Presence of a vertebrate fibrinogen-like sequence in an echinoderm

Analysis of texture properties and water-soluble fraction proteome of sea cucumber body wall with different boiling heating treatment

Label-free quantitative proteomic analysis was utilized to determine the key proteins that affect texture properties of sea cucumber body wall (SCBW) with different boiling heating treatment. 862, 363, 315, and 258 proteins were confirmed in water-soluble fractions from fresh group, 0.5 h-, 2 h- and 4 h-heat treatment group, respectively. During boiling heating treatment, proteins with an increased abundance in water-soluble fraction primarily belong to structural proteins, such as collagens, microfibril-associated proteins, glycoproteins, and muscle proteins. It was speculated that the degradation of these structural proteins caused the progressive disintegration of network skeleton of collagen fibres and FMs as well as the gelatinization, thus resulted in the decrease of hardness and shear force. Besides, the degradation of FMs was occurred layer by layer during boiling heating treatment, and the fibrilin-1 outer layer degraded first, followed by the fibrilin-2 core component.

Dipteran endoparasitoid Exorista bombycis utilizes antihemocyte components against host defense of silkworm Bombyx mori

Dipteran endoparasitoids avoid host immune response; however, antidefense components from the Dipterans are unknown. Infestation of commercial silkworm Bombyx mori Linnaeus (Lepidoptera: Bombycidae) by endoparasitoid Exorista bombycis Louis (Diptera: Tachinidae) induced immune reactions, cytotoxicity, granulation, degranulation, and augmented release of cytotoxic marker enzyme lactate dehydrogenase (LDH), and degranulation-mediator enzyme β-hexosaminidase in hemocytes. In this study, by reverse phase high-performance liquid chromatography, fractions of E. bombycis larval tissue protein with antihemocytic activity are separated. From the fraction, peptides of hemocyte aggregation inhibitor protein (HAIP) and pyridoxamine phosphate oxidase (PNPO) are identified by mass spectrometry. Interacting partners of HAIP and PNPO are retrieved that further enhance the virulence of the parasitoid. PNPO and HAIP genes showed a four- to seven fold increase in expression in the integument of the parasitoid larva. Together, the dipteran endoparasitoid E. bombycis exploit antihemocyte activity to inhibit host defense reactions in addition to defense evasion contemplated.

Immune diversity in lophotrochozoans, with a focus on recognition and effector systems

Lophotrochozoa is one of the most species-rich but immunologically poorly explored phyla. Although lack of acquired response in a narrow sense, lophotrochozoans possess various genetic mechanisms that enhance the diversity and specificity of innate immune system. Here, we review the recent advances of comparative immunology studies in lophotrochozoans with focus on immune recognition and effector systems. Haemocytes and coelomocytes are general important yet understudied player. Comparative genomics studies suggest expansion and functional divergence of lophotrochozoan immune reorganization systems is not as "homogeneous and simple" as we thought including the large-scale expansion and molecular divergence of pattern recognition receptors (PRRs) (TLRs, RLRs, lectins, etc.) and signaling adapters (MyD88s etc.), significant domain recombination of immune receptors (RLR, NLRs, lectins, etc.), extensive somatic recombination of fibrinogenrelated proteins (FREPs) in snails. Furthermore, there are repeatedly identified molecular mechanisms that generate immune effector diversity, including high polymorphism of antimicrobial peptides and proteins (AMPs), reactive oxygen and nitrogen species (RONS) and cytokines. Finally, we argue that the next generation omics tools and the recently emerged genome editing technicism will revolutionize our understanding of innate immune system in a comparative immunology perspective.

