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Moving into shape: cell migration during the development and histogenesis of the cerebellum

The enormous expansion the vertebrate nervous system goes through from its first anlage to its adult shape and organization goes along with extensive rearrangements of its constituent cells and typical cellular migrations, often over long distances, and by convoluted pathways. Here, I try to summarize how the cells that form the cerebellum move and migrate during normal cerebellar histogenesis. The cerebellum is made up of a limited set of clearly distinguishable classes of cells, some of which are also readily accessible by genetic tools. Its structure and development have been the focus of studies dating back to at least Ramon y Cajal which have yielded fundamental insights into basic mechanisms of the development of the nervous. During cerebellar histogenesis, several distinct and well-discernable modes of migration may be recognized, some of which have been studied in considerable morphological and molecular detail. Still, often grace to the detail known, a wealth of open questions remains, and the cerebellar anlage remains a highly accessible and promising paradigm for those interested in nervous system development and cell migration in general. I also point out some of the issues that may warrant consideration when results from technically distinct studies are compared and integrated.     

Protease activity and proteolytic modification of cellulases from a Trichoderma reesei QM 9414 selectant

Summary The secretion of multiple forms of cellulolytic enzymes by a Trichoderma reesei QM 9414 selectant exhibiting high protease activity (T. reesei QM 9414/A 30) was investigated using monoclonal, domain-specific antibodies against cellobiohydrolase (CBH) I, CBH II and -glucosidase, and a polyclonal antibody against endoglucanase I. The pattern of appearance of these proteins was followed during growth of the fungus on Avicel cellulose, using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting/immunostaining. Evidence was obtained that, at late cultivation stages, CBH I and II became partially modified to lower molecular weight components, whereas -glucosidase and endoglucanase I appeared to remain largely intact. Modification of CBH I appeared to commence from the carboxy-terminal AB region, whereas CBH II appeared to become modified both from the amino- (ABB') and the carboxy-terminal. Evidence for a protease activity that modifies the already truncated cellobiohydrolases in the culture filtrate was obtained. These results show that proteolysis at late culture stages may contribute to the multiplicity of cellulases found in T. reesei culture fluids. Initial proteolytic cleavage of CBH I and II may, however, involve an unusual protease not detectable by the azocasein method.Offprint requests to: C. P. Kubicek     

Effects of Adult Dreissena polymorpha on Settling Juveniles and Associated Macroinvertebrates

The impact of Dreissena polymorpha settlement on recruitment of juvenile mussels and density of other macroinvertebrates was studied in field experiments using blank concrete blocks and tiles (control), blocks and tiles with attached empty zebra mussel shells, and blocks and tiles with attached living mussels. On blocks, dominant invertebrate taxa showed colonization patterns coinciding with increased habitat complexity owing to zebra mussel settlement or the biodeposition of faeces and pseudofaeces. Adult and especially juvenile zebra mussels preferred blocks with empty shells to blank blocks and blocks with living mussels; this might possibly be caused by a chemical cue that induces gregarious settlement. Lower recruitment on blocks with attached living mussels compared to blocks with only shells could be the consequence of ingestion of larvae by adult mussels and of competition for food. On tiles, the sediments deposited and the organic content of the sediment were investigated. Sedimentation was significantly higher on shell‐only and live‐mussel tiles compared to blank tiles. Organic matter differed significantly between blank and live‐mussel tiles.     

Cooperativity in the calcium ion-induced quenching of the intrinsic fluorescence of a series of normal and GLA-deficient bovine prothrombin fragment 1 molecules

