Effects of Light on BDBT Puncta Formation in the Drosophila Eye Reveal Involvement of BDBT with Color Preference Behavior and Distinct Nuclear Localization Pathways for DBT and PER

Abstract

In this dissertation, the research focus is on elucidating the mechanism behind BRIDE OF DOUBLETIME (BDBT) puncta/foci formation. During this process it was discovered that both the circadian and visual photoreceptors have roles for normal cycles of BDBT foci formation. This BDBT foci cycling is needed for normal changes in subcellular localization of the circadian regulators PERIOD (PER) and DOUBLETIME (DBT) in the Drosophila eye. Finally, BDBT is demonstrated to have a role with the eye clock in altering circadian color preference in flies. The kinase DBT is a regulator of the Drosophila circadian clock and phosphorylates PER during the day, targeting PER for degradation. BDBT interacts with DBT, enhancing DBT kinase activity towards PER, and accumulates during the dark of a 12 hr light/12 hr dark cycle in PER- and DBT-dependent cytosolic foci. This accumulation of BDBT is shown here to be constitutively high when flies are raised under constant dark (circadian time: CT), but decreases during constant light conditions (LL), demonstrating a light/dark responsive mechanism. Analysis of circadian loss of function CRYPTOCHROME (cry) mutants and mutants of the RHODOPSIN 1(ninaE) visual transduction pathway indicated that disappearance of cytosolic BDBT foci in response to light is dependent upon both the CRY and the RHODOPSIN-1 visual transduction pathways. The ARR1 (Arr1) and ARR2 (Arr2) mutants eliminated the wild-type accumulation of BDBT foci under dark conditions in LD and constant darkness (DD) conditions, indicating a novel mechanism in which ARRESTINS are able to regulate accumulation of BDBT cytosolic foci. Arr1 and Arr2 mutants also lead to increased nuclear accumulation of PER protein during stimulated day and night, likely affecting circadian regulation in the Drosophila eye. As arrestins have been shown to affect endocytosis of RHODOPSIN, I examined the effect of overexpression of a temperature sensitive dynamin GTPase in the eye SHIBIRE (SHI) and observed increased membrane vesicle formation at restrictive temperatures. Knock-down of BDBT specifically in the eye was achieved producing a loss of circadian molecular oscillations for both PER and DBT with uncoupling of their sub cellular localizations: PER was constitutively nuclear and DBT was constitutively cytosolic. The loss of eye-specific molecular rhythm was reflected in an altered rhythm of visual preference that has been observed with other loss of circadian function mutations. The research put forth in this dissertation has illustrated the importance of BDBT foci formation to maintaining a functional eye clock in Drosophila and novel role where the eye clock can influence behavior.