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  • 1
    ISSN: 1432-041X
    Keywords: Bombyx mori ; Genetic mosaic ; Chromosomal fragment ; Larval body marking ; Pattern formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A separable chromosomal fragment of about 2.5 Mb, which carries the larval body marking gene striped (p S), is present in a recessive background in the kind of genetic mosaic called “mottled striped” in the silkworm, Bombyx mori. The somatic loss of this chromosomal fragment during cell division gives rise to white patches (variegated pigmentation) in the dorsal black stripes of the fifth instar larva. Each larger white patch in the black p S stripe represents the clonal expansion of an epidermal cell that lost the fragment carrying p S during an early developmental stage. To gain information on the developmental history of the larval epidermal cells, we have analysed a variety of mosaic individuals showing extreme mottling patterns. Based on several common features observed in mosaic patterns, we constructed a schematic model for migration of epidermal cells, which implies that several polyclonal founding cells on each lateral side of a segment move and expand toward the dorsal mid-line. To determine the timing of loss of the fragment in “half-stripe mosaics”, which are completely lacking the mottled black stripe on one half of the larval body, we examined several tissues from either body side for the chromosomal fragment. Pulsed field gel electrophoresis (PFGE) and restriction fragment length polymorphism (RFLP) analysis showed that testes and silk glands from each side of the half-stripe mosaics (two and five individuals, respectively) contained the chromosomal fragment carrying the p S allele, independent of the epidermal phenotypes of the respective body half. This result suggests that loss of the chromosomal fragment leading to external half-stripe mosaics might occur, not at an early stage of development such as the first nuclear division, but rather after the progenies of epidermis and internal tissues examined here diverged from each other developmentally.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 51 (2000), S. 265-277 
    ISSN: 1432-1432
    Keywords: Key words: Planthopper — Aphid — Fungus — Symbiosis —Symbiont — Uricase — Uric acid — Yeast-like — PTS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Aphids belonging to the three genera Tuberaphis, Glyphinaphis, and Cerataphis contain extracellular fungal symbionts that resemble endocellular yeast-like symbionts of planthoppers. Whereas the symbiont of planthoppers has a uricase (urate oxidase; EC 1.7.3.3) and recycles uric acid that the host stores, no uric acid was found in Tuberaphis styraci, and its fungal symbiont did not exhibit the uricase activity. However, the fungal symbionts of these aphids, including that of T. styraci, were shown to have putative uricase genes, or pseudogenes, for the uricase. Sequence analysis of these genes revealed that deleterious mutations occurred independently on each lineage of Glyphinaphis and Tuberaphis, while no such mutation was found in the lineage of Cerataphis. These genes were almost identical to those cloned from the symbionts of planthoppers, though the host aphids and planthoppers are phylogenetically distant. To estimate the phylogenetic relationship in detail between the fungal symbionts of aphids and those of planthoppers, a gene tree was constructed based on the sequences of the uricase genes including their flanking regions. As a result, the symbionts of planthoppers and Tuberaphis aphids formed a sister group against those of Glyphinaphis and Cerataphis aphids with high bootstrap confidence levels, which strongly suggests that symbionts have been horizontally transferred from the aphids' lineage to the planthoppers'.
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  • 3
    ISSN: 1432-1432
    Keywords: Aphids ; Endosymbiosis ; Symbionin ; Chaperonin 60 ; Chaperonin 10 ; Immunoblotting ; Immunohistochemistry ; Primary symbiont ; Secondary symbiont ; Endosymbiotic evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary All aphids harbor symbiotrophic prokaryotes (“primary symbionts”) in a specialized-abdominal cell, the bacteriocyte. Chaperonin 60 (Cpn60, symbionin) and chaperonin 10 (Cpn10), which are high and low molecular weight heatshock proteins, were sought in tissues of more than 60 aphid species. The endosymbionts were compared immunologically and histologically. It was demonstrated that (1) there are two types of aphids in terms of the endosymbiotic system: some with only primary symbionts and others with, in addition, secondary symbionts; (2) the primary symbionts of various aphids are quite similar in morphology whereas the secondary symbionts vary; and (3) irrespective of the aphid species, Cpn60 is abundant in both the primary and secondary symbionts, while Cpn10 is abundant in the secondary symbionts but present in small amounts in the primary ones. Based on these results, we suggest that the primary symbionts have been derived from a prokaryote that was acquired by the common ancestor of aphids whereas the secondary symbionts have been acquired by various aphids independently after divergence of the aphid species. In addition, we point out the possibility that the prokaryotes under intracellular conditions have been subject to some common evolutionary pressures, and as a result, have come to resemble cell organelles.
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  • 4
    ISSN: 1432-1432
    Keywords: Aphid ; 28S rRNA ; Secondary structure model ; G + C content ; Variable region ; Divergent evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Determination of the entire nucleotide sequence of the aphid 28S ribosomal RNA gene (28S rDNA) revealed that it is 4,147 by in length with a G + C content of 60.3%. Based on the nucleotide sequence, we constructed a presumed secondary-structure model of the aphid 28S rRNA which indicated that the aphid 28S rRNA is characterized by the length and high G + C content of its variable regions. The G + C content of the aphid's variable regions was much higher than that of the entire sequence of the 28S rRNA, which formed a striking contrast to those ofDrosophila with the G + C content much lower than the entire 28S molecule. In this respect, the aphid 28S rRNA somewhat resembled those of vertebrates. This is the third report of a complete large-subunit rRNA sequence from an arthropod, and the first 28S rRNA sequence for a nondipterous insect.