Ca²⁺ titrations of the intrinsic fluorescence of a series of -carboxyglutamic acid (GLA)-deficient bovine prothrombin fragments 1 yield response Hill plot parameters useful for characterization of the metal ion-binding process. 11-, 10-, and 9-GLA fragments 1 exhibitT _m (the (Ca²⁺)_total concentration at which ln (B/F)=0 in the response Hill plot) values between 0.2 and 0.3 mM. A 22-fold increase inT _m to 5.4 mM is observed for 8-GLA fragment 1.T _m decreases to 3.8 mM for the 7- and 6-GLA proteins. The value ofh, about 2.8±0.2 for 11-, 10-, and 9-GLA fragments 1, abruptly decreases to 1.2–1.3 for 8-, 7-, and 6-GLA fragments 1. The observed degree of quenching induced by saturating levels of calcium ions is affected by both changes in the intrinsic fluorescence of the metal ion-free proteins and in the maximum possible degree of quenching in the presence of calcium. The kinetic characteristics of the calcium ion-induced quenching of the intrinsic fluorescence of 6-GLA fragment 1 are identical to those observed in 10-GLA fragment 1, suggesting that the fluorescence quenching observed in the 6- and 10-GLA fragments 1, while different in magnitude, involves similar processes. Observation of an abrupt change in the relative electrophoretic mobilities of 11- to 9-GLA fragments 1 compared to 8- to 6-GLA fragments 1, in the absence or presence of Ca²⁺, suggests the existence of a major protein conformation change which occurs concomitantly with the noted changes inT _m andh response Hill plot parameters. Molecular mechanics calculations suggest a structural hypothesis unifying these observations. Central to this model is the presumption of the existence of hydrogen bond-mediated interactions between metal ion-binding sites.     

Role of Abca7 in Mouse Behaviours Relevant to Neurodegenerative Diseases

ATP-binding cassette transporters of the subfamily A (ABCA) are responsible for the translocation of lipids including cholesterol, which is crucial for neurological function. Recent studies suggest that the ABC transporter ABCA7 may play a role in the development of brain disorders such as schizophrenia and Alzheimer’s disease. However, Abca7’s role in cognition and other behaviours has not been investigated. Therefore, we characterised homozygous Abca7 knockout mice in a battery of tests for baseline behaviours (i.e. physical exam, baseline locomotion and anxiety) and behaviours relevant to schizophrenia (i.e. prepulse inhibition and locomotor response to psychotropic drugs) and Alzheimer’s disease (i.e. cognitive domains). Knockout mice had normal motor functions and sensory abilities and performed the same as wild type-like animals in anxiety tasks. Short-term spatial memory and fear-associated learning was also intact in Abca7 knockout mice. However, male knockout mice exhibited significantly impaired novel object recognition memory. Task acquisition was unaffected in the cheeseboard task. Female mice exhibited impaired spatial reference memory. This phenomenon was more pronounced in female Abca7 null mice. Acoustic startle response, sensorimotor gating and baseline locomotion was unaltered in Abca7 knockout mice. Female knockouts showed a moderately increased motor response to MK-801 than control mice. In conclusion, Abca7 appears to play only a minor role in behavioural domains with a subtle sex-specific impact on particular cognitive domains.     

Stimulation of Cortical Myosin Phosphorylation by p114RhoGEF Drives Cell Migration and Tumor Cell Invasion

Actinomyosin activity is an important driver of cell locomotion and has been shown to promote collective cell migration of epithelial sheets as well as single cell migration and tumor cell invasion. However, the molecular mechanisms underlying activation of cortical myosin to stimulate single cell movement, and the relationship between the mechanisms that drive single cell locomotion and those that mediate collective cell migration of epithelial sheets are incompletely understood. Here, we demonstrate that p114RhoGEF, an activator of RhoA that associates with non-muscle myosin IIA, regulates collective cell migration of epithelial sheets and tumor cell invasion. Depletion of p114RhoGEF resulted in specific spatial inhibition of myosin activation at cell-cell contacts in migrating epithelial sheets and the cortex of migrating single cells, but only affected double and not single phosphorylation of myosin light chain. In agreement, overall elasticity and contractility of the cells, processes that rely on persistent and more constant forces, were not affected, suggesting that p114RhoGEF mediates process-specific myosin activation. Locomotion was p114RhoGEF-dependent on Matrigel, which favors more roundish cells and amoeboid-like actinomyosin-driven movement, but not on fibronectin, which stimulates flatter cells and lamellipodia-driven, mesenchymal-like migration. Accordingly, depletion of p114RhoGEF led to reduced RhoA, but increased Rac activity. Invasion of 3D matrices was p114RhoGEF-dependent under conditions that do not require metalloproteinase activity, supporting a role of p114RhoGEF in myosin-dependent, amoeboid-like locomotion. Our data demonstrate that p114RhoGEF drives cortical myosin activation by stimulating myosin light chain double phosphorylation and, thereby, collective cell migration of epithelial sheets and amoeboid-like motility of tumor cells.     

