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941.
Thermal performance of quartz capillaries for vitrification 总被引:1,自引:1,他引:0
In this paper we report the thermal behavior of a new approach for vitrification. Thermal performance of traditional open pulled straws is compared with a new technique based on the combined use of quartz capillaries with slush nitrogen. This new method of vitrification achieved ultrafast cooling rates of 250,000 °C/min. As a result, a much lower concentration of cryoprotectant was needed to reach vitrification. In fact, a cryoprotectant solution typically used in oocyte slow freezing protocols was shown to remain transparent after cooling to liquid nitrogen temperatures indicating apparent “vitrification”. This approach offers a new and very promising technique for vitrification of cells using low levels of cryoprotectants. 相似文献
942.
Batch cultures of Chlorella vulgaris and C. variegata reproducing about twice every 5 d within 0-15 d had vegetative cells and autospore mother cells in the ratio of about 19 : 1. Continuous slow or negligible and/or no growth in > 15-d-old control cultures or in young cultures supplied with the antibiotics streptomycin, penicillin, amoxycillin (10-1000 ppm) or tetracycline (10, 100 ppm), and pesticides carbofuran, gammaxine, moticop or iralon (1-100 ppm) was due to slow autospore mother cells dehiscence (leading to an increase in their percentage); while negligible and/or no growth of both algal species in sewage water (100, 25%), detergent (0.1-1%), petrol or kerosene (5-20 %), benzene, toluene or phenol (5, 10%) and pesticides rogor or endosulfan (1, 10 ppm) was due to vegetative cells failure to differentiate into auto-spore mother cells (leading to decreased/zero autospore mother cells percentage) and/or rapid death of all cells. C. variegata was equally or slightly more sensitive to different chemical stress than C. vulgaris. 相似文献
943.
The common yellow butterfly Eurema hecabe is widely distributed in East Asia, and is one of the most burdensome species for taxonomists due to the numerous geographic
and seasonal wing colour patterns. Moreover, within this species, individuals with a yellow wing fringe that occur in temperate
regions of Japan (Y type) proved to be biologically different from others that occur widely in subtropical regions of Japan
and all over East Asia (B type). To unveil the genetic variation within and between the two types, a total of 50 butterflies
collected at 18 geographic localities in East Asia were examined for nucleotide sequence variation of three mitochondrial
regions: cytochrome c oxidase subunit I (COI), cytochrome c oxidase subunit III (COIII) and NADH dehydrogenase subunit 5 (ND5). In addition, they were also examined for infection status
with the endosymbiotic bacteria Wolbachia. The three mitochondrial sequences consistently showed that (i) Y type and B type were highly divergent, (ii) nucleotide
variation within B type was very small although sampled from a geographically wide range, and (iii) a weak association existed
between mitochondrial DNA haplotypes and Wolbachia infection status. 相似文献
944.
Developmental systems are regulated by a web of interacting loci. One common and useful approach in studying the evolution of development is to focus on classes of interacting elements within these systems. Here, we use individual-based simulations to study the evolution of traits controlled by branched developmental pathways involving three loci, where one locus regulates two different traits. We examined the system under a variety of selective regimes. In the case where one branch was under stabilizing selection and the other under directional selection, we observed "developmental system drift": the trait under stabilizing selection showed little phenotypic change even though the loci underlying that trait showed considerable evolutionary divergence. This occurs because the pleiotropic locus responds to directional selection and compensatory mutants are then favored in the pathway under stabilizing selection. Though developmental system drift may be caused by other mechanisms, it seems likely that it is accelerated by the same underlying genetic mechanism as that producing the Dobzhansky-Muller incompatibilities that lead to speciation in both linear and branched pathways. We also discuss predictions of our model for developmental system drift and how different selective regimes affect probabilities of speciation in the branched pathway system. 相似文献
945.
In order to examine the evolution of lineage specific genes, we analyzed intron phase distributions and exon-bordering domains
in primate and rodent specific genes. We found that the expansion of symmetric exon-bordering domains could not explain the
evolution of lineage specific genes. Rather internal intron loss of a domain can partially explain the excess of class 1–1
intron phases in the lineage specific genes. We suggest the event that led to excess of symmetric exons in lineage specific
genes had little bearing on shaping the phenotypes specific to the individual lineage. Instead, Kruppel-associated box (KRAB)
proteins associated with zinc finger C2H2 (zf-C2H2) type are likely to be responsible for the lineage specific function. 相似文献
946.
