Induction of phenoloxidase and other immunological activities in the humoral fluids of amphioxus Branchiostoma belcheri challenged with Lipopolysaccharide (LPS)

The knowledge concerning the humoral immunity is scarce in amphioxus Branchiostoma belcheri. This study measured the humoral parameters including phenoloxidase (PO) activity, lysozyme activity, antimicrobial activity, microbial agglutinin, and hemagglutinin in amphioxus humoral fluids before and after lipopolysaccharide (LPS) challenge. Humoral fluids from unchallenged Branchiostoma belcheri (B. belcheri) had PO activity, lysozyme, antimicrobial, microbial agglutinating, and hemagglutinating activities, which may represent part of the baseline level of innate immunity in this organism. After challenge with LPS, many humoral parameters were all increased significantly including the PO activity, lysozyme activity, growth-inhibiting activities against Gram-negative bacteria Escherichia coli (E. coli) and Vibrio alginolyticus (V. alginolyticus), growth-inhibiting activities against Gram-positive bacteria Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis), microbial agglutinating activities against Micrococcus lysodeikticus (M. lysodeikticus), B. subtilis, and S. aureus, and hemagglutinating activities against rabbit and human A and O erythrocytes. In contrast, the agglutinating activities against V. harveyi and E. coli and the hemagglutinating activity against human B erythrocytes in the humoral fluids were reduced in response to LPS challenge. It appears that the humoral fluids of B. belcheri contain components that are able to differentiate different microbes and different human blood cell types.

Amphioxus CaVPT and creatine kinase are crucial immune-related molecules in response to bacterial infection and immunization

Although a great progress has been made, our understanding of innate immunity is incomplete. Here, we hypothesize that the innate immune response to pathogens is attributed into a group of functional proteins. The group contains information on host status post bacterial entry (infection or immunity) and bacterial species (Gram-positive or Gram-negative bacteria). Investigation of the group of proteins may result in disclosing of biomarkers identifying the status and species. For this regard, differential proteomics approach coupled with the pattern recognition methods are used to identify biomarkers from the proteins that being specifically regulated during the innate immune response of amphioxus to Gram-positive and Gram-negative bacteria with live or dead status. Four proteins, Calcium vector protein (CaVP), sarcoplasmic calcium-binding protein (SCP), CaVP-target protein (CaVPT) and creatine kinase (CK), are selected as the key biomarkers. Since immunoprotection of CaVP and SCP has been reported, the role of CaVPT and CK are further investigated. Gut CaVPT appears in dying amphioxus, whereas humoral fluid CK downregulates and gut CK keep no change in animals with immunity. The responses are stronger in Gram-negative than Gram-positive bacteria. These results indicate that CaVPT, CK, CaVP and SCP are the most important biomarkers to uncover amphioxus innate immunity to bacteria, and the approach is an efficient way to identify key biomarkers.

Identification and characterization of an amphioxus matrix metalloproteinase homolog BbMMPL2 responding to bacteria challenge

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases mainly involved in extracellular matrix (ECM) degradation. We have cloned and identified BbMMPL2 as homolog of MMPs from adult amphioxus. Recombinant BbMMPL2 proteins underwent self-processing during refolding in vitro. The final ~23 kDa polypeptide displayed proteolytic activity against ECM components like casein, gelatin, collagen IV and fibrinogen, but not laminin, fibronectin or α1-PI. This activity could be inhibited by GM6001 and TIMP-1/2. In addition, real-time RT-PCR analysis revealed that BbMMPL2 expressed in all issues/organs in adult amphioxus we tested. Its transcription was significantly up-regulated 12 h post immune challenge by Escherichia coli in epidermis and hepatic diverticulum but only slightly increased by Staphyloccocus aureus in epidermis. Furthermore, recombinant BbMMPL2-EGFP expressed in 293T and NIH/3T3 cells showed aggregation in cytoplasm and induced cell death. Our results provided new evidence that MMP was involved in immune response which could be conserved through evolution.

New insights into the evolution of metazoan tyrosinase gene family

Tyrosinases, widely distributed among animals, plants and fungi, are involved in the biosynthesis of melanin, a pigment that has been exploited, in the course of evolution, to serve different functions. We conducted a deep evolutionary analysis of tyrosinase family amongst metazoa, thanks to the availability of new sequenced genomes, assessing that tyrosinases (tyr) represent a distinctive feature of all the organisms included in our study and, interestingly, they show an independent expansion in most of the analyzed phyla. Tyrosinase-related proteins (tyrp), which derive from tyr but show distinct key residues in the catalytic domain, constitute an invention of chordate lineage. In addition we here reported a detailed study of the expression territories of the ascidian Ciona intestinalis tyr and tyrps. Furthermore, we put efforts in the identification of the regulatory sequences responsible for their expression in pigment cell lineage. Collectively, the results reported here enlarge our knowledge about the tyrosinase gene family as valuable resource for understanding the genetic components involved in pigment cells evolution and development.

