Expression of mitochondrial HMGCoA synthase and glutaminase in the colonic mucosa is modulated by bacterial species.

The expression of the colonic mitochondrial 3-hydroxy 3-methyl glutaryl CoA (mHMGCoA) synthase, a key control site of ketogenesis from butyrate, is lower in germ-free (GF) than in conventional (CV) rats. In contrast, the activity of glutaminase is higher. The objective of this study was to investigate whether the intestinal flora can affect gene expression through short chain fatty acid (SCFA) and butyrate production. GF rats were inoculated with a conventional flora (Ino-CV) or with a bacterial strain producing butyrate (Clostridium paraputrificum, Ino-Cp) or not (Bifidobacterium breve, Ino-Bb). In the Ino-CV rats, mHMGCoA synthase expression was restored to the CV values 2 days after the inoculation, i.e. concomitantly with SCFA production. In the Ino-Cp group, but not in the Ino-Bb group, mHMGCoA synthase and glutaminase were expressed at the level observed in the CV rats. These data suggest that the intestinal flora, through butyrate production, could control the expression of colonic mHMGCoA synthase and glutaminase. These modifications in gene expression by butyrate in vivo seem unrelated to a modification of histone acetylation.     

A new hypothesis for the origin of pentaploid Holcus from diploid Holcus lanatus L. and tetraploid Holcus mollis L. in France

The Holcus complex in France consists of two species, Holcus lanatus L. (Yorkshire fog; 2n= 2x= 14) and Holcus mollis L. (Creeping soft-grass; 2n= 4x= 28) and an interspecific hybrid H.m.×H.l. (2n= 5x= 35), which is morphologically similar to Holcus mollis. A heterologous rDNA probe from wheat was used to detect the corresponding region in Holcus (s. l.) genomic DNA'fragments, for six to eight plants from 13 populations located south-west of Paris. A restriction enzyme map of the ribosomal RNA genes (rDNA) in Holcus (s. l.) was also constructed. The length polymorphism detected in the IGS region was used as a DNA fingerprint for the identification of different cytotypes and species of the Holcus complex and for the typing and delimitation of individuals in populations. In the light of the results we reconsider the assumption that the pentaploid hybrid H.m.×H.l. is purely clonal. New hypotheses concerning the origin of the pentaploid hybrid and its reproduction are proposed, and the consequences for genetic diversity in natural populations discussed.     

A method to determine the mean pollen dispersal of individual plants growing within a large pollen source

Pollen dispersal has been recently focused on as a major issue in the risk assessment of transgenic crop plants. The shape of the pollen dispersal of individual plants is hard to determine since a very large number of plants must be monitored in order to track rare longdistance dispersal events. Conversely, studies using large plots as a pollen source provide a pollen distribution that depends on the shape of the source plot. We report here on a method based on the use of Fourier transforms by which the pollen dispersal of a single, average individual can be obtained from data using large plots as pollen sources, thus allowing the estimation of the probability of long-distance dispersal for single plants. This method is subsequently implemented on simulated data to test its susceptibility to random noise and edge effects. Its conditions of application and value for use in ecological studies, in particular risk assessment of the deliberate release of transgenic plants, are discussed.     

Plant domestication: a model for studying the selection of linkage

The process of domestication leads to acquisition of traits that are often similar between plant species that belong to the same family but have different breeding systems. Hence domestication is a useful model for studying evolutionary responses to selection in plants with contrasting breeding systems. We consider a stochastic model simulating gene flow between a natural population and an initial population containing mutants with domesticated phenotypes at low frequency. We assume that a large number of loci contribute equally to the cultivated phenotype. Our results indicate that the number of loci for which the mutant (‘domestication’) allele is maintained is larger in autogamous plants than in allogamous ones and that domestication can lead to the selection of tightly linked combinations of genes in allogamous plants. This work provides a general model for the selection of gene clusters through a sieve effect and it is discussed in comparison with models proposed to explain the evolution of linkage of genes determining wing patterns in butterflies exhibiting Batesian mimicry.     

Homogeneous triploidy in 2 premature infants (69 XXY)

Two new cases of 69 XXY triploidy in live-born neonates are reported. As in 40 others cases of literature observed after 24 weeks of gestation, this chromosome abnormality was lethal. The clinical features are: a large posterior fontanelle, low set ears, syndactylies of hands and feet, and genital abnormalities in the presence of a 69 XXY karyotype. The first patient present a macrocytosis of red blood cells. Macrocytosis, large polymorphonuclear leukocytes and platelets can evoke the diagnosis of triploidy in a malformed newborn.