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31.
Benjamin G. Fanson Christopher W. Weldon Diana Pérez-Staples Stephen J. Simpson Phillip W. Taylor 《Aging cell》2009,8(5):514-523
Caloric restriction (CR) has been widely accepted as a mechanism explaining increased lifespan (LS) in organisms subjected to dietary restriction (DR), but recent studies investigating the role of nutrients have challenged the role of CR in extending longevity. Fuelling this debate is the difficulty in experimentally disentangling CR and nutrient effects due to compensatory feeding (CF) behaviour. We quantified CF by measuring the volume of solution imbibed and determined how calories and nutrients influenced LS and fecundity in unmated females of the Queensland fruit fly, Bactocera tryoni (Diptera: Tephritidae). We restricted flies to one of 28 diets varying in carbohydrate:protein (C:P) ratios and concentrations. On imbalanced diets, flies overcame dietary dilutions, consuming similar caloric intakes for most dilutions. The response surface for LS revealed that increasing C:P ratio while keeping calories constant extended LS, with the maximum LS along C:P ratio of 21:1. In general, LS was reduced as caloric intake decreased. Lifetime egg production was maximized at a C:P ratio of 3:1. When given a choice of separate sucrose and yeast solutions, each at one of five concentrations (yielding 25 choice treatments), flies regulated their nutrient intake to match C:P ratio of 3:1. Our results (i) demonstrate that CF can overcome dietary dilutions; (ii) reveal difficulties with methods presenting fixed amounts of liquid diet; (iii) illustrate the need to measure intake to account for CF in DR studies and (iv) highlight nutrients rather than CR as a dominant influence on LS. 相似文献
32.
Forty crossbred barrows (Camborough 15 Line female×Canabred sire) weighing an average of 79.6±8.0?kg were used in a factorial design experiment (5 barleys×2 enzyme levels) conducted to determine the effects of phytase supplementation on nutrient digestibility in low-phytate barleys fed to finishing pigs. The pigs were assigned to one of 10 dietary treatments comprised of a normal 2-rowed, hulled variety of barley (CDC Fleet, 0.26% phytate) or 2 low-phytate hulled genotypes designated as LP422 (0.14% phytate) and LP635 (0.09% phytate). A normal, hulless barley (CDC Dawn, 0.26% phytate) and a hulless genotype designated as LP422H (0.14% phytate) were also included. All barleys were fed with and without phytase (Natuphos 5000 FTU/kg). The diets fed contained 98% barley, 0.5% vitamin premix, 0.5% trace mineral premix, 0.5% NaCl and 0.5% chromic oxide but no supplemental phosphorus. The marked feed was provided for a 7-day acclimatization period, followed by a 3-day faecal collection. In the absence of phytase, phosphorus digestibility increased substantially (P<0.05) as the level of phytate in the barley declined. For the hulled varieties, phosphorus digestibility increased from 12.9% for the normal barley (0.26% phytate) to 35.3 and 39.8% for the two low-phytate genotypes (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 9.2% for the normal barley (0.26% phytate) to 34.7% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In contrast, when phytase was added to the diet, there was little difference in phosphorus digestibility between pigs fed normal barley and those fed the low-phytate genotypes (significant barley×enzyme interaction, P=0.01). For the hulled varieties, phosphorus digestibility was 50.1% for the barley with the normal level of phytate (0.26% phytate) compared with 51.1 and 52.4% for the varieties with 54 and 35% of the normal level of phytate (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 47.1% for the normal barley (0.26% phytate) to 54.4% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In conclusion, both supplementation with phytase and selection for low-phytate genotypes of barley were successful in increasing the digestibility of phosphorus for pigs. Unfortunately, the effects did not appear to be additive. Whether or not swine producers will choose low-phytate barley or supplementation with phytase as a means to improve phosphorus utilization, will likely depend on the yield potential of low-phytate barley and the additional costs associated with supplementation with phytase. 相似文献
33.
