Ultrabithorax function in butterfly wings and the evolution of insect wing patterns.
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BACKGROUND: . The morphological and functional evolution of appendages has played a critical role in animal evolution, but the developmental genetic mechanisms underlying appendage diversity are not understood. Given that homologous appendage development is controlled by the same Hox gene in different organisms, and that Hox genes are transcription factors, diversity may evolve from changes in the regulation of Hox target genes. Two impediments to understanding the role of Hox genes in morphological evolution have been the limited number of organisms in which Hox gene function can be studied and the paucity of known Hox-regulated target genes. We have therefore analyzed a butterfly homeotic mutant 'Hindsight', in which portions of the ventral hindwing pattern are transformed to ventral forewing identity, and we have compared the regulation of target genes by the Ultrabithorax (Ubx) gene product in Lepidopteran and Dipteran hindwings. RESULTS: . We show that Ubx gene expression is lost from patches of cells in developing Hindsight hindwings, correlating with changes in wing pigmentation, color pattern elements, and scale morphology. We use this mutant to study how regulation of target genes by Ubx protein differs between species. We find that several Ubx-regulated genes in the Drosophila haltere are not repressed by Ubx in butterfly hindwings, but that Distal-less (Dll) expression is regulated by Ubx in a unique manner in butterflies. CONCLUSIONS: . The morphological diversification of insect hindwings has involved the acquisition of different sets of target genes by Ubx in different lineages. Changes in Hox-regulated target gene sets are, in general, likely to underlie the morphological divergence of homologous structures between animals. (+info)
Predicting insecticide resistance: mutagenesis, selection and response.
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Strategies to manage resistance to a particular insecticide have usually been devised after resistance has evolved. If it were possible to predict likely resistance mechanisms to novel insecticides before they evolved in the field, it might be feasible to have programmes that manage susceptibility. With this approach in mind, single-gene variants of the Australian sheep blowfly, Lucilia cuprina, resistant to dieldrin, diazinon and malathion, were selected in the laboratory after mutagenesis of susceptible strains. The genetic and molecular bases of resistance in these variants were identical to those that had previously evolved in natural populations. Given this predictive capacity for known resistances, the approach was extended to anticipate possible mechanisms of resistance to cyromazine, an insecticide to which L. cuprina populations remain susceptible after almost 20 years of exposure. Analysis of the laboratory-generated resistant variants provides an explanation for this observation. The variants show low levels of resistance and a selective advantage over susceptibles for only a limited concentration range. These results are discussed in the context of the choice of insecticides for control purposes and of delivery strategies to minimize the evolution of resistance. (+info)
The putative bioactive surface of insect-selective scorpion excitatory neurotoxins.
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Scorpion neurotoxins of the excitatory group show total specificity for insects and serve as invaluable probes for insect sodium channels. However, despite their significance and potential for application in insect-pest control, the structural basis for their bioactivity is still unknown. We isolated, characterized, and expressed an atypically long excitatory toxin, Bj-xtrIT, whose bioactive features resembled those of classical excitatory toxins, despite only 49% sequence identity. With the objective of clarifying the toxic site of this unique pharmacological group, Bj-xtrIT was employed in a genetic approach using point mutagenesis and biological and structural assays of the mutant products. A primary target for modification was the structurally unique C-terminal region. Sequential deletions of C-terminal residues suggested an inevitable significance of Ile73 and Ile74 for toxicity. Based on the bioactive role of the C-terminal region and a comparison of Bj-xtrIT with a Bj-xtrIT-based model of a classical excitatory toxin, AaHIT, a conserved surface comprising the C terminus is suggested to form the site of recognition with the sodium channel receptor. (+info)
The development and evolution of bristle patterns in Diptera.
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The spatial distribution of sensory bristles on the notum of different species of Diptera is compared. Species displaying ancestral features have a simple organization of randomly distributed, but uniformly spaced, bristles, whereas species thought to be more derived bear patterns in which the bristles are aligned into longitudinal rows. The number of rows of large bristles on the scutum was probably restricted to four early on in the evolution of cyclorraphous Brachyceran flies. Most species have stereotyped patterns based on modifications of these four rows. The possible constraints placed upon the patterning mechanisms due to growth and moulting within the Diptera are discussed, as well as within hemimetabolous insects. The holometabolic life cycle and the setting aside of groups of imaginal cells whose function is not required during the growth period, may have provided the freedom necessary for the evolution of elaborate bristle patterns. We briefly review the current state of knowledge concerning the complex genetic pathways regulating achaete-scute gene expression and bristle pattern in Drosophila melanogaster, and consider mechanisms for the genetic regulation of the bristle patterns of other species of Diptera. (+info)
Variability in spike trains during constant and dynamic stimulation.
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In a recent study, it was concluded that natural time-varying stimuli are represented more reliably in the brain than constant stimuli are. The results presented here disagree with this conclusion, although they were obtained from the same identified neuron (H1) in the fly's visual system. For large parts of the neuron's activity range, the variability of the responses was very similar for constant and time-varying stimuli and was considerably smaller than that in many visual interneurons of vertebrates. (+info)
A novel egg-derived tyrosine phosphatase, EDTP, that participates in the embryogenesis of Sarcophaga peregrina (flesh fly).
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We have previously reported that cathepsin L mRNA is present in unfertilized eggs of Sarcophaga peregrina (flesh fly) as a maternal mRNA, which suggests that cathepsin L is required for embryogenesis. Now we have identified an egg protein, with a molecular mass of 100 kDa, that is extremely susceptible to cathepsin L digestion and which disappears rapidly as the embryos develop. We purified this protein to homogeneity, cloned its cDNA, and found that it contained a consensus sequence for the active site of tyrosine phosphatase. In fact this protein showed tyrosine phosphatase activity, indicating that it is a novel tyrosine phosphatase. The expression and subsequent disappearance of this protein, which we have named egg-derived tyrosine phosphatase (EDTP), may be indispensable for embryogenesis of Sarcophaga. (+info)
An aural myiasis case in a 54-year-old male farmer in Korea.
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A 54-year-old male farmer residing in Chunchon, Korea, complaining of blood tinged discharge and tinnitus in the left ear for two days, was examined in August 16, 1996. Otoscopic examination revealed live maggots from the ear canal. The patient did not complain of any symptoms after removal of maggots. Five maggots recovered were identified as the third stage larvae of Lucilia sericata (Diptera: Calliphoridae). This is the first record of aural myiasis in Korea. (+info)
The planarian HOM/HOX homeobox genes (Plox) expressed along the anteroposterior axis.
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In the freshwater planarian Dugesia japonica, five cDNAs for HOM/HOX homeobox genes were cloned and sequenced. Together with sequence data on HOM/HOX homeobox genes of platyhelminthes deposited in databases, comparison of the deduced amino acid sequences revealed that planarians have at least seven HOM/HOX homeobox genes, Plox1 to Plox7 (planarian HOM/HOX homeobox genes). Whole-mount in situ hybridization and RT-PCR revealed that Plox4 and Plox5 were increasingly expressed along a spatial gradient in the posterior region of intact animals. During regeneration, Plox5 was expressed only in the posterior region of regenerating body pieces, suggesting that the gene is involved in the anteroposterior patterning in planarians. Plox5 was not found to be expressed in a blastema-specific manner, which contradicts a previous report (J. R. Bayascas, E. Castillo, A. M. Munos-Marmol, and E. Salo. Development 124, 141-148, 1997). X-ray irradiation experiments showed that Plox5 was expressed at least in some cells other than neoblasts, but that the induction of Plox5 expression during regeneration might require neoblasts. (+info)