High sequence turnover in the regulatory regions of the developmental gene hunchback in insects.
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Extensive sequence analysis of the developmental gene hunchback and its 5' and 3' regulatory regions in Drosophila melanogaster, Drosophila virilis, Musca domestica, and Tribolium castaneum, using a variety of computer algorithms, reveals regions of high sequence simplicity probably generated by slippage-like mechanisms of turnover. No regions are entirely refractory to the action of slippage, although the density and composition of simple sequence motifs varies from region to region. Interestingly, the 5' and 3' flanking regions share short repetitive motifs despite their separation by the gene itself, and the motifs are different in composition from those in the exons and introns. Furthermore, there are high levels of conservation of motifs in equivalent orthologous regions. Detailed sequence analysis of the P2 promoter and DNA footprinting assays reveal that the number, orientation, sequence, spacing, and protein-binding affinities of the BICOID-binding sites varies between species and that the 'P2' promoter, the nanos response element in the 3' untranslated region, and several conserved boxes of sequence in the gene (e.g., the two zinc-finger regions) are surrounded by cryptically-simple-sequence DNA. We argue that high sequence turnover and genetic redundancy permit both the general maintenance of promoter functions through the establishment of coevolutionary (compensatory) changes in cis- and trans-acting genetic elements and, at the same time, the possibility of subtle changes in the regulation of hunchback in the different species. (+info)
Elimination of EVE protein by CALI in the short germ band insect Tribolium suggests a conserved pair-rule function for even skipped.
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The question of the degree of evolutionary conservation of the pair-rule patterning mechanism known from Drosophila is still contentious. We have employed chromophore-assisted laser inactivation (CALI) to inactivate the function of the pair-rule gene even skipped (eve) in the short germ embryo of the flour beetle Tribolium. We show that it is possible to generate pair-rule type phenocopies with defects in alternating segments. Interestingly, we find the defects in odd numbered segments and not in even numbered ones as in Drosophila. However, this apparent discrepancy can be explained if one takes into account that the primary action of eve is at the level of parasegments and that different cuticular markers are used for defining the segment borders in the two species. In this light, we find that eve appears to be required for the formation of the anterior borders of the same odd numbered parasegments in both species. We conclude that the primary function of eve as a pair rule gene is conserved between the two species. (+info)
Toll homologue expression in the beetle tribolium suggests a different mode of dorsoventral patterning than in drosophila embryos.
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The gene Toll (Tl) encodes a maternally supplied interleukin 1 receptor-related transmembrane protein, a key component required to establish dorsoventral polarity in the Drosophila embryo. We have isolated Tl homologs of a primitive dipteran, Clogmia albipunctata, and of the beetle Tribolium castaneum. Tribolium Tl protein (Tl) lacks sequences in the C-terminal portion of the cytoplasmic domains that are conserved in the dipteran homologs. The Tl homolog of Tribolium mediates the ventralizing activity when expressed as a gain-of-function variant in transgenic Drosophila, indicating that the sequences conserved in the Diptera are not essential for Tl signaling. In contrast to Drosophila where Tl gene expression occurs maternally and supplies uniformly distributed Tl in the egg membrane, Tl transcripts form a ventral-to-dorsal gradient in the Tribolium blastoderm stage embryo. This localized expression pattern of Tl transcripts, as compared with the strong maternal and ubiquitous expression in Drosophila and Clogmia embryos, suggests that dorsoventral patterning in long-germ band and short-germ band insects involves the same components but different modes of their action. (+info)
Developmental evolution: Axial patterning in insects.
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The Drosophila bicoid gene is well known for encoding a protein that forms a morphogenetic gradient with a key role in anterior patterning of the fruitfly embryo. Recent results suggest the evolution of bicoid might have involved dramatic changes in function - essentially the invention of a new regulatory protein. (+info)
RAPD-based genetic linkage maps of Tribolium castaneum.
