Some properties of transmission lines composed of random networks

This paper discusses some properties of a nerve-axon-like transmission line made up from random networks of threshold elements. A random network contains a large number of threshold elements of which the threshold values are Gaussian random variables, and it can act as a monostable or a bistable multivibrator. The signal wave propagation in a transmission line is analyzed by a statistical method. The results show that a signal wave can propagate along the line and that its waveform is shaped, during propagation, into a specific form peculiar to the line. A self-oscillatory system that consists of two random networks is also analyzed. Even in this simple system, various modes of oscillation can exist, with periods varying over a wide range according to the values of system parameters. Examples of self-oscillations obtained by a graphical method are presented, and also some results of computer experiments are shown.     

Characterization of a Neurospora crassa photolyase-deficient mutant generated by repeat induced point mutation of the phr gene.

We produced a photolyase-deficient mutant by repeat induced point mutation using the Neurospora crassa photolyase gene cloned previously. This mutation identified a new gene, phr, which was mapped on the right arm of linkage group I by both RFLP mapping and conventional mapping. To investigate the relationship between photoreactivation and dark repair processes, especially excision repair, double mutants of phr with representative repair-defective mutants of different types were constructed and tested for UV sensitivity and photoreactivation. The results show that the phr mutation has no influence on dark repair. Tests with CPD and TC(6-4) photoproduct-specific antibodies demonstrated that the phr mutant is defective in CPD photolyase and confirmed that there is no TC(6-4) photolyase activity in N. crassa. Furthermore, N. crassa photolyase is not a blue light receptor in the signal transduction that induces carotenoid biosynthesis.     

Multiple centrosome formation induced by the expression of Vpr gene of human immunodeficiency virus.

We previously established a cell line called MIT-23 in which expression of the Vpr gene of human immunodeficiency virus 1 (HIV-1) can be controlled by the addition of tetracycline. Vpr expression induces multiple nuclear formation and increased ploidy in MIT-23 cells. We herein report that multipolar mitotic spindles were formed upon induction of Vpr. Further analysis of centrosomes with anti-gamma-tubulin immunostaining revealed that a significant population of cells 1 week after expression of Vpr gene product had an increased number of centrosomes in the cells with abnormal nuclei. Taking into account that the centrosome plays an important role in genome integrity, the abnormal number of centrosomes in cells expressing Vpr may be directly related to aneuploidy or the formation of micronuclei in MIT-23 cells, suggesting that Vpr has an oncogenic role in HIV infected cells.     

Viral induction and suppression of RNA silencing in plants

RNA silencing in plants and insects can function as a defence mechanism against invading viruses. RNA silencing-based antiviral defence entails the production of virus-derived small interfering RNAs which guide specific antiviral effector complexes to inactivate viral genomes. As a response to this defence system, viruses have evolved viral suppressors of RNA silencing (VSRs) to overcome the host defence. VSRs can act on various steps of the different silencing pathways. Viral infection can have a profound impact on the host endogenous RNA silencing regulatory pathways; alterations of endogenous short RNA expression profile and gene expression are often associated with viral infections and their symptoms. Here we discuss our current understanding of the main steps of RNA-silencing responses to viral invasion in plants and the effects of VSRs on endogenous pathways. This article is part of a Special Issue entitled: MicroRNAs in viral gene regulation.     

Genetic analyses of signalling in flower development using Arabidopsis

Flower development can be divided into four major steps: phase transition from vegetative to reproductive growth, formation of inflorescence meristem, formation and identity determination of floral organs, and growth and maturation of floral organs. Intercellular and intracellular signalling mechanisms must have important roles in each step of flower development, because it requires cell division, cell growth, and cell differentiation in a concerted fashion. Molecular genetic analysis of the process has started by isolation of a series of mutants with unusual flowering time, with aberrant structure in inflorescence and in flowers, and with no self-fertilization. At present more than 60 genes are identified from Arabidopsis thaliana and some of them have cloned. Although the information is still limited, several types of signalling systems are revealed. In this review, we summarize the present genetic aspects of the signalling network underlying the processes of flower development.     

