Centrophobism inDrosophila melanogaster

Summary The term centrophobism is introduced to describe a newly discovered modification of search behavior in the walking fruitfly,Drosophila melanogaster: the avoidance of the center of an arena after diethylether narcosis. Evidence for the effect is obtained by comparison of the tracks of etherized and non-etherized flies under the influence of olfactory attractant around the center of the arena (Fig. 3). The tracks can be distinguished by their mean radial distance from the central district of the arena. Centrophobia denotes the relative difference of the distances of etherized flies and non-etherized controls (Fig. 4).Etherized flies avoid the center of the arena in spite of the attraction of olfactory, thermal or visual cues. The avoidance is significant even in the absence of conspicuous sensory cues for the discrimination of center and surround. The centrophobia obtained in the arena can be used to estimate the efficacy of attractants in the non-etherized control flies (Figs. 6, 7).The lowest possible dose of ether sufficient to elicit narcosis is sufficient to induce centrophobia. None of the other prevalent insect anaesthetics, CO₂, N₂ and cold, substitutes ether in the present experiments (Figs. 8, 9).Centrophobia arises immediately after ether narcosis. Once induced the effect lasts apparently undiminished for the life time of the flies (Fig. 9).Centrophobia has been found in either sex of the 9 strains tested so far (Fig. 5). Four strains including mutants deficient in wing formation (vestigial) or learning (dunce) show either temporal decline or partial suppression of centrophobia. The anomalous properties are actually due to enhanced spontaneous centrophobism in the non-etherized control groups of these strains (Fig. 10).     

Osmotropotaxis inDrosophila melanogaster

Summary Drosophila melanogaster is able to perform osmotropotaxis under open-loop conditions. With an optimal stimulus the average turning tendency to the side of higher concentration corresponds to a circular track with radiusr=0.8 cm. The response amplitude does not decrease within 1 or 2 h. Unilaterally antennectomized flies in an homogeneous odor field show a permanent turning tendency towards their intact side.The smallest concentration ratio to elicit osmotropotaxis in normal flies ranges between 610 and 910 at high and between 210 and 510 at an about 50 times lower odor intensity. No negative tropotaxis (i.e. turning to the side of lower concentration) is observed, even with strong repellents.     

The occurrence of the transposable elementpogo inDrosophila melanogaster

We examined the genomic occurrence of the transposable elementpogo in over 120 strains ofDrosophila melanogaster, from around the world and from different eras. All had multiple copies of a 2.1 kilobase (kb)pogo element, and multiple copies of several size classes between 1.0 and 1.8 kb. There were differences between strains in intensities or presences of deletion-derivative size classes, suggesting current or recent mobility in the species. We were unable to find anypogo-hybridization in eight other species in the genus, in three subgenera, or in the relatedScaptomyza pallida. Thepogo element may be a ‘middle-aged’ element in the genome ofD. melanogaster, having entered the species since its divergence from its sibling species, but long before theP andhobo elements.     

Wingless mutation inDrosophila melanogaster

A temperature sensitive lethal allele of thewingless locus ofDrosophila melanogaster together with previously studied lethal and viable alleles in this locus, has been used to study some properties of this locus. These studies show the existence of two lethal phases for thewingless lesion; one during embryogenesis and another during pupation. By growing embryos with temperature sensitivewingless lesion at the permissive temperature and letting the larvae develop at non-permissive temperature, a large-scale cell death and subsequent regeneration were seen to occur in the mutant wing discs. This cell death followed by regeneration alters the normal developmental potential of the wing disc. Disc transplantation experiments show that these discs are incapable of differentiating into wing blade structures.     

Colour vision inDrosophila melanogaster

Summary Using a fully automatized procedure and a training scheme symmetrical with respect to the visual stimuli as well as to the aversive stimulus,Drosophila could be conditioned to blue and yellow lights. With constant test conditions and variation of the light intensities during the training procedure, it could be shown that the flies respond primarily to the colour of the light.We are grateful to Dr. W. Edrich and K.-F. Fischbach for exchange of ideas. Dr. J. Bammert gave advice for the statistical treatment.     

Analysis of chromosome 4 inDrosophila melanogaster. I. Spontaneous and X-ray-induced lethals

An analysis of 17 spontaneous and 37 X-ray-induced lethal mutations on the fourth chromosome ofDrosophila melanogaster has revealed a minimum of 22 loci on this microchromosome capable of mutating to lethality. A few of these loci had been identified earlier by their visible alleles but 16 are new discoveries. Seven of the 22 lethal loci are situated within that proximal section of the right arm of chromosome 4 delimited by theMinute-4 deficiency.Genetic tests indicate that two translocations and five deletions are included among the lethals of X-ray origin. No chromosomal aberrations were found among the spontaneous mutants. Allelism was encountered both within and between lethals from the two groups.Three independent estimates of the total number of lethal loci to be expected on this small autosome are presented. These appraisals are based on (1) the size of theMinute-4 deficiency, (2) the number of bands in salivary chromosome 4, and (3) the frequency of recurrence among the lethals. Considering the uncertainties inherent in each determination, the three estimates (34, 35 and 38) show remarkably good agreement.This investigation was supported in part by U.S. Public Health Service Research Grant GM 11627-01, from the Division of General Medical Sciences.     