In this review, we focus on the assembly of DNA/protein complexes that trigger transposition in eukaryotic members of the
IS630–Tc1–mariner (ITm) super-family, the Tc1- and mariner-like elements (TLEs and MLEs). Elements belonging to this super-family encode transposases with DNA binding domains of different
origins, and recent data indicate that the chimerization of functional domains has been an important evolutionary aspect in
the generation of new transposons within the ITm super-family. These data also reveal that the inverted terminal repeats (ITRs) at the ends of transposons contain three kinds
of motif within their sequences. The first two are well known and correspond to the cleavage site on the outer ITR extremities,
and the transposase DNA binding site. The organization of ITRs and of the transposase DNA binding domains implies that differing
pathways are used by MLEs and TLEs to regulate transposition initiation. These differences imply that the ways ITRs are recognized
also differ leading to the formation of differently organized synaptic complexes. The third kind of motif is the transposition
enhancers, which have been found in almost all the functional MLEs and TLEs analyzed to date. Finally, in vitro and in vivo
assays of various elements all suggest that the transposition initiation complex is not formed randomly, but involves a mechanism
of oriented transposon scanning.
Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .
An erratum to this article can be found at 相似文献
947.
Considerable effort has been invested in determining traits underlying invasiveness. Yet, identifying a set of traits that
commonly confers invasiveness in a range of species has proven elusive, and almost nothing is known about genetic loci affecting
invasive success. Incorporating genetic model organisms into ecologically relevant studies is one promising avenue to begin
dissecting the genetic underpinnings of invasiveness. Molecular biologists are rapidly characterizing genes mediating developmental
responses to diverse environmental cues, i.e., genes for plasticity, as well as to environmental factors likely to impose
strong selection on invading species, e.g., resistance to herbivores and competitors, coordination of life-history events
with seasonal changes, and physiological tolerance of heat, drought, or cold. Here, we give an overview of molecular genetic
tools increasingly used to characterize the genetic basis of adaptation and that may be used to begin identifying genetic
mechanisms of invasiveness. Given the divergent traits that affect invasiveness, “invasiveness genes” common to many clades
are unlikely, but the combination of developmental genetic advances with further evolutionary studies and modeling may provide
a framework for identifying genes that account for invasiveness in related species. 相似文献
948.
Haag ES 《Genetica》2007,129(1):45-55
The evolution of molecules, developmental circuits, and new species are all characterized by the accumulation of incompatibilities
between ancestors and descendants. When specific interactions between components are necessary at any of these levels, this
requires compensatory coevolution. Theoretical treatments of compensatory evolution that only consider the endpoints predict
that it should be rare because intermediate states are deleterious. However, empirical data suggest that compensatory evolution
is common at all levels of molecular interaction. A general solution to this paradox is provided by plausible neutral or nearly
neutral intermediates that possess informational redundancy. These intermediates provide an evolutionary path between coadapted
allelic combinations. Although they allow incompatible end points to evolve, at no point was a deleterious mutation ever in
need of compensation. As a result, what appears to be compensatory evolution may often actually be “pseudocompensatory.” Both
theoretical and empirical studies indicate that pseudocompensation can speed the evolution of intergenic incompatibility,
especially when driven by adaptation. However, under strong stabilizing selection the rate of pseudocompensatory evolution
is still significant. Important examples of this process at work discussed here include the evolution of rRNA secondary structures,
intra- and inter-protein interactions, and developmental genetic pathways. Future empirical work in this area should focus
on comparing the details of intra- and intergenic interactions in closely related organisms. 相似文献
949.
The osmotolerant and cell wall properties of the two most studied wild-type Zygosaccharomyces rouxii strains (CBS 732 and ATCC 42981) were examined. Differences in their (1) tolerance to high salt content in the medium, (2) resistance to the lysing enzymes Lyticase and Zymolyase, (3) cell-wall polymer content and (4) cell wall micromorphology suggested that the less osmotolerant CBS 732 strain possesses a more rigid cell wall than the more osmotolerant ATCC 42981, whose cell wall seems to be more flexible and elastic. 相似文献
950.
Di Bonaventura G Stepanović S Picciani C Pompilio A Piccolomini R 《Folia microbiologica》2007,52(1):86-90
The influence of environmental factors (temperature, aerobiosis-anaerobiosis, static-dynamic conditions, pH) was determined on biofilm formation by 51 S. maltophilia clinical isolates. The strains produced more biofilm at 32 degrees C than at 37 or 18 degrees C. Aerobic and 6% CO2 atmosphere yielded comparable biofilm amounts, higher than under anaerobic conditions. Biofilm production was not affected by static vs. agitated culture conditions. Biofilm production at pH 7.5 and 8.5 was comparable but significantly higher than at pH 5.5. The capacity of individual strains to form biofilm and thus contribute to the severity of some diseases is influenced by host traits and environmental conditions at the site of infection, and play an important role in the pathogenesis of biomaterial-related disease caused by S. maltophilia. 相似文献