Purification and Assays of Tachylectin-5

Tachylectin-5, a 41-kDa protein with a common fold of the C-terminal globular domain of the γ-chain of fibrinogen, is purified from horseshoe crab hemolymph plasma by affinity column chromatography, using acetyl-group-immobilized resin. Two types of isolectins, tachylectin-5A and tachylectin-5B, are obtained by stepwise elution with GlcNAc at 25 and 250 mM, respectively. Tachylectins-5A and -5B exhibit extraordinarily strong hemagglutinating activity against all types of human erythrocytes (the minimum agglutinating concentration of 0.004-0.008 μg/mL for tachylectin-5A and 0.077-0.27 μg/mL for tachylectin-5B). Their hemagglutinating activities are inhibited by acetyl group-containing sugars and noncarbohydrates such as sodium acetate, acetylcholine, and acetyl CoA (the minimum inhibitory concentrations of 1.3-1.6 mM), indicating that the acetyl group is required and sufficient for recognition by tachylectins-5A and -5B. EDTA inhibits their hemagglutinating activity, whereas the inhibition is overcome by adding an excess amount of Ca²⁺. Tachylectins-5A and -5B also exhibit bacterial agglutinating activity against both Gram-negative bacteria (the minimum agglutinating concentrations of 0.04-0.08 μg/mL for tachylectin-5A and 0.05-0.11 μg/mL for tachylectin-5B) and Gram-positive bacteria (the minimum agglutinating concentrations of 0.3-2.4 μg/mL for tachylectin-5A and 15.1-26.8 μg/mL for tachylectin-5B). Interestingly, tachylectins-5A and -5B enhance the antimicrobial activity of a hemocyte-derived peptide, big defensin.

The end of evolution? Michael J. Behe HarperOne, 2019. 352 pp

A biochemist's crusade to overturn evolution misrepresents theory and ignores evidence

A fibrinogen-related protein, LvFREP2, from Litopenaeus vannamei facilitates the clearance of Vibrio harveyi

Fibrinogen-related proteins (FREPs) play a crucial role in invertebrate immune response. In this study, we acquired a novel fibrinogen-related protein gene in Litopenaeus vannamei coding for one kind of fibrinogen-related protein, designated as LvFREP2. The complete cDNA sequence of LvFREP2 was 1903 bp long, containing an open reading frame of 1479 bp coding for LvFREP2. The LvFREP2 protein contained a putative signal peptide and a fibrinogen-related protein domain. qRT-PCRs indicated that LvFREP2 mRNA ubiquitously distributed in all examined tissues, and it was up-regulated in gills after V. harveyi and LPS challenges. The recombinant LvFREP2 agglutinated Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Vibrio alginolyticus, V. cholerae, V. vulnificus, V. parahaemolyticus, V. harveyi, Pseudomonas aeruginosa, P. fluorescens) in a calcium-dependent manner. LvFREP2 also facilitated the clearance of Vibrio harveyi in vivo. Therefore, our results suggested that lvFREP2 may have important roles in the anti-bacterial immunity of L. vannamei.

Fundamental aspects of arm repair phase in two echinoderm models

Regeneration is a post-embryonic developmental process that ensures complete morphological and functional restoration of lost body parts. The repair phase is a key step for the effectiveness of the subsequent regenerative process: in vertebrates, efficient re-epithelialisation, rapid inflammatory/immune response and post-injury tissue remodelling are fundamental aspects for the success of this phase, their impairment leading to an inhibition or total prevention of regeneration. Among deuterostomes, echinoderms display a unique combination of striking regenerative abilities and diversity of useful experimental models, although still largely unexplored. Therefore, the brittle star Amphiura filiformis and the starfish Echinaster sepositus were here used to comparatively investigate the main repair phase events after injury as well as the presence and expression of immune system and extracellular matrix (i.e. collagen) molecules using both microscopy and molecular tools. Our results showed that emergency reaction and re-epithelialisation are similar in both echinoderm models, being faster and more effective than in mammals. Moreover, in comparison to the latter, both echinoderms showed delayed and less abundant collagen deposition at the wound site (absence of fibrosis). The gene expression patterns of molecules related to the immune response, such as Ese-fib-like (starfishes) and Afi-ficolin (brittle stars), were described for the first time during echinoderm regeneration providing promising starting points to investigate the immune system role in these regeneration models. Overall, the similarities in repair events and timing within the echinoderms and the differences with what has been reported in mammals suggest that effective repair processes in echinoderms play an important role for their subsequent ability to regenerate. Targeted molecular and functional analyses will shed light on the evolution of these abilities in the deuterostomian lineage.

