Deficiency of rds/peripherin causes photoreceptor death in mouse models of digenic and dominant retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of inherited blinding diseases caused by mutations in multiple genes including RDS. RDS encodes rds/peripherin (rds), a 36-kDa glycoprotein in the rims of rod and cone outer-segment (OS) discs. Rom1 is related to rds with similar membrane topology and the identical distribution in OS. In contrast to RDS, no mutations in ROM1 alone have been associated with retinal disease. However, an unusual digenic form of RP has been described. Affected individuals in several families were doubly heterozygous for a mutation in RDS causing a leucine 185 to proline substitution in rds (L185P) and a null mutation in ROM1. Neither mutation alone caused clinical abnormalities. Here, we generated transgenic/knockout mice that duplicate the amino acid substitutions and predicted levels of rds and rom1 in patients with RDS-mediated digenic and dominant RP. Photoreceptor degeneration in the mouse model of digenic RP was faster than in the wild-type and monogenic controls by histological, electroretinographic, and biochemical analysis. We observed a positive correlation between the rate of photoreceptor loss and the extent of OS disorganization in mice of several genotypes. Photoreceptor degeneration in RDS-mediated RP appears to be caused by a simple deficiency of rds and rom1. The critical threshold for the combined abundance of rds and rom1 is ≈60% of wild type. Below this value, the extent of OS disorganization results in clinically significant photoreceptor degeneration.

Immunization with DNA vaccines encoding glycoprotein D or glycoprotein B, alone or in combination, induces protective immunity in animal models of herpes simplex virus-2 disease.

DNA vaccines expressing herpes simplex virus type 2 (HSV-2) full-length glycoprotein D (gD), or a truncated form of HSV-2 glycoprotein B (gB) were evaluated for protective efficacy in two experimental models of HSV-2 infection. Intramuscular (i.m.) injection of mice showed that each construction induced neutralizing serum antibodies and protected the mice from lethal HSV-2 infection. Dose-titration studies showed that low doses (< or = 1 microgram) of either DNA construction induced protective immunity, and that a single immunization with the gD construction was effective. The two DNAs were then tested in a low-dosage combination in guinea pigs. Immune sera from DNA-injected animals had antibodies to both gD and gB, and virus neutralizing activity. When challenged by vaginal infection with HSV-2, the DNA-immunized animals were significantly protected from primary genital disease.

Onconeural antigens and the paraneoplastic neurologic disorders: at the intersection of cancer, immunity, and the brain.

Paraneoplastic neurologic disorders (PNDs) are believed to be autoimmune neuronal degenerations that develop in some patients with systemic cancer. A series of genes encoding previously undiscovered neuronal proteins have been cloned using antiserum from PND patients. Identification of these onconeural antigens suggests a reclassification of the disorders into four groups: those in which neuromuscular junction proteins, nerve terminal/vesicle-associated proteins, neuronal RNA binding proteins, or neuronal signal-transduction proteins serve as target antigens. This review considers insights into basic neurobiology, tumor immunology, and autoimmune neuronal degeneration offered by the characterization of the onconeural antigens.

Rock friction and its implications for earthquake prediction examined via models of Parkfield earthquakes.

The friction of rocks in the laboratory is a function of time, velocity of sliding, and displacement. Although the processes responsible for these dependencies are unknown, constitutive equations have been developed that do a reasonable job of describing the laboratory behavior. These constitutive laws have been used to create a model of earthquakes at Parkfield, CA, by using boundary conditions appropriate for the section of the fault that slips in magnitude 6 earthquakes every 20-30 years. The behavior of this model prior to the earthquakes is investigated to determine whether or not the model earthquakes could be predicted in the real world by using realistic instruments and instrument locations. Premonitory slip does occur in the model, but it is relatively restricted in time and space and detecting it from the surface may be difficult. The magnitude of the strain rate at the earth's surface due to this accelerating slip seems lower than the detectability limit of instruments in the presence of earth noise. Although not specifically modeled, microseismicity related to the accelerating creep and to creep events in the model should be detectable. In fact the logarithm of the moment rate on the hypocentral cell of the fault due to slip increases linearly with minus the logarithm of the time to the earthquake. This could conceivably be used to determine when the earthquake was going to occur. An unresolved question is whether this pattern of accelerating slip could be recognized from the microseismicity, given the discrete nature of seismic events. Nevertheless, the model results suggest that the most likely solution to earthquake prediction is to look for a pattern of acceleration in microseismicity and thereby identify the microearthquakes as foreshocks.

Slip complexity in dynamic models of earthquake faults.

We summarize recent evidence that models of earthquake faults with dynamically unstable friction laws but no externally imposed heterogeneities can exhibit slip complexity. Two models are described here. The first is a one-dimensional model with velocity-weakening stick-slip friction; the second is a two-dimensional elastodynamic model with slip-weakening friction. Both exhibit small-event complexity and chaotic sequences of large characteristic events. The large events in both models are composed of Heaton pulses. We argue that the key ingredients of these models are reasonably accurate representations of the properties of real faults.

Bystander killing of cancer cells by herpes simplex virus thymidine kinase gene is mediated by connexins.

