Mohylyak I. Mutations and tissue-specific expression of the swiss cheese gene: influence on phenotypic changes in Drosophila melanogaster

Dissertation is devoted to evaluation of phenotypic characteristics of the sws neurodegenerative mutants and investigation of sws gene functional inhibition impact on different tissues of D. melanogaster nervous system. sws mutants characterize with elevation of lipid peroxidation, high sensitivity to oxidative stress conditions, increased levels of superoxide dismutase activity, behavioral disorders and lifespan reduction. Neuronal phenotype in sws mutants was described as rapid and progressive vacuolization of neuropile with visible signs of degeneration. Functional knockdown of sws gene in neurons has no effect on their normal functioning. There were no signs of neuronal degeneration neither in young (3-days old) or old (20-days old) flies. For additional verification of sws gene RNA interference effect on the neurons, driver line with exclusive activity in laminar L4 neurons was used. The L4 neurons were formed correctly in flies with sws knockdown. They develop collaterals in proximal part of lamina, and their cell bodies were regularly distributed. Thus, decreased level of sws gene expression does not lead to the neuronal degeneration changes in Drosophila. As for sws mutants, it is possible, that neuronal degeneration in these flies arise as a consequence of mutant SWS protein aggregation in neuronal cells, which triggers stress of endoplasmic reticulum (ER), which triggers an adaptive program called the unfolded protein response. ER stress was shown to have an important role in a range of neurological disorders, including Alzheimer's disease, Parkinson disease, multiple sclerosis, amyotrophic lateral sclerosis etc. The glial cells of sws mutants form hyperwraping around the neuronal cell bodies, and this phenotype is visible at the light microscopy level as dense structures in area of lamina cortex. The slight signs of glial cells degeneration were found in young transgenic flies with sws RNAi-mediated knockdown. This degeneration was dramatically progressing in age-depended manner, and in old flies strong vacuolization of cortex glia and giant glia of the first optic chiasm could be detected, together with some compound eye cells degeneration. After simultaneous sws knockdown in glia, neurons and eye cells significant changes in the optic lobe morphology were found already in the young flies. Fenestrated membrane was superseded to the eye region and rhabdomeres continued to grow into the brain area invading lamina region ("deep rhabdomeres" phenotype). sws functional inhibition in compound eye altered location of the fenestrated membrane. Rhabdomeres were crossing fenestrated membrane, which was displaced toward eye, and invade into the lamina region. Collected data suggest that SWS protein in brain plays exclusively important role in formation and functioning of specific structures and cell types, such as fenestrated membrane and some glial cells of lamina cortex. The reduction of SWS level causes progressive degeneration of lamina cortex glia and glial cells of the first optic chiasm. However the availability of SWS is not connected with neuronal tissue development or functioning.