Expression analysis of immune related genes identified from the coelomocytes of sea cucumber (Apostichopus japonicus) in response to LPS challenge

The sea cucumber (Apostichopus japonicus) occupies a basal position during the evolution of deuterostomes and is also an important aquaculture species. In order to identify more immune effectors, transcriptome sequencing of A. japonicus coelomocytes in response to lipopolysaccharide (LPS) challenge was performed using the Illumina HiSeq™ 2000 platform. One hundred and seven differentially expressed genes were selected and divided into four functional categories including pathogen recognition (25 genes), reorganization of cytoskeleton (27 genes), inflammation (41 genes) and apoptosis (14 genes). They were analyzed to elucidate the mechanisms of host-pathogen interactions and downstream signaling transduction. Quantitative real-time polymerase chain reactions (qRT-PCRs) of 10 representative genes validated the accuracy and reliability of RNA sequencing results with the correlation coefficients from 0.88 to 0.98 and p-value <0.05. Expression analysis of immune-related genes after LPS challenge will be useful in understanding the immune response mechanisms of A. japonicus against pathogen invasion and developing strategies for resistant markers selection.

Identification and expression analysis of two Toll-like receptor genes from sea cucumber (Apostichopus japonicus)

Toll-like receptors (TLRs) are a family of type I integral membrane glycoproteins which play pivotal roles in innate immunity. In this study, two TLRs named AjTLR3 and AjToll were cloned from sea cucumber (Apostichopus japonicus). The full-length cDNA sequences of AjTLR3 and AjToll are 3484 bp and 4211 bp, with an open reading frame (ORF) of 2679 bp and 2853 bp, encoding 892 and 950 amino acids, respectively. Both AjTLR3 and AjToll are composed of a leucine-rich repeat (LRR) domain, a transmembrane (TM) domain and an intracellular Toll/interleukin-1 receptor (TIR) domain. Evolution analysis revealed that AjTLR3 and AjToll were clustered with the vertebrate-like TLRs (V-TLRs) and the protostome-like TLRs (P-TLRs), respectively. These two genes were widely expressed in all five tested tissues (body wall, coelomocytes, tube feet, intestine and respiratory tree), but showed different expression patterns. The significantly up-regulated expressions of AjTLR3 and AjToll after peptidoglycan (PGN), lipopolysaccharides (LPS), Zymosan A and polyinosinic-polycytidylic acid (PolyI:C) challenges suggested that they were functionally involved in the immune responses to the Cram-positive bacteria, Gram-negative bacteria, fungi and double-stranded RNA (dsRNA) viruses, respectively.

Correlating structure and function during the evolution of fibrinogen-related domains

Fibrinogen-related domains (FReDs) are found in a variety of animal proteins with widely different functions, ranging from non-self recognition to clot formation. All appear to have a common surface where binding of one sort or other occurs. An examination of 19 completed animal genomes--including a sponge and sea anemone, six protostomes, and 11 deuterostomes--has allowed phylogenies to be constructed that show where various types of FReP (proteins containing FReDs) first made their appearance. Comparisons of sequences and structures also reveal particular features that correlate with function, including the influence of neighbor-domains. A particular set of insertions in the carboxyl-terminal subdomain was involved in the transition from structures known to bind sugars to those known to bind amino-terminal peptides. Perhaps not unexpectedly, FReDs with different functions have changed at different rates, with ficolins by far the fastest changing group. Significantly, the greatest amount of change in ficolin FReDs occurs in the third subdomain ("P domain"), the very opposite of the situation in most other vertebrate FReDs. The unbalanced style of change was also observed in FReDs from non-chordates, many of which have been implicated in innate immunity.

