Molecular cloning and characterization of an invertebrate cellular retinoic acid binding protein

Expression and function analysis of crustacyanin gene family involved in resistance to heavy metal stress and body color formation in Exopalaemon carinicauda

Crustacyanin has the function of binding astaxanthin which is the best antioxidant, and plays an important role in the body color variation of crustaceans. To investigate the causes of body color variation of the ridgetail white prawn, Exopalaemon carinicauda, the present study obtained four subtypes of crustacyanin gene: C1, C2, A1, and A2. Based on fluorescence quantitative polymerase chain reaction, lipocalin-C1 is mainly expressed in the eyestalk, lipocalin-C2 is in the ventral nerve cord, and lipocalin-A1 and lipocalin-A2 are in subcutaneous adipose tissues. Under the inhibiting effect of Cd²⁺ stress, the expression of four subtypes first increases and then decreases within 24 h, and reaches the maximum at 6 or 12 h. RNA interference experiments showed a decrease in the expression of lipocalin genes in subcutaneous adipose tissue for each subtype, with the body color changing from transparent to red, and the dark red spots on the epidermis changing to bright red. Moreover, the blue protein in the subcutaneous adipose tissue largely disappeared, based on the light micrographs. In view of these findings, the crustacyanin gene appears to fulfill some function in the resistance to heavy metal stress and body color formation of E. carinicauda.

Cloning and functional study of lipocalin: retinol-binding protein-like gene family of the ridgetail white prawn, Exopalaemon carinicauda

Lipocalin is a large family with complex functions including retinol-binding protein (RBP), crustacyanin (CRCN), apolipoprotein D, etc. In shrimps, it is well known that CRCN is related to body color. Recently, retinoic acid/retinol-binding protein was found in shrimp. However, little is known about the function of RBP and relationships among the gene members of lipocalin in shrimps. Based on the transcriptome sequences responding to starvation stress, three genes of the lipocalin-retinol-binding protein-like gene family (lipocalin-1, lipocalin-2, and lipocalin-3) were cloned by RACE from the ridgetail white prawn, Exopalaemon carinicauda. Homology analysis showed that these three genes had high similarity with the known insect apolipoprotein D gene and vertebrate retinol-binding protein gene, and they are of the same type in terms of evolution. Fluorescence quantitative PCR showed that the above three genes were mainly expressed in the ventral nerve cord of E. carinicauda. The expression characteristics of the three genes at different developmental stages showed that they were more highly expressed at the larval stage, which suggests that they might be related to embryonic and larval development. The RNA interference tests showed that after silencing lipocalin-1 and lipocalin-3, the body color of individual shrimps turned slightly red and the blue pigment in the epidermis largely disappeared, but no significant change took place in the appearance of individuals after silencing lipocalin-2. In addition, on the 6th and 16th days of interference, dead shrimps appeared in the lipocalin-1 and lipocalin-3 interference groups. The dead shrimps had hard crusts and remained in a molting posture. Totally, this study showed that the retinol-binding protein-like gene obtained in this study had certain biological functions in the growth and development and body color formation as CRCN; in addition, it also plays a role in nerve system and molting of E. carinicauda.

The ancestral retinoic acid receptor was a low-affinity sensor triggering neuronal differentiation

Retinoic acid (RA) is an important intercellular signaling molecule in vertebrate development, with a well-established role in the regulation of hox genes during hindbrain patterning and in neurogenesis. However, the evolutionary origin of the RA signaling pathway remains elusive. To elucidate the evolution of the RA signaling system, we characterized RA metabolism and signaling in the marine annelid Platynereis dumerilii, a powerful model for evolution, development, and neurobiology. Binding assays and crystal structure analyses show that the annelid retinoic acid receptor (RAR) binds RA and activates transcription just as vertebrate RARs, yet with a different ligand-binding pocket and lower binding affinity, suggesting a permissive rather than instructive role of RA signaling. RAR knockdown and RA treatment of swimming annelid larvae further reveal that the RA signal is locally received in the medial neuroectoderm, where it controls neurogenesis and axon outgrowth, whereas the spatial colinear hox gene expression in the neuroectoderm remains unaffected. These findings suggest that one early role of the new RAR in bilaterian evolution was to control the spatially restricted onset of motor and interneuron differentiation in the developing ventral nerve cord and to indicate that the regulation of hox-controlled anterior-posterior patterning arose only at the base of the chordates, concomitant with a high-affinity RAR needed for the interpretation of a complex RA gradient.

