Polyploidization is an important process in the evolution of eukaryotic genomes, but ensuing molecular mechanisms remain to be clarified. Autopolyploidization or whole-genome duplication events frequently are resolved in resulting lineages by the loss of single genes from most duplicated pairs, causing transient gene dosage imbalance and accelerating speciation through meiotic infertility. Allopolyploidization or formation of interspecies hybrids raises the problem of genetic incompatibility (Bateson-Dobzhansky-Muller effect) and may be resolved by the accumulation of mutational changes in resulting lineages. In this article, we show that an osmotolerant yeast species, Pichia sorbitophila, recently isolated in a concentrated sorbitol solution in industry, illustrates this last situation. Its genome is a mosaic of homologous and homeologous chromosomes, or parts thereof, that corresponds to a recently formed hybrid in the process of evolution. The respective parental contributions to this genome were characterized using existing variations in GC content. The genomic changes that occurred during the short period since hybrid formation were identified (e.g., loss of heterozygosity, unilateral loss of rDNA, reciprocal exchange) and distinguished from those undergone by the two parental genomes after separation from their common ancestor (i.e., NUMT (NUclear sequences of MiTochondrial origin) insertions, gene acquisitions, gene location movements, reciprocal translocation). We found that the physiological characteristics of this new yeast species are determined by specific but unequal contributions of its two parents, one of which could be identified as very closely related to an extant Pichia farinosa strain.
Saccharomyces cerevisiae has been used for millennia in winemaking, but little is known about the selective forces acting on the wine yeast genome. We sequenced the complete genome of the diploid commercial wine yeast EC1118, resulting in an assembly of 31 scaffolds covering 97% of the S288c reference genome. The wine yeast differed strikingly from the other S. cerevisiae isolates in possessing 3 unique large regions, 2 of which were subtelomeric, the other being inserted within an EC1118 chromosome. These regions encompass 34 genes involved in key wine fermentation functions. Phylogeny and synteny analyses showed that 1 of these regions originated from a species closely related to the Saccharomyces genus, whereas the 2 other regions were of non-Saccharomyces origin. We identified Zygosaccharomyces bailii, a major contaminant of wine fermentations, as the donor species for 1 of these 2 regions. Although natural hybridization between Saccharomyces strains has been described, this report provides evidence that gene transfer may occur between Saccharomyces and non-Saccharomyces species. We show that the regions identified are frequent and differentially distributed among S. cerevisiae clades, being found almost exclusively in wine strains, suggesting acquisition through recent transfer events. Overall, these data show that the wine yeast genome is subject to constant remodeling through the contribution of exogenous genes. Our results suggest that these processes are favored by ecologic proximity and are involved in the molecular adaptation of wine yeasts to conditions of high sugar, low nitrogen, and high ethanol concentrations.
Title: Role of acetylcholinesterase (AChE) secreted by parasitic nematodes on the growth of the cell line from epithelial origin HT29-D4 Huby F, Mallet S, Hoste H Ref: Parasitology, 118:489, 1999 : PubMed
The excretory-secretory (E-S) products of the parasitic nematodes Trichostrongylus colubriformis and Nematodirus battus were found to modify the in vitro proliferation of the tumorous colic HT29-D4 cell line of epithelial origin. A characteristic feature of these E-S products is the presence of a high level of acetylcholinesterase (AChE) activity, the biological significance of which remains unclear. To determine a possible role of AChE on cell growth, the enzyme was purified from E-S products using edrophonium chloride. Purity was confirmed by polyacrylamide gel electrophoresis, using silver and Karnovsky stains, before assessing its effects on cell proliferation. The purified AChE was incorporated at different concentrations in a culture medium of HT29-D4 cells. A mitogenic effect was shown for low concentrations (0.1-14 units). By contrast, an inhibitory effect was noted at high concentrations (35-1400 units). Furthermore, polyclonal antibodies were prepared and depletion of AChE in E-S products by immunoprecipitation or affinity chromatography resulted in a partial or total disappearance of the stimulatory effect of cell growth. Thus, the results form this in vitro study suggest a modulatory role for AChE secreted by nematode parasites on the proliferation of epithelial cells of the host.
