EFFECTS OF A VISUAL HORIZON ON DROSOPHILA MELANOGASTER OBJECT-TRACKING RESPONSES

To navigate effectively in three-dimensional space, flying insects must approximate distances to nearby objects. Humans are able to use an array of cues to guide depth perception in the visual world. However, some of these cues are not available to insects that are constrained by their rigid eyes and relatively small body size. Flying fruit flies can use motion parallax to gauge the distance of nearby objects, but using this cue becomes a less effective strategy as objects become more remote. Humans are able to infer depth across far distances by comparing the angular distance of an object to the horizon. This study tested if flying fruit flies, like humans, use the relative position of the horizon as a depth cue. Fruit flies in tethered flight were stimulated with a virtual environment that displayed vertical bars of varying elevation relative to a horizon, and their tracking responses were recorded. This study showed that tracking responses of the flies were strongly increased by reducing the apparent elevation of the bar against the horizon, indicating that fruit flies may be able to assess the distance of far off objects in the natural world by comparing them against a visual horizon.

Drosophila Flight Stabilization Depends on Apparent Distances in Optic Flow Field

To perform daily flight tasks, insects rely heavily on their visual perception of a dynamic environment. They must process visual signals quickly and accurately and update their behavior. Flies are vulnerable to environmental disturbances, such as gusts of wind blowing them off course, but they may use the altered visual field to compensate and regain their original course. In studies using Drosophila melanogaster, it has been shown that their corrective responses can be analyzed by measuring changes in their wing beats. By enclosing a tethered fly in a cuboidal visual arena displaying a computerized optic flow field, it is possible to calculate the change in wing beat amplitudes from an infrared shadow of its wings using photodiodes and a custom wing beat analyzer. In this experiment, manipulations ofthe optic flow field are used to create a field where points have varying relative forward speed, to study how the insect performs corrective maneuvers. The results show that Drosophila have a stronger corrective response to the quickly moving, apparently near points compared to the slower moving, apparently distant points. This implies the flies are distinguishing points based on their relative speeds, inferring distance, and adjusting their corrective actions with this information.

Proteomic Analysis of Wolbachia Symbiosis within the Drosophila

Wolbachia pipientis are bacterial endosymbionts of arthropods and in some filarial nematodes. Wolbachia are of particular interest because nematodeWolbachia have been shown to cause the diseases African river blindness and Lymphatic Filariasis. Doxycycline can be used to eliminate nematode Wolbachia, however, more efficient treatments are needed. Ideally, we would like to repurpose another FDA approved drug that helps to shorten treatment duration. Vitamins are one of the best classes of FDA approved compounds, generally recognized as safe. Interestingly, prior work by Serbus and colleagues found that dietary yeast, which is highly enriched in vitamins, dramatically reducesWolbachia titer in Drosophila melanogaster ovarian tissue. Imaging data indicated that the Wolbachia nucleoids were disrupted in response to yeast. This raised the possibility that yeast cells contain a bio-reactive, anti-Wolbachiacompound. Our close examination of yeast nutritional information identified which vitamins are most highly enriched in yeast. We then administered several of these to D. melanogaster, and saw that two of these led to reduced ovarianWolbachia titers, analogous to yeast-fed flies. This was especially interesting, as both vitamins are critical for functioning of the same biochemical pathway. We used retested effect of one of these vitamins in oogenesis by performing a dilution series, and achieved positive correlation from this dilution series. This opens up the avenue for clarifying the mechanism of how vitamins suppressWolbachia titer, and for testing enhancement of Doxycycline, to hopefully provide faster, more affordable treatment for millions of patients.