Individual sequence variability and functional activities of fibrinogen-related proteins (FREPs) in the Mediterranean mussel (Mytilus galloprovincialis) suggest ancient and complex immune recognition models in invertebrates

In this paper, we describe sequences of fibrinogen-related proteins (FREPs) in the Mediterranean mussel Mytilus galloprovincialis (MuFREPs) with the fibrinogen domain probably involved in the antigen recognition, but without the additional collagen-like domain of ficolins, molecules responsible for complement activation by the lectin pathway. Although they do not seem to be true or primive ficolins since the phylogenetic analysis are not conclusive enough, their expression is increased after bacterial infection or PAMPs treatment and they present opsonic activities similar to mammalian ficolins. The most remarkable aspect of these sequences was the existence of a very diverse set of FREP sequences among and within individuals (different mussels do not share any identical sequence) which parallels the extraordinary complexity of the immune system, suggesting the existence of a primitive system with a potential capacity to recognize and eliminate different kind of pathogens.

The primary role of fibrinogen-related proteins in invertebrates is defense, not coagulation

In vertebrates, the conversion of fibrinogen into fibrin is an essential process that underlies the establishment of the supporting protein framework required for coagulation. In invertebrates, fibrinogen-domain-containing proteins play a role in the defense response generated against pathogens; however, they do not function in coagulation, suggesting that this role has been recently acquired. Molecules containing fibrinogen motifs have been identified in numerous invertebrate organisms, and most of these molecules known to date have been linked to defense. Moreover, recent genome projects of invertebrate animals have revealed surprisingly high numbers of fibrinogen-like loci in their genomes, suggesting important and perhaps diverse functions of fibrinogen-like proteins in invertebrates. The ancestral role of molecules containing fibrinogen-related domains (FReDs) with immunity is the focus of this review, with emphasis on specific FReDs called fibrinogen-related proteins (FREPs) identified from the schistosome-transmitting mollusc Biomphalaria glabrata. Herein, we outline the range of invertebrate organisms FREPs can be found in, and detail the roles these molecules play in defense and protection against infection.

In search of the origin of FREPs: characterization of Aplysia californica fibrinogen-related proteins

All haemolymph lectins with uniquely juxtaposed N-terminal domain similar to the immunoglobulin superfamily (IgSF) and C-terminal fibrinogen (FBG) termed FBG-related proteins (FREP) are documented till now only in the pulmonate mollusc Biomphalaria glabrata. Using genomic WGS database we have found two FREP genes from marine opistobranch Aplysia californica named AcFREP1 and AcFREP2. The AcFREP1 and AcFREP2 mRNA molecules have been subsequently isolated from cDNA of sea hare larvae as well as adult mollusc tissues. These genes encode proteins (504 and 510aa respectively) with domain architecture typical for FREPs with two N-terminal IgSF domains and C-terminal FBG domain. Although cDNA sequences of AcFREP1 and AcFREP2 are 81% identical, their genomic structure is entirely different: AcFREP1 is intronless and AcFREP2 is encoded in four exons. These genes are paralogous pair in which AcFREP2 is a parental gene and AcFREP1 is the new transposed copy that has lost the introns (retrogene). Using RT-PCR analysis, expression of AcFREP1 and AcFREP2 was shown to be developmentally and tissue-specific and no constitutive expression in haemocytes was found. The overall frequency of nucleotide substitutions in genomic DNA trace sequences of coding region of the AcFREP1 and AcFREP2 is not higher than in the sequences of control conserved genes (actin, FMRFamide). Thus, previously reported high diversification of Biomphalaria FREP gene, BgFREP3, is not detected in Aplysia FREPs. A search for FREP homologs in other available complete genome of mollusc, Lottia gigantea (Patellogastropoda), a representative of the evolutionary earliest gastropod clade, did not reveal any DNA sequences coding for similar lectins. We suggest that unique domain architecture of FREPs is an evolutionary novelty that appeared and evolved only within one branch of Protostomata species, exclusively in heterobranch molluscs (Pulmonata and Opistobranchia).