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A genetic map of the red flour beetle (Tribolium castaneum) integrating molecular with morphological markers was constructed using a backcross population of 147 siblings. The map defines 10 linkage groups (LGs), presumably corresponding to the 10 chromosomes, and consists of 122 randomly amplified polymorphic DNA (RAPD) markers, six molecular markers representing identified genes, and five morphological markers. The total map length is 570 cM, giving an average marker resolution of 4.3 cM. The average physical distance per genetic distance was estimated at 350 kb/cM. A cluster of loci showing distorted segregation was detected on LG9. The process of converting RAPD markers to sequence-tagged site markers was initiated: 18 RAPD markers were cloned and sequenced, and single-strand conformational polymorphisms were identified for 4 of the 18. The map positions of all 4 coincided with those of the parent RAPD markers. (+info)
Functional conservation of the wingless-engrailed interaction as shown by a widely applicable baculovirus misexpression system.
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BACKGROUND: The expression patterns of the segment polarity genes wingless and engrailed are conserved during segmentation in a variety of arthropods, suggesting that the regulatory interactions between these two genes are also evolutionarily conserved. Hypotheses derived from such comparisons of gene expression patterns are difficult to test experimentally as genetic manipulation is currently possible for only a few model organisms. RESULTS: We have developed a system, using recombinant baculoviruses, that can be applied to a wide variety of organisms to study the effects of ectopic expression of genes. As a first step, we studied the range and type of infection of several reporter viruses in the embryos of two arthropod and one vertebrate species. Using this system to express wingless, we were able to induce expression of engrailed in the anterior half of each parasegment in embryos of the fruit fly Drosophila melanogaster. Virus-mediated wingless expression also caused ectopic naked ventral cuticle formation in wild-type Drosophila larvae. In the flour beetle, Tribolium castaneum, ectopic wingless also induced engrailed expression. As in Drosophila, this expression was only detectable in the anterior half of the parasegment. CONCLUSIONS: The functional interaction between wingless and engrailed, and the establishment of cells competent to express engrailed, appears to be conserved between Drosophila and Tribolium. The data on the establishment of an engrailed-competent domain also support the idea that prepatterning by pair-rule genes is conserved between these two insects. The recombinant baculovirus technology reported here may help answer other long-standing comparative evolutionary questions. (+info)
Ectopic gene expression and homeotic transformations in arthropods using recombinant Sindbis viruses.
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BACKGROUND: The morphological diversity of arthropods makes them attractive subjects for studying the evolution of developmental mechanisms. Comparative analyses suggest that arthropod diversity has arisen largely as a result of changes in expression patterns of genes that control development. Direct analysis of how a particular gene functions in a given species during development is hindered by the lack of broadly applicable techniques for manipulating gene expression. RESULTS: We report that the Arbovirus Sindbis can be used to deliver high levels of gene expression in vivo in a number of non-host arthropod species without causing cytopathic effects in infected cells or impairing development. Using recombinant Sindbis virus, we investigated the function of the homeotic gene Ultrabithorax in the development of butterfly wings and beetle embryos. Ectopic Ultrabithorax expression in butterfly forewing imaginal discs was sufficient to cause the transformation of characteristic forewing properties in the adult, including scale morphology and pigmentation, to those of the hindwing. Expression of Ultrabithorax in beetle embryos outside of its endogenous expression domain affected normal development of the body wall cuticle and appendages. CONCLUSIONS: The homeotic genes have long been thought to play an important role in the diversification of arthropod appendages. Using recombinant Sindbis virus, we were able to investigate homeotic gene function in non-model arthropod species. We found that Ultrabithorax is sufficient to confer hindwing identity in butterflies and alter normal development of anterior structures in beetles. Recombinant Sindbis virus has broad potential as a tool for analyzing how the function of developmental genes has changed during the diversification of arthropods. (+info)
Group selections among laboratory populations of Tribolium.
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Selection at the population level or group selection is defined as genetic change that is brought about or maintained by the differential extinction and/or proliferation of populations. Group selection for both increased and decreased adult population size was carried out among laboratory populations of Tribolium castaneum at 37-day intervals. The effect of individual selection within populations on adult population size was evaluated in an additional control series of populations. The response in the group selection treatments occurred rapidly, within three or four generations, and was large in magnitude, at times differing from the controls by over 200%. This response to selection at the populational level occurred despite strong individual selection which caused a decline in the mean size of the control populations from over 200 adults to near 50 adults in nine 37-day intervals. "Assay" experiments indicated that selective changes in fecundity, developmental time, body weight, and cannibalism rates were responsible in part for the observed treatment differences in adult population size. These findings have implications in terms of speciation in organisms whose range is composed of many partially isolated local populations. (+info)