A nearly universal feature of intron sequences is that even closely related
species exhibit a large number of insertion/deletion differences. The goal
of the analysis described here is to test whether the observed pattern of
insertion/deletion events in the genealogy of the myosin alkali light chain
(Mlc1) gene is consistent with neutrality, and if not, to determine the
underlying forces of evolutionary change. Mlc1 pre-mRNA is alternatively
spliced, and one constraint is that signals necessary for
tissue-specificity of directed splicing must be conserved. If the total
length of an intron is functionally constrained, then the distribution of
indels on branches of the gene genealogy should reflect a departure from
randomness. Here we perform a phylogenetic analysis, inferring ancestral
states wherever possible on a phylogeny of 29 alleles of Mlc1 from six
species of Drosophila. Observed patterns of indels on the genealogy were
compared to those from simulated data, with the result that we cannot
reject the null hypothesis of neutrality. A clear departure from a neutral
prediction was seen in the excess folding free energy predicted for the
introns flanking the alternatively spliced exon. Relative rate tests also
suggest a retardation in the rate of Mlc1 sequence evolution in the
simulans clade.
相似文献
34.
Role of cryptic genes in microbial evolution 总被引:24,自引:1,他引:23
Cryptic genes are phenotypically silent DNA sequences, not normally
expressed during the life cycle of an individual. They may, however, be
activated in a few individuals of a large population by mutation,
recombination, insertion elements, or other genetic mechanisms. A
consideration of the microbial literature concerning biochemical evolution,
physiology, and taxonomy provides the basis for a hypothesis of microbial
adaptation and evolution by mutational activation of cryptic genes.
Evidence is presented, and a mathematical model is derived, indicating that
powerful and biologically important mechanisms exist to prevent the loss of
cryptic genes. We propose that cryptic genes persist as a vital element of
the genetic repertoire, ready for recall by mutational activation in future
generations. Cryptic genes provide a versatile endogenous genetic reservoir
that enhances the adaptive potential of a species by a mechanism that is
independent of genetic exchange.
相似文献
35.
Conservation of alternative splicing and genomic organization of the myosin alkali light-chain (Mlc1) gene among Drosophila species 总被引:3,自引:0,他引:3
The Mlc1 gene of Drosophila melanogaster encodes two MLC1 isoforms via
developmentally regulated alternative pre-mRNA splicing. In larval muscle
and tubular and abdominal muscles of adults, all of the six exons are
included in the spliced mRNA, whereas, in the fibrillar indirect flight
muscle of adult, exon 5 is excluded from the mRNA. We show that this
tissue-specific pattern of alternative splicing of the Mlc1 pre-mRNA is
conserved in D. simulans, D. pseudoobscura, and D. virilis. Isolation and
sequencing of the Mlc1 genes from these three other Drosophila species have
revealed that the overall organization of the genes is identical and that
the genes have maintained a very high level of sequence identity within the
coding region. Pairwise amino acid identities are 94%-99%, and there are no
charge changes among the proteins. Total nucleotide divergence within the
coding region of the four genes supports the accepted genealogy of these
species, but the data indicate a significantly higher rate of amino acid
replacement in the branch leading to D. pseudoobscura. A comparison of
nucleotide substitutions in the coding portions of exon 5 and exon 6, which
encode the alternative carboxyl termini of the two MLC1 isoforms, suggests
that exon 5 is subject to greater evolutionary constraints than is exon 6.
In addition to the coding sequences, there is significant sequence
conservation within the 5' and 3' noncoding DNA and two of the introns,
including one that flanks exon 5. These regions are candidates for cis-
regulatory elements. Our results suggest that evolutionary constraints are
acting on both the coding and noncoding sequences of the Mlc1 gene to
maintain proper expression and function of the two MLC1 polypeptides.
相似文献
36.
Sequence evolution and phylogenetic signal in control-region and cytochrome b sequences of rainbow fishes (Melanotaeniidae) 总被引:3,自引:0,他引:3
The nucleotide sequences of segments of the cytochrome b gene (351 bp), the
tRNA(Pro) gene (49 bp), and the control region (approximately 313 bp) of
mitochondrial DNA were obtained from 26 fish representing different
populations and species of Melanotaenia and one species of Glossolepis,
freshwater rainbow fishes confined to Australia and New Guinea. The purpose
was to investigate relative rates and patterns of sequence evolution.
