Sex-biased dispersal promotes adaptive parental effects

Background  

In heterogeneous environments, sex-biased dispersal could lead to environmental adaptive parental effects, with offspring selected to perform in the same way as the parent dispersing least, because this parent is more likely to be locally adapted. We investigate this hypothesis by simulating varying levels of sex-biased dispersal in a patchy environment. The relative advantage of a strategy involving pure maternal (or paternal) inheritance is then compared with a strategy involving classical biparental inheritance in plants and in animals.     

Molecular Reclassification of Crohn’s Disease: A Cautionary Note on Population Stratification

Complex human diseases commonly differ in their phenotypic characteristics, e.g., Crohn’s disease (CD) patients are heterogeneous with regard to disease location and disease extent. The genetic susceptibility to Crohn’s disease is widely acknowledged and has been demonstrated by identification of over 100 CD associated genetic loci. However, relating CD subphenotypes to disease susceptible loci has proven to be a difficult task. In this paper we discuss the use of cluster analysis on genetic markers to identify genetic-based subgroups while taking into account possible confounding by population stratification. We show that it is highly relevant to consider the confounding nature of population stratification in order to avoid that detected clusters are strongly related to population groups instead of disease-specific groups. Therefore, we explain the use of principal components to correct for population stratification while clustering affected individuals into genetic-based subgroups. The principal components are obtained using 30 ancestry informative markers (AIM), and the first two PCs are determined to discriminate between continental origins of the affected individuals. Genotypes on 51 CD associated single nucleotide polymorphisms (SNPs) are used to perform latent class analysis, hierarchical and Partitioning Around Medoids (PAM) cluster analysis within a sample of affected individuals with and without the use of principal components to adjust for population stratification. It is seen that without correction for population stratification clusters seem to be influenced by population stratification while with correction clusters are unrelated to continental origin of individuals.     

Latency of Botrytis cinerea Pers.: Fr. and Biochemical Studies During Growth and Ripening of Two Grape Berry Cultivars, Respectively Susceptible and Resistant to Grey Mould

Latency and development of Botrytis cinerea were assessed under field conditions and after artificial inoculation of two grape varieties, Gamay (susceptible) and Gamaret (resistant). When the percentage of latent Botrytis was the same for both varieties, severity of visible grey mould remained very low in Gamaret berries, while Gamay clusters were destroyed by the disease to a high percentage. Some biochemical parameters were measured in berries, such as constitutive and induced anti‐fungal compounds, polymeric proanthocyanidins and lipid peroxidation products as markers of senescence. Differences were observed in polymeric proanthocyanidins (PPRA) of Gamaret compared with those of Gamay. Concentration and mean degree of polymerization (mDP) of PPRA were always higher in the berries of the resistant variety. The inhibitory effect of Gamaret PPRA on enzyme activity remained until harvest whereas Gamay PPRA lost their inhibitory activity at the beginning of véraison. Based on these results, resistance to B. cinerea seems to be linked to the maintainance of the fungus in its latent form in berries, mainly due to the ability of Gamaret PPRA to inhibit macerating fungal enzyme activities.     

Reactivity of HDL subfractions towards lecithin-cholesterol acyltransferase. Modulation by their content in free cholesterol

(1) Human HDL2 (d 1.070-1.125) and HDL3 (d 1.125-1.21) labelled with unesterified [14C]cholesterol, were incubated with a source of lecithin-cholesterol acyltransferase. For optimal activity, the reaction required the addition of albumin in excess, at least 3-times greater than the concentration of HDL-free cholesterol. Under such conditions, the reaction appeared saturable. HDL3 was found the most efficient substrate and the Vmax values expressed for 1.5 IU LCAT/ml and with an albumin/free cholesterol ratio of 3, were 8.3 nmol free cholesterol esterified/ml per h and 4.1 nmol/ml per h for HDL3 and HDL2, respectively. (2) HDL3 were modified in the presence of VLDL by inducing triacylglycerol lipolysis with a semipurified lipoprotein lipase from bovine milk. The newly formed HDL had gained free cholesterol and phospholipids, so that about 50% of these modified HDL, referred to as light-LIP-HDL3, were reisolated in the HDL2 density range. Light-LIP-HDL3 were enriched mostly in free cholesterol (+ 160%) and in phospholipid (+ 40%). Their reactivity towards LCAT was half-reduced compared to parent HDL3, which correlated well with a decrease in their phospholipid/free cholesterol molar ratio. Moreover, HDL3 artificially enriched in free cholesterol and exhibiting a comparable PL/FC behaved like lipolysis-modified HDL in their reactivity towards LCAT. (3) HDL3 were also modified by co-incubation with VLDL (post-VLDL-HDL3), or with VLDL and a source of lipid transfer protein (CET-HDL3). The latter treatment greatly affected the lipid composition of the core particle (-25% esterified cholesterol, +190% TG). In both cases, the moderate decreasing LCAT reactivity observed could be related to the phospholipid/free cholesterol ratio. Thus, like in artificial substrates, the lipid composition of the HDL surface may control the rate of LCAT-mediated cholesterol esterification.     