LPS-induced genes in intestinal tissue of the sea cucumber Holothuria glaberrima

Metazoan immunity is mainly associated with specialized cells that are directly involved with the immune response. Nevertheless, both in vertebrates and invertebrates other organs might respond to immune activation and participate either directly or indirectly in the ongoing immune process. However, most of what is known about invertebrate immunity has been restricted to immune effector cells and little information is available on the immune responses of other tissues or organs. We now focus on the immune reactions of the intestinal tissue of an echinoderm. Our study employs a non-conventional model, the echinoderm Holothuria glaberrima, to identify intestinal molecules expressed after an immune challenge presented by an intra-coelomic injection of lipopolysaccharides (LPS). The expression profiles of intestinal genes expressed differentially between LPS-injected animals and control sea water-injected animals were determined using a custom-made Agilent microarray with 7209 sea cucumber intestinal ESTs. Fifty (50) unique sequences were found to be differentially expressed in the intestine of LPS-treated sea cucumbers. Seven (7) of these sequences represented homologues of known proteins, while the remaining (43) had no significant similarity with any protein, EST or RNA database. The known sequences corresponded to cytoskeletal proteins (Actin and alpha-actinin), metabolic enzymes (GAPDH, Ahcy and Gnmt), metal ion transport/metabolism (major yolk protein) and defense/recognition (fibrinogen-like protein). The expression pattern of 11 genes was validated using semi-quantitative RT-PCR. Nine of these corroborated the microarray results and the remaining two showed a similar trend but without statistical significance. Our results show some of the molecular events by which the holothurian intestine responds to an immune challenge and provide important information to the study of the evolution of the immune response.

Hepatocyte-derived fibrinogen-related protein-1 is associated with the fibrin matrix of a plasma clot

In order to study the multiple functions of fibrinogen and fibrin, we are investigating which proteins bind to the fibrin matrix of a plasma clot by using a proteomic approach. Extracts from washed plasma clots were analysed by 2-D gel electrophoresis. A relatively abundant spot was identified as hepatocyte-derived fibrinogen-related protein-1 (HFREP-1) by MALDI-TOF analysis, molecular mass (34 kDa), iso-electric point (pI 5.5) as well as by Western blot analysis. HFREP-1 in plasma almost completely bound to the fibrin matrix during clot formation. Several purified fibrinogen preparations proved to be contaminated with HFREP-1. It is concluded that HFREP-1 (also named hepassocin), a protein with liver cell growth regulatory properties, occurs in plasma and strongly associates with fibrin and possibly fibrinogen.

Tick lectins: structural and functional properties

Few papers have been published on tick lectins so far, and therefore more data are needed to complete the mosaic of knowledge of their structural and functional properties. Tissue-specific lectin/haemagglutinin activities of both soft and hard ticks have been investigated. Some tick lectins are proteins with binding affinity for sialic acid, various derivatives of hexosamines and different glycoconjugates. Most tick lectin/haemagglutinin activities are blood meal enhanced, and could serve as molecular factors of self/non-self recognition in defence reactions against bacteria or fungi, as well as in pathogen/parasite transmission. Dorin M, the plasma lectin of Ornithodoros moubata, is the first tick lectin purified so far from tick haemolymph, and the first that has been fully characterized. Partial characterization of other tick lectins/haemagglutinins has been performed mainly with respect to their carbohydrate binding specificities and immunochemical features.

The tick plasma lectin, Dorin M, is a fibrinogen-related molecule

A lectin, named Dorin M, previously isolated and characterized from the hemolymph plasma of the soft tick, Ornithodoros moubata, was cloned and sequenced. The immunofluorescence using confocal microscopy revealed that Dorin M is produced in the tick hemocytes. A tryptic cleavage of Dorin M was performed and the resulting peptide fragments were sequenced by Edman degradation and/or mass spectrometry. Two of three internal peptide sequences displayed a significant similarity to the family of fibrinogen-related molecules. Degenerate primers were designed and used for PCR with hemocyte cDNA as a template. The sequence of the whole Dorin M cDNA was completed by the method of RACE. The tissue-specific expression investigated by RT-PCR revealed that Dorin M, in addition to hemocytes, is significantly expressed in salivary glands. The derived amino-acid sequence clearly shows that Dorin M has a fibrinogen-like domain, and exhibited the most significant similarity with tachylectins 5A and 5B from a horseshoe crab, Tachypleus tridentatus. In addition, other protein and binding characteristics suggest that Dorin M is closely related to tachylectins-5. Since these lectins have been reported to function as non-self recognizing molecules, we believe that Dorin M may play a similar role in an innate immunity of the tick and, possibly, also in pathogen transmission by this vector.