Proteomic Analysis of Wolbachia Symbiosis within the Drosophila

Wolbachia pipientis are bacterial endosymbionts of arthropods and in some filarial nematodes. Wolbachia are of particular interest because nematodeWolbachia have been shown to cause the diseases African river blindness and Lymphatic Filariasis. Doxycycline can be used to eliminate nematode Wolbachia, however, more efficient treatments are needed. Ideally, we would like to repurpose another FDA approved drug that helps to shorten treatment duration. Vitamins are one of the best classes of FDA approved compounds, generally recognized as safe. Interestingly, prior work by Serbus and colleagues found that dietary yeast, which is highly enriched in vitamins, dramatically reducesWolbachia titer in Drosophila melanogaster ovarian tissue. Imaging data indicated that the Wolbachia nucleoids were disrupted in response to yeast. This raised the possibility that yeast cells contain a bio-reactive, anti-Wolbachiacompound. Our close examination of yeast nutritional information identified which vitamins are most highly enriched in yeast. We then administered several of these to D. melanogaster, and saw that two of these led to reduced ovarianWolbachia titers, analogous to yeast-fed flies. This was especially interesting, as both vitamins are critical for functioning of the same biochemical pathway. We used retested effect of one of these vitamins in oogenesis by performing a dilution series, and achieved positive correlation from this dilution series. This opens up the avenue for clarifying the mechanism of how vitamins suppressWolbachia titer, and for testing enhancement of Doxycycline, to hopefully provide faster, more affordable treatment for millions of patients.

Identification of Conserved Splicing Motifs in Mutually Exclusive Exons of 15 Insect Species

Background: During alternative splicing, the inclusion of an exon in the final mRNA molecule is determined by nuclear proteins that bind cis-regulatory sequences in a target pre-mRNA molecule. A recent study suggested that the regulatory codes of individual RNA-binding proteins may be nearly immutable between very diverse species such as mammals and insects. The model system Drosophila melanogaster therefore presents an excellent opportunity for the study of alternative splicing due to the availability of quality EST annotations in FlyBase. Methods: In this paper, we describe an in silico analysis pipeline to extract putative exonic splicing regulatory sequences from a multiple alignment of 15 species of insects. Our method, ESTs-to-ESRs (E2E), uses graph analysis of EST splicing graphs to identify mutually exclusive (ME) exons and combines phylogenetic measures, a sliding window approach along the multiple alignment and the Welch’s t statistic to extract conserved ESR motifs. Results: The most frequent 100% conserved word of length 5 bp in different insect exons was “ATGGA”. We identified 799 statistically significant “spike” hexamers, 218 motifs with either a left or right FDR corrected spike magnitude p-value < 0.05 and 83 with both left and right uncorrected p < 0.01. 11 genes were identified with highly significant motifs in one ME exon but not in the other, suggesting regulation of ME exon splicing through these highly conserved hexamers. The majority of these genes have been shown to have regulated spatiotemporal expression. 10 elements were found to match three mammalian splicing regulator databases. A putative ESR motif, GATGCAG, was identified in the ME-13b but not in the ME-13a of Drosophila N-Cadherin, a gene that has been shown to have a distinct spatiotemporal expression pattern of spliced isoforms in a recent study. Conclusions: Analysis of phylogenetic relationships and variability of sequence conservation as implemented in the E2E spikes method may lead to improved identification of ESRs. We found that approximately half of the putative ESRs in common between insects and mammals have a high statistical support (p < 0.01). Several Drosophila genes with spatiotemporal expression patterns were identified to contain putative ESRs located in one exon of the ME exon pairs but not in the other.

PROTEOMIC ANALYSIS OF WOLBACHIA SYMBIOSIS WITHIN THE DROSOPHILA OVARY

Wolbachia pipientis are bacterial endosymbionts carried by millions of invertebrate species, including ~40% of insect species and some filarial nematodes. In insects, basic Wolbachia research has potential applications in controlling vector borne disease. Conversely, Wolbachia of filarial nematodes are causative agents of neglected tropical diseases such as lymphatic filariasis and African river blindness. However, remarkably little is known about how Wolbachia interact with their hosts at the molecular level. Understanding this is important to inform the basis for symbiosis and help prevent human disease. I used a high-throughput proteomics approach to study how Drosophila host cells are modified by Wolbachia infection. This analysis identified 23 Drosophila proteins that significantly changed in amount as a result of Wolbachia infection. A subset of differentially abundant host proteins were consistent with Wolbachia-associated phenotypes reported previously. This study also provides the first ever discovery-based evidence for a Wolbachia-associated change in maternal germline histone loads, which has possible implications in Rescue of a common Wolbachia-induced reproductive manipulation known as Cytoplasmic Incompatibility.