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  • 5
    ISSN: 1432-1432
    Keywords: Key words: Aphid — 28S rRNA — Secondary structure model — G + C content — Variable region — Divergent evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Determination of the entire nucleotide sequence of the aphid 28S ribosomal RNA gene (28S rDNA) revealed that it is 4,147 bp in length with a G + C content of 60.3%. Based on the nucleotide sequence, we constructed a presumed secondary-structure model of the aphid 28S rRNA which indicated that the aphid 28S rRNA is characterized by the length and high G + C content of its variable regions. The G + C content of the aphid's variable regions was much higher than that of the entire sequence of the 28S rRNA, which formed a striking contrast to those of Drosophila with the G + C content much lower than the entire 28S molecule. In this respect, the aphid 28S rRNA somewhat resembled those of vertebrates. This is the third report of a complete large-subunit rRNA sequence from an arthropod, and the first 28S rRNA sequence for a nondipterous insect.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 48 (1999), S. 142-150 
    ISSN: 1432-1432
    Keywords: Key words:Buchnera—Acyrthosiphon pisum— Pea aphid — Pulse-field gel electrophoresis — Genome size — Genetic map — Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Abstract The genome of Buchnera, an endosymbiotic bacterium of the pea aphid Acyrthosiphon pisum, was characterized by pulse-field gel electrophoresis (PFGE) as a circular DNA molecule of 657 kb. The enzymes I-CeuI, CpoI, ApaI, SmaI, NaeI, SacII, MluI, FspI, and NruI were used to cleave the DNA of Buchnera into fragments of suitable size for PFGE analysis. A physical map of the Buchnera genome, including restriction fragments from seven of these enzymes, was constructed using double cutting, partial digestion, and hybridization with linking fragments, and 29 genes and operons were localized on the map. In addition, the genomic map of Buchnera was compared with those of Escherichia coli and Haemophilus influenzae. The gene order in Buchnera is more similar to that of E. coli than to H. influenzae. The dramatic shrinkage of the Buchnera genome compared with those of other members of the closely related Enterobacteriaceae family is discussed in terms of evolution under the influence of the intracellular symbiotic association.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 24 (1987), S. 205-211 
    ISSN: 1432-1432
    Keywords: Endosymbiont ; Aphid ; Genome size ; Nucleotide composition ; Cell organelle ; Mycoplasma ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An intracellular symbiont was isolated from the mycetocyte of the pea aphidAcyrthosiphon pisum, and its genomic DNA was compared with those ofEscherichia coli andMycoplasma capricolum with respect to nucleotide composition and kinetic complexity. Thermal dissociation, CsCl density equilibrium centrifugation, and high-performance liquid chromatography of the nuclease P1 digest all indicated that the G+C content of the endosymbiont DNA is as low as 30%. In this respect, the endosymbiont resembledMycoplasma species. The reassociation kinetics of genomic DNA labeled by nick translation suggested that the endosymbiont genome is 1.4×1010 daltons in size, about 5 and 18 times as large as those ofE. coli andM. capricolum, respectively. The results were confirmed by reassociation of endosymbiont DNA labeled by incubation with [3Hthymidine in Grace's medium. The endosymbiont genome of the aphid was about 500 times larger than those of leafhopper endosymbionts previously analyzed by ultracentrifugation. These characteristic properties of the aphid endosymbiont genome are discussed in connection with the evolution of cell organelles, and with reference to a previous finding that most of the genes of the aphid endosymbiont are not expressed when present intracellularly.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 30 (1990), S. 509-513 
    ISSN: 1432-1432
    Keywords: Aphid ; 28S rRNA ; Hidden break ; Gap region ; Stem-loop structure ; UAAU tract ; Protostomes ; Deuterostomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In order to determine why the aphid 28S rRNA lacks the hidden break otherwise found in insects, the structure of the region of the aphid ribosomal DNA (rDNA) corresponding to the gap region, which in other insect rDNA transcripts is excised posttranscriptionally, was studied. Sequence comparison suggested that, in contradistinction to what is found in rDNA transcripts of other insects, a stem-loop structure formed in this region of the aphid rDNA transcript is not AU-rich. Nor did the loop of the aphid molecule contain the UAAU tract that can be a signal for the introduction of the hidden break, suggesting that in this particular region the aphid 28S rRNA resembles 28S rRNAs of deuterostomes, which do not contain the hidden break.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 36 (1993), S. 121-126 
    ISSN: 1432-1432
    Keywords: Aphid ; Intracellular symbiont ; groE operon ; Nucleotide sequence ; Codon usage ; Directional mutation ; A/T pressure ; Selection ; Cell organelles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary As a result of the nucleotide sequence analysis of an aphid endosymbiont's operon homologous to theEscherichia coli groE, we noted that directional base substitutions tending toward an increase of A + T content represent an obvious evolutionary trend in this prokaryotic operon, housed for a long period by an eukaryotic cell. This result, when taken together with previous reports, raised the possibility that genomic DNA of prokaryotes residing in an eukaryotic cell is subject to A/T-biased directional mutation pressure and/or both negative and positive selection operating under conditions specific to the intracellular environments.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 48 (1999), S. 717-722 
    ISSN: 1432-1432
    Keywords: Key words:Buchnera— Pea aphid — Symbiosis — Genomic copy number — Dot-blot analysis — Microscope photon-counting system — Polyploidy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Although Buchnera, the endosymbiotic bacteria of aphids, are close relatives of Escherichia coli, their genome size is only a seventh that of E. coli. In this study, we estimated the genomic copy number of Buchnera by dot-blot hybridization and fluorimetry using a video-intensified microscope photon-counting system and obtained convincing evidence that each cell of these bacteria contains an average of 120 genomic copies. Thus, the Buchnera symbiont, with many copies of a small-sized genome, is reminiscent of cell organelles such as mitochondria and chloroplasts.
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