Derangement in hepatic enzymes caused by sucrose-drinking and its implication for the development of hyperglycemia in female Wistar fatty rats

Eight-week-old, female Wistar fatty rats and their lean littermates were given a 30% sucrose solution in addition to a laboratory chow diet and water for 7 weeks. The fatty rats were hyperinsulinemic and hyperlipidemic, but normoglycemic when they drank only water. The hepatic activities of insulin-inducible glucokinase (GK), pyruvate kinase (PK), and malic enzyme (ME) were higher in the fatty rats than in the lean rats, whereas the insulin-suppressible glucose-6-phosphatase (G6Pase) activity was similar in both types of rats, indicating the normal response of hepatic enzymes to hyperinsulinemia in the fatty rats. When they drank the sucrose solution, the fatty rats, but not the lean rats, developed hyperglycemia over 200 mg/dl. Plasma insulin and triglyceride concentrations increased in both types of rats. Although the hepatic activities of GK, PK, and ME in the lean rats, and PK and ME in the fatty rats increased in response to the increase in plasma insulin, GK activity decreased in the fatty rats. On the other hand, G6Pase activity increased in both types of rats. As a result, the G6Pase/GK ratio, which may reflect net glucose handling in the liver, increased twofold in the fatty rats, but did not alter in the lean rats. From these findings, we conclude that sucrose ingestion induces an increase in hepatic glucose production through derangement of the hepatic enzyme profile and that the resultant decrease in hepatic glucose handling may be one of the pathogenic factors participating in the development of hyperglycemia in Wistar fatty rats.     

Polypurine sequences within a downstream exon function as a splicing enhancer.

We have previously shown that a purine-rich sequence located within exon M2 of the mouse immunoglobulin mu gene functions as a splicing enhancer, as judged by its ability to stimulate splicing of a distant upstream intron. This sequence element has been designated ERS (exon recognition sequence). In this study, we investigated the stimulatory effects of various ERS-like sequences, using the in vitro splicing system with HeLa cell nuclear extracts. Here, we show that purine-rich sequences of several natural exons that have previously been shown to be required for splicing function as a splicing enhancer like the ERS of the immunoglobulin mu gene. Moreover, even synthetic polypurine sequences had stimulatory effects on the upstream splicing. Evaluation of the data obtained from the analyses of both natural and synthetic purine-rich sequences shows that (i) alternating purine sequences can stimulate splicing, while poly(A) or poly(G) sequences cannot, and (ii) the presence of U residues within the polypurine sequence greatly reduces the level of stimulation. Competition experiments strongly suggest that the stimulatory effects of various purine-rich sequences are mediated by the same trans-acting factor(s). We conclude from these results that the purine-rich sequences that we examined in this study also represent examples of ERS. Thus, ERS is considered a general splicing element that is present in various exons and plays an important role in splice site selection.     

Some critical factors involved in formation of conditioned taste aversion to sodium chloride in rats

Some factors concerning acquisition and retention of conditionedtaste aversions (CTAs) were behaviorally examined in the rat.In the CTA paradigm, aqueous solution of 0.1 M NaCl was usedas the conditioned stimulus (CS) and an intraperitoneal (i.p.)injection of 0.15 M LiCl was employed as the unconditioned stimulus(US). In experiment 1, CTAs to 0.1 M NaCl were examined in bothforward (CS–US) and backward (US–CS) conditioningparadigms. Reliable CTAs were produced in the US–CS conditioningparadigm when the US–CS interval was less than 10 min,as well as in the CS–US conditioning paradigm. In experiment2, strong CTAs to 0.1 M NaCl were established when water-deprivedrats made at least 500 continuous licks, corresponding to 2.5ml intake and 2 min of drinking time. In experiment 3, effectsof gustatory deafferentation on CTA formation were studied.Only the chorda tympani played an important role in acquisitionand retention of CTAs to NaCl solutions. These results ipHimMthat strong CTAs can be acquired to 0.1 M NaCl, if its tasteinformation which is conveyed via the chorda tympani duringthe 500 continuous licks is followed by LiCl-induced sickness.