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21.
Haug Marion F Biehlmaier Oliver Mueller Kaspar P Neuhauss Stephan CF 《Frontiers in zoology》2010,7(1):1-7
Background
Mating plugs that males place onto the female genital tract are generally assumed to prevent remating with other males. Mating plugs are usually explained as a consequence of male-male competition in multiply mating species. Here, we investigated whether mating plugs also have collateral effects on female fitness. These effects are negative when plugging reduces female mating rate below an optimum. However, plugging may also be positive when plugging prevents excessive forced mating and keeps mating rate closer to a females' optimum. Here, we studied these consequences in the gonochoristic nematode Caenorhabditis remanei. We employed a new CO2-sedation technique to interrupt matings before or after the production of a plug. We then measured mating rate, attractiveness and offspring number.Results
The presence of a mating plug did not affect mating rate or attractiveness to roving males. Instead, females with mating plugs produced more offspring than females without copulatory plugs.Conclusions
Our experiment suggests that plugging might have evolved under male-male competition but represents a poor protection against competing males in our experiment. Even if plugging does not reduce mating rate, our results indicate that females may benefit from being plugged in a different sense than remating prevention. 相似文献22.
Microsatellite variation in Drosophila melanogaster and Drosophila simulans: a reciprocal test of the ascertainment bias hypothesis 总被引:2,自引:1,他引:1
Interspecific comparisons of microsatellite loci have repeatedly shown that
the loci are longer and more variable in the species from which they are
derived (the focal species) than are homologous loci in other (nonfocal)
species. There is debate as to whether this is due to directional evolution
or to an ascertainment bias during the cloning and locus selection
processes. This study tests these hypotheses by performing a reciprocal
study. Eighteen perfect dinucleotide microsatellite loci identified from a
Drosophila simulans library screen and 18 previously identified in an
identical Drosophila melanogaster library screen were used to survey
natural populations of each species. No difference between focal and
nonfocal species was observed for mean PCR fragment length. However,
heterozygosity and number of alleles were significantly higher in the focal
species than in the nonfocal species. The most common allele in the
Zimbabwe population of both species was sequenced for 31 of the 36 loci.
The length of the longest stretch of perfect repeat units is, on average,
longer in the focal species than in the non-focal species. There is a
positive correlation between the length of the longest stretch of perfect
repeats and heterozygosity. The difference in heterozygosity can thus be
explained by a reduction in the length of the longest stretch of perfect
repeats in the nonfocal species. Furthermore, flanking-sequence length
difference was noted between the two species at 58% of the loci sequenced.
These data do not support the predictions of the directional-evolution
hypothesis; however, consistent with the ascertainment bias hypothesis, the
lower variability in nonfocal species is an artifact of the microsatellite
cloning and isolation process. Our results also suggest that the magnitude
of ascertainment bias for repeat unit length is a function of the
microsatellite size distribution in the genomes of different species.
相似文献
23.
Jain RK; Piskorz CF; Huang BG; Locke RD; Han HL; Koenig A; Varki A; Matta KL 《Glycobiology》1998,8(7):707-717
The selectins interact in important normal and pathological situations with
certain sialylated, fucosylated glycoconjugate ligands containing sialyl
Lewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has gone
into the synthesis of sialylated and sulfated Lewisxanalogs as competitive
ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and
PSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure,
we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1++
+-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for L
and P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studies
have shown that sulfate esters can replace sialic acid in some selectin
ligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. ,
Nature, 361, 555, 1993). Based upon these observations, we hypothesized
that Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability of
interacting with L- and P-selectin. To examine this hypothesis, we
synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2++
+-3Galbeta1-3)- GalNAc alpha1-OB, which was found to be 2- to 3-fold better
than sialyl Lexfor P and L selectin, respectively. We also report the
synthesis of an unusual structure GalNAcbeta1-4(Fucalpha1-
3)GlcNAcbeta1-OMe (GalNAc- Lewisx-O-methyl glycoside), which also proved to
be a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe.
Combining this with our knowledge of Core 2 branched structures, we have
synthesized a molecule that is 5- to 6-fold better at inhibiting L- and
P-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures,
substitution of a sulfate ester group for a sialic acid residue in such a
molecule resulted in a considerable loss of inhibition ability. Thus, the
combination of a sialic acid residue on the primary (beta1-3) arm, and a
modified Lexunit on the branched (beta1-6) arm on an O-linked Core 2
structure generated a monovalent synthetic oliogosaccharide inhibitor
superior to SLexfor both L- and P-selectin.
相似文献
24.
25.
Background
Binding of serum components by surface M-related proteins, encoded by the emm genes, in streptococci constitutes a major virulence factor in this important group of organisms. The present study demonstrates fibrinogen binding by S. iniae, a Lancefield non-typeable pathogen causing devastating fish losses in the aquaculture industry and an opportunistic pathogen of humans, and identifies the proteins involved and their encoding genes. 相似文献26.