Novel allocolchicinoids with an eight membered B-ring: design, synthesis and inhibition of tubulin assembly

Several B-ring variations of O-methyl androbiphenyline (8), newly accessible from (-)-(M,7S)-colchicine via photooxygenation and subsequent endoperoxide-transformation, were synthesized and evaluated for their inhibitory effects on tubulin assembly in vitro. The amino-allocolchicinoid (9), a key compound in this study, was transformed to the highly potent ketone 10 and by oxidation with H2O2/Na2WO4 to a mixture of syn/anti-oximes, like 11 and 12. These could easily be transformed to hitherto unknown allocolchicinoids 13 and 14 with an eight membered B-ring lactam obtained via a Beckmann rearrangement. Surprisingly both do not notably affect tubulin assembly, despite obvious structural similarities with active analogues of the thiocolchicine- and azasteganacin-series.     

Natural climate solutions versus bioenergy: Can carbon benefits of natural succession compete with bioenergy from short rotation coppice?

Short rotation plantations are often considered as holding vast potentials for future global bioenergy supply. In contrast to raising biomass harvests in forests, purpose‐grown biomass does not interfere with forest carbon (C) stocks. Provided that agricultural land can be diverted from food and feed production without impairing food security, energy plantations on current agricultural land appear as a beneficial option in terms of renewable, climate‐friendly energy supply. However, instead of supporting energy plantations, land could also be devoted to natural succession. It then acts as a long‐term C sink which also results in C benefits. We here compare the sink strength of natural succession on arable land with the C saving effects of bioenergy from plantations. Using geographically explicit data on global cropland distribution among climate and ecological zones, regionally specific C accumulation rates are calculated with IPCC default methods and values. C savings from bioenergy are given for a range of displacement factors (DFs), acknowledging the varying efficiency of bioenergy routes and technologies in fossil fuel displacement. A uniform spatial pattern is assumed for succession and bioenergy plantations, and the considered timeframes range from 20 to 100 years. For many parameter settings—in particular, longer timeframes and high DFs—bioenergy yields higher cumulative C savings than natural succession. Still, if woody biomass displaces liquid transport fuels or natural gas‐based electricity generation, natural succession is competitive or even superior for timeframes of 20–50 years. This finding has strong implications with climate and environmental policies: Freeing land for natural succession is a worthwhile low‐cost natural climate solution that has many co‐benefits for biodiversity and other ecosystem services. A considerable risk, however, is C stock losses (i.e., emissions) due to disturbances or land conversion at a later time.     

Ventilation of termite mounds: new results require a new model

In 1955, Lüscher proposed a ventilation mechanism forcathedral-shaped termite mounds to exchange respiratory gases. This mechanism was generally accepted, although it had neverbeen tested critically. We tested this mechanism by investigatingtemperatures, CO₂ concentrations, and air currents in and aroundtwo types of Macrotermes bellicosus mounds: cathedral-shapedmounds with many ridges and thin walls located in the savannaand dome-shaped mounds without ridges and with thick wallsin the forest. These two mound shapes have two different mechanismsof ventilation, depending on the environmental temperature.In the savanna during the day, sun heats the air in the peripheralair channels inside the ridges of the mound above the centralnest temperatures and produces a temperature gradient in theperipheral air channels with decreased temperatures at thetop of the mound. This temperature gradient leads to convectioncurrents with air rising inside the air channels of the ridgesto the top of the mound, meanwhile exchanging CO₂. In contrast,in the savanna during the night and generally in the forest,the temperatures inside the air channels are lower than thoseof the central nest, and no air currents rising upward insidethe air channels were detected. The CO₂ concentrations in theair channels of savanna mounds at night and forest mounds ingeneral were higher than during the day in the savanna. Therefore,our data do not support Lüscher's proposed mechanism.