Information-Theoretic Analysis of Neural Coding

We describe an approach to analyzing single- and multiunit (ensemble) discharge patterns based on information-theoretic distance measures and on empirical theories derived from work in universal signal processing. In this approach, we quantify the difference between response patterns, whether time-varying or not, using information-theoretic distance measures. We apply these techniques to single- and multiple-unit processing of sound amplitude and sound location. These examples illustrate that neurons can simultaneously represent at least two kinds of information with different levels of fidelity. The fidelity can persist through a transient and a subsequent steady-state response, indicating that it is possible for an evolving neural code to represent information with constant fidelity.     

Characterization of an antigenically related family of cell-type specific proteins implicated in slug migration in Dictyostelium discoideum

The monoclonal antibody MUD50 recognizes a group of developmentally regulated proteins, which are almost exclusively expressed by prespore cells in developing aggregates of Dictyostelium discoideum. Some of these antigens are integrally associated with the cell membrane, as assessed by physical and detergent-fractionation procedures. The MUD50-reactive proteins are glycosylated and some are phosphorylated. Post-translational modification is the common antigenic feature that is recognized by the MUD50 antibody in these cell-type-specific proteins. A glycosylation-defective mutant, DL118, (modB) does not express the MUD50 epitope, but does express the MUD52 epitope, which is found on a different group of glycoproteins. Therefore, we conclude that MUD50 recognizes a particular carbohydrate epitope on a restricted group of proteins. These proteins are structurally diverse, but are apparently involved in the maintenance of structure and movement of the multicellular D. discoideum slug.     

Dual infection and superinfection inhibition of epithelial skin cells by two alphaherpesviruses co-occur in the natural host

Hosts can be infected with multiple herpesviruses, known as superinfection; however, superinfection of cells is rare due to the phenomenon known as superinfection inhibition. It is believed that dual infection of cells occurs in nature, based on studies examining genetic exchange between homologous alphaherpesviruses in the host, but to date, this has not been directly shown in a natural model. In this report, gallid herpesvirus 2 (GaHV-2), better known as Marek's disease virus (MDV), was used in its natural host, the chicken, to determine whether two homologous alphaherpesviruses can infect the same cells in vivo. MDV shares close similarities with the human alphaherpesvirus, varicella zoster virus (VZV), with respect to replication in the skin and exit from the host. Recombinant MDVs were generated that express either the enhanced GFP (eGFP) or monomeric RFP (mRFP) fused to the UL47 (VP13/14) herpesvirus tegument protein. These viruses exhibited no alteration in pathogenic potential and expressed abundant UL47-eGFP or -mRFP in feather follicle epithelial cells in vivo. Using laser scanning confocal microscopy, it was evident that these two similar, but distinguishable, viruses were able to replicate within the same cells of their natural host. Evidence of superinfection inhibition was also observed. These results have important implications for two reasons. First, these results show that during natural infection, both dual infection of cells and superinfection inhibition can co-occur at the cellular level. Secondly, vaccination against MDV with homologous alphaherpesvirus like attenuated GaHV-2, or non-oncogenic GaHV-3 or meleagrid herpesvirus (MeHV-1) has driven the virus to greater virulence and these results implicate the potential for genetic exchange between homologous avian alphaherpesviruses that could drive increased virulence. Because the live attenuated varicella vaccine is currently being administered to children, who in turn could be superinfected by wild-type VZV, this could potentiate recombination events of VZV as well.     

Nonenzymatic incorporation of glucose and galactose into brain cytoskeletal proteins in vitro.

Initial studies demonstrated the loss of lysine and simultaneous appearance of glucitollysine in intracellular proteins following incubation with sugar. For example, when a crude nervous tissue cytoskeletal preparation was incubated in 100 mM glucose for 10 days, > 60% of the lysine residues were modified. Over 20% of the lysyl residues in a spinal cord neurofilament preparation are susceptible to Schiff base formation after one day and over 30% following five days of incubation with 100 mM glucose. When incubated with 100 mM galactose, F- and G-actin were found to be significantly modified in as few as 15 h, with > 70% of the lysyl residues lost. After 45 h of incubation, > 90% of the residues had been modified. These data also indicate that many of the lysyl residues in F- and G-actin are exposed and very susceptible to modification by sugar. This rapid and extensive modification of lysine in actin in vitro suggest that it may be modified in diabetic nervous tissue.     

STRUCTURE OF THE ANISOGAMETES OF THE GREEN SIPHON PSEUDOBRYOPSIS SP. (CHLOROPHYTA)1

The fine structure of the male and female gametes of Pseudobryopsis, particularly that of the flagellar apparatus, is compared with that of swarmers of other green algae. There is general similarity, with differences in detail, to the Ulvales and other green siphons that have been studied. The similarities include overlapping basal bodies, the capping plate type of connective between basal bodies, terminal caps, and system II fibrous roots (rhizoplasts). The capping plate of the female gamete differs from that in other green siphons and the Ulvales in form and in the presence of a faint striation. A diagram illustrating the actual arrangement of the components of the flagellar apparatus is given, along with a discussion of the fact that the mirror image of the true arrangement has been given in some reports on ulvaphycean algae.     

Interaction of multiple factors with a GC-rich rlement within the mitogen responsive region of the human transferrin receptor gene

Nuclear factors from HeLa cells were isolated by elution of DNA-cellulose bound proteins with a double stranded synthetic oligonucleotide corresponding to the region from ?34 to ?79 of the human transferrin receptor (TR) gene promoter. The eluted proteins were further purified and separated from the oligonucleotide by ion exchange chromatography. Proteins within the resulting fraction bound with specificity to the TR promoter. Retardation gel analysis and competition with specific double-stranded oligonucleotides show that multiple factors present in this fraction compete for binding within the same region of the TR promoter. Footprinting experiments demonstrate that these factors contact a GC-rich element that is within the region that is required for enhanced expression of the gene in proliferating cells. One of the factors protects an extended DNA sequence but, still contacts the GC-rich element.     

Selective effects of nonionic detergent and salt solutions in dissolving nuclear envelope protein

Protein has been selectively extracted from isolated chicken erythrocyte nuclear envelope by (1) dilute MgCl₂/Triton X-100 followed by (2) concentrated MgCl₂/Triton X-100 solutions. Certain proteins appear to be selectively dissolved in the first solvent and may occur in the nuclear envelope primarily as lipoproteins. Among the proteins insoluble in the low MgCl₂/Triton X-100 wash, as well as in 500 mM MgCl₂ without Triton previously used in the preparation of the envelope fraction, the quantitatively major polypeptides dissolve in a combination of high MgCl₂ and Triton X-100. Further, much of this dissolved protein precipitates when the MgCl₂ concentration is lowered by dialysis. The insolubility of these proteins appears to result from a combination of ionic and hydrophobic interactions and may explain the resistance of nuclei to various manipulative procedures including nonionic detergent washes. The procedures described provide a route for gently and selectively dissolving representative proteins from the nuclear envelope lipoprotein matrix and from the envelope “residual” protein.