Development of quantitative proteomics using iTRAQ based on the immunological response of Galleria mellonella larvae challenged with Fusarium oxysporum microconidia

Galleria mellonella has emerged as a potential invertebrate model for scrutinizing innate immunity. Larvae are easy to handle in host-pathogen assays. We undertook proteomics research in order to understand immune response in a heterologous host when challenged with microconidia of Fusarium oxysporum. The aim of this study was to investigate hemolymph proteins that were differentially expressed between control and immunized larvae sets, tested with F. oxysporum at two temperatures. The iTRAQ approach allowed us to observe the effects of immune challenges in a lucid and robust manner, identifying more than 50 proteins, 17 of them probably involved in the immune response. Changes in protein expression were statistically significant, especially when temperature was increased because this was notoriously affected by F. oxysporum 104 or 106 microconidia/mL. Some proteins were up-regulated upon immune fungal microconidia challenge when temperature changed from 25 to 37°C. After analysis of identified proteins by bioinformatics and meta-analysis, results revealed that they were involved in transport, immune response, storage, oxide-reduction and catabolism: 20 from G. mellonella, 20 from the Lepidoptera species and 19 spread across bacteria, protista, fungi and animal species. Among these, 13 proteins and 2 peptides were examined for their immune expression, and the hypothetical 3D structures of 2 well-known proteins, unannotated for G. mellonella, i.e., actin and CREBP, were resolved using peptides matched with Bombyx mori and Danaus plexippus, respectively. The main conclusion in this study was that iTRAQ tool constitutes a consistent method to detect proteins associated with the innate immune system of G. mellonella in response to infection caused by F. oxysporum. In addition, iTRAQ was a reliable quantitative proteomic approach to detect and quantify the expression levels of immune system proteins and peptides, in particular, it was found that 104 microconidia/mL at 37°C over expressed many more proteins than other treatments.

Retinoid metabolism in invertebrates: when evolution meets endocrine disruption

Recent genomic and biochemical evidence in invertebrate species pushes back the origin of the retinoid metabolic and signaling modules to the last common ancestor of all bilaterians. However, the evolution of retinoid pathways are far from fully understood. In the majority of non-chordate invertebrate lineages, the ongoing functional characterization of retinoid-related genes (metabolism and signaling pathways), as well as the characterization of the endogenous retinoid content (precursors and active retinoids), is still incomplete. Despite limited, the available data supports the presence of biologically active retinoid pathways in invertebrates. Yet, the mechanisms controlling the spatial and temporal distribution of retinoids as well as their physiological significance share similarities and differences with vertebrates. For instance, retinol storage in the form of retinyl esters, a key feature for the maintenance of retinoid homeostatic balance in vertebrates, was only recently demonstrated in some mollusk species, suggesting that such ability is older than previously anticipated. In contrast, the enzymatic repertoire involved in this process is probably unlike that of vertebrates. The suggested ancestry of active retinoid pathways implies that many more metazoan species might be potential targets for endocrine disrupting chemicals. Here, we review the current knowledge about the occurrence and functionality of retinoid metabolic and signaling pathways in invertebrate lineages, paying special attention to the evolutionary origin of retinoid storage mechanisms. Additionally, we summarize existing information on the endocrine disruption of invertebrate retinoid modules by environmental chemicals. Research priorities in the field are highlighted.

Retinoic acid as a survival factor in neuronal development of the grasshopper, Locusta migratoria

Based on experience with cell cultures of adult insect neurons, we develop a serum-free culture system for embryonic locust neurons. Influences of trophic substances on survival and neurite outgrowth of developing neurons are investigated. For the first time, a positive trophic effect of 9-cis retinoic acid (9-cis RA) was shown in vitro on embryonic neurons of an insect. We observed longer cell survival of 50 % developmental stage neurons in cultures supplemented with 0.3 nM 9-cis RA. Furthermore, an influence on neuron morphology was revealed, as the addition of 9-cis RA to cell culture medium led to an increase in the number of neurites per cell. Although an RA receptor gene, LmRXR (Locusta migratoria retinoid X receptor), was expressed in the central nervous system throughout development, the influence of 9-cis RA on neuronal survival and outgrowth was restricted to 50 % stage embryonic cells.

Cloning and characterization of a midgut-specific fatty acid binding protein in Spodoptera litura

A fatty acid binding protein (FABP) gene (Slfabp1) was cloned from the midgut of Spodoptera litura larvae. The gene consists of four exons and three introns and encodes a peptide of 134 amino acid residues with a predicted molecular mass of 14.7 kDa, which was confirmed by in vitro protein expression. Northern blot and Western blot analyses indicated that both of Slfabp1 mRNA and protein were highly and specifically expressed in the midgut during the fifth and sixth instar feeding larval stages. In situ hybridization and immunohistochemistry analyses confirmed the midgut-specific localization of Slfabp1 mRNA and protein. The result of Western blot showed that expression of the protein was downregulated by starvation and upregulated by refeeding in sixth instar larvae. All of the results taken together suggest that the SlFABP1 plays important role(s) in FA uptake and transport in the midgut during the larval feeding stages of the insect.