The genomic organization of HeT-A retroposons inDrosophila melanogaster

Members of theDrosophila HeT-A family of transposable elements are LINE-like retroposons that are found at telomeres and in centric heterochromatin. We recently characterized an active HeT-A element that had transposed to a broken chromosome end fewer than mine generations before it was isolated. The sequence arerangement of this element, called 9D4, most likely represents the organization of an actively transposing member of the HeT-A family. Here we assess the degree of divergence among members of the HeT-A family and test a model of telomere length maintenance based on HeT-A transposition. The region containing the single open reading frame of this element appears to be more highly conserved than the non-coding regions. The HeT-A element has been implicated in theDrosophila telomere elongation process, because frequent transpositions to chromosome ends are sufficient to counter-balance nucleotide loss due to incomplete DNA replication. The proposed elongation model and the hypothetical mechanism of HeT-A transposition predict a predominant orientation of HeT-A elements with their oligo (A) tails facing proximally at chromosome ends, as well as the existence of irregular tandem arrays of HeT-A elements at chromosome ends resulting from transposition of new HeT-A elements onto chromosome ends with existing elements. Twenty-nine different HeT-A fragments were isolated from directional libraries that were enriched in terminal DNA fragments. Sequence analyses of these fragments and comparisons with the organization of the HeT-A element, 9D4, fit these two predictions and support the model ofDrosophila telomere elongation by transposition of HeT-A elements.     

Rapid divergence of gene duplicates on the Drosophila melanogaster X chromosome

The recent sequencing of several eukaryotic genomes has generated considerable interest in the study of gene duplication events. The classical model of duplicate gene evolution is that recurrent mutation ultimately results in one copy becoming a pseudogene, and only rarely will a beneficial new function evolve. Here, we study divergence between coding sequence duplications in Drosophila melanogaster as a function of the linkage relationship between paralogs. The mean K(a)/K(s) between all duplicates in the D. melanogaster genome is 0.2803, indicating that purifying selection is maintaining the structure of duplicate coding sequences. However, the mean K(a)/K(s) between duplicates that are both on the X chromosome is 0.4701, significantly higher than the genome average. Further, the distribution of K(a)/K(s) for these X-linked duplicates is significantly shifted toward higher values when compared with the distributions for paralogs in other linkage relationships. Two models of molecular evolution provide qualitative explanations of these observations-relaxation of selective pressure on the duplicate copies and, more likely, positive selection on recessive adaptations. We also show that there is an excess of X-linked duplicates with low K(s), suggesting a larger proportion of relatively young duplicates on the D. melanogaster X chromosome relative to autosomes.     

Suppression of abdominal legs inDrosophila melanogaster

Summary Drosophila melanogaster normally have six thoracic legs and no abdominal legs. However, one or two legs often appear in the first abdominal segment ofbithoraxoid mutants. The extent to which these extra legs develop is determined both by thecis-regulatory action ofbithoraxoid lesions onUltrabithorax and by the number of copies of the adjacent homeotic geneabdominal-A. Thebithoraxoid region does notcis-regulateabdominal-A.     

Genomic imprinting of chromatin inDrosophila melanogaster

During gametogenesis, chromosomes may become imprinted with information which facilitates proper expression of the DNA in offspring. We have used a position effect variegation mutant as a reporter system to investigate the possibility of imprinting inDrosophila melanogaster. Genetic crosses were performed in which the variegating gene and a strong modifier of variegation were present either within the same parental genome or in opposite parental genomes in all possible combinations. Our results indicate that the presence of the variegating chromosome and a modifier chromosome in the same parental genome can alter the amount of variegation formed in progeny. The genomic imprinting we observed is not determined by the parental origin of the variegating chromosome but is instead determined by the genetic background the variegating chromosome is subjected to during gametogenesis.     

Development of thoracic curvature inDrosophila melanogaster

Summary The influence of muscle development on thorax morphogenesis has been investigated inDrosophila melanogaster. The development of an indirect flight muscle, the dorsal longitudinal muscle (DLM), has been thought to be responsible for the formation of the distinct thoracic curvature. Using aDrosophila mutant (sr/Df(3)sr) in which the DLM is completely missing, we have shown that a normally curved thorax still is produced. Such results indicate that an external structure (epidermis) is capable of developing wholly independent of an absent internal structure (muscle).