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Barbaraanne Battelle - One of the best experts on this subject based on the ideXlab platform.
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opsin repertoire and expression patterns in horseshoe crabs evidence from the genome of Limulus polyphemus arthropoda chelicerata
Genome Biology and Evolution, 2016Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Joseph F Ryan, Wesley C Warren, Patrick Minx, Michael J Montague, Pamela J Green, Skye A SchmidtAbstract:Horseshoe crabs are xiphosuran chelicerates, the sister group to arachnids. As such, they are important for understanding the most recent common ancestor of Euchelicerata and the evolution and diversification of Arthropoda. Limulus polyphemus is the most investigated of the four extant species of horseshoe crabs, and the structure and function of its visual system have long been a major focus of studies critical for understanding the evolution of visual systems in arthropods. Likewise, studies of genes encoding Limulus opsins, the protein component of the visual pigments, are critical for understanding opsin evolution and diversification among chelicerates, where knowledge of opsins is limited, and more broadly among arthropods. In the present study, we sequenced and assembled a high quality nuclear genomic sequence of L. polyphemus and used these data to annotate the full repertoire of Limulus opsins. We conducted a detailed phylogenetic analysis of Limulus opsins, including using gene structure and synteny information to identify relationships among different opsin classes. We used our phylogeny to identify significant genomic events that shaped opsin evolution and therefore the visual system of Limulus We also describe the tissue expression patterns of the 18 opsins identified and show that transcripts encoding a number, including a peropsin, are present throughout the central nervous system. In addition to significantly extending our understanding of photosensitivity in Limulus and providing critical insight into the genomic evolution of horseshoe crab opsins, this work provides a valuable genomic resource for addressing myriad questions related to xiphosuran physiology and arthropod evolution.
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opsins in Limulus eyes characterization of three visible light sensitive opsins unique to and co expressed in median eye photoreceptors and a peropsin rgr that is expressed in all eyes
The Journal of Experimental Biology, 2015Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Donald R Dugger, Daniel I Speiser, Todd H OakleyAbstract:The eyes of the horseshoe crab Limulus polyphemus have long been used for studies of basic mechanisms of vision, and the structure and physiology of Limulus photoreceptors have been examined in detail. Less is known about the opsins Limulus photoreceptors express. We previously characterized a UV opsin (LpUVOps1) that is expressed in all three types of Limulus eyes (lateral compound eyes, median ocelli and larval eyes) and three visible light-sensitive rhabdomeric opsins (LpOps1, -2 and -5) that are expressed in Limulus lateral compound and larval eyes. Physiological studies showed that visible light-sensitive photoreceptors are also present in median ocelli, but the visible light-sensitive opsins they express were unknown. In the current study we characterize three newly identified, visible light-sensitive rhabdomeric opsins (LpOps6, -7 and -8) that are expressed in median ocelli. We show that they are ocellar specific and that all three are co-expressed in photoreceptors distinct from those expressing LpUVOps1. Our current findings show that the pattern of opsin expression in Limulus eyes is much more complex than previously thought and extend our previous observations of opsin co-expression in visible light-sensitive Limulus photoreceptors. We also characterize a Limulus peropsin/RGR (LpPerOps1). We examine the phylogenetic relationship of LpPerOps1 with other peropsins and RGRs, demonstrate that LpPerOps1 transcripts are expressed in each of the three types of Limulus eyes and show that the encoded protein is expressed in membranes of cells closely associated with photoreceptors in each eye type. These finding suggest that peropsin was in the opsin repertoire of euchelicerates.
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Opsin co-expression in Limulus photoreceptors: differential regulation by light and a circadian clock
Journal of Experimental Biology, 2010Co-Authors: C. Katti, Karen E Kempler, Donald R Dugger, Megan L. Porter, A. Legg, R. Gonzalez, E. Garcia-rivera, Barbaraanne BattelleAbstract:SUMMARY A long-standing concept in vision science has held that a single photoreceptor expresses a single type of opsin, the protein component of visual pigment. However, the number of examples in the literature of photoreceptors from vertebrates and invertebrates that break this rule is increasing. Here, we describe a newly discovered Limulus opsin, Limulus opsin5, which is significantly different from previously characterized Limulus opsins, opsins1 and 2. We show that opsin5 is co-expressed with opsins1 and 2 in Limulus lateral and ventral eye photoreceptors and provide the first evidence that the expression of co-expressed opsins can be differentially regulated. We show that the relative levels of opsin5 and opsin1 and 2 in the rhabdom change with a diurnal rhythm and that their relative levels are also influenced by the animal9s central circadian clock. An analysis of the sequence of opsin5 suggests it is sensitive to visible light (400–700 nm) but that its spectral properties may be different from that of opsins1 and 2. Changes in the relative levels of these opsins may underlie some of the dramatic day–night changes in Limulus photoreceptor function and may produce a diurnal change in their spectral sensitivity.