Evolution of retinoid and steroid signaling: vertebrate diversification from an amphioxus perspective

Although the physiological relevance of retinoids and steroids in vertebrates is very well established, the origin and evolution of the genetic machineries implicated in their metabolic pathways is still very poorly understood. We investigated the evolution of these genetic networks by conducting an exhaustive survey of components of the retinoid and steroid pathways in the genome of the invertebrate chordate amphioxus (Branchiostoma floridae). Due to its phylogenetic position at the base of chordates, amphioxus is a very useful model to identify and study chordate versus vertebrate innovations, both on a morphological and a genomic level. We have characterized more than 220 amphioxus genes evolutionarily related to vertebrate components of the retinoid and steroid pathways and found that, globally, amphioxus has orthologs of most of the vertebrate components of these two pathways, with some very important exceptions. For example, we failed to identify a vertebrate-like machinery for retinoid storage, transport, and delivery in amphioxus and were also unable to characterize components of the adrenal steroid pathway in this invertebrate chordate. The absence of these genes from the amphioxus genome suggests that both an elaboration and a refinement of the retinoid and steroid pathways took place at the base of the vertebrate lineage. In stark contrast, we also identified massive amplifications in some amphioxus gene families, most extensively in the short-chain dehydrogenase/reductase superfamily, which, based on phylogenetic and genomic linkage analyses, were likely the result of duplications specific to the amphioxus lineage. In sum, this detailed characterization of genes implicated in retinoid and steroid signaling in amphioxus allows us not only to reconstruct an outline of these pathways in the ancestral chordate but also to discuss functional innovations in retinoid homeostasis and steroid-dependent regulation in both cephalochordate and vertebrate evolution.

Proteome changes in the plasma of Pieris rapae parasitized by the endoparasitoid wasp Pteromalus puparum

Parasitism by the endoparasitoid wasp Pteromalus puparum causes alterations in the plasma proteins of Pieris rapae. Analysis of plasma proteins using a proteomic approach showed that seven proteins were differentially expressed in the host pupae after 24-h parasitism. They were masquerade-like serine proteinase homolog (MSPH), enolase (Eno), bilin-binding protein (BBP), imaginal disc growth factor (IDGF), ornithine decarboxylase (ODC), cellular retinoic acid binding protein (CRABP), and one unknown function protein. The full length cDNA sequences of MSPH, Eno, and BBP were successfully cloned using rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR). Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicated that the transcript levels of MSPH and BBP in the fat bodies of host pupae were inducible in response to the parasitism and their variations were consistent with translational changes of these genes after parasitism, while the transcript levels of Eno and IDGF were not affected by parasitism. This study will contribute to the better understanding of the molecular bases of parasitoid-induced host alterations associated with innate immune responses, detoxification, and energy metabolism.

Developmental expression of a molluscan RXR and evidence for its novel, nongenomic role in growth cone guidance

It is well known that the vitamin A metabolite, retinoic acid, plays an important role in vertebrate development and regeneration. We have previously shown that the effects of RA in mediating neurite outgrowth, are conserved between vertebrates and invertebrates (Dmetrichuk et al., 2005, 2006) and that RA can induce growth cone turning in regenerating molluscan neurons (Farrar et al., 2009). In this study, we have cloned a retinoid receptor from the mollusc Lymnaea stagnalis (LymRXR) that shares about 80% amino acid identity with the vertebrate RXRalpha. We demonstrate using Western blot analysis that the LymRXR is present in the developing Lymnaea embryo and that treatment of embryos with the putative RXR ligand, 9-cis RA, or a RXR pan-agonist, PA024, significantly disrupts embryogenesis. We also demonstrate cytoplasmic localization of LymRXR in adult central neurons, with a strong localization in the neuritic (or axonal) domains. Using regenerating cultured motor neurons, we show that LymRXR is also present in the growth cones and that application of a RXR pan-agonist produces growth cone turning in isolated neurites (in the absence of the cell body and nucleus). These data support a role for RXR in growth cone guidance and are the first studies to suggest a nongenomic action for RXR in the nervous system.