Evolution at the tip and base of the X chromosome in an African population of Drosophila melanogaster 总被引:1,自引:0,他引:1
Hitchhiking effects of advantageous mutations have been invoked to explain
reduced polymorphism in regions of low crossing-over in Drosophila. Besides
reducing DNA heterozygosity, hitchhiking effects should produce strong
linkage disequilibrium and a frequency spectrum skewed toward an excess of
rare polymorphisms (compared to the neutral expectation). We measured DNA
polymorphism in a Zimbabwe population of D. melanogaster at three loci,
yellow, achaete, and suppressor of forked, located in regions of reduced
crossing-over. Similar to previously published surveys of these genomic
regions in other populations, we observed low levels of nucleotide
variability. However, the frequency spectrum was compatible with a neutral
model, and there was abundant evidence for recombination in the history of
the yellow and ac genes. Thus, some aspects of the data cannot be accounted
for by a simple hitchhiking model. An alternative hypothesis, background
selection, might be compatible with the observed patterns of linkage
disequilibrium and the frequency spectrum. However, this model cannot
account for the observed reduction in nucleotide heterozygosity. Thus,
there is currently no satisfactory theoretical model for the data from the
tip and base of the X chromosome in D. melanogaster.
相似文献
27.
Absorption of power in large body volumes can occur with some approaches used for hyperthermia treatment of cancer. A systemic heat absorption rate exceeding the heat dissipation rate can lead to systemic temperature elevation that limits the magnitude and duration of application of power and hence the degree of preferential tumor temperature rise. We describe a hyperthermia approach consisting of regional electromagnetic power absorption and extracorporeal blood cooling with regulation of both systemic heat absorption and dissipation rates ("balanced heat transfer"). A test of this approach in five dogs with nonperfused tumor models demonstrated intratumoral temperatures greater than 42 degrees C, while systemic temperature remained at 33 degrees C and visceral temperatures within the heated region equilibrated between 33 and 42 degrees C. Solutions of the bioheat transfer equation were obtained for a simplified model with a tumor perfusion rate lower than surrounding normal tissue perfusion rate. In this model, the use of arterial blood temperatures less than 37 degrees C allowed higher power densities to be used, for given normal tissue temperatures, than when arterial temperature was greater than or equal to 37 degrees C. As a result, higher intratumoral temperatures were predicted. Control of arterial blood temperature using extracorporeal cooling may thus (1) limit systemic temperature rise produced by regional heating devices and (2) offer a means of improving intratumoral temperature elevations. 相似文献
28.
Tempo and mode of concerted evolution in the L1 repeat family of mice 总被引:10,自引:0,他引:10
Martin SL; Voliva CF; Hardies SC; Edgell MH; Hutchison CA d 《Molecular biology and evolution》1985,2(2):127-140
A 300-bp DNA sequence has been determined for 30 (10 from each of three
species of mice) random isolates of a subset of the long interspersed
repeat family L1. From these data we conclude that members of the L1 family
are evolving in concert at the DNA sequence level in Mus domesticus, Mus
caroli, and Mus platythrix. The mechanism responsible for this phenomenon
may be either duplicative transposition, gene conversion, or a combination
of the two. The amount of intraspecies divergence averages 4.4%, although
between species base substitutions accumulate at the rate of approximately
0.85%/Myr to a maximum divergence of 9.1% between M. platythrix and both M.
domesticus and M. caroli. Parsimony analysis reveals that the M. platythrix
L1 family has evolved into a distinct clade in the 10-12 Myr since M.
platythrix last shared a common ancestor with M. domesticus and M. caroli.
The parsimony tree also provides a means to derive the average half-life of
L1 sequences in the genome. The rates of gain and loss of individual copies
of L1 were estimated to be approximately equal, such that approximately
one-half of them turn over every 3.3 Myr.
相似文献
29.
Polymorphism and divergence at the 5' flanking region of the sex- determining locus, Sry, in mice 总被引:3,自引:0,他引:3
We have investigated patterns of evolution in the nonrecombining portion of
the Y chromosome in mice by comparing levels of polymorphism within Mus
domesticus with levels of divergence between M. domesticus and M. spretus.
A 1,277-bp fragment of noncoding sequence flanking the sex determining
locus (Sry) was PCR amplified, and 1,063 bases were sequenced and compared
among 20 M. domesticus and 1 M. spretus. Two polymorphic base substitutions
and two polymorphic insertion/deletion sites were identified within M.
domesticus; nucleotide diversity was estimated to be 0.1%. Divergence
between M. domesticus and M. spretus for this region (1.9%) was slightly
lower than the average divergence of single-copy nuclear DNA for these
species. Comparison of levels of polymorphism and divergence at Sry with
levels of polymorphism and divergence in the mitochondrial DNA control
region provided no evidence of a departure from the expectations of neutral
molecular evolution. These findings are consistent with the presumed lack
of function for much of the Y chromosome.
相似文献
30.
We describe a new scaffold-free three-dimensional (3D) cell culture model using cholesteryl ester based lyotropic liquid crystal (LC) substrates. Keratinocytes were deposited randomly on the LC surface where they self-assembled into 3D microtissues or keratinospheroids. The cell density required to form spheroids was optimized. We investigated cell viability using dead/live cell assays. The adhesion characteristics of cells within the microtissues were determined using histological sectioning and immunofluorescence staining. Fourier transform infrared spectroscopy (FTIR) was used to characterize the biochemistry of the keratinospheroids. We found that both cells and microtissues could migrate on the LC surface. The viability study indicated approximately 80% viability of cells in the microtissues up to 20 days of culture. Strong intercellular adhesion was observed in the stratification of the multi-layered microspheroids using field emission-scanning electron microscopy (FE-SEM) and histochemical staining. The cytoskeleton and vinculins of the cells in the microtissues were expressed diffusely, but the microtissues were enriched with lipids and nucleic acids, which indicates close resemblance to the conditions in vivo. The basic 3D culture model based on LC may be used for cell and microtissue migration studies in response to cytochemical treatment. 相似文献