Comments on 'Significance of developmental expression of amphioxus Branchiostoma belcheri and zebrafish Danio rerio Hsd17b10 in biological and medical research'

The reported data on the developmental expression of Hsd17b10 gene in Danio rerio is crucial to the utilization of the D. rerio embryo as an animal model for human developmental disorders caused either by mutations on HSD17B10 (formerly HADH2) or by defective expression of the gene. Related diseases were summarized, and it was noticed that hyperinsulinaemic hypoglycaemia is not linked to HSD17B10. This inherited disease is actually caused by a deletion in the HADH gene on chromosome 4. Moreover, it was found by a revision of the reported phylogenetic tree that hydroxyacyl-CoA dehydrogenase II or rather hydroxysteroid (17beta) dehydrogenase 10 (HSD10) of amphioxus Branchiostoma belcheri-occupies a transition position from HSD10 orthologs of invertebrates to those of vertebrates.

Induction of phenoloxidases in the humoral fluids of amphioxus Branchiostoma belcheri by Vibrio alginolyticus and Escherichia coli

The humoral immune responses of amphioxus Branchiostoma belcheri to microbial challenge remain open to date. Here we examined the changes in PO activity in the humoral fluids in amphioxus before and after challenge with Escherichia coli and Vibrio alginolyticus. It was found that PO activity in the humoral fluids is markedly increased by challenge with E. coli and V. alginolyticus; and the microbial challenge results in a significant rise in subunit 2 of the three PO subunits, making PO subunit 2 a marker enzyme responsive to microbial challenge. This is the first report on microbial induction of the immune-related molecules like PO in B. belcheri.

Presence of sex steroids and cytochrome P450 genes in amphioxus

The presence of sex steroids and their receptors has been demonstrated in all vertebrate groups from Agnatha to Mammalia but not in invertebrates. In genomic analyses of urochordates, cytochrome P450 (CYP) genes important for biosynthesis of sex steroids are absent. In the present study, we confirmed the presence of estrogen, androgen, and progesterone by using radioimmunoassay in gonads of amphioxus, Branchiostoma belcheri, which is considered to be evolutionarily closer to vertebrates than other invertebrates. Furthermore, CYP genes encoding CYP11A, CYP17, and CYP19 and transcripts for 17beta-hydroxysteroid dehydrogenase were cloned from amphioxus ovaries. Among invertebrates, the presence of hydroxysteroid dehydrogenase enzymes and metabolized steroids was shown in paracytic Taenia and corals. However, CYPs metabolizing sex steroids have not been demonstrated in invertebrates, nor has an attempt been made to consider the entire pathway from cholesterol to estrogen. This study is the first evidence to suggest the presence of CYP enzymes in sex steroid production in invertebrates.

Developmental expression of amphioxus RACK1

Vertebrate RACK1 plays a key role in embryonic development. This paper described the cloning, phylogenetic analysis and developmental expression of AmphiRACK1, the RACK1 homologous gene in amphioxus. Phylogenetic analysis indicated that amphioxus RACK1 was located at the base of vertebrate clade. AmphiRACK1 expression in lithium-treated embryos was also examined. During embryonic development, AmphiRACK1 was expressed strongly in cerebral vesicles, neural tubes and somites. In lithium-treated embryos, the segmental expression of AmphiRACK1 in somites became blurry and decreased. Its expression in cerebral vesicles and neural tubes was also weaker or disappeared. In the adult animal, AmphiRACK1 transcripts were detected in the epithelium of midgut diverticulus and gut, wheel organ, gill blood vessels and testis.

A tryptophan in the bottleneck of the catalytic gorge of an invertebrate acetylcholinesterase confers relative resistance to carbamate and organophosphate inhibitors

Amphioxus, an invertebrate chordate, has two acetylcholinesterases (AChEs): cholinesterase 1 (ChE1) and cholinesterase 2 (ChE2). ChE1 is up to 329-fold more resistant to a variety of carbamate and organophosphate inhibitors, including a number of insecticides, when compared with ChE2. One difference between the two enzymes is at the position homologous to Phe331 in Torpedo AChE. In Torpedo AChE, this residue is a component of the hydrophobic subsite and defines one side of the bottleneck in the catalytic gorge of the enzyme. In ChE1, the homologous residue is Trp353; in ChE2, it is Phe353. We used site-directed mutagenesis to investigate the proposal that the resistance of ChE1 to inhibition by carbamates and organophosphates was due to this difference, creating a ChE1 W353F mutant to widen the bottleneck. The mutation virtually abolishes the difference in sensitivity to the inhibitors. The ChE1 W353F mutant is only 2- to 3-fold more resistant than ChE2 to carbamates and is actually 2.5- to 10-fold more sensitive to inhibition by organophosphates. The differences in resistance are due to different affinities of the enzymes for the inhibitors, not different reactivities. Molecular modeling supports the proposal that the difference in inhibition is due to the width of the bottleneck of the gorge. Our results have implications for insecticide resistance in insects, in particular mosquitoes and aphids.

