Transgenic Fruit Flies
As we develop new genetic approaches in monarch butterflies, we have used existing trans-species genetic methods to address issues of monarch clock protein function—specifically, we have expressed monarch transgenes in Drosophila.
For example, we asked whether monarch CRY1 can function as a circadian photoreceptor by expressing the monarch cry1 transgene in flies; a monarch cry2 transgene was used as a control. We used the binary GAL4-UAS system, with tim-GAL4 as the driver, which drives transgene expression in most neurons that normally express Drosophila CRY and in the clock neurons that generate the circadian locomotor activity rhythm. For these studies, we took advantage of the cryb mutation in Drosophila, because the mutant protein is non-functional and induces severe light-input defects. We were able to rescue these light defects by expressing the monarch cry1 transgene in the cryb background, but not with the monarch cry2 transgene (Zhu et al., 2008).
We used the same transgenic approach for evaluating the functional roles of the two monarch butterfly CRYs in magnetosensitivity, as discussed under Magnetoreception (Gegear et al., 2010). Because monarch butterflies posses both a Drosophila-like Cry and a vertebrate-like Cry, they provided a unique opportunity to directly compare the functional equivalency for magnetosensitivity of each Cry type from the same species in vivo, using transgenesis.