Proteome changes in the plasma of Papilio xuthus (Lepidoptera: Papilionidae): effect of parasitization by the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

Although the biochemical dissection of parasitoid-host interactions is becoming well characterized, the molecular knowledge concerning them is minimal. In order to understand the molecular bases of the host immune response to parasitoid attack, we explored the response of Papilio xuthus parasitized by the endoparasitic wasp Pteromalus puparum using proteomic approach. By examining the differential expression of plasma proteins in the parasitized and unparasitized host pupae by two-dimensional (2D) electrophoresis, 16 proteins were found to vary in relation to parasitization compared with unparasitized control samples. All of them were submitted to identification by mass spectrometry coupled with a database search. The modulated proteins were found to fall into the following functional groups: humoral or cellular immunity, detoxification, energy metabolism, and others. This study contributes insights into the molecular mechanism of the relationships between parasitoids and their host insects.

Detection of endogenous retinoids in the molluscan CNS and characterization of the trophic and tropic actions of 9-cis retinoic acid on isolated neurons

Retinoic acid (RA) is an active metabolite of Vitamin A that plays an important role in the growth and differentiation of many cell types. All-trans RA (atRA) is the retinoic acid isomer that has been most widely studied in the nervous system, and can induce and direct neurite outgrowth from both vertebrate and invertebrate preparations. The presence and role of the 9-cis-RA isomer in the nervous system is far less well defined. Here, we used high-pressure liquid chromatography (HPLC) and mass spectrometry (MS) to show for the first time, the presence of both atRA and 9-cis-RA in the CNS of an invertebrate. We then demonstrated that 9-cis-RA was capable of exerting the same neurotrophic and chemotropic effects on cultured neurons as atRA. In this study, significantly more cells showed neurite outgrowth in 9-cis-RA versus the EtOH vehicle control, and 9-cis-RA significantly increased the number and length of neurites from identified neurons after 4 d in culture. 9-cis-RA also extended the duration of time that cells remained electrically excitable in culture. Furthermore, we showed for the first time in any species, that exogenous application of 9-cis-RA induced positive growth cone turning of cultured neurons. This study provides the first evidence for the presence of both atRA and 9-cis-RA in an invertebrate CNS and also provides the first direct evidence for a potential physiological role for 9-cis-RA in neuronal regeneration and axon pathfinding.

Synthesis and in vitro biological activity of retinyl retinoate, a novel hybrid retinoid derivative

A new hybrid, retinyl retinoate 1, was synthesized with a condensing reaction between retinol and retinoic acid to improve the photo-stability, and the in vitro biological activity of the hybrid was analyzed. This retinol derivative had enhanced thermal stability and decreased photosensitivity, and exhibited decreased cell toxicity compared to that of retinol. In addition, RAR activity analysis showed that retinyl retinoate 1 had higher inhibitory activity against c-Jun than retinol and showed superior effects on collagen synthesis compared to retinol. Thus, retinyl retinoate 1 may have the potential to be conveniently used as an additive in cosmetics for prevention and improvement of skin aging and medicines for the treatment of skin troubles due to its excellent stability under severe and accelerated conditions.

The search for non-chordate retinoic acid signaling: lessons from chordates

Signaling by retinoic acid (RA) is an important pathway in the development and homeostasis of vertebrate and invertebrate chordates, with a critical role in mesoderm patterning. Classical studies on the distribution of nuclear receptors of animals suggested that the family of RA receptors (RARs/NR1B) was restricted to chordates, while the family of RA X receptors (RXR/NR2B) was distributed from cnidarians to chordates. However, the accumulation of data from genome projects and studies in non-model species is questioning this traditional view. Here we discuss the evidence for non-chordate RA signaling systems in the light of recent advances in our understanding of carotene (pro-Vitamin A) metabolism and of the identification of potential RARs and members of the NR1 family in echinoderms and lophotrochozoan trematodes, respectively. We conclude, as have others before (Bertrand et al., 2004. Mol Biol Evol 21(10):1923-1937), that signaling by RA is more likely an ancestral feature of bilaterians than a chordate innovation.

Effects of retinoids and juvenoids on moult and on phenoloxidase activity in the blood-sucking insect Rhodnius prolixus

Retinoic acid and insect juvenile hormone (JH) are structurally related terpenoids which are widespread in nature and are involved in many biological events such as morphogenesis, embryogenesis and cellular differentiation. Here, we investigated the effects of the retinoids 9-cis retinoic acid (9cisRA), all trans retinol (atROH), all trans retinoic acid (atRA) and the juvenoids methoprene (Met) and JH injection on moult and on phenoloxidase activity in the blood-sucking insect Rhodnius prolixus. Overall, we observed that injection of retinoids or juvenoids (120 pmols) in the hemocoel of 4th instar nymphs reduced the percentage of insects which appeared normal in morphology upon moult. Noteworthy, insects exposed to 9cisRA or JH underwent profound morphological changes upon moult, generating abnormal 5th instar nymphs and also markedly increased the death of insects during the moulting process. In addition, reduction in the percentage of insects that moult without any morphological alteration, induced by retinoids or juvenoids treatment, was negatively correlated with insects that both display abnormal moult and those that die during moult. Hemolymphatic phenoloxidase activity in adult male insects injected with 9cisRA, Met and JH were significantly reduced after a bacterial challenge. Together, these results indicate that not only juvenoids but also retinoids play an important role on morphogenesis and on immune response in R. prolixus, suggesting that the molecular mechanisms involved in these events recognize the terpenoid backbone as an important structural determinant in insects.