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isolation and expression of pax6 and atonal homologues in the american horseshoe crab Limulus polyphemus
Developmental Dynamics, 2008Co-Authors: David C Blackburn, Barbaraanne Battelle, K.e. Kempler, Kevin W Conley, David C Plachetzki, Nadean L BrownAbstract:Pax6 regulates eye development in many animals. In addition, Pax6 activates atonal transcription factors in both invertebrate and vertebrate eyes. Here, we investigate the roles of Pax6 and atonal during embryonic development of Limulus polyphemus rudimentary lateral, medial and ventral eyes, and the initiation of lateral ommatidial eye and medial ocelli formation. Limulus eye development is of particular interest because these animals hold a unique position in arthropod phylogeny and possess multiple eye types. Furthermore, the molecular underpinnings of eye development have yet to be investigated in chelicerates. We characterized a Limulus Pax6 gene, with multiple splice products and predicted protein isoforms, and one atonal homologue. Unexpectedly, neither gene is expressed in the developing eye types examined, although both genes are present in the lateral sense organ, a structure of unknown function.
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Loop 2 of Limulus myosin III is phosphorylated by protein kinase A and autophosphorylation.
Biochemistry, 2007Co-Authors: K.e. Kempler, Judit Tóth, Roxanne Yamashita, Gretchen Mapel, Kimberly Robinson, Helene L. Cardasis, Stanley M. Stevens, James R. Sellers, Barbaraanne BattelleAbstract:Little is known about the functions of class III unconventional myosins although, with an N-terminal kinase domain, they are potentially both signaling and motor proteins. Limulus myosin III is particularly interesting because it is a phosphoprotein abundant in photoreceptors that becomes more heavily phosphorylated at night by protein kinase A. This enhanced nighttime phosphorylation occurs in response to signals from an endogenous circadian clock and correlates with dramatic changes in photoreceptor structure and function. We seek to understand the role of Limulus myosin III and its phosphorylation in photoreceptors. Here we determined the sites that become phosphorylated in Limulus myosin III and investigated its kinase, actin binding, and myosin ATPase activities. We show that Limulus myosin III exhibits kinase activity and that a major site for both protein kinase A and autophosphorylation is located within loop 2 of the myosin domain, an important actin binding region. We also identify the phosphorylation of an additional protein kinase A and autophosphorylation site near loop 2, and a predicted phosphorylation site within loop 2. We show that the kinase domain of Limulus myosin III shares some pharmacological properties with protein kinase A, and that it is a potential opsin kinase. Finally, we demonstrate that Limulus myosin III binds actin but lacks ATPase activity. We conclude that Limulus myosin III is an actin-binding and signaling protein and speculate that interactions between actin and Limulus myosin III are regulated by both second messenger mediated phosphorylation and autophosphorylation of its myosin domain within and near loop 2.
Sadaaki Iwanaga - One of the best experts on this subject based on the ideXlab platform.