Identification and expression of a novel class of glutathione-S-transferase from amphioxus Branchiostoma belcheri with implications to the origin of vertebrate liver

Glutathione-S-transferases have been identified in all the living species examined so far, yet little is known to date about them in amphioxus, a model organism for insights into the origin and evolution of vertebrates. We have isolated a cDNA encoding an amphioxus (Branchiostoma belcheri) glutathione-S-transferase with a predicted molecular mass of approximately 26 kDa, from the gut cDNA library. The glutathione-S-transferase had 43.7-51.8% identity to most glutathione-S-transferases identified from aquatic organisms including fish and green alga, but it was much less identical (<27%) to other cytosolic glutathione-S-transferase classes. The phylogenetic analysis revealed that the glutathione-S-transferase was grouped together with most piscine and algal glutathione-S-transferases, separating from other cytosolic glutathione-S-transferase classes. Moreover, the glutathione-S-transferase had an exon-intron organization typical of zebrafish putative GST, red sea bream GSTR1 and plaice GSTA1 genes. The recombinant glutathione-S-transferase has been successfully expressed and purified, which showed a relatively high catalytic activity (3.37+/-0.1 unit/mg) toward 1-chloro-2, 4-dinitrobenzene and a moderate activity toward ethacrynic acid (0.41+/-0.01 unit/mg), although it had no detectable activity toward 1, 2-dichloro-4-nitrobenzene, 4-hydroxynonenal, 4-nitrobenzyl chloride and cumene hydroperoxide. In addition, we have revealed a tissue-specific expression pattern of the glutathione-S-transferase gene in B. belcheri, with the most abundant expression in the hepatic caecum. All these indicate that the amphioxus glutathione-S-transferase belongs to a novel rho-class of glutathione-S-transferases with a tissue-specific expression pattern. The relation between the glutathione-S-transferase expression in amphioxus hepatic caecum and the origin of vertebrate liver is also discussed.

Alanine Aminotransferase in Amphioxus: Presence, Localization and Up-regulation after Acute Lipopolysaccharide Exposure

Alanine aminotransferase (AAT) is mainly synthesized in the liver, and its level in mammalian serum is elevated after acute phase induction. Here we demonstrated that sheep anti-human AAT antibody cross-reacted with amphioxus humoral fluids as well as human serum; and the concentration of AAT in the humoral fluids in amphioxus increased after the acute challenge with lipopolysaccharide, while the level of total proteins remains unchanged. These suggest the presence of the same acute phase response pattern in amphioxus, as observed in some mammalian species. Immunohistochemically, AAT was localized in the hepatic diverticulum, ovary and testis. It appears that the hepatic diverticulum in amphioxus is functionally homologous to the vertebrate liver in respect of AAT synthesis, supporting the hypothesis that the vertebrate liver evolved from the hepatic diverticulum of an amphioxus-like ancestor during early chordate evolution.

Verification, characterization and tissue-specific expression of UreG, a urease accessory protein gene, from the amphioxus Branchiostoma belcheri

UreG genes have been found in bacteria, fungi and plants but have not yet identified in animals, although a putative UreG-like gene has been documented in sea urchin. In the course of a large-scale sequencing of amphioxus gut cDNA library, we have identified a cDNA with high similarity to UreG genes. Both reverse transcription-polymerase chain reaction and nested polymerase chain reaction, as well as in situ hybridization histochemistry, verified that the cDNA represented an amphioxus UreG gene (AmphiUreG) rather than a microbial contaminant of the cDNA library. This is further supported by the presence of urease activity in amphioxus gut, gill and ovary. AmphiUreG encodes a deduced protein of 200 amino acid residues including a highly conserved P-loop, bearing approximately 46%-49%, 44%-48%, and 29%-37% similarity to fungal, plant and bacterial UreG proteins, respectively. It shows a tissue-specific expression pattern in amphioxus, and is especially abundant in the digestive system. This is the first UreG gene identified in animal species.