Prawn lipocalin: characteristics and expressional pattern in subepidermal adipose tissue during reproductive molting cycle

In crustaceans, the fascinating processes of maturation, reproductive molting and carapace coloration are regulated by hydrophobic molecules. Interestingly, most of the molecules are ligands of lipocalin. To understand the role of lipocalin in the aforementioned processes at molecular level, we isolated a cDNA that belongs to the lipocalin family, from a central nervous system cDNA library of Macrobrachium rosenbergii. We monitored the spatial and temporal distributions of the mRNA by using Northern Blotting analysis. Our results demonstrated that this gene expresses abundantly in the subepidermal adipose tissue, while faintly in the hepatopancreas and central nervous system. However, no signal was detected in other tissues including muscle, gill and ovary. Its expression levels in subepidermal adipose tissue during various stages of maturation as well as through the whole molting cycle showed that prawn lipocalin is involved in sexual maturation, as the maximal level was observed just after molt.

Characterization of a hemocyte intracellular fatty acid-binding protein from crayfish (Pacifastacus leniusculus) and shrimp (Penaeus monodon)

Intracellular fatty acid-binding proteins (FABPs) are small members of the superfamily of lipid-binding proteins, which occur in invertebrates and vertebrates. Included in this superfamily are the cellular retinoic acid-binding proteins and retinol-binding proteins, which seem to be restricted to vertebrates. Here, we report the cDNA cloning and characterization of two FABPs from hemocytes of the freshwater crayfish Pacifastacus leniusculus and the shrimp Penaeus monodon. In both these proteins, the binding triad residues involved in interaction with ligand carboxylate groups are present. From the sequence and homology modeling, the proteins are probably FABPs and not retinoic acid-binding proteins. The crayfish transcript (plFABP) was detected at high level in hemocytes, hepatopancreas, intestine and ovary and at low level in hematopoietic tissue and testis. Its expression in hematopoietic cells varied depending on the state of the crayfish from which it was isolated. Expression was 10-15 times higher in cultures isolated from crayfish with red colored plasma, in which hemocyte synthesis was high, if retinoic acid was added to the culture medium. In normal colored crayfish, with normal levels of hemocytes, no increase in expression of p1FABP was detected. Two other putative plFABP ligands, stearic acid and oleic acid, did not have any effect on plFABP expression in hematopoietic cells. These results suggest that retinoic acid-dependent signaling may be present in crustaceans.

Retinoic acid induces neurite outgrowth and growth cone turning in invertebrate neurons

Identification of molecules involved in neurite outgrowth during development and/or regeneration is a major goal in the field of neuroscience. Retinoic acid (RA) is a biologically important metabolite of vitamin A that acts as a trophic factor and has been implicated in neurite outgrowth and regeneration in many vertebrate species. Although abundant in the CNS of many vertebrates, the precise role of RA in neural regeneration has yet to be determined. Moreover, very little information is available regarding the role of RA in invertebrate nervous systems. Here, we demonstrate for the first time that RA induces neurite outgrowth from invertebrate neurons. Using individually identified neurons isolated from the CNS of Lymnaea stagnalis, we demonstrated that a significantly greater proportion of cells produced neurite outgrowth in RA. RA also extended the duration of time that cells remained electrically excitable in vitro, and we showed that exogenously applied RA acted as a chemoattractive factor and induced growth cone turning toward the source of RA. This is the first demonstration that RA can induce turning of an individual growth cone. These data strongly suggest that the actions of RA on neurite outgrowth and cell survival are highly conserved across species.

Invertebrate intracellular fatty acid binding proteins

Fatty acid binding proteins are multigenic cytosolic proteins largely distributed along the zoological scale. Their overall identity at primary and tertiary structure is conserved. They are involved in the uptake and transport of hydrophobic ligands to different cellular fates. The precise functions of each FABP type remain imperfectly understood, since sub-specialization of functions is suggested. Evolutionary studies have distinguished major subfamilies that could have been derived from a common ancestor close to vertebrate/invertebrate split. Since the isolation of the first invertebrate FABP from Schistocerca gregaria in 1990, the number of FABPs isolated from invertebrates has been increasing. Differences at the sequence level are appreciable and relationships with vertebrate FABPs are not clear, and lesser among invertebrate proteins, introducing some uncertainty to infer functional relatedness and phylogenetic relationships. The objective of this review is to summarize the information available on invertebrate FABPs to elucidate their mutual relationships, the relationship with their vertebrate counterparts and putative functions. Structure, gene structure, putative functions, expression studies and phylogenetic relationships with vertebrate counterparts are analyzed. Previous suggestions of the ancestral position concerning the heart-type of FABPs are reinforced by evidence from invertebrate models.

