Meeting Abstract
P1.184 Saturday, Jan. 4 15:30 Opsin expression in the Limulus visual system: Too many opsins? SARAF, S.R.*; KEMPLER, K.E.; DUGGER, D.R.; SPEISER, D.I.; OAKELY, T.H.; WILSON, R.K.; BATTELLE, B-A.; Whitney Lab., Univ. of Florida; Whitney Lab., Univ. of Florida; Dept. of Ophthalmology, Univ. Florida; Univ. California, Santa Barbara; Univ. California, Santa Barbara; The Genome Institute, Washington Univ.; Whitney Lab., Univ. of Florida battelle@whitney.ufl.edu
The horseshoe crab Limulus polyphemus is a classic model for studies of vision. It has three types of eyes: lateral, median and larval. Much is known about Limulus photoreceptor structure and function; less is known about the opsins the photoreceptors express. Just two spectral types of photoreceptors have been detected in Limulus eyes: visible light-sensitive, all with a maximum sensitivity of about 520 nm, and UV-light sensitive. So it was surprising when a preliminary assembly of the Limulus genome revealed 12 rhabdomeral opsin sequences, many more opsin genes than there are identified photoreceptor types. The questions arise: Are all of these opsins expressed and where? The expression patterns of four of the opsins (LpOps1, 2, 5 and UVops) are known from previous work. Our current goal was to determine whether and where the newly identified opsins, all predicted visible light-sensitive opsins, are expressed. Several approaches were used: PCR amplification from cDNA confirmed by sequencing, in situ hybridization and immunocytochemistry. Two of the opsins, LpOps6 and 7 were detected in a median eye (ME) transcriptome. In situ hybridization and immunocytochemical assays confirmed that both are expressed in ME photoreceptors but not in the photoreceptors of lateral or larval eyes. With PCR and sequencing, LpOps8 and 11 were detected in MEs; LpOps11 was also detected in larval eyes, and the central nerve cord; LpOps6, 7, 8, 10 and 11 were detected in the tail. The tail is known to contain extraocular photoreceptors. LpOps9 was not detected in any of the tissues examined so far. Accumulating evidence suggests most Limulus photoreceptors express multiple opsins.