Title: Characterization of acetylcholinesterase secreted by the trichostrongyle nematode parasites of ruminants Mallet S, Huby F, Hoste H Ref: Vet Res, 28:287, 1997 : PubMed
Acetylcholinesterase (AChE) secreted by seven different ruminant trichostrongyles was studied in vitro. AChE activity was particularly high (84 and 160 x 10(-3) M.g-1.min-1) in the excretion products of Nematodirus spathiger and N battus, moderate (3 and 5 x 10(-3) M.g-1.min-1) for Trichostrongylus colubriformis and T vitrinus and low (0.9 x 10(-3) M.g-1.min-1) for Teladorsagia circumcincta. No activity was observed with Haemonchus contortus and Cooperia curticei. At 4 degrees C, 80% of AChE activity was maintained over 72 h except for T circumcincta where a loss of 50% was observed after 24 h. At 37 degrees C, N spathiger and T colubriformis maintained an activity over 72 h, but for the other species, a loss of 50% was observed after 24 h. The molecular weights of the AChE from the different species, estimated by gel filtration (Sephadex S300HR), ranged between 64 and 150 kDa. The coefficients of sedimentation estimated by sucrose density gradient ranged between 4.8 S and 7.8 S and corresponded to a monomeric hydrophilic form (G1). For T vitrinus, an amphiphilic form was suspected.
Title: Physiology of two strains of Trichostrongylus colubriformis resistant and susceptible to thiabendazole and mucosal response of experimentally infected rabbits Mallet S, Hoste H Ref: International Journal for Parasitology, 25:23, 1995 : PubMed
Two strains of Trichostrongylus colubriformis of ovine origin, one resistant and one susceptible to thiabendazole, were compared during experimental infection in rabbits. Groups of rabbits were infected with 5000 infective larvae (L3) of either the resistant or the susceptible strain. On days 21 and 42 post-infection (p.i.), 5 rabbits of each group were killed and the small intestine divided into three sections for worm counts and histological or biochemical analysis. Faecal egg counts were performed twice a week from day 15 to day 42 p.i. The physiology of the worms was characterised by in vitro acetylcholinesterase secretion of adult worms. The host inflammatory response was determined by peroxidase activity in mucosal homogenates and by histological counts of mast cells and eosinophils. Infectivity was not significantly different between the two strains. However, egg production was delayed and was significantly lower for the resistant strain. Conversely, in vitro secretion of resistant worms was significantly higher than the susceptible ones. The mucosal homogenetates of rabbits infected with the resistant strain had significantly higher levels of peroxidase activity in the duodenum on days 21 and 42 p.i. Mast cell counts were also significantly higher in the duodenum on day 42 p.i., in rabbits infected with the resistant strain. No difference was observed in the eosinophil counts. These results suggest that genetic variation in the nematode, such as anthelminthic resistance, is associated with variations in worm biology and physiology as well as differences in the inflammatory response of the host.
Title: The effect of levamisole on acetylcholinesterase secretion by male and female Heligmosomoides polygyrus during ageing Mallet S, Kerboeuf D Ref: Journal of Helminthology, 67:243, 1993 : PubMed
The inhibition of acetylcholinesterase secretion by male and female Heligmosomoides polygyrus was tested on worms taken from experimentally infected mice and maintained for 3 days in vitro in levamisole. The dose inhibiting 50% of enzyme secretion (ID 50) of male worms was twice the ID 50 for female worms. A similar difference was observed in vivo between the dose of levamisole removing 50% (LD50) of male and female worms from the mouse. Acetylcholinesterase secretion by worms and ID 50 were tested in vitro at 3-weekly intervals from 3 to 21 weeks post infection (WPI). Acetylcholinesterase secretion was always significantly higher for male than for female worms. A decrease of ID 50, correlated with the age of the worms was observed: from 1.5 to 0.5 micrograms/ml for males and from 0.7 to 0.1 micrograms/ml for females. These results were confirmed in vivo by a higher efficacy of the anthelminthic at 21 than at 4 WPI.