Purification and characterisation of phenoloxidase from amphioxus Branchiostoma belcheri tsingtauense

Phenoloxidase (PO) from the humoral fluid of amphioxus B. belcheri tsingtauense was purified using a sequential combination of ammonium sulphate precipitation, Sephadex G-200 chromatography and DEAE Sepharose Fast Flow chromatography. In PAGE, the purified enzyme exhibited a single band of 150 kDa under non-reducing conditions, and was resolved to three bands with molecular masses of 72, 46 and 44 kDa, respectively, under reducing conditions, suggesting that the PO in amphioxus humoral fluid seems to be a heterotrimer of three polypeptides held together by disulphide bonds. The substrate specificity and inhibition characteristics both indicate that the PO isolated from amphioxus humoral fluid is a tyrosinase-type enzyme. In addition, mouse antisera against the purified PO were prepared, and their specificity was confirmed by Western blotting, facilitating the future determination of the origin of PO in the humoral fluid and the distribution of PO-synthesising tissues in amphioxus.

Presence of prophenoloxidase in the humoral fluid of amphioxus Branchiostoma belcheri tsingtauense

The presence of phenoloxidase (PO) activity in the humoral fluid of amphioxus Branchiostoma belcheri tsingtauense was electrophoretically and spectrophotometrically studied. The enzyme was present in the humoral fluid predominantly as an inactive proenzyme, prophenoloxidase (proPO). The optimum temperature for activation of the proPO ranged from 30 degrees C to 35 degrees C, and the enzyme exhibited optimum activity at pH between 7.0 and 7.5. ProPO in the humoral fluid was readily activated to active form PO by exogenous elicitors such as trypsin, zymosan and LPS. The activation of the proPO by exogenous elicitors was significantly enhanced in the presence of 10 mM Ca2+, but was susceptible to serine protease inhibitors like soybean trypsin inhibitor and p-nitrophenyl-p'-guanidinobenzoate. PAGE revealed a single band of PO activity in the humoral fluid with an apparent molecular mass of 150 kDa, which was resolved to three bands with molecular masses of 44, 46 and 72 kDa, respectively, after SDS-PAGE. This is the first report on the presence of the enzyme PO in amphioxus humoral fluid.

Phylogeny of Antigen-Processing Enzymes: Cathepsins of a Cephalochordate, an Agnathan and a Bony Fish

Cathepsins are enzymes that have been cleaving peptide bonds of lysosomal proteins probably since lysosomes appeared in early eucaryotes. When the adaptive system emerged in gnathostomes, cathepsins were recruited to produce peptides for loading onto the major histocompatibility complex class II molecules and for degrading the class II-associated invariant chain just before the loading. The circumstances under which this recruitment took place are unclear because the knowledge about vertebrate cathepsins is limited largely to mammals. To shed light on the recruitment, 10 amphioxus, one lamprey and one cichlid fish cathepsin cDNA clone were characterized and analysed phylogenetically. Disregarding cathepsin O, whose phylogenetic position is uncertain, the analysis confirms the existence of two old lines of descent, the B and the L lineages of cathepsins, which diverged from each other early in the evolution of eucaryotes. The B lineage encompasses cathepsins B, C and Z (X). The L lineage splits off sublineages encompassing cathepsins F and W before the plant-animal separation and cathepsin H early in the evolution of the metazoa. The remaining cathepsins belonging to the L lineage diverged from one another during the evolution of vertebrates: S, K and L before the emergence of bony fishes, and the group of rodent placentally expressed cathepsins [J (P), M, Q, R, 3, 6, 7 and 8] as well as the testis/ova-expressed cathepsins (testins) probably after the divergence of rodents from primates. The part possibly played by the adaptive immune system in some of these divergences is discussed.

Isolation of AmphiCASP-3/7, an ancestral caspase from amphioxus (Branchiostoma floridae). Evolutionary considerations for vertebrate caspases

Caspases are a large family of cysteine proteases that play an essential role as effectors of apoptosis in metazoans. Thirteen different caspases have been identified in vertebrates so far, and their function in apoptotic or inflammatory responses is well documented. We have taken advantage of the broadly accepted condition of amphioxus (Cephalochordata, Branchiostoma floridae) as the closest living relative to vertebrates to study the molecular evolution of caspases. Here we report for the first time the pattern of programmed cell death during development of cephalochordates. We also describe the isolation and functional characterisation of the first caspase related gene in amphioxus, which we named AmphiCASP-3/7. The amphioxus caspase is expressed throughout development, from the gastrula to larva stage. AmphiCASP-3/7 induced cell death when ectopically expressed in human HEK 293T cells, and the recombinant protein was inhibited by DEVD peptides. AmphiCASP-3/7 reflects the primitive condition of the executor vertebrates caspases -3 and -7, prior to vertebrate specific duplication. Interestingly, AmphiCASP-3/7 is functionally closer to vertebrate caspase-7, as shown by substrate specificity both in vitro and in MCF7 cells. Our phylogenetic and functional data help in drawing the evolutionary history of caspases, and illustrates an example of acquisition in vertebrates of novel functional properties after gene duplication.

