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31.
MARGOT PARIS SÉBASTIEN BOYER AURÉLIE BONIN AMANDINE COLLADO JEAN‐PHILIPPE DAVID LAURENCE DESPRES 《Molecular ecology》2010,19(2):325-337
Identification of genes involved in local adaptation is particularly challenging for species functioning as a network of interconnected populations undergoing frequent extinctions–recolonizations, because populations are submitted to contrasted evolutionary pressures. Using amplified fragment length polymorphism markers, population genetic structure of the mosquito Aedes rusticus was analysed in five geographical areas of the French Rhône‐Alpes region. We included a number of sites that were treated with the bio‐insecticide Bacillus thuringiensis israelensis (Bti) for more than 15 years. Analysis of molecular variance revealed that most of the genetic variability was found within populations (96%), with no significant variation among geographical areas, although variation among populations within areas (4%) was significant. The global genetic differentiation index FST was low (0.0366 ± 0.167). However, pairwise FST values were significant and no isolation‐by‐distance at the regional level was observed, suggesting a metapopulation structure in this species. Bti‐treatment had no effect on genetic structure and on within‐population genetic diversity. Potential signatures of positive selection associated with Bti‐treatment were detected for five loci, even though toxicological bioassays performed on field‐collected larvae showed no significant difference in mortality between Bti‐treated and nontreated sites. The difficulty of detecting moderate resistance in field‐collected larvae together with possible differential persistence of toxins in the environment may explain our inability to detect a toxicological response to Bti in treated sites. The evidence for positive selection occurring at several genomic regions suggests a first step towards Bti resistance in natural mosquito populations treated with this bio‐insecticide. Furthermore, this signal was detectable using genomic tools before any toxicological evidence for resistance could be identified. 相似文献
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Colin PD Birch Ambrose C Chikukwa Kieran Hyder Victor J Del Rio Vilas 《BMC veterinary research》2009,5(1):1-14
Background
This paper explores the spatial distribution of sampling within the active surveillance of sheep scrapie in Great Britain. We investigated the geographic distribution of the birth holdings of sheep sampled for scrapie during 2002 – 2005, including samples taken in abattoir surveys (c. 83,100) and from sheep that died in the field ("fallen stock", c. 14,600). We mapped the birth holdings by county and calculated the sampling rate, defined as the proportion of the holdings in each county sampled by the surveys. The Moran index was used to estimate the global spatial autocorrelation across Great Britain. The contributions of each county to the global Moran index were analysed by a local indicator of spatial autocorrelation (LISA). 相似文献35.
SYNOPSIS. The Spiralia, an assemblage of phyla united by theirstereotypic pattern of early embryonic cell divisions (spiralcleavage), is an interesting group in which to investigate theevolution of development. This paper examines modificationsof developmental mechanisms within the Spiralia with emphasison the basallybranching forms. Although demonstrating a notabledegree of evolutionary conservation, the equal quartet cleavagepattern, which appears to be the ancestral condition, nonethelessexhibits modifications within the various spiralian groups,such as unequal cleavage, changes in cell size and rate of division,formation of two rather than four quadrants (duet spiral cleavage),and in extreme cases the loss of any trace of the spiral pattern.While the cell lineages of spiralians are remarkably conserved,one can discern evolutionary changes, for example in the cellsthat give rise to mesodenn. Studies of blastomere specificationin many spiralian groups and analyses of axis determinationindicate that embryos with equal versus unequal cleavage typicallyuse different determinative mechanisms to establish cell fatesand the dorsoventral axis. These properties are establishedearly in species exhibiting unequal cleavage. While previousexperiments suggested that equal cleavage was associated withlate specification, there is now evidence of precocious specificationof quadrant fates in some equal-cleaving species, such as thenemerteans and the polyclad turbellarians 相似文献
36.