The expression of the sIgD isotype in wild-derived mice

IgD and IgM are concomitantly expressed on the surface of most mouse B lymphocytes and both molecules serve as receptor for antigen. In this communication we report that in contrast to IgM, which is expressed in a constant manner on the surface of spleen B lymphocytes of different laboratory and wild-derived mice, IgD expression is variable among the spleen cells of wild-derived mice. SPE, SEI, and SFM mice belonging to the Mus 3 subgroup show a fluorescence profile characterized by a marked diminution in the population of B lymphocytes expressing the IgD isotype; in addition, these cells have a low sIgD density on their membranes. These findings were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the iodinated membrane proteins. Polyclonal in vitro activation with lipopolysaccharide increases the frequency of surface IgD (sIgD)-bearing spleen cells and sIgD density in the SPE strain but decreases both the frequency and the density of IgD bearing cells in the BALB/c strain. This result suggests that delta gene expression is regulated differently in SPE and BALB/c mice. In addition, genetic analysis of sIgD expression in (BALB/c X SPE)F1 hybrids suggests that the proportion of sIgD-bearing cells and sIgD density are independently regulated.     

Lactococcus lactis and stress

It is now generally recognized that cell growth conditions in nature are often suboptimal compared to controlled conditions provided in the laboratory. Natural stresses like starvation and acidity are generated by cell growth itself. Other stresses like temperature or osmotic shock, or oxygen, are imposed by the environment. It is now clear that defense mechanisms to withstand different stresses must be present in all organisms. The exploration of stress responses in lactic acid bacteria has just begun. Several stress response genes have been revealed through homologies with known genes in other organisms. While stress response genes appear to be highly conserved, however, their regulation may not be. Thus, search of the regulation of stress response in lactic acid bacteria may reveal new regulatory circuits. The first part of this report addresses the available information on stress response in Lactococcus lactis.Acid stress response may be particularly important in lactic acid bacteria, whose growth and transition to stationary phase is accompanied by the production of lactic acid, which results in acidification of the media, arrest of cell multiplication, and possible cell death. The second part of this report will focus on progress made in acid stress response, particularly in L. lactis and on factors which may affect its regulation. Acid tolerance is presently under study in L. lactis. Our results with strain MG1363 show that it survives a lethal challenge at pH 4.0 if adapted briefly (5 to 15 minutes) at a pH between 4.5 and 6.5. Adaptation requires protein synthesis, indicating that acid conditions induce expression of newly synthesized genes. These results show that L. lactis possesses an inducible response to acid stress in exponential phase.To identify possible regulatory genes involved in acid stress response, we determined low pH conditions in which MG1363 is unable to grow, and selected at 37°C for transposition insertional mutants which were able to survive. About thirty mutants resistant to low pH conditions were characterized. The interrupted genes were identified by sequence homology with known genes. One insertion interrupts ahrC, the putative regulator of arginine metabolism; possibly, increased arginine catabolism in the mutant produces metabolites which increase the pH. Several other mutations putatively map at some step in the pathway of (p)ppGpp synthesis. Our results suggest that the stringent response pathway, which is involved in starvation and stationary phase survival, may also be implicated in acid pH tolerance.     

Insect cell density in bioreactor cultures can be estimated from on-line measurements of optical density

Total cell density in growing insect cell suspension cultures was accurately estimated from both off-line and on-line measurements of optical density (OD). The latter measurements were done with an in-situ autoclavable OD sensor. The ability to continuously monitor cell density in insect cell cultures may be useful for the development of a large-scale process for recombinant protein production using baculovirus expression vectors.     

IPG (inositolphosphate glycan) as a cellular signal for TGF-β1 modulation of chondrocyte cell cycle

The knowledge of transforming growth factor (TGF)-β receptors has greatly progressed in the recent years. TGF-β receptors type I and II have been implicated in the modulation of cell proliferation, whereas type III (betaglycan) may act as a component presenting TGF-β to its signaling receptors. In addition, four other proteins that bind TGF-β1 or TGF-β2 have been recently identified in some cell lines, three being anchored to the membrane through a glycosylphosphatidylinositol (GPI). Despite this knowledge, the molecular mechanism of signal transduction through the TGF-β receptors remain an enigma. TGF-β family does not signal via any of the classical pathways. As GPI anchors of membrane proteins have been implicated in the transduction of some hormonal effects, we investigated the putative role of GPI in signaling the TGF-β effects on the proliferation of rabbit articular chondrocytes (RAC). We previously showed that TGF-β1 increased DNA replication rate of RAC, with a recruitment of cells in G2/M followed by a subsequent mitosis wave. Here, we find that the factor causes specific GPI hydrolysis, with correlated increase of inositolphosphate glycan (IPG). This effect was specifically inhibited by antibodies that bind TGF-β1. Using [³H]-inositol labeling and Triton X-114 extraction, we demonstrate that a hydrophobic material from the membrane is cleaved by treatment of cell cultures with phosphatidylinositol specific phospholipase C (PI-PLC) or by exposure to TGF-β, supporting that a PI-anchored molecule gives rise to IPG by TGF-β-induced hydrolysis. The biological relevance of this hydrolysis was demonstrated by the enhancing effect of purified IPG on the DNA synthesis rate, which mimicked the TGF-β action. These results demonstrate that IPG could be an early messenger in the cellular signaling that mediates the effect of TGF-β on RAC growth. © 1993 Wiley-Liss, Inc.     

Germination and regeneration mechanisms in Mediterranean degenerate forests

Abstract. Germination and developmental behaviour during juvenile stages are of importance in relation to succession mechanisms acting on plant communities. This is particularly so in the Mediterranean region, where the climatic summer drought causes stress. We investigated and compared germination and development of four tree species in two parts of the French Mediterranean region where the original dominant tree species (Quercus pubescens) has been largely replaced by Quercus ilex in the southern part, and Castanea sativa in the northern part. Observed differences in germination rates and developmental behaviour, especially shootroot ratio and the role of water supply, suggest that other species may eventually replace the current dominant species.     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.