The evolution of the cortico-cerebellar complex in primates: anatomical connections predict patterns of correlated evolution

Investigations into the evolution of the primate brain have tended to neglect the role of connectivity in determining which brain structures have changed in size, focusing instead on changes in the size of the whole brain or of individual brain structures, such as the neocortex, in isolation. We show that the primate cerebellum, neocortex, vestibular nuclei and relays between them exhibit correlated volumetric evolution, even after removing the effects of change in other structures. The patterns of correlated evolution among individual nuclei correspond to their known patterns of connectivity. These results support the idea that the brain evolved by mosaic size change in arrays of functionally connected structures. Furthermore, they suggest that the much discussed expansion of the primate neocortex should be re-evaluated in the light of conjoint cerebellar expansion.     

Rapid staining and enumeration of small numbers of total bacteria in water by solid-phase laser cytometry

The nucleic acid stain SYBR Green I was evaluated for use with solid-phase laser cytometry to obtain total bacterial cell counts from several water sources with small bacterial numbers. Results were obtained within 30 min and exceeded or equaled counts on R2A agar plates incubated for 14 days at room temperature.     

Structure and axon outgrowth inhibitor binding of the Nogo-66 receptor and related proteins

The myelin-derived proteins Nogo, MAG and OMgp limit axonal regeneration after injury of the spinal cord and brain. These cell-surface proteins signal through multi-subunit neuronal receptors that contain a common ligand-binding glycosylphosphatidylinositol-anchored subunit termed the Nogo-66 receptor (NgR). By deletion analysis, we show that the binding of soluble fragments of Nogo, MAG and NgR to cell-surface NgR requires the entire leucine-rich repeat (LRR) region of NgR, but not other portions of the protein. Despite sharing extensive sequence similarity with NgR, two related proteins, NgR2 and NgR3, which we have identified, do not bind Nogo, MAG, OMgp or NgR. To investigate NgR specificity and multi-ligand binding, we determined the crystal structure of the biologically active ligand-binding soluble ectodomain of NgR. The molecule is banana shaped with elongation and curvature arising from eight LRRs flanked by an N-terminal cap and a small C-terminal subdomain. The NgR structure analysis, as well as a comparison of NgR surface residues not conserved in NgR2 and NgR3, identifies potential protein interaction sites important in the assembly of a functional signaling complex.     

Mutation detection by electrocatalysis at DNA-modified electrodes

Detection of mutations and damaged DNA bases is important for the early diagnosis of genetic disease. Here we describe an electrocatalytic method for the detection of single-base mismatches as well as DNA base lesions in fully hybridized duplexes, based on charge transport through DNA films. Gold electrodes modified with preassembled DNA duplexes are used to monitor the electrocatalytic signal of methylene blue, a redox-active DNA intercalator, coupled to [Fe(CN)6]3-. The presence of mismatched or damaged DNA bases substantially diminishes the electrocatalytic signal. Because this assay is not a measure of differential hybridization, all single-base mismatches, including thermodynamically stable GT and GA mismatches, can be detected without stringent hybridization conditions. Furthermore, many common DNA lesions and "hot spot" mutations in the human p53 genome can be distinguished from perfect duplexes. Finally, we have demonstrated the application of this technology in a chip-based format. This system provides a sensitive method for probing the integrity of DNA sequences and a completely new approach to single-base mismatch detection.     

Influence of high biomass concentrations on alkane solubilities

Alkane solubilities were measured experimentally for high-density biomass. The resulting Henry's law constants for propane were found to decrease significantly for both dense yeast suspensions and an actual propane-degrading biofilm consortium. At the biomass densities of a typical biofilm, propane solubility was about an order of magnitude greater than that in pure water. For example, a dense biofilm had a propane Henry's law constant of 0.09+/-0.04 atm m(3) mol(-1) compared to 0.6+/-0.1 atm m(3) mol(-1) measured in pure water. The results were modeled with mixing rules and compared with octanol-water mixtures. Hydrogels (agar) and salts decreased the alkane solubility. By considering a theoretical solubility of propane in dry biomass, estimates were made of intrinsic Henry's law constants for propane in pure yeast and biomass, which were 13+/-2 and 5+/-2 atm kg biomass mol(-1) for yeast and biofilm consortium, respectively.