Minisatellite instability at the Adh locus reveals somatic polymorphism in amphioxus

Amphioxus (subphylum Cephalochordata) is the closest living relative to vertebrates and widely used for phylogenetic analyses of vertebrate gene evolution. Amphioxus genes are highly polymorphic, but the origin and nature of this variability is unknown. We have analyzed the alcohol dehydrogenase locus (Adh3) in two amphioxus species (Branchiostoma lanceolatum and Branchiostoma floridae) and found that genetic variation is related to repetitive DNA sequences, mainly minisatellites. Small pool-PCR assays indicated that allelic variants are generated by minisatellite instability. We conclude that the generation of new forms was not preferentially linked to germline processes but rather to somatic events leading to mosaic adult animals. Furthermore, most Adh minisatellites belong to a novel class, which we have named mirages. Their distinctive feature is that the repeat subunit spans the exon-intron boundaries and generates potential duplications of the splice sites. However, splicing may not be compromised as no aberrant mRNA variants were detected.

Crystallization and preliminary X-ray diffraction analysis of a cold-adapted uracil-DNA glycosylase from Atlantic cod (Gadus morhua)

Uracil-DNA glycosylase (UDG) is a DNA-repair enzyme involved in the removal of uracil from DNA. The Atlantic cod UDG (cUDG) possesses typical cold-adaptation features, with higher catalytic efficiency and lower thermal stability than the mammalian counterparts. cUDG has been crystallized by the vapour-diffusion method using sodium citrate as the precipitant at pH 7.5. The crystals are monoclinic and belong to space group P2(1), with unit-cell parameters a = 68.58, b = 67.19, c = 68.64 A, beta = 119.85 degrees. There are two molecules in the asymmetric unit, with a corresponding V(M) value of 2.71 A(3) Da(-1) and a solvent content of 54.7%. Synchrotron diffraction data have been collected to 1.9 A resolution using cryogenic conditions (120 K).

Gene duplication events producing muscle (M) and brain (B) isoforms of cytoplasmic creatine kinase: cDNA and deduced amino acid sequences from two lower chordates

Creatine kinase (CK) is coded for by at least four loci in higher vertebrates--two cytoplasmic isoforms, muscle (M) and brain (B), and two mitochondrial isoforms, sarcomeric and ubiquitous. M is expressed primarily in skeletal muscle, while B is expressed in a variety of cells, including cardiac and smooth muscle fibers, neurons, transport epithelia, and photoreceptors. M and B subunits form very stable homodimers (MM [M-CK], BB [B-CK]) and heterodimers (MB). M-CK is capable of binding to the M line of the myofibril, thereby creating an energy transfer microcompartment; BB and MB CKs are not. M- and B-like CKs are present in all vertebrates yet examined, including fish. Cytoplasmic, dimeric CKs are widely distributed in the invertebrates. The only available amino acid sequence for an invertebrate dimeric CK, that of the protostome polychaete Chaetopterus variopedatus, is just as similar to the vertebrate M isoform as to the B isoform. Echinoderms lack dimeric, cytoplasmic CKs, which appear to be replaced by a dimeric arginine kinase which evolved secondarily from CK. Thus, it is likely that the gene duplication event producing the M and B isoforms occurred after the divergence of the chordates from echinoderms. To narrow down the timing of this duplication event, we obtained the cDNA and deduced amino acid sequences of dimeric CKs from the tunicate Ciona intestinalis (subphylum Urochordata) and the lancelet Branchiostoma floridae (subphylum Cephalochordata). Our results show that these CKs are strikingly similar to both invertebrate and vertebrate CKs. However, phylogenetic analyses by neighbor-joining and parsimony show that these two enzymes appeared to have diverged before the point of divergence of the M and B isoforms. Thus, the gene duplication event for formation of the muscle and brain isoforms of CK most likely occurred during the radiation of the fish, a time noted for gene duplication events at a variety of other loci.

Endogenous beta-galactosidase activity in amphioxus: a useful histochemical marker for the digestive system

Endogenous beta-galactosidase activity has been shown in the digestive tract of amphioxus from the larval to the adult stage and it can be easily followed as a histochemical marker. Enzymatic activity first appeared in 30-h larvae, became evident in 36-h larvae and remained in adults. In situ detection of beta-galactosidase activity was used to monitor morphological and functional differentiation of the digestive system and the posteriorization of the endodermal structures in retinoic-acid treated embryos. The endogenous beta-galactosidase activity was distinguished from the bacterial lacZ reporter by incubation at low pH.

