Investigating Connective Tissue Disorders in Drosophila melanogaster
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Abstract
The Ehlers-Danlos Syndrome (EDS) is a wide classification of tissue and joint connectivity disorders, with symptoms primarily manifesting as extended joint flexibility and reduced motor coordination. EDS primarily impacts collagenous tissues, though the exact impact and tissues affected varies among subtypes. For example, classical EDS (cEDS) impacts type I collagen, whereas Vascular Ehlers-Danlos Syndrome (vEDS) impacts type III. Other varieties of EDS impact connective tissues via a more indirect method. The rare spondylocheirodysplastic subtype (SCDâEDS / spEDS) impacts the production of a metal ion transporter protein (Xiao and Zhou, 2018). This protein is tasked with the influx of Fe(II) into the ER/golgi, and the efflux of Zn(II) ions into the cytosol (Calap-Quintana et al., 2017). Impacted synthesis of the transporter protein results in a two-factor effect: a build-up of Zn(II) in and a decrease of Fe(II) in the golgi. The Zn(II) ions interfere with the enzymatic activity of Lysyl hydroxylases, which use iron as a cofactor to facilitate a post-translational hydroxylation of lysine residues during collagen synthesis. Hydroxylysine and lysine both contribute to the stabilization of the collagen triple helix through bond networks on the alpha-chain (Eyre, Weis, & Rai, 2019). However, hydroxylysine is more effective due to its additional bonding opportunities. Collagen stability is important for structural support, especially as a component of more complex structures such as basement membranes. Basement membranes are support structures that contribute to the integrity and organization of connective tissues. Collagen type IV is a large component of basement membranes, and malformations in its structure have been linked to EDS subtypes. These malformations can be induced a number of ways, including the method utilized below. In this experiment, I attempted to trigger the development of EDS-like symptoms by reducing Fe(II) availability and therefore causing underhydroxylation of lysine residues, resulting in decreased connective tissue stability. This was done using the competitive relationship between zinc and iron for absorption in the small intestine /midgut, where the excess of one can lead to a deficit of the other (Bettedi et al., 2011). Excess zinc was added by supplementing three different quantities of ZnCl2 into D. melanogaster food. The goal was to reduce Fe(II) availability, therefore weaken the structure of collagen by decreasing the amount of hydroxylysine residues. Post-eclosion, experimental progeny were tested for motor discoordination behavior using flight and climbing assays. Zinc concentration in tissues was quantified using a colorimetric analysis as well. Initial motor assay results suggested positive correlation in failure rates and Zn food concentrations, however further data analysis provided conflicting and inconsistent results.
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Biological Sciences, Drosophila Melanogaster, Connective Tissues, Hypermobility, Collagen, Ehlers-Danlos Syndrome, EDS, Zinc, Iron, Hydroxylation, Metal Ions, Motor Coordination, Protein Synthesis