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Limulus intracellular coagulation inhibitor type 3 purification characterization cdna cloning and tissue localization
Journal of Biological Chemistry, 1995Co-Authors: Yoshiki Miura, Takanori Nakamura, Shunichiro Kawabata, Yukako Wakamiya, Sadaaki IwanagaAbstract:Abstract We reported that Limulus intracellular coagulation inhibitor type-1 (LICI-1) (Miura, Y., Kawabata, S., and Iwanaga, S. (1994) J. Biol. Chem. 269, 542-547) and LICI type-2 (LICI-2) (Miura, Y., Kawabata, S., Wakamiya, Y., Nakamura, T., and Iwanaga, S. (1995) J. Biol. Chem. 270, 558-565) found in the hemocyte lysate belong to the serpin family. The LICI-1 specifically inhibits Limulus lipopolysaccharide-sensitive serine protease, factor C (k1 = 2.5 × 106 M−1 s−1), whereas LICI-2 inhibits preferentially Limulus clotting enzyme (k1 = 4.3 × 105 M−1 s−1). In our ongoing studies on Limulus serpin, we found another inhibitor, named LICI type-3 (LICI-3), which strongly inhibits (1,3)-β-D-glucan-sensitive serine protease, factor (k1 = 3.9 × 105 M−1 s−1). Thus, the Limulus hemolymph coagulation cascade is effectively regulated by at least the three endogenous serpins. LICI-3, newly identified in hemocytes, is a single chain glycoprotein with an apparent Mr = 53,000, the largest one among known Limulus serpins. A cDNA sequence for LICI-3 coded a mature protein of 392 amino acids, of which 68 residues were confirmed by peptide sequencing. LICI-3 showed significant sequence similarity to LICI-1 (45.8% identity) and LICI-2 (33.7% identity). LICI-3 contained a putative reactive site, -Arg-Ser-, distinct from that of LICI-2 (-Lys-Ser-) but the same as that of LICI-1. Expression of LICI-3 mRNA was detected only in hemocytes, and not in heart, brain, stomach, intestine, coxal gland, and skeletal muscle. Immunoblotting of the hemocyte-derived large and small granules with antiserum against LICI-3 suggested that it is stored specifically in large granules, as in the case of LICI-1 and LICI-2, and is released in response to external stimuli.
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a Limulus intracellular coagulation inhibitor with characteristics of the serpin superfamily purification characterization and cdna cloning
Journal of Biological Chemistry, 1994Co-Authors: Yoshiki Miura, Shunichiro Kawabata, Sadaaki IwanagaAbstract:Abstract A Limulus intracellular coagulation inhibitor, designated LICI, was isolated from hemocytes of the Japanese horseshoe crab (Tachypleus tridentatus), using three steps of chromatography, including dextran sulfate-Sepharose CL-6B, Sephacryl S-200, and Mono S. LICI is a single-chain glycoprotein with an apparent M(r) = 48,000 estimated by SDS-polyacrylamide gel electrophoresis. It blocks the amidolytic activities of Limulus lipopolysaccharide-sensitive serine protease, factor C, by forming a covalent 1:1 complex with the protease. The second-order rate constant for inhibition of factor C was 2.5 x 10(6) M-1 s-1 at 37 degrees C. LICI also inhibited human alpha-thrombin, rat salivary kallikrein, bovine plasmin, and trypsin but not Limulus clotting enzyme, Limulus factor B, bovine factor Xa, human factor XIa, human tissue plasminogen activator, human urokinase, chymotrypsin, elastase, and papain. Glycosaminoglycans such as heparin and heparan sulfate had no effect on the inhibitory activity. A cDNA coding for LICI was isolated from a hemocyte cDNA library. The open reading frame of the 1,257-base pair cDNA codes for the mature protein of 394 amino acids, of which 223 residues were confirmed by amino acid sequence analysis. LICI shows significant sequence identities to members of the serpin superfamily, such as human plasminogen activator inhibitor type 2 (40%) and human monocyte/neutrophil elastase inhibitor (39%). LICI contains a putative reactive site, -Arg-Ser-, at the corresponding position present in several inhibitors of the serpin superfamily. The subcellular localization, determined using an anti-LICI polyclonal antibody, indicated that LICI colocates with the Limulus serine protease zymogens in large granules in the hemocyte.