Schistosoma mansoni (Platyhelminthes, Trematoda) nuclear receptors: Sixteen new members and a novel subfamily

Nuclear receptors (NRs) are important transcriptional modulators in metazoans. Sixteen new NRs were identified in the Platyhelminth trematode, Schistosoma mansoni. Three were found to possess novel tandem DNA-binding domains that identify a new subfamily of NR. Two NRs are homologues of the thyroid hormone receptor that previously were thought to be restricted to chordates. This study brings the total number of identified NR in S. mansoni to 21. Phylogenetic and comparative genomic analyses demonstrate that S. mansoni NRs share an evolutionary lineage with that of arthropods and vertebrates. Phylogenic analysis shows that more than half of the S. mansoni nuclear receptors evolved from a second gene duplication. As the second gene duplication of NRs was thought to be specific to vertebrates, our data challenge the current theory of NR evolution.

Ligand-binding specificity of an invertebrate (Manduca sexta) putative cellular retinoic acid binding protein

Intracellular lipid-binding proteins (iLBPs) are small cytoplasmic proteins that specifically interact with hydrophobic ligands. Fatty acid-binding proteins (FABPs), cellular retinoic acid-binding proteins (CRABPs) and cellular retinol-binding proteins (CRBPs) belong to the iLBP family. A recently identified insect (Manduca sexta) iLBP has been reported to possibly represent an invertebrate CRABP mimicking the role of CRABPs in vertebrate organisms. The presence in this protein of the characteristic binding triad residues involved in the interaction with ligand carboxylate head groups, a feature pertaining to several FABPs and to CRABPs, and the close phylogenetic relationships with both groups of vertebrate heart-type FABPs and CRBPs/CRABPs, makes it difficult to assign it to either FABPs or CRABPs. However, its negligible interaction with retinoic acid and high affinity (K(d) values in the 10(-8) M range) for fatty acids have been established by means of direct and competitive binding assays. As shown by phylogenetic analysis, the M. sexta iLBP belongs to a wide group of invertebrate iLBPs, which, besides being closely related phylogenetically, share distinctive features, such as the conservation of chemically distinct residues in their amino acid sequences and the ability to bind fatty acids. Our results are in keeping with the lack of cellular retinoid-binding proteins in invertebrates and with their later appearance during the course of chordate evolution.

Evolutionary Genomics of Nuclear Receptors: From Twenty-Five Ancestral Genes to Derived Endocrine Systems

Bilaterian animals are notably characterized by complex endocrine systems. The receptors for many steroids, retinoids, and other hormones belong to the superfamily of nuclear receptors, which are transcription factors regulating many aspects of development and homeostasis. Despite a diversity of regulatory mechanisms and physiological roles, nuclear receptors share a common protein organization. To obtain the broad picture of bilaterian nuclear hormone receptor evolution, we have characterized the complete set of nuclear receptor genes from nine animal genome sequences and analyzed it in a phylogenetic framework. In addition, expressed sequence tags from key lineages with no available genome sequence were also searched. This allows us to date the evolutionary events that led from an ancestral nuclear receptor gene, in an early metazoan, to present day diversity. We show that there were approximately 25 nuclear receptor genes in Urbilateria, the ancestor of bilaterians, at which point the fundamental diversity of the subfamily was already established. Surprisingly, differential gene loss played an important role in the evolution of different nuclear receptor sets in bilaterian lineages. The nuclear receptor distribution was also shaped by periods of gene duplication, essentially in vertebrates, as well as a lineage-specific duplication burst in nematodes. Our results imply that the genes for major receptors such as steroid receptors or thyroid hormone receptors were present in Urbilateria.

