Localization of cryptochrome-immunopositive neurons in the visual system of Drosophila melanogaster
Cryptochrome (CRY) is a blue light absorbing protein involved in the photic entrainment of circadian clock in the fruit fl y. It has also been suggested that CRY may play role in molecular circadian clock that generates circadian rhythms in the visual system. The aim of our study was to examine localization of CRY-immunopositive neurons in the visual system of Drosophila and changes in abundance of CRY protein in these neurons. We used Drosophila transgenic lines which express green fl uorescent protein (GFP) under control of the cry promotor. Analyses of GFP fl uorescence showed that CRY is present in the dorsal neurons DN3, and in the dorsal (LNd) and ventral lateral neurons (LNv) and its density decreases during the day and increases during the night. In the LNv and in the processes of DN3, the CRY abundance was the highest at ZT1 (1 h after lights-on) and the lowest at ZT13 (1 h after lights-off) in both males and females. In addition we found that the LNvs project to the second visual neuropil (medulla) and form CRY-immunopositive network of many varicose processes in the medulla. We also detected numerous CRY-immunopositive processes in the fi rst optic neuropil (lamina) which origin from a single fi bre extending from the LNvs. In the lamina it divides into many thin branches next to the retina. Our results showed for the fi rst time that the lamina is invaded directly by processes of clock neurons which seem to control circadian plasticity of neurons and synapses in the lamina.