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Limulus hemocyte transglutaminase cdna cloning amino acid sequence and tissue localization
Journal of Biological Chemistry, 1993Co-Authors: Fuminori Tokunaga, Tatsushi Muta, Sadaaki Iwanaga, Akitada Ichinose, Earl W Davie, K I Kuma, Toshio MiyataAbstract:Abstract We have evidence that the Limulus (Tachypleus tri-dentatus) hemocyte transglutaminase (TGase) has a molecular mass of 86 kDa and properties of the mammalian type II TGase-like enzyme (Tokunaga, F., Yamada, M., Miyata, T., Ding, Y.-L., Hiranaga-Kawabata, M., Muta, T., Iwanaga, S., Ichinose, A., and Davie, E.W. (1993) J. Biol. Chem. 268, 252-261). We present here the cDNA and amino acid sequences, and localization of the TGase in various tissues of Limulus. The cloned cDNA for TGase consists of 2,884 base pairs. An open reading frame of 2,292 base pairs encodes a sequence comprising 764 residues of the mature protein with molecular masses of 87,021 and 87,110 Da, due to two different clones. The discrepancies of nucleotides in these two clones result in 3 amino acid exchanges at positions Gly452(GGT)-Arg(CGT), Ser477(AGT)-Cys(TGT), and Ile486(ATC)-Ser(AGC), respectively. Northern blot analysis on a total RNA extracted from various tissues of Limulus revealed that TGase is expressed with 3.0 kilobases of a single type of mRNA, mainly in hemocytes, hepatopancreas, and gastric tissues. Limulus TGase shows significant sequence similarity with the mammalian TGase family, as follows: guinea pig liver TGase (32.7%), human factor XIIIa subunit (34.7%), human keratinocyte TGase (37.6%), and human erythrocyte band 4.2 (23.0%). Limulus TGase has a unique NH2-terminal cationic extension of 60 residues with no homology to the NH2 termini of mammalian TGases. Based on the alignment of the amino acid sequence of Limulus TGase with those of the known TGase family, a phylogenetic tree representing an evolutionary relationship among the family members was inferred by the neighbor joining method.
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Limulus proclotting enzyme.
Methods in Enzymology, 1993Co-Authors: Tatsushi Muta, Takanori Nakamura, Ryuji Hashimoto, Takashi Morita, Sadaaki IwanagaAbstract:Publisher Summary This chapter describes the purification and properties of Limulus proclotting enzyme. Exposure of the Limulus hemocytes to bacterial endotoxins, which are lipopolysaccharides (LPS), results in the activation of the intracellular clotting system leading to gel formation. This phenomenon is known to be one of the self-defense systems of the horseshoe crab against invading micro-organisms. To elucidate the overall molecular events of the LPS induced activation of the Limulus clotting system, the chapter isolates the clotting factors from the hemocyte lysate. The Limulus hemocytes contain two types of granules, large but less dense granules and smaller but denser ones. Immunohistochemical studies show that the proclotting enzyme is localized exclusively in the large granules, and is apparently released through exocytosis on LPS stimulation of the hemocytes. The amidase activity of the clotting enzyme is inhibited by antithrombin III in the presence of heparin and α2-plasmin inhibitor, but is not inhibited by hirudin, aprotinin, and soybean trypsin inhibitor.
Karen E Kempler - One of the best experts on this subject based on the ideXlab platform.
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opsin repertoire and expression patterns in horseshoe crabs evidence from the genome of Limulus polyphemus arthropoda chelicerata
Genome Biology and Evolution, 2016Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Joseph F Ryan, Wesley C Warren, Patrick Minx, Michael J Montague, Pamela J Green, Skye A SchmidtAbstract:Horseshoe crabs are xiphosuran chelicerates, the sister group to arachnids. As such, they are important for understanding the most recent common ancestor of Euchelicerata and the evolution and diversification of Arthropoda. Limulus polyphemus is the most investigated of the four extant species of horseshoe crabs, and the structure and function of its visual system have long been a major focus of studies critical for understanding the evolution of visual systems in arthropods. Likewise, studies of genes encoding Limulus opsins, the protein component of the visual pigments, are critical for understanding opsin evolution and diversification among chelicerates, where knowledge of opsins is limited, and more broadly among arthropods. In the present study, we sequenced and assembled a high quality nuclear genomic sequence of L. polyphemus and used these data to annotate the full repertoire of Limulus opsins. We conducted a detailed phylogenetic analysis of Limulus opsins, including using gene structure and synteny information to identify relationships among different opsin classes. We used our phylogeny to identify significant genomic events that shaped opsin evolution and therefore the visual system of Limulus We also describe the tissue expression patterns of the 18 opsins identified and show that transcripts encoding a number, including a peropsin, are present throughout the central nervous system. In addition to significantly extending our understanding of photosensitivity in Limulus and providing critical insight into the genomic evolution of horseshoe crab opsins, this work provides a valuable genomic resource for addressing myriad questions related to xiphosuran physiology and arthropod evolution.