Ligand specificity and developmental expression of RXR and ecdysone receptor in the migratory locust

The ecdysone receptor(1), which is a heterodimer of EcR and the retinoic acid receptor (RXR) homolog, Ultraspiracle (USP), has been well studied in the evolutionarily advanced and derived insects, the flies and moths. It is less well characterized in more primitive insect orders such as the Orthoptera, which include the grasshoppers and locusts. Following our previous isolation from Locusta migratoria (Lm) of a shorter RXR isoform (now called LmRXR-S), the isolation of a second, longer isoform (LmRXR-L) that appears to have characteristics of a ligand-modulated nuclear receptor is reported here. Transcripts for both isoforms, as well as LmEcR, were detected in embryos and in females during oocyte maturation. After expression in E. coli, both LmRXR-S and LmRXR-L form heterodimers with recombinant LmEcR in vitro which bind the active ecdysteroid, ponasterone A. Binding was only weakly competed for by ecdysone agonists that are known to be toxic to more advanced insects, suggesting functionally significant divergence in EcR ligand binding domains. In contrast, the DNA binding domain of LmEcR is less divergent and a protein complex, presumably LmEcR/LmRXR, that bound the ecdysone response element, IR-1, was detected in locust nuclear extracts. Because of reports of juvenile hormone (JH III) binding to Drosophila USP and the observed in silico RXR-like ligand-binding site in LmRXR-L, the recombinant proteins were also tested for binding to JH III. Neither LmRXR isoform, alone or in combination with LmEcR, bound JH III at nanomolar concentrations.

A cellular retinoic acid-binding protein from zebrafish (Danio rerio): cDNA sequence, phylogenetic analysis, mRNA expression, and gene linkage mapping

We report the sequence of a cDNA clone coding for a cellular retinoic acid-binding protein (CRABP) in zebrafish. The encoded polypeptide is 142 amino acids in length with an estimated molecular mass of 15.8 kDa and a calculated isoelectric point of 5.2. The zebrafish CRABP exhibits highest sequence identity to the pufferfish CRABPIIa (83%) and CRABPIIb (79%), and human CRABPII (74%) than to any other member of the intracellular lipid-binding protein (ILBP) family. A phylogenetic tree for different members of the ILBP multigene family including fatty acid-binding proteins (FABPs), cellular retinol-binding proteins (CRBPs) and CRABPs shows that the cloned zebrafish cDNA encodes a protein that clusters with CRABPs from other species and not with CRBPs and FABPs. Reverse-transcription polymerase chain reactions (RT-PCR), using oligonucleotide primers specific to the zebrafish CRABP cDNA made from total RNA of embryos collected at various developmental stages, did not detect the CRABP mRNA until 12 h post-fertilization. In adult zebrafish, CRABP mRNA was detected by RT-PCR in total RNA extracted from muscle, testes and skin, barely detectable in heart, ovary and brain and undetectable in liver, kidney and intestine. Quantitative RT-PCR (qRT-PCR) revealed a similar tissue-specific distribution for zebrafish CRABP mRNA with highest levels of CRABP mRNA in muscle followed by testes, skin, ovary and much lower levels in heart. Radiation hybrid mapping assigned the CRABP gene to linkage group 16 in the zebrafish genome. Comparison of the mapped zebrafish CRABP and human CRABPII genes revealed that zebrafish linkage group 16 has a syntenic relationship with human chromosome 1. Based on phylogenetic analysis and the syntenic relationship to the CRABPII gene in human, the zebrafish cDNA clone appears to code for a type II CRABP.

Ligand binding and structural analysis of a human putative cellular retinol-binding protein

Three cellular retinol-binding protein (CRBP) types (CRBP I, II, and III) with distinct tissue distributions and retinoid binding properties have been structurally characterized thus far. A human binding protein, whose mRNA is expressed primarily in kidney, heart, and transverse colon, is shown here to be a CRBP family member (human CRBP IV), according to amino acid sequence, phylogenetic analysis, gene structure organization, and x-ray structural analysis. Retinol binding to CRBP IV leads to an absorption spectrum distinct from a typical holo-CRBP spectrum and is characterized by an affinity (K(d) = approximately 200 nm) lower than those for CRBP I, II, and III, as established in direct and competitive binding assays. As revealed by mutagenic analysis, the presence in CRBP IV of His(108) in place of Gln(108) is not responsible for the unusual holo-CRBP IV spectrum. The 2-A resolution crystal structure of human apo-CRBP IV is very similar to those of other structurally characterized CRBPs. The side chain of Tyr(60) is present within the binding cavity of the apoprotein and might affect the interaction with the retinol molecule. These results indicate that human CRBP IV belongs to a clearly distinct CRBP subfamily and suggest a relatively different mode of retinol binding for this binding protein.