Characterization of a microsomal retinol dehydrogenase gene from amphioxus: retinoid metabolism before vertebrates

Amphioxus, a member of the subphylum Cephalochordata, is thought to be the closest living relative to vertebrates. Although these animals have a vertebrate-like response to retinoic acid, the pathway of retinoid metabolism remains unknown. Two different enzyme systems - the short chain dehydrogenase/reductases and the cytosolic medium-chain alcohol dehydrogenases (ADHs) - have been postulated in vertebrates. Nevertheless, recent data show that the vertebrate-ADH1 and ADH4 retinol-active forms originated after the divergence of cephalochordates and vertebrates. Moreover, no data has been gathered in support of medium-chain retinol active forms in amphioxus. Then, if the cytosolic ADH system is absent and these animals use retinol, the microsomal retinol dehydrogenases could be involved in retinol oxidation. We have identified the genomic region and cDNA of an amphioxus Rdh gene as a preliminary step for functional characterization. Besides, phylogenetic analysis supports the ancestral position of amphioxus Rdh in relation to the vertebrate forms.

Amphioxus alcohol dehydrogenase is a class 3 form of single type and of structural conservation but with unique developmental expression

The coding region of amphioxus alcohol dehydrogenase class 3 (ADH3) has been characterized from two species, Branchiostoma lanceolatum and Branchiostoma floridae. The species variants have residue differences at positions that result in only marginal functional distinctions. Activity measurements show a class 3 glutathione-dependent formaldehyde dehydrogenase, with kcat/Km values about threefold those of the human class 3 ADH enzyme. Only a single ADH3 form is identified in each of the two amphioxus species, and no ethanol activity ascribed to other classes is detectable, supporting the conclusion that evolution of ethanol-active ADH classes by gene duplications occurred at early vertebrate radiation after the formation of the amphioxus lineage. Similarly, Southern blot analysis indicated that amphioxus ADH3 is encoded by a single gene present in the methylated fraction of the amphioxus genome and northern blots revealed a single 1.4-kb transcript. In situ experiments showed that amphioxus Adh3 expression is restricted to particular cell types in the embryos. Transcripts were first evident at the neurula stage and then located at the larval ventral region, in the intestinal epithelium. This tissue-specific pattern contrasts with the ubiquitous Adh3 expression in mammals.

Phenoloxidase, a marker enzyme for differentiation of the neural ectoderm and the epidermal ectoderm during embryonic development of amphioxus Branchiostoma belcheri tsingtaunese

The development of phenoloxidase during amphioxus embryogenesis was spectrophotometrically and histochemically studied for the first time in the present study. It was found that (1) PO activity initially appeared in the general ectoderm including the neural ectoderm and the epidermal ectoderm at the early neurula stage but not in the mesoderm or the endoderm, and (2) PO activity disappeared in the neural plate cells but remained unchanged in the epidermal cells when the neural plate was morphologically quite distinct from the rest of the ectoderm. It is apparent that PO could serve as a marker enzyme for differentiation of the neural ectoderm from the epidermal ectoderm during embryonic development of amphioxus.

Evolution of the prohormone convertases: identification of a homologue of PC6 in the protochordate amphioxus

Many of the protein precursors traversing the secretory pathway undergo cleavage at multibasic sites to generate their bioactive forms. The proprotein convertases (PCs), a family of subtilisin-like proteases, are the major endoproteases that serve this function. Genes encoding seven distinct members of this family have so far been characterized in vertebrates: furin, PC2, PC1/PC3, PC4, PACE4, PC5/PC6 and PC7/PC8/LPC. Multiple PC genes have also been cloned from a number of invertebrates, including Drosophila melanogaster and Caenorhabditis elegans. These findings suggest that gene duplication and diversification of the PCs have occurred throughout metazoan evolution. To investigate the structural and functional changes which have occurred during vertebrate development, we have analyzed the expression of PC genes in the protochordate amphioxus. We have previously shown that amphioxus express homologous PC2 and PC1/PC3 genes [Proc. Natl. Acad. Sci. USA 92 (1995) 3591]. Here we report the characterization of amphioxus cDNAs encoding proteases with a high degree of similarity to mammalian PC6. Three cDNAs encoding three PC6 isoforms differing only in their carboxy-terminal sequences were found, derived by alternative splicing. Two isoforms appear to be soluble enzymes, whereas the third contains a transmembrane hydrophobic segment and thus is likely to be membrane-bound. All three variants contain many repeats of a cysteine-rich motif that is found in several other PC family members. Thus, amphioxus, like the vertebrates, expresses two types of PCs, e.g., PC2 and PC1/PC3 which function in the regulated secretory pathway in neuroendocrine cells, and the more widely expressed PC6 which functions mainly in the constitutive pathway.

