Meeting Abstract

45.2  Tuesday, Jan. 5  Diurnal and circadian regulation of opsins co-expressed in Limulus photoreceptors BATTELLE, B-A.*; KATTI, C; LEGG, A; GONZALES, R; RIVERA, E; KEMPLER, K; Whitney Laboratory, Univ. of Florida battelle@whitney.ufl.edu

Three opsins co-express in Limulus lateral eye (LE) photoreceptors: opsins1 and 2, which are 99% identical to one another and called here ops1-2, and ops5, which is only 45% identical to ops1-2. Ops5, like ops1-2, is probably sensitive to visible light, but its spectral properties may be different from ops1-2. In phylogenetic analyses, ops5 does not cluster with ops1-2 and other chelicerate long wavelength sensitive opsins, but with crustacean opsins with largely unknown spectral properties. To test whether ops5 could contribute significantly to Limulus vision, we quantified ops5 levels relative to ops1-2 in LE membranes. Antibodies specific for ops5 and ops1-2 were used to immunostain Western blots of LE membranes and known amounts of the antigens against which the antibodies were raised. Immunoreactivity (ir) in the membranes was then compared to that of the antigen standards. We also quantified immunocytochemically changes in relative levels of these opsins at the rhabdom. In nighttime dark-adapted LEs, when most opsin-ir is in the rhabdom, ops5 in LE membranes is about 35% of ops1-2. Immunocytochemistry showed that rhabdomeral ops1-2-ir falls during the day to about 50% of its nighttime level due to rhabdom shedding while rhabdomeral levels of ops5 do not change. Thus, during the day, rhabdomeral ops5 is about 70% of ops1-2. Also, rhabdomeral ops1-2-ir is about 40% lower in nighttime LEs deprived of circadian clock input compared to control eyes with clock input, while ops5 levels are not significantly reduced. We conclude that ops5 can contribute significantly to Limulus vision especially during the day, and that the levels of ops5 and ops1-2 in the rhabdom are regulated differently by diurnal light and the circadian clock.