Meeting Abstract

P3.151  Friday, Jan. 6   UV opsin is expressed in Limulus lateral, median and ventral eyes and is coexpressed with a visible light sensitive opsin HARRISON, A*; KEMPLER, K.E.; DUGGER, JR., D; BATTELLE, B-A.; Whitney Lab., Univ.of Florida, St. Augustine and Spelman College, Atlanta, GA; Whitney Lab., Univ. of Florida, St. Augustine; Dept. of Ophthalmology, Univ. of Florida, Gainesville; Whitney Lab., Univ. of Florida, St. Augustine

The horseshoe crab Limulus polyphemus (Lp) has three types of eyes, lateral (LE), median (ME) and rudimentary. The latter consist of clusters of giant and somewhat smaller photoreceptors. Sensitivity to UV light was thought restricted to MEs. We recently cloned a predicted UV-sensitive opsin from Limulus (LpUVops). Surprisingly, the clone originated from a cDNA library prepared from the ventral rudimentary eye (VE). Using gene specific primers, we detected the transcript for this LpUVops also in cDNA libraries from LE and ME. A monoclonal antibody specific for the C-terminus of LpUVops applied to fixed, frozen sections of each of the eyes, revealed LpUVops-like immunoreactivity in some but not all rhabdomeres of the ME, in rhabdomeres of smaller but not giant VE photoreceptors, and perhaps most surprisingly, in the membrane of the eccentric cell dendrite in LE. Eccentric cells have been considered a type of second order neuron in Limulus LE and ME because they are electrically coupled to photoreceptors, generate action potentials in response to photoreceptor depolarization and project to the brain. We also applied immunocytochemistry to test whether LpUVops is coexpressed with either of the visible light sensitive Lp opsins previously characterized, Ops1-2 or 5. So far, we have detected coexpression LpUVops with Ops5 in VE and ME photoreceptors. Our studies show LpUVops is expressed in all Limulus eyes, that Limulus VE contains two biochemically distinct populations of photoreceptors and that photoreceptors in ME and VE coexpress UV- and visible light-sensitive opsins. They also suggest that LE eccentric cells may be UV sensitive photoreceptors.