Protein tyrosine phosphatases from amphioxus, hagfish, and ray: divergence of tissue-specific isoform genes in the early evolution of vertebrates

Since separation from fungi and plants, multicellular animals evolved a variety of gene families involved in cell-cell communication from a limited number of ancestral precursors by gene duplications in two separate periods of animal evolution. In the very early evolution of animals before the separation of parazoans and eumetazoans, animals underwent extensive gene duplications by which different subtypes (subfamilies) with distinct functions diverged. The multiplicity of members (isoforms) in the same subtype increased by further gene duplications (isoform duplications) in the first half of chordate evolution before the fish-tetrapod split; different isoforms are virtually identical in structure and function but differ in tissue distribution. From cloning and phylogenetic analyses of four subfamilies of the protein tyrosine kinase (PTK) family, we recently showed extensive isoform duplications in a limited period around or just before the cyclostome-gnathostome split. To obtain a reliable estimate for the divergence time of vertebrate isoforms, we have conducted isolation of cDNAs encoding the protein tyrosine phosphatases (PTPs) from Branchiostoma belcheri, an amphioxus, Eptatretus burgeri, a hagfish, and Potamotrygon motoro, a ray. We obtained 33 different cDNAs in total, most of which belong to known PTP subfamilies. The phylogenetic analyses of five subfamilies based on the maximum likelihood method revealed frequent isoform duplications in a period around or just before the gnathostome-cyclostome split. An evolutionary implication was discussed in relation to the Cambrian explosion.

cDNA cloning, in vitro expression, and biochemical characterization of cholinesterase 1 and cholinesterase 2 from amphioxus--comparison with cholinesterase 1 and cholinesterase 2 produced in vivo

We have isolated cDNAs coding for the complete amino acid sequences of cholinesterase 1 (ChE1) and cholinesterase 2 (ChE2) from amphioxus. Both ChE transcripts have the characteristics of H-type catalytic subunits, which are inserted in the membrane via an ethanolamine-glycan-phosphatidylinositol anchor. The members of the catalytic triad of ChEs, the three pairs of cysteine residues involved in intrachain disulfide bonding, a cysteine near the carboxy terminal of both sequences, which could mediate interchain disulfide bonding, and 11 of the 14 aromatic amino acids that line the catalytic gorge of AChE are conserved. A remarkable difference between the two enzymes is in the region of the acyl-binding pocket, which plays an important role in determining substrate specificity in cholinesterases. ChE2 contains a sequence that resembles the acyl pocket of invertebrate ChE, while the acyl-binding site of ChE1 is novel. There are also differences between the two enzymes in the peripheral anionic site, which mediates inhibition by certain ligands. In vitro expression in COS-7 cells demonstrates that ChE2 hydrolyzes acetylthiocholine almost exclusively, while ChE1 hydrolyzes both acetylthiocholine and butyrylthiocholine. Both enzymes are inhibited comparably by BW284c51, but ChE1 is considerably more resistant to inhibition by propidium, ethopropazine, and eserine than is ChE2. Velocity sedimentation indicates that ChE1 and ChE2 are present as amphiphilic and nonamphiphilic G2 forms in vivo and in vitro. Another molecular form, which sediments at 17 S, is also present in vivo. Nondenaturing gel electrophoresis in conjunction with digestion by phosphatidylinositol-specific phospholipase C demonstrates that the vast majority of ChE1 and ChE2 is present as ethanolamine-glycan-phosphatidylinositol-anchored G2 forms in vivo. ChE1 also possesses an ethanolamine-glycan-phosphatidylinositol-anchor in vitro; however, ChE2 produced in vitro could not be detected on nondenaturing gels.

Molecular evolution of amphioxus fructose-1,6-bisphosphate aldolase

The cDNA for amphioxus fructose-1,6-bisphosphate (FBP)-aldolase was isolated and its nucleotide sequence was determined. In the cDNA, there existed a probable open reading frame comprising 1080 bp; hence, 359 amino acid residues were deduced. The amino acid sequence indicates the deletion of 4 residues from N-terminus, in comparison with the sequence of FBP-aldolase isozymes from other sources. There was only one FBP-aldolase gene, and one enzyme species corresponding, in the amphioxus; this is the first report of the existence of a single FBP-aldolase species in animals. Enzymatic studies of both native and the recombinant FBP-aldolase suggest that the amphioxus enzyme belongs to an ancestral class I type which is not discovered among vertebrate aldolase isozymes.