Characterization of a novel cellular retinoic acid/retinol binding protein from shrimp: expression of the recombinant protein for immunohistochemical detection and binding assay

Members of the cellular retinoic acid (CRABP) and retinol binding (CRBP) proteins family are involved in the metabolic pathways of retinoic acid (RA) and retinal respectively. The objective of this study is to determine whether such proteins are present in crustaceans. We report here the cloning and isolation of a novel complementary DNA (cDNA) that showed characteristics of the CRABP/CRBP from the ovary and eyestalk of the shrimp. The cDNA is 0.9 Kb in size and the deduced shrimp protein is encoded for a protein of 14 kDa. Although it shows high amino acids sequence similarity to both the vertebrate and invertebrate CRABP, some conserved amino acids identified in other CRABPs were not found in MeCRABP. MeCRABP is expressed in the ovary, eyestalk, testis, epidermis and early larvae. The presence of MeCRABP in early larval stages suggests that the protein may be involved in the early larval development. Recombinant MeCRABP was produced and used to generate a polyclonal antibody. In the immunohistochemical detection study, anti-rCRABP antibody recognized the presence of CRABP in several cell types of the eyestalk as well as the smaller oocytes of the ovary. Although MeCRABP messenger RNA transcripts can be detected in the ovary throughout the ovarian maturation period, CRABP was detected only in the primary oocytes of the ovary. The results suggest that CRABP transcripts in the mature ovary are not translated and may be supplied to the oocyte as maternal messages. The binding property of the recombinant MeCRABP was also tested by a fluorometeric method. The result indicates that rMeCRABP binds to both RA and retinal with similar affinity. This study represents the first cloning and characterization of a cDNA that belongs to a member of retinoid/fatty acid binding protein family in crustaceans.

Cloning and sequence of the gene encoding the muscle fatty acid binding protein from the desert locust, Schistocerca gregaria

Muscle fatty acid binding protein (FABP) is a major cytosolic protein in flight muscle of the desert locust, Schistocerca gregaria. FABP expression varies greatly during development and periods of increased fatty acid utilization, but the molecular mechanisms that regulate its expression are not known. In this study, the gene coding for locust muscle FABP was amplified by PCR and cloned, together with 1.2 kb of upstream sequence. The sequence coding for the 607 bp cDNA is interrupted by two introns of 12.7 and 2.9 kb, inserted in analogous positions as the first and third intron of the mammalian homologues. Both introns contain repetitive sequences also found in other locust genes, and the second intron contains a GT-microsatellite. The promoter sequence includes a canonical TATA box 24 bp upstream of the transcription start site. The upstream sequence contains various potential myocyte enhancer sequences and a 160 bp segment that is repeated three times. In database searches in the genome database of Drosophila melanogaster, a gene with the same gene organization and promoter structure was identified, likely the dipteran homologue of muscle FABP. Upstream of both insect genes, a conserved 19 bp inverted repeat sequence was detected. A similar but reverse palindrome is also present upstream of all mammalian heart FABP genes, possibly representing a novel element involved in muscle FABP expression.

Presence of a fatty acid-binding protein and lipid stores in flight muscles of Dipetalogaster maximus (Hemiptera: Reduviidae)

A fatty acid-binding protein (FABP) from the cytosolic fraction of the triatomine Dipetalogaster maximus (Uhler) flight muscles was purified by a procedure based on gel filtration, reverse-phase high performance liquid chromatography, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein has an apparent molecular mass of 14 kDa, and its N-terminus is unblocked. Its N-terminal sequence was obtained by submitting an SDS-PAGE band blotted onto a polyvinylidene difluoride membrane to Edman degradation. The sequence obtained indicates that this FABP belongs to the heart type. This is the first time that a fatty acid-binding protein has been reported for a triatomine. The presence of said FABP, abundant mitochondria, and lipid stores in the flight muscles of D. maximus suggests that beta oxidation of fatty acids is used by the triatomine thoracic muscle as an energy source, and could be related to its dispersal capacity.

Differential gene expression between developing queens and workers in the honey bee, Apis mellifera

Many insects show polyphenisms, or alternative morphologies, which are based on differential gene expression rather than genetic polymorphism. Queens and workers are alternative forms of the adult female honey bee and represent one of the best known examples of insect polyphenism. Hormonal regulation of caste determination in honey bees has been studied in detail, but little is known about the proximate molecular mechanisms underlying this process, or any other such polyphenism. We report the success of a molecular-genetic approach for studying queen- and worker-specific gene expression in the development of the honey bee (Apis mellifera). Numerous genes appear to be differentially expressed between the two castes. Seven differentially expressed loci described here belong to at least five distinctly different evolutionary and functional groups. Two are particularly promising as potential regulators of caste differentiation. One is homologous to a widespread class of proteins that bind lipids and other hydrophobic ligands, including retinoic acid. The second locus shows sequence similarity to a DNA-binding domain in the Ets family of transcription factors. The remaining loci appear to be involved with downstream changes inherent to queen- or worker-specific developmental pathways. Caste determination in honey bees is typically thought of as primarily queen determination; our results make it clear that the process involves specific activation of genes in workers as well as in queens.