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opsins in Limulus eyes characterization of three visible light sensitive opsins unique to and co expressed in median eye photoreceptors and a peropsin rgr that is expressed in all eyes
The Journal of Experimental Biology, 2015Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Donald R Dugger, Daniel I Speiser, Todd H OakleyAbstract:The eyes of the horseshoe crab Limulus polyphemus have long been used for studies of basic mechanisms of vision, and the structure and physiology of Limulus photoreceptors have been examined in detail. Less is known about the opsins Limulus photoreceptors express. We previously characterized a UV opsin (LpUVOps1) that is expressed in all three types of Limulus eyes (lateral compound eyes, median ocelli and larval eyes) and three visible light-sensitive rhabdomeric opsins (LpOps1, -2 and -5) that are expressed in Limulus lateral compound and larval eyes. Physiological studies showed that visible light-sensitive photoreceptors are also present in median ocelli, but the visible light-sensitive opsins they express were unknown. In the current study we characterize three newly identified, visible light-sensitive rhabdomeric opsins (LpOps6, -7 and -8) that are expressed in median ocelli. We show that they are ocellar specific and that all three are co-expressed in photoreceptors distinct from those expressing LpUVOps1. Our current findings show that the pattern of opsin expression in Limulus eyes is much more complex than previously thought and extend our previous observations of opsin co-expression in visible light-sensitive Limulus photoreceptors. We also characterize a Limulus peropsin/RGR (LpPerOps1). We examine the phylogenetic relationship of LpPerOps1 with other peropsins and RGRs, demonstrate that LpPerOps1 transcripts are expressed in each of the three types of Limulus eyes and show that the encoded protein is expressed in membranes of cells closely associated with photoreceptors in each eye type. These finding suggest that peropsin was in the opsin repertoire of euchelicerates.
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Opsin co-expression in Limulus photoreceptors: differential regulation by light and a circadian clock
Journal of Experimental Biology, 2010Co-Authors: C. Katti, Karen E Kempler, Donald R Dugger, Megan L. Porter, A. Legg, R. Gonzalez, E. Garcia-rivera, Barbaraanne BattelleAbstract:SUMMARY A long-standing concept in vision science has held that a single photoreceptor expresses a single type of opsin, the protein component of visual pigment. However, the number of examples in the literature of photoreceptors from vertebrates and invertebrates that break this rule is increasing. Here, we describe a newly discovered Limulus opsin, Limulus opsin5, which is significantly different from previously characterized Limulus opsins, opsins1 and 2. We show that opsin5 is co-expressed with opsins1 and 2 in Limulus lateral and ventral eye photoreceptors and provide the first evidence that the expression of co-expressed opsins can be differentially regulated. We show that the relative levels of opsin5 and opsin1 and 2 in the rhabdom change with a diurnal rhythm and that their relative levels are also influenced by the animal9s central circadian clock. An analysis of the sequence of opsin5 suggests it is sensitive to visible light (400–700 nm) but that its spectral properties may be different from that of opsins1 and 2. Changes in the relative levels of these opsins may underlie some of the dramatic day–night changes in Limulus photoreceptor function and may produce a diurnal change in their spectral sensitivity.
Skye A Schmidt - One of the best experts on this subject based on the ideXlab platform.
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opsin repertoire and expression patterns in horseshoe crabs evidence from the genome of Limulus polyphemus arthropoda chelicerata
Genome Biology and Evolution, 2016Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Joseph F Ryan, Wesley C Warren, Patrick Minx, Michael J Montague, Pamela J Green, Skye A SchmidtAbstract:Horseshoe crabs are xiphosuran chelicerates, the sister group to arachnids. As such, they are important for understanding the most recent common ancestor of Euchelicerata and the evolution and diversification of Arthropoda. Limulus polyphemus is the most investigated of the four extant species of horseshoe crabs, and the structure and function of its visual system have long been a major focus of studies critical for understanding the evolution of visual systems in arthropods. Likewise, studies of genes encoding Limulus opsins, the protein component of the visual pigments, are critical for understanding opsin evolution and diversification among chelicerates, where knowledge of opsins is limited, and more broadly among arthropods. In the present study, we sequenced and assembled a high quality nuclear genomic sequence of L. polyphemus and used these data to annotate the full repertoire of Limulus opsins. We conducted a detailed phylogenetic analysis of Limulus opsins, including using gene structure and synteny information to identify relationships among different opsin classes. We used our phylogeny to identify significant genomic events that shaped opsin evolution and therefore the visual system of Limulus We also describe the tissue expression patterns of the 18 opsins identified and show that transcripts encoding a number, including a peropsin, are present throughout the central nervous system. In addition to significantly extending our understanding of photosensitivity in Limulus and providing critical insight into the genomic evolution of horseshoe crab opsins, this work provides a valuable genomic resource for addressing myriad questions related to xiphosuran physiology and arthropod evolution.
