Cytoplasmic incompatibilities in the mosquito Culex pipiens: How to explain a cytotype polymorphism?*

Although cytoplasmic incompatibilities have been used as a means of eradicating the mosquito Culex pipiens, the population dynamics of these sterilities in relation to the coexistence of multiple incompatible cytotypes in a single area has not been investigated, except in the case of two unidirectionally incompatible cytotypes. An analytical model of the evolution of n cytotypes in an infinite panmictic population has been developed in order to investigate polymorphic equilibrium. A necessary criterion for the stability of such an equilibrium is established; it is shown that a stable polymorphism cannot exist between incompatible cytotypes. This result is discussed in the light of population dynamics and genetics of Culex pipiens, and of our present knowledge on incompatibilities. The consequences of a geographic structuring and of homogamy are considered. A careful reconsideration of previous experimental results disclosed probable nuclear effects and a serious experimental weakness: with the common procedure of backcrossing hybrid females to males of constant genotype it is not possible to rule out probable nuclear effects with paternal expression. It is concluded that incompatibilities in Culex pipiens may have a nuclear-cytoplasmic determinism.     

Genetic Network Analyzer: qualitative simulation of genetic regulatory networks

MOTIVATION: The study of genetic regulatory networks has received a major impetus from the recent development of experimental techniques allowing the measurement of patterns of gene expression in a massively parallel way. This experimental progress calls for the development of appropriate computer tools for the modeling and simulation of gene regulation processes. RESULTS: We present Genetic Network Analyzer (GNA), a computer tool for the modeling and simulation of genetic regulatory networks. The tool is based on a qualitative simulation method that employs coarse-grained models of regulatory networks. The use of GNA is illustrated by a case study of the network of genes and interactions regulating the initiation of sporulation in Bacillus subtilis. AVAILABILITY: GNA and the model of the sporulation network are available at http://www-helix.inrialpes.fr/gna.     

ISOZYME VARIABILITY IN TRYPANOSOMA CRUZI,THE AGENT OF CHAGAS' DISEASE: GENETICAL,TAXONOMICAL, AND EPIDEMIOLOGICAL SIGNIFICANCE

A genetic interpretation of the zymograms of 524 Trypanosoma cruzi stocks from various hosts and representing a broad geographical range (United States to Southern Brazil) reveals high genetic variability (only one monomorphic locus out of 15) and suggests that this parasite has a diploid structure. The data do not give any indication of Mendelian sexuality, although many opportunities are present for genetic exchange between extremely different genotypes. The population structure of T. cruzi appears to be multiclonal and complex. The natural clones evidenced by isozyme analysis are numerous (43 different ones are recorded among 121 stocks assayed at 15 gene loci) and exhibit a large range of genotypes, in a nonhierarchical structure; it is not possible to cluster them into a few strictly delimited groups which could represent natural taxa. The available data suggest that the genetic variability of T. cruzi reflects the long separate evolution of multiple clones. It is suggested that long clonal evolution may explain the present biological and medical variability of the causative agent of Chagas' disease.     

13C-NMR spectroscopic investigation of α- and β-1,4-D-glucose homooligomers

A complete, unambiguous assignment of all the ¹³C signals of cellobiose and maltose has been achieved using methods such as selective proton decoupling, ¹³C selective spin labeling, and isotopic chemical shift induced by deuterium. The chemical-shift variation of the ¹³C signals with the degree of polymerization in each α or β (1 → 4) series is discussed. The chemical-shift dependence on temperature and solvent in these two series is shown and interpreted in terms of modifications of the solvation and of the conformation.