SPAETHE, Johannes; BRISCOE, Adriana* D.; University of California, Irvine ; University of California, Irvine: Ultraviolet opsin molecular characterization and expression: Three ommatidial subtypes in the retina and a new photoreceptor organ in the brains of bees

Ultraviolet-sensitive photoreceptors have been shown to be important for a variety of visual tasks performed by bees, such as orientation, color, and polarization vision, yet little is known about their spatial distribution in the compound eye or optic lobe. We cloned and sequenced a UV opsin mRNA transcript from Bombus impatiens head-specific cDNA, and using Western blot analysis, detected an eye protein band of ~40kDa, corresponding to the predicted molecular weight of the encoded opsin. We then characterized UV opsin expression in the retina and brain using immunocytochemistry. In the main retina we found three different ommatidial types with respect to the number of UV opsin expressing receptor cells, namely ommatidia containing two, one or no UV opsin-immunoreactive cells. This result indicates that the cloned opsin likely encodes the P350 nm pigment which was earlier characterized by physiological recordings. Surprisingly, in addition to expression in the retina we found opsin expression in different parts of the brain. UV opsin immunoreactivity was detected in the proximal rim of the lamina adjacent to the first optic chiasm where studies in other insects have found expression of proteins involved in the circadian clock, period and cryptochrome. We also found UV opsin immunoreactivity in the core region of the antennal lobe glomeruli, indicating a putative function of this brain region along with the lamina organ in the entrainment of circadian rhythms. In order to test for a possible overlap of clock protein and the UV opsin spatial expression, we also examined the expression of the period protein in this region.