Four chemoreceptors in Escherichia coli mediate responses to chemicals in the environment. The receptors self-associate and localize to the cell poles. This aggregation implies that interactions among receptors are important parameters of signal processing during chemotaxis. We examined this phenomenon using a receptor-coupled in vitro assay of CheA kinase activity. The ability of homogeneous populations of the serine receptor Tsr and the aspartate receptor Tar to stimulate CheA was directly proportional to the ratio of the receptor to total protein in cell membranes up to a fraction of 50%. Membranes containing mixed populations of Tar and Tsr supported an up to 4-fold greater stimulation of CheA than expected on the basis of the contributions of the individual receptors. Peak activity was seen at a Tar:Tsr ratio of 1:4. This synergy was observed only when the two proteins were expressed simultaneously, suggesting that, under our conditions, the fundamental "cooperative receptor unit" is relatively static, even in the absence of CheA and CheW. Finally, we observed that inhibition of receptor-stimulated CheA activity by serine or aspartate required significantly higher concentrations of ligand for membranes containing mixed Tsr and Tar populations than for membranes containing only Tsr (up to 10(2)-fold more serine) or Tar (up to 10(4)-fold more aspartate). Together with recent analyses of the interactions of Tsr and Tar in vivo, our results reveal the emergent properties of mixed receptor populations and emphasize their importance in the integrated signal processing that underlies bacterial chemotaxis.

Forest fires constitute a major environmental problem in tropical countries, especially in the context of climate change and increasing human populations. This paper aims to identify the causes of frequent forest fires in Son La Province, a fire-prone and forested mountainous region in northwest Vietnam, with a view to constructing a forest fire-related database with multiple layers of natural, social and economic information, extracted largely on the basis of Landsat 7 images. The assessment followed an expert systems approach, applying multi-criteria analysis (MCA) with an analytical hierarchy process (AHP) to determine the weights of the individual parameters related to forest fires. A multi-indicator function with nine parameters was constructed to establish a forest fire risk map at a scale of 1:100,000 for use at the provincial level. The results were verified through regression analysis, yielding R2 = 0.86. A real-time early warning system for forest fire areas has been developed for practical use by the relevant government authorities to provide more effective forest fire prevention planning for Son La Province.

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Phylogenetic relationships of novel Vietnamese strains of feline immunodeficiency virus (FIV) were analysed. One Vietnamese strain was found to cluster with subtype D, which was previously known only in Japan, while the other seven strains were placed with members of subtype C. Calculation of the relative numbers of mutations resulting in amino acid and silent changes in FIV env subtypes suggested that subtype C isolates may be less structurally constrained (potentially more pathogenic) than subtype B.

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ABSTRACT. A serosurvey of feline herpesvirus type 1 (FHV-1), feline calicivirus (FCV), and feline parvovirus (FPV) in cats from Ho Chi Minh City area in southern Vietnam was conducted in December 1998, and we compared the results with our previous results in northern Vietnam (Hanoi area). The positive rate of FHV and FCV in domestic cats were 44% and 74%, respectively. They were rather higher than those in Hanoi area, while the seropositivity of FPV (44%) was similar to that in Hanoi area. In leopard cats, the positive rate of FPV was high (3/4) and it indicated that FPV was prevailing in leopard cats in Vietnam.-KEY WORDS: feline calicivirus, feline herpesvirus type 1, feline parvovirus.J. Vet. Med. Sci. 61(12): 1313-1315 countries, cats are recognized as a working animal to catch mice. Previously we conducted a serosurvey for the viruses in domestic and leopard cats from Hanoi area in northern Vietnam in 1997 [8, 10]. In the present study, we expanded the study and collected samples of cats from Ho Chi Minh City (HCM) area in southern Vietnam and compared the results with our previous reports in northern Vietnam. As a consequence, we found that prevalence of the viruses was different between the areas. A total of 54 blood samples were collected from 50 domestic cats (Felis catus) and 4 leopard cats (Felis bengalensis) in December 1998. Most of the domestic cats were less than 4 years old. In addition, all the cats are considered to be unvaccinated for prophylaxis of viral infections because the vaccines are not commercially sold. As for the leopard cats, one cat from the Saigon ZooBotanical Garderns, one cat was household, two cats were captured in the vicinity of HCM. The cats were immobilized by an intramuscular injection with 20 mg/kg of Ketamine before sampling. The blood samples, from which plasmas were isolated, were collected by adding heparin for anticoagulation. The antibodies against FHV-1, FCV and FPV were tested by the indirect immunofluorescence assay (IFA) as described previously [8]. Plasma samples were screened at a dilution of 1:50 in the IFA.The results of this survey together with our previous reports [8,10] were summarized in Table 1. In Hanoi area, a positive rate for FHV-1 antibody was only 1.4%. The positive rates of FCV and FPV were 39 and 54%, respectively. On the contrary, in HCM area, the positive rate of FHV-1 antibody was 44%, which is by far higher than in Hanoi area. In addition, we found that the positive rate in male cats was three times higher than that in female cats. The positive rate of FCV antibody was 74% which was two times higher than that in Hanoi area. Unlike the FHV-1 infection, in FCV positive rates, we could not find a

Repetitive or prolonged seizures (status epilepticus) can damage neurons within the hippocampus, trigger gliosis, and generate an enduring state of hyperexcitability. Recent studies have suggested that microvesicles including exosomes are released from brain cells following stimulation and tissue injury, conveying contents between cells including microRNAs (miRNAs). Here, we characterized the effects of experimental status epilepticus on the expression of exosome biosynthesis components and analyzed miRNA content in exosome-enriched fractions. Status epilepticus induced by unilateral intra-amygdala kainic acid in mice resulted in acute subfield-specific, bidirectional changes in hippocampal transcripts associated with exosome biosynthesis including up-regulation of endosomal sorting complexes required for transport (ESCRT)dependent and-independent pathways. Increased expression of exosome components including Alix were detectable in samples obtained 2 weeks after status epilepticus and changes occurred in both the ipsilateral and contralateral hippocampus. RNA sequencing of exosome-enriched fractions prepared using two different techniques detected a rich diversity of conserved miRNAs and showed that status epilepticus selectively alters miRNA contents. We also characterized editing sites of the exosomeenriched miRNAs and found six exosome-enriched miRNAs that were adenosine-toinosine (ADAR) edited with the majority of the editing events predicted to occur within miRNA seed regions. However, the prevalence of these editing events was not altered by status epilepticus. These studies demonstrate that status epilepticus alters the exosome pathway and its miRNA content, but not editing patterns. Further functional studies will be needed to determine if these changes have pathophysiological significance for epileptogenesis.

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