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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
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Peggy A. Sellner 《Molecular and cellular biochemistry》1993,123(1-2):121-127
The presence of fatty acid-binding protein (FABP) in the embryonic chick retina may be linked to the demand for polyunsaturated fatty acids in this developing neural tissue. There is a decline in the overall level of FABP as the retina matures, suggesting a role for FABP in cellular differentiation. However, this pattern is not present in the chick brain, indicating a unique function for FABP in the retina. Immunohistochemical staining of paraffin sections of chick retina from embryonic day 21 revealed immunopositive photoreceptor inner segments, outer nuclear layer, radial processes in the inner nuclear layer, a subpopulation of cells in the ganglion cell layer, and inner limiting membrane. This pattern suggested that FABP positive cells were photoreceptors, Müller (glial) cells, and possibly ganglion cells. Staining of sections for glutamine synthetase, an enzyme specific for Müller cells, was similar but not identical to the pattern observed with FABP; thus identification of these cells as FABP-positive was not conclusive. However, in retinal cells dissociated from day E14 embryos and cultured for one week, staining with FABP was more intense in the neurons than in the flat cells (presumed to be derived from the Müller cells). Retinal FABP thus appears to be localized predominantly in neurons, and may serve to sequester fatty acids in preparation for neurite outgrowth as the retinal cells differentiate.Abbreviations FABP
Fatty Acid-Binding Protein
- PUFA
Polyunsaturated Fatty Acid 相似文献
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Incorporation of tritium from tritiated water into lipid fractions was measured in isolated hepatocytes from rainbow trout (Salmo gairdneri) acclimated to 5 degrees C and 20 degrees C. Hepatocytes from cold-acclimated trout exhibited significantly higher rates of tritium incorporation into both fatty acid and sterol fractions at assay temperatures of 15 degrees C and 20 degrees C than did hepatocytes from warm-acclimated trout. Tritium incorporation into the fatty acid fraction was nearly temperature independent in hepatocytes from warm-acclimated trout (Q10 = 1.39) but markedly temperature dependent (Q10 = 2.63) in hepatocytes from cold-acclimated trout; in contrast, rates of sterol synthesis were more temperature dependent in warm-acclimated trout. At 5 degrees C, fatty acid lipogenesis comprised a significantly greater percentage of the total tritium incorporation in hepatocytes from warm-acclimated trout and the percentage of total lipogenesis attributable to fatty acids decreased significantly in warm-acclimated trout as the assay temperature increased; the opposite trends were observed in cold-acclimated trout. 相似文献
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