Besprechungen

Ohne Zusammenfassung     

Besprechungen

Ohne Zusammenfassung     

Vitaminstudien

Ohne Zusammenfassung     

Step-Wise Assembly,Maturation and Dynamic Behavior of the Human CENP-P/O/R/Q/U Kinetochore Sub-Complex

Kinetochores are multi-protein megadalton assemblies that are required for attachment of microtubules to centromeres and, in turn, the segregation of chromosomes in mitosis. Kinetochore assembly is a cell cycle regulated multi-step process. The initial step occurs during interphase and involves loading of the 15-subunit constitutive centromere associated complex (CCAN), which contains a 5-subunit (CENP-P/O/R/Q/U) sub-complex. Here we show using a fluorescent three-hybrid (F3H) assay and fluorescence resonance energy transfer (FRET) in living mammalian cells that CENP-P/O/R/Q/U subunits exist in a tightly packed arrangement that involves multifold protein-protein interactions. This sub-complex is, however, not pre-assembled in the cytoplasm, but rather assembled on kinetochores through the step-wise recruitment of CENP-O/P heterodimers and the CENP-P, -O, -R, -Q and -U single protein units. SNAP-tag experiments and immuno-staining indicate that these loading events occur during S-phase in a manner similar to the nucleosome binding components of the CCAN, CENP-T/W/N. Furthermore, CENP-P/O/R/Q/U binding to the CCAN is largely mediated through interactions with the CENP-N binding protein CENP-L as well as CENP-K. Once assembled, CENP-P/O/R/Q/U exchanges slowly with the free nucleoplasmic pool indicating a low off-rate for individual CENP-P/O/R/Q/U subunits. Surprisingly, we then find that during late S-phase, following the kinetochore-binding step, both CENP-Q and -U but not -R undergo oligomerization. We propose that CENP-P/O/R/Q/U self-assembles on kinetochores with varying stoichiometry and undergoes a pre-mitotic maturation step that could be important for kinetochores switching into the correct conformation necessary for microtubule-attachment.     

Frizzled-3a and slit2 genetically interact to modulate midline axon crossing in the telencephalon

The anterior commissure forms the first axon connections between the two sides of the embryonic telencephalon. We investigated the role of the transmembrane receptor Frizzled-3a in the development of this commissure using zebrafish as an experimental model. Knock down of Frizzled-3a resulted in complete loss of the anterior commissure. This defect was accompanied by a loss of the glial bridge, expansion of the slit2 expression domain and perturbation of the midline telencephalic-diencephalic boundary. Blocking Slit2 activity following knock down of Frizzled-3a effectively rescued the anterior commissure defect which suggested that Frizzled-3a was indirectly controlling the growth of axons across the rostral midline. We have shown here that Frizzled-3a is essential for normal development of the commissural plate and that loss-of-function causes Slit2-dependent defects in axon midline crossing in the embryonic vertebrate forebrain. These data supports a model whereby Wnt signaling through Frizzled-3a attenuates expression of Slit2 in the rostral midline of the forebrain. The absence of Slit2 facilitates the formation of a midline bridge of glial cells which is used as a substrate for commissural axons. In the absence of this platform of glia, commissural axons fail to cross the rostral midline of the forebrain.     

The Novel Deacetylase Inhibitor AR-42 Demonstrates Pre-Clinical Activity in B-Cell Malignancies In Vitro and In Vivo

Background

While deacetylase (DAC) inhibitors show promise for the treatment of B-cell malignancies, those introduced to date are weak inhibitors of class I and II DACs or potent inhibitors of class I DAC only, and have shown suboptimal activity or unacceptable toxicities. We therefore investigated the novel DAC inhibitor AR-42 to determine its efficacy in B-cell malignancies.

Principal Findings

In mantle cell lymphoma (JeKo-1), Burkitt''s lymphoma (Raji), and acute lymphoblastic leukemia (697) cell lines, the 48-hr IC₅₀ (50% growth inhibitory concentration) of AR-42 is 0.61 µM or less. In chronic lymphocytic leukemia (CLL) patient cells, the 48-hr LC₅₀ (concentration lethal to 50%) of AR-42 is 0.76 µM. AR-42 produces dose- and time-dependent acetylation both of histones and tubulin, and induces caspase-dependent apoptosis that is not reduced in the presence of stromal cells. AR-42 also sensitizes CLL cells to TNF-Related Apoptosis Inducing Ligand (TRAIL), potentially through reduction of c-FLIP. AR-42 significantly reduced leukocyte counts and/or prolonged survival in three separate mouse models of B-cell malignancy without evidence of toxicity.

Conclusions/Significance

Together, these data demonstrate that AR-42 has in vitro and in vivo efficacy at tolerable doses. These results strongly support upcoming phase I testing of AR-42 in B-cell malignancies.     

Über die Plasmagrenzschichten im Pollenkorn

Zusammenfassung Das vegetative Plasma der Pollenkörner ist mit Wasser mischbar. Dieser Umstand ist der Tatsache zu verdanken, daß es keine Grenzschicht besitzt, welche dem Plasmalemma der durchschnittlichen Pflanzenzellen mechanisch oder physiologisch gleichwertig wäre.Pollenkörner verschiedener Pflanzen lassen sich aus diesem Grunde nicht plasmolysieren.Zahlreicher sind die Pollensorten, welche in Anelektrolyt- und Salzlösungen trotzdem plasmolysiert werden können. Auch da scheint keine dem Plasmalemma gleichwertige semipermeable Membran vorzuliegen. Die extrem hohe Permeabilität mancher Pollenkörner und mancher Stadien von solchen für Anelekrolyte und besonders für Traubenzucker entspricht diesen Verhältnissen.Die generative Zelle besitzt ein echtes Plasmalemma.