpression of Dcn1p in yeast results in the accumulation of Nedd8-modified cullin Cdc53p. Both in vivo and in vitro experiments indicate that Dcn1p does not inhibit deneddylation of Cdc53p by the COP9 signalosome, but greatly increases the kinetics of the neddylation reaction.     

Temperature and salinity relationships in marine bottom invertebrates

Zusammenfassung Das Ausmass des Temperaturbereiches mariner Arten ist in erster Linie durch erbliche zellphysiologische Eigenschaften bedingt. An isolierten Gewebestücken mariner Bodenevertebraten aus kaltem Tiefenwasser und aus wärmeren oberflächlichen Schichten lässt sich dementsprechend zeigen, dass ihr genotypischer thermischer Resistenz-und Leistungsbereich quantitativ verschieden ist und bei stenothermen Arten auch nicht individuell phänotypisch verändert werden kann.Der Umfang des Salzgehaltsbereiches stenohaliner und euryhaliner Arten ist ebenfalls in erster Linie zellulär genetisch bedingt. Jedoch beruhen thermische und osmotische Resistenz auf verschiedenen zellphysiologischen Mechanismen. Nur bei euryhalinen Formen lösen Veränderungen der Salzkonzentration des Aussenmediums individuelle zelluläre Resistenz- und Leistungsverschiebungen aus.Niedere Temperaturen begünstigen innerhalb des artspezifischen thermischen Resistenzbereiches Anpassung an extrem niedrige und hohe Salzkonzentrationen.Die starke Einwanderung mariner Arten in tropische Brackwässer kann nicht durch die Annahme erklärt werden, dass die Osmoregulation in der Wärme leichter ist.

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Presented at the Internat. Oceanographic Congress, New York 1959.     

Monoclonal mice generated by nuclear transfer from mature B and T donor cells

Cloning from somatic cells is inefficient, with most clones dying during gestation. Cloning from embryonic stem (ES) cells is much more effective, suggesting that the nucleus of an embryonic cell is easier to reprogram. It is thus possible that most surviving clones are, in fact, derived from the nuclei of rare somatic stem cells present in adult tissues, rather than from the nuclei of differentiated cells, as has been assumed. Here we report the generation of monoclonal mice by nuclear transfer from mature lymphocytes. In a modified two-step cloning procedure, we established ES cells from cloned blastocysts and injected them into tetraploid blastocysts to generate mice. In this approach, the embryo is derived from the ES cells and the extra-embryonic tissues from the tetraploid host. Animals cloned from a B-cell nucleus were viable and carried fully rearranged immunoglobulin alleles in all tissues. Similarly, a mouse cloned from a T-cell nucleus carried rearranged T-cell-receptor genes in all tissues. This is an unequivocal demonstration that a terminally differentiated cell can be reprogrammed to produce an adult cloned animal.     

Nanoscale imaging magnetometry with diamond spins under ambient conditions

Magnetic resonance imaging and optical microscopy are key technologies in the life sciences. For microbiological studies, especially of the inner workings of single cells, optical microscopy is normally used because it easily achieves resolution close to the optical wavelength. But in conventional microscopy, diffraction limits the resolution to about half the wavelength. Recently, it was shown that this limit can be partly overcome by nonlinear imaging techniques, but there is still a barrier to reaching the molecular scale. In contrast, in magnetic resonance imaging the spatial resolution is not determined by diffraction; rather, it is limited by magnetic field sensitivity, and so can in principle go well below the optical wavelength. The sensitivity of magnetic resonance imaging has recently been improved enough to image single cells, and magnetic resonance force microscopy has succeeded in detecting single electrons and small nuclear spin ensembles. However, this technique currently requires cryogenic temperatures, which limit most potential biological applications. Alternatively, single-electron spin states can be detected optically, even at room temperature in some systems. Here we show how magneto-optical spin detection can be used to determine the location of a spin associated with a single nitrogen-vacancy centre in diamond with nanometre resolution under ambient conditions. By placing these nitrogen-vacancy spins in functionalized diamond nanocrystals, biologically specific magnetofluorescent spin markers can be produced. Significantly, we show that this nanometre-scale resolution can be achieved without any probes located closer than typical cell dimensions. Furthermore, we demonstrate the use of a single diamond spin as a scanning probe magnetometer to map nanoscale magnetic field variations. The potential impact of single-spin imaging at room temperature is far-reaching. It could lead to the capability to probe biologically relevant spins in living cells.     

CAS directly interacts with vinculin to control mechanosensing and focal adhesion dynamics

Focal adhesions are cellular structures through which both mechanical forces and regulatory signals are transmitted. Two focal adhesion-associated proteins, Crk-associated substrate (CAS) and vinculin, were both independently shown to be crucial for the ability of cells to transmit mechanical forces and to regulate cytoskeletal tension. Here, we identify a novel, direct binding interaction between CAS and vinculin. This interaction is mediated by the CAS SRC homology 3 domain and a proline-rich sequence in the hinge region of vinculin. We show that CAS localization in focal adhesions is partially dependent on vinculin, and that CAS–vinculin coupling is required for stretch-induced activation of CAS at the Y410 phosphorylation site. Moreover, CAS–vinculin binding significantly affects the dynamics of CAS and vinculin within focal adhesions as well as the size of focal adhesions. Finally, disruption of CAS binding to vinculin reduces cell stiffness and traction force generation. Taken together, these findings strongly implicate a crucial role of CAS–vinculin interaction in mechanosensing and focal adhesion dynamics.