Two cholinesterase activities and genes are present in amphioxus

To obtain information about the evolution of the cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the vertebrates, we investigated the cholinesterase (ChE) activity of the cephalochordate amphioxus (Branchiostoma floridae and Branchiostoma lanceolatum). On the basis of evidence from enzymology, pharmacology, and molecular biology, we conclude that amphioxus possesses two ChE activities and two ChE genes. Two covalent inhibitors of cholinesterases were able to pharmacologically isolate the two activities as drug-sensitive ChE and drug-resistant ChE. Kinetically, in terms of substrate specificity, the drug-sensitive ChE resembles vertebrate AChE, and the drug-resistant ChE resembles the BuChE of cartilaginous and bony fish or the intermediate ChE of protostome invertebrates. We also used the polymerase chain reaction with degenerate oligonucleotide primers and genomic DNA to obtain clones of 1,574 and 1,011 bp corresponding to two cholinesterase genes from amphioxus, which we designated as ChE1 and ChE2. ChE2 codes for an enzyme with an acyl-binding pocket sequence, a portion of the protein that plays an important role in determining substrate specificity, typical of invertebrate ChE. ChE1, which contains a 503-bp intron, encodes a protein with a novel acyl binding site. Phylogenetic analysis of the sequences suggests that the two genes are a result of a duplication event in the lineage leading to amphioxus. We discuss the relevance of our results to the evolution of the cholinesterases in the chordates. Previously, we reported that amphioxus contained a single cholinesterase activity with properties intermediate to AChE and BuChE (Pezzementi et al. [1991] In: Cholinesterases: Structure, Function, Mechanism, Genetics and Cell Biology. J. Massoulié et al., eds. ACS: Washington, D.C., pp. 24-31).

Proprotein convertases in amphioxus: predicted structure and expression of proteases SPC2 and SPC3

SPC2 and SPC3 are two members of a family of subtilisin-related proteases which play essential roles in the processing of prohormones into their mature forms in the pancreatic B cell and many other neuroendocrine cells. To investigate the phylogenetic origins and evolutionary functions of SPC2 and SPC3 we have identified and cloned cDNAs encoding these enzymes from amphioxus (Branchiostoma californiensis), a primitive chordate. The amino acid sequence of preproSPC2 contains 689 aa and is 71% identical to human SPC2. In contrast, amphioxus prproSPC3 consists of 774 aa and exhibits 55% identity to human SPC3. These results suggest that the primary structure of SPC2 has been more highly conserved during evolution than that of SPC3. To further investigate the function(s) of SPC2 and SPC3 in amphioxus, we have determined the regional expression of these genes by using a reverse transcriptase-linked polymerase chain reaction (RT-PCR) assay. Whole amphioxus was dissected longitudinally into four equal-length segments and RNA was extracted. Using RT-PCR to simultaneously amplify SPC2 and SPC3 DNA fragments, we found that the cranial region (section 1) expressed equal amounts of SPC2 and SPC3 mRNAs, whereas in the caudal region (section 4) the SPC2-to-SPC3 ratio was 5:1. In the mid-body sections 2 and 3 the SPC2-to-SPC3 ratio was 1:5. By RT-PCR we also determined that amphioxus ILP, a homologue of mammalian insulin/insulin-like growth factor, was expressed predominately in section 3. These results suggest that the relative levels of SPC2 and SPC3 mRNAs are specifically regulated in various amphioxus tissues. Furthermore, the ubiquitous expression of these mRNAs in the organism indicates that they are involved in the processing of other precursor proteins in addition to proILP.

Protein tyrosine phosphatase domains from the protochordate Styela plicata

Protein tyrosine phosphorylation is an important regulatory mechanism in cell physiology. While the protein tyrosine kinase (PTKase) family has been extensively studied, only six protein tyrosine phosphatases (PTPases) have been described. By Southern blot analysis, genomic DNA from several different phyla were found to cross-hybridize with a cDNA probe encoding the human leukocyte-common antigen (LCA; CD45) PTPase domains. To pursue this observation further, total mRNA from the protochordate Styela plicata was used as a template to copy and amplify, using polymerase chain reaction (PCR) technology, PTPase domains. Twenty-seven distinct sequences were identified that contain hallmark residues of PTPases; two of these are similar to described mammalian PTPases. Southern blot analysis indicates that at least one other Styela sequence is highly conserved in a variety of phyla. Seven of the Styela domains have significant similarity to each other, indicating a subfamily of PTPases. However, most of the sequences are disparate. A comparison of the 27 Styela sequences with the ten known PTPase domain sequences reveals that only three residues are absolutely conserved and identifies regions that are highly divergent. The data indicate that the PTPase family will be equally as large and diverse as the PTKases. The extent and diversity of the PTPase family suggests that these enzymes are, in their own right, important regulators of cell behavior.

Histochemical distribution of peroxidase in amphioxus and cyclostomes with special reference to the endostyle

The histochemical distribution of peroxidase was studied in amphioxus, ammocoetes larvae, adult lampreys, and hagfish. The endostyle of amphioxus displayed peroxidase activity in zone 5 and, in some individuals, in zone 1 as well. The endostyle of ammocoetes exhibited strong peroxidase activity in type 2c and type 3 cells. These peroxidase-positive regions coincide well with radioiodine-binding regions previously described. Thyroid follicles of adult lampreys stained strongly for peroxidase, but those of the hagfish did not. The branchial sac of amphioxus showed peroxidase activity, but the gill sac of cyclostomes did not. The intestine did not show peroxidase activity in amphioxus or in cyclostomes.