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Color vision is widespread in the animal kingdom, and describes the ability to discriminate between objects purely based on the wavelengths that they reflect. Experiments across many species have isolated wavelength comparison in the brain as a computation underlying color vision. This comparison takes place in color opponent neurons, which respond with opposite polarity to wavelengths in different parts of the spectrum. In this work, I explore color opponency in the genetically tractable organism Drosophila melanogaster, where these circuits have only just begun to be described. Using two-photon calcium imaging, I measure the spectral tuning of photoreceptors in the fruit fly and identify circuit mechanisms that give rise to opponency. I find two pathways: an insect-specific pathway that compares wavelengths at each point in space, and a horizontal-cell-mediated pathway similar to that found in mammals. The horizontal-cell-mediated pathway enables additional spectral comparisons through lateral inhibition, expanding the range of chromatic encoding in the fly. Together, these two pathways enable efficient decorrelation and dimensionality reduction of photoreceptor signals while retaining maximal chromatic information. This dual mechanism combines motifs of both an insect-specific visual circuit and an evolutionarily convergent circuit architecture, endowing flies with the ability to extract chromatic information at distinct spatial resolutions.

Damage to DNA from a variety of sources can lead to damaged proteins, genomic instability, aneuploidy, and cancer. It is therefore essential to repair DNA damage, and to do so a variety of DNA repair mechanisms have evolved. One of the repair mechanisms, known as homologous recombination (HR) repair, uses an undamaged sister chromatid as a template to make error free repairs to double-strand (ds) DNA breaks. While many proteins are involved in HR, this work focuses on testing the interactions of a subset of these proteins known as the Rad51 paralogs. The goal of this study is to determine if the putative Rad51 paralogs in Drosophila melanogaster are sufficiently conserved as to function in the same manner as their human counterparts. This research is part of a larger project to determine if Drosophila melanogaster is a good model organism for studying HR in humans (Hs). The D. melanogaster Rad51 gene, and its four paralogs Spn D, Spn B, Rad51D, XRCC2 (the last 2 identified by sequence homology), and human hsRad51D and hsXRCC2, were cloned into Invitrogen's TOPO protein expression vector. When induced with IPTG, the resulting fusion proteins contains either aN-terminal Xpress TM epitope or a C-terminal V5 epitope. The fusion proteins were used in immunoprecipitation assays with antibodies against the epitope tags to test for proteinprotein interactions. While many of the assays were inconclusive and are still being optimized, the interaction of the C-terminally tagged dmXRCC2 with theN-terminally tagged hsRad51D gave a positive result. This single interspecies result suggests that homologous recombination is highly conserved between D. melanogaster and humans.

Sex chromosomes and autosomes often differ in their relative rates of evolution, with sex chromosomes generally accumulating changes more rapidly (faster-X evolution). Transposable elements (TEs) make up a significant portion of eukaryotic genomes and are some of the most rapidly evolving genetic elements. We compared relative rates of insertion on the X and autosomes for 78 families found in Drosophila melanogaster. The average X/A ratio for these TE families was 1.11, similar to the mean dS X/A ratio, indicating no male-bias in mutation rate or TE insertion. The major mode of the distribution was ~0.8, indicating stronger purifying selection on the X chromosome for most TEs. We found no effect on X/A from sex-specific TE expression, but TEs with male-specific piRNA had an average X/A ratio of 0.62. We also found that TEs with very high X/A ratios (top 5%) had X chromosome insertions in areas of relative low recombination.

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Optimal fitness ser oftast olika ut för honor och hanar, och denna skillnad kan påverkas av endast en allel. När denna allel däremot ger ena könet en bättre chans att reproducera sig, medan den ger det andra könet en försämrad sexuell fitness. Då talar vi om en sexuell konflikt mellan lokus; en effekt som heter sexuell antagonism. Tidigare studier har kartlagt gener som ansetts vara högt rankade kandidater med en sexuell antagonistisk effekt.  En sådan effekt är rörelseaktivitet, vilket är en fenotypisk förmåga som selekteras fram hos hanar av Drosophila melanogaster. Genen CG3589 påverkar rörelseaktiviteten genom att påverka produktionen av muskelfibriller i sarkomererna. Min undersökning testade hanflugor av Drosophila melanogaster som härstammar från en wild-type population, Canton-S, med olika genetiska linjer. Med metoden CRISPR/Cas9 har två varianter av CG3598 skapats, och båda dessa ingår i min studie. Den en allelen (A2) uppvisar en högre rörelseaktivitet än den andra (A1). Jag observerade fem individers rörelse från varje genetisk linje i separata rör, samt mätte deras thoraxlängder. Min hypotes var att hanflugor med allel A2 har en högre fitness genom höge nivåer av fysisk aktivitet eller större kroppsstorlek än hanar med allel A1. Analyserna visade en signifikant skillnad mellan de genetiska linjerna inom de två allelerna. Slutsatsen är att det inte är genens två olika alleler som skapade de signifikanta skillnaderna mellan rörelseaktivitet och thoraxlängd, utan något i de genetiska linjernas bakgrund som skapar variationerna. / Optimal fitness usually looks different for females and males, and this difference can be affected by one allele. When this allele, on the other hand, gives one sex a better chance of reproducing, while it gives the other sex a negative effect on their sexual fitness. Then we are talking about a sexual conflict between loci, an effect called sexual antagonism. Previous studies have mapped genes that are highly ranked candidates with a sexual antagonistic effect. One such effect is locomotory activity, which is a phenotypic ability that is selected in males by Drosophila melanogaster. The gene CG3589 affects locomotory activity by affecting the production of muscle fibrils in the sarcomeres. My study tested male flies of Drosophila melanogaster derived from a wild-type population, Canton-S, with different excision lines. With the CRISPR / Cas9 method, two variants of CG3598 have been created, and both are included in my study. One allele (A2) shows a higher movement activity than the other (A1). I observed the movement of five individuals from each genetic line in separate tubes and measured their thoracic lengths. My hypothesis was that male flies with allele A2 have a higher fitness through high levels of physical activity and/or larger body size than males with allele A1. The analyzes showed a significant difference between the excision lines within the two alleles. The conclusion is that it is not the two different alleles of the gene that created the significant differences between locomotory activity and thoracic length, but something in the background of the excision lines that creates the variations.

Drosophila melanogaster has a tubular heart called the dorsal vessel, which is composed of contractile cardiomyocytes and hemolymph filtering pericardial cells. During larval development the dorsal vessel (heart) grows in size, and the luminal space inside the heart expands, however it has not been clear which cells are responsible for laying the extracellular matrix (ECM) during this expansion. Hemocytes (white blood cells), pericardial cells and cells of the fat body are candidate cell types that may secrete ECM for assembly during the growth of the heart lumen. With gene knock-down techniques we are exploring whether hemocytes participate in assembly of the heart ECM at this location. Additionally, studies of fluorescently tagged hemocytes in intact larvae reveal that hemocytes aggregate around pericardial cells of the dorsal vessel in 3rd instars. Confocal studies of dissected larval hearts indicate that hemocytes aggregate within infoldings of basement membrane associated with pericardial cells. Hemocyte-pericardial cell association could indicate that hemocytes take up proteins that are produced by pericardial cells and deliver them to other locations or that there might be a previously unidentified hematopoietic site at the Drosophila larval heart. / Thesis / Master of Science (MSc)