Spencer R Saraf - One of the best experts on this subject based on the ideXlab platform.
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opsin repertoire and expression patterns in horseshoe crabs evidence from the genome of Limulus polyphemus arthropoda chelicerata
Genome Biology and Evolution, 2016Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Joseph F Ryan, Wesley C Warren, Patrick Minx, Michael J Montague, Pamela J Green, Skye A SchmidtAbstract:Horseshoe crabs are xiphosuran chelicerates, the sister group to arachnids. As such, they are important for understanding the most recent common ancestor of Euchelicerata and the evolution and diversification of Arthropoda. Limulus polyphemus is the most investigated of the four extant species of horseshoe crabs, and the structure and function of its visual system have long been a major focus of studies critical for understanding the evolution of visual systems in arthropods. Likewise, studies of genes encoding Limulus opsins, the protein component of the visual pigments, are critical for understanding opsin evolution and diversification among chelicerates, where knowledge of opsins is limited, and more broadly among arthropods. In the present study, we sequenced and assembled a high quality nuclear genomic sequence of L. polyphemus and used these data to annotate the full repertoire of Limulus opsins. We conducted a detailed phylogenetic analysis of Limulus opsins, including using gene structure and synteny information to identify relationships among different opsin classes. We used our phylogeny to identify significant genomic events that shaped opsin evolution and therefore the visual system of Limulus We also describe the tissue expression patterns of the 18 opsins identified and show that transcripts encoding a number, including a peropsin, are present throughout the central nervous system. In addition to significantly extending our understanding of photosensitivity in Limulus and providing critical insight into the genomic evolution of horseshoe crab opsins, this work provides a valuable genomic resource for addressing myriad questions related to xiphosuran physiology and arthropod evolution.
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opsins in Limulus eyes characterization of three visible light sensitive opsins unique to and co expressed in median eye photoreceptors and a peropsin rgr that is expressed in all eyes
The Journal of Experimental Biology, 2015Co-Authors: Barbaraanne Battelle, Karen E Kempler, Spencer R Saraf, Catherine E Marten, Donald R Dugger, Daniel I Speiser, Todd H OakleyAbstract:The eyes of the horseshoe crab Limulus polyphemus have long been used for studies of basic mechanisms of vision, and the structure and physiology of Limulus photoreceptors have been examined in detail. Less is known about the opsins Limulus photoreceptors express. We previously characterized a UV opsin (LpUVOps1) that is expressed in all three types of Limulus eyes (lateral compound eyes, median ocelli and larval eyes) and three visible light-sensitive rhabdomeric opsins (LpOps1, -2 and -5) that are expressed in Limulus lateral compound and larval eyes. Physiological studies showed that visible light-sensitive photoreceptors are also present in median ocelli, but the visible light-sensitive opsins they express were unknown. In the current study we characterize three newly identified, visible light-sensitive rhabdomeric opsins (LpOps6, -7 and -8) that are expressed in median ocelli. We show that they are ocellar specific and that all three are co-expressed in photoreceptors distinct from those expressing LpUVOps1. Our current findings show that the pattern of opsin expression in Limulus eyes is much more complex than previously thought and extend our previous observations of opsin co-expression in visible light-sensitive Limulus photoreceptors. We also characterize a Limulus peropsin/RGR (LpPerOps1). We examine the phylogenetic relationship of LpPerOps1 with other peropsins and RGRs, demonstrate that LpPerOps1 transcripts are expressed in each of the three types of Limulus eyes and show that the encoded protein is expressed in membranes of cells closely associated with photoreceptors in each eye type. These finding suggest that peropsin was in the opsin repertoire of euchelicerates.