Rick PD; Hubbard GL; Kitaoka M; Nagaki H; Kinoshita T; Dowd S; Simplaceanu V; Ho C 《Glycobiology》1998,8(6):557-567
The polysaccharide chains of enterobacterial common antigen (ECA) consist
of linear trisaccharide repeat units with the structure -->3)-
alpha-d-Fuc4NAc-(1-->4)-beta-d-ManNAcA-(1-->
4)-alpha-d-GlcNAc-(1-->, where Fuc4NAc is 4-acetamido-4,
6-dideoxy-d-galactose, ManNAcA is N - acetyl-d- mannosaminuronic acid, and
GlcNAc is N -acetyl-d-glucosamine. The major form of ECA (ECAPG) consists
of polysaccharide chains that are believed to be covalently linked to
diacylglycerol through phosphodiester linkage; the phospholipid moiety
functions to anchor molecules in the outer membrane. The ECA trisaccharide
repeat unit is assembled as a polyisoprenyl-linked intermediate which has
been tentatively identified as Fuc4NAc-ManNAcA-GlcNAc-
pyrophosphorylundecaprenol (lipid III). Subsequent chain-elongation
presumably occurs by a block-polymerization mechanism. However, the
identity of the polyisoprenoid carrier-lipid has not been established.
Accordingly, the current studies were conducted in an effort to
structurally characterize the polyisoprenyl lipid-carrier involved in ECA
synthesis. Isolation and characterization of the lipid carrier was
facilitated by the accumulation of a ManNAcA-GlcNAc-
pyrophosphorylpolyisoprenyl lipid (lipid II) in mutants of Salmonella
typhimurium defective in the synthesis of TDP-Fuc4NAc, the donor of Fuc4NAc
residues for ECA synthesis. Analyses of lipid II preparations by fast atom
bombardment tandem mass spectroscopy (FAB-MS/MS) resulted in the
identification of the lipid-carrier as the 55-carbon polyisoprenyl alcohol,
undecaprenol. These analyses also resulted in the identification of a novel
glycolipid which copurified with lipid II. FAB-MS/MS analyses of this
glycolipid revealed its structure to be 1,2-diacyl- sn
-glycero-3-pryophosphoryl-GlcNAc-ManNAcA (DGP- disaccharide). An
examination of purified ECAPGby phosphorus-31 nuclear magnetic resonance
spectroscopy confirmed that the polysaccharide chains are linked to
diacylglycerol through phosphodiester linkage. Thus, DGP-disaccharide does
not appear to be an intermediate in ECAPGsynthesis. Nevertheless, although
the available evidence clearly indicate that lipid II is a precursor of
DGP-disaccharide, the function of this novel glycolipid is not yet known,
and it may be an intermediate in the biosynthesis of a molecule other than
ECAPG.
相似文献
37.
Summary The apical portion of the uterine lining of the ovoviviparous fire salamander, Salamandra salamandra, was studied by the freeze-fracture technique in conjunction with the polyene antibiotic filipin. Filipin-sterol complexes were found in the luminal plasmalemma and in the membranes limiting the mucous secretory granules typical of this epithelium. In all females, but particularly in non-pregnant females, more or less discrete clusters of filipinsterol complexes were occasionally found overlying heavily affected secretory granules. The findings are discussed with regard to comparable results (Orci et al. 1980) based on the examination of collapsed and stretched urinary bladders of toads.We are indebted to Mrs. K. Ott for excellent technical assistance, to Miss E.S. MacLure for linguistic corrections and to Dr. J.E. Grady of the Upjohn Co., Kalamazoo, Michigan USA, for kindly providing the filipin 相似文献
38.
Joubert syndrome generally represents an autosomal recessive and rarely X-linked disorder characterized by hypotonia, an irregular breathing pattern, abnormal eye movements, ataxia, developmental delay and a complex mid-hindbrain malformation causing the molar tooth sign on magnetic resonance imaging (MRI). Many patients have additional features, with nephronophthisis, retinal dystrophy, coloboma and hepatic fibrosis representing the most frequent features. Due to its clinical variability and overlap with other syndromes, the term “Joubert syndrome and related disorders” (JSRD) was proposed. To date 10 genes are known to cause JSRD. The encoded proteins are localized to cilia, linking JSRD to other human ciliopathies. 相似文献
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