Overall levels of divergence were similar for the cytochrome b and tRNA
control-region sequences, both ranging from < 1% within subspecies to
15%-19% between genera. However, the patterns of sequence evolution
differed. For the cytochrome b gene, transitions consistently exceeded
transversions, the bias ranging from 4.2:1 to 2:1, depending on the level
of sequence divergence. However, in the control-region sequence, a bias
toward transitions (2:1) was observed only in comparisons between very
similar sequences, and transversions outnumbered transitions in comparisons
of divergent sequences. Graphic comparisons suggested that the control
region was saturated for transitions at relatively low levels of sequence
divergence but accumulated transversions at a greater rate than did the
cytochrome b sequence. These distinct patterns of base substitution are
associated with differences in A+T content, which is 70% for the tRNA
control- region segment versus 50% for cytochrome b. A test for skewness in
the distribution of lengths of random trees indicated that both segments
contained phylogenetic signal. Parsimony analyses of the data from the two
regions, with or without weighting schemes appropriate to the respective
patterns of sequence evolution, identified the same five groupings of
sequences, but the relationships among the groups differed. However, in
most cases the branches uniting different combinations of groups were
poorly supported, and the differences among topologies were insignificant.
Considering the observed patterns of base substitution and the results of
the phylogenetic analyses, we deduce that both the control region and
cytochrome b are appropriate for population genetic studies but that the
control region is less effective than cytochrome b for resolving
relationships among divergent lineages of rainbow fishes.
相似文献
37.
Insect lifespan is often closely linked to diet, and diet manipulations have been central to studies of ageing. Recent research has found that lifespan for some flies is maximised on a very low yeast diet, but once all yeast is removed, lifespan drops precipitously. Although effects of yeast availability on lifespan are commonly interpreted in terms of protein, yeast is a complex mix of nutrients and provides a rich source of vitamins, minerals and sterols. Elucidating which components of yeast are involved in this lifespan drop provides insights into more specific nutritional requirements and also provides a test for the commonplace interpretation of yeast in terms of protein. To this end, we fed Queensland fruit flies (Bactrocera tryoni) one of eight experimental diets that differed in the nutrient group(s) found in yeast that were added to sucrose: none, vitamins, minerals, amino acids, cholesterol, vitamin+mineral+cholesterol (VMC), vitamin+mineral+cholesterol+amino acids (VMCA), and yeast. We measured survival rates and egg production in single sex and mixed sex cages, as well as nutrient intake of individual flies. We found that the addition of minerals increased lifespan of both male and female flies housed in single sex cages by decreasing baseline mortality. The addition of just amino acids decreased lifespan in female flies; however, when combined with other nutrient groups found in yeast, amino acids increased lifespan by decreasing both baseline mortality and age-specific mortality. Flies on the yeast and VMCA diets were the only ones to show significant egg production. We conclude that the drop in lifespan observed when all yeast is removed is explained by missing micronutrients (vitamins, minerals and cholesterol) as well as the absence of protein in females, whereas minerals alone can explain the pattern for males. These results indicate a need for caution when interpreting effects of dietary yeast as effects of protein. 相似文献
38.
39.
Widespread distribution of deletions of the bgl operon in natural isolates of Escherichia coli 总被引:2,自引:0,他引:2
A deletion that includes the bgl (beta-glucoside utilization) operon of
Escherichia coli was originally detected in several rarely occurring
natural isolates that utilize cellobiose. Here I show that bgl deletions
are present in 95% of the Cel+ isolates obtained from diverse sources. They
are also present in 29% of the Cel- strains in two different collections of
natural isolates of E. coli. At least three versions of bgl deletions are
present in E. coli populations. In the most common version approximately 8
kb of DNA around the bgl region of E. coli K12 is replaced by a specific
6.5-kb DNA fragment. In another version a deletion of similar length is not
replaced by the same sequence. A third version involves deletion of
approximately 14 kb without the replacement fragment being present. The
distribution of these deletions suggests that the version 1 deletion
occurred very early in the history of E coli. It also appears likely that
there is selection for bgl deletions in Cel+ strains of E. coli. The
presence of the version 1 deletion within distantly related phylogenetic
groups of E. coli provides evidence for recombination within natural
populations of E coli.
相似文献
40.