In gene therapy to treat cancer, typically only a fraction of the tumor cells can be successfully transfected with a gene. However, in the case of brain tumor therapy with the thymidine kinase gene from herpes simplex virus (HSV-tk), not only the cells transfected with the gene but also neighboring others can be killed in the presence of ganciclovir. Such a "bystander" effect is reminiscent of our previous observation that the effect of certain therapeutic agents may be enhanced by their diffusion through gap junctional intercellular communication (GJIC). Herein, we present the evidence, from in vitro studies, that gap junctions could indeed be responsible for such a gene therapy bystander effect. We used HeLa cells for this purpose, since they show very little, if any, ability to communicate through gap junctions. When HeLa cells were transfected with HSV-tk gene and cocultured with nontransfected cells, only HSV-tk-transfected HeLa cells (tk+) were killed by ganciclovir. However, when HeLa cells transfected with a gene encoding for the gap junction protein, connexin 43 (Cx43), were used, not only tk+ cells, but also tk- cells were killed, presumably due to the transfer, via Cx43-mediated GJIC, of toxic ganciclovir molecules phosphorylated by HSV-tk to the tk- cells. Such bystander effect was not observed when tk+ and tk- cells were cocultured without direct cell-cell contact between those two types of cells. Thus, our results give strong evidence that the bystander effect seen in HSV-tk gene therapy may be due to Cx-mediated GJIC.

Computational models of cortical visual processing.

The visual responses of neurons in the cerebral cortex were first adequately characterized in the 1960s by D. H. Hubel and T. N. Wiesel [(1962) J. Physiol. (London) 160, 106-154; (1968) J. Physiol. (London) 195, 215-243] using qualitative analyses based on simple geometric visual targets. Over the past 30 years, it has become common to consider the properties of these neurons by attempting to make formal descriptions of these transformations they execute on the visual image. Most such models have their roots in linear-systems approaches pioneered in the retina by C. Enroth-Cugell and J. R. Robson [(1966) J. Physiol. (London) 187, 517-552], but it is clear that purely linear models of cortical neurons are inadequate. We present two related models: one designed to account for the responses of simple cells in primary visual cortex (V1) and one designed to account for the responses of pattern direction selective cells in MT (or V5), an extrastriate visual area thought to be involved in the analysis of visual motion. These models share a common structure that operates in the same way on different kinds of input, and instantiate the widely held view that computational strategies are similar throughout the cerebral cortex. Implementations of these models for Macintosh microcomputers are available and can be used to explore the models' properties.

Models of speech synthesis.

The term "speech synthesis" has been used for diverse technical approaches. In this paper, some of the approaches used to generate synthetic speech in a text-to-speech system are reviewed, and some of the basic motivations for choosing one method over another are discussed. It is important to keep in mind, however, that speech synthesis models are needed not just for speech generation but to help us understand how speech is created, or even how articulation can explain language structure. General issues such as the synthesis of different voices, accents, and multiple languages are discussed as special challenges facing the speech synthesis community.

Models of natural language understanding.

This paper surveys some of the fundamental problems in natural language (NL) understanding (syntax, semantics, pragmatics, and discourse) and the current approaches to solving them. Some recent developments in NL processing include increased emphasis on corpus-based rather than example- or intuition-based work, attempts to measure the coverage and effectiveness of NL systems, dealing with discourse and dialogue phenomena, and attempts to use both analytic and stochastic knowledge. Critical areas for the future include grammars that are appropriate to processing large amounts of real language; automatic (or at least semi-automatic) methods for deriving models of syntax, semantics, and pragmatics; self-adapting systems; and integration with speech processing. Of particular importance are techniques that can be tuned to such requirements as full versus partial understanding and spoken language versus text. Portability (the ease with which one can configure an NL system for a particular application) is one of the largest barriers to application of this technology.

Mathematical analysis of activation thresholds in enzyme-catalyzed positive feedbacks: application to the feedbacks of blood coagulation.

A hierarchy of enzyme-catalyzed positive feedback loops is examined by mathematical and numerical analysis. Four systems are described, from the simplest, in which an enzyme catalyzes its own formation from an inactive precursor, to the most complex, in which two sequential feedback loops act in a cascade. In the latter we also examine the function of a long-range feedback, in which the final enzyme produced in the second loop activates the initial step in the first loop. When the enzymes generated are subject to inhibition or inactivation, all four systems exhibit threshold properties akin to excitable systems like neuron firing. For those that are amenable to mathematical analysis, expressions are derived that relate the excitation threshold to the kinetics of enzyme generation and inhibition and the initial conditions. For the most complex system, it was expedient to employ numerical simulation to demonstrate threshold behavior, and in this case long-range feedback was seen to have two distinct effects. At sufficiently high catalytic rates, this feedback is capable of exciting an otherwise subthreshold system. At lower catalytic rates, where the long-range feedback does not significantly affect the threshold, it nonetheless has a major effect in potentiating the response above the threshold. In particular, oscillatory behavior observed in simulations of sequential feedback loops is abolished when a long-range feedback is present.

The causes and prevention of cancer.

Epidemiological evidence indicates that avoidance of smoking, increased consumption of fruits and vegetables, and control of infections will have a major effect on reducing rates of cancer. Other factors include avoidance of intense sun exposure, increases in physical activity, and reduction of alcohol consumption and possibly red meat. A substantial reduction in breast cancer is likely to require modification of sex hormone levels, and development of practical methods for doing so is a high research priority. Resolution of the potential protective roles of specific antioxidants and other constituents of fruits and vegetables deserves major attention. Mechanistic studies of carcinogenesis indicate an important role of endogenous oxidative damage to DNA that is balanced by elaborate defense and repair processes. Also key is the rate of cell division, which is influenced by hormones, growth, cytotoxicity, and inflammation, as this determines the probability of converting DNA lesions to mutations. These mechanisms may underlie many epidemiologic observations.