Molecular cloning and comparative analysis of fibrinogen-related proteins from the soft tick Ornithodoros moubata and the hard tick Ixodes ricinus

Among disease-vectors, the evolution of the tick innate immune system is still lagging when compared to insects. Such an investigation, which was initiated, by first cloning and sequencing lectins associated in the innate immunity of invertebrates and having fibrinogen related domains, helped in the sequencing of cDNA encoding for OMFREP from the soft tick, Ornithodoros moubata. Also obtained were Ixoderin A and Ixoderin B cDNA sequences from the hard tick Ixodes ricinus. Tissue-specific expression of OMFREP showed that it was present primarily in the hemocytes and salivary glands. Ixoderin A besides sharing a similar expression profile was also expressed in the midgut. Both showed significantly high homology to the lectin Dorin M, from O. moubata. Further, phylogenetic comparisons between these molecules of the soft and hard ticks showed their relatedness to Tachylectins 5A and 5B, involved in the innate immunity of Tachypleus tridentatus and ficolins from both vertebrates and invertebrates. Ixoderin B showing tissue-specific expression only in the salivary glands and the sequence displaying certain motif differences in homology point towards a possible function different from the other two molecules. This is the first report of lectin-like sequences, with a fibrinogen-domain, from the hard tick I. ricinus and a preliminary phylogenetic study of these tick sequences with related fibrinogen-domain containing sequences highlights a possible role for them in the innate immunity of the ticks.

Representation of an immune responsive gene family encoding fibrinogen-related proteins in the freshwater mollusc Biomphalaria glabrata, an intermediate host for Schistosoma mansoni

Fibrinogen-related proteins (FREPs) are found in the hemolymph of the freshwater snail Biomphalaria glabrata, are up-regulated following exposure to digenetic trematode parasites, and bind to trematode larval surfaces, suggestive of a role in internal defense. Southern blot and degenerate-polymerase chain reaction (PCR) analyses were undertaken to better understand the diversity of the FREP-encoding gene family. Probes corresponding to the N-terminal IgSF domains of specific FREP gene subfamilies (FREPs 2, 3, 4, 7, 12 and 13) revealed between 1 to 8 loci per subfamily on Southern blots. Probes representing the relatively conserved C-terminal fibrinogen domain of FREPs bound many sequences in Southern blots of genomic DNA from B. glabrata, and from two related gastropod species, Biomphalaria pfeifferi and Helisoma trivolvis. Using degenerate-PCR, we obtained 42 unique fibrinogen-encoding sequences from 180 clones derived from a single individual of the M-line strain of B. glabrata, further supporting the notion of their abundant representation in the B. glabrata genome. The fibrinogen-encoding sequences of FREPs encoding one or two IgSF domains tended to separate into distinct clades, but bootstrap support for this separation was low. A novel category of fibrinogen-encoding sequence was also revealed. This study provides the approximate number of gene copies in several FREP subfamilies, confirms the existence of a diverse FREP gene family, reports additional unusual sequences encoding fibrinogen-like molecules, and provides further justification to explore the functional roles of FREPs in both B. glabrata and B. pfeifferi, both important intermediate hosts of the human pathogen, Schistosoma mansoni.

Differential expression of FREP genes in two strains of Biomphalaria glabrata following exposure to the digenetic trematodes Schistosoma mansoni and Echinostoma paraensei

Fibrinogen-related proteins (FREPs) are hypothesized to function in non-self-recognition in the snail Biomphalaria glabrata. To investigate this assumption, the expression of four members of the FREP gene family was studied using quantitative PCR at 0.5-16 days following exposure of M line and BS-90 strain B. glabrata to Echinostoma paraensei and Schistosoma mansoni. Both strains react to, but fail to eliminate E. paraensei. Only the BS-90 strain is immunologically resistant to S. mansoni. Both snail strains responded to E. paraensei with significantly elevated expression of FREP 2 and 4. Following exposure to S. mansoni, resistant BS-90 snails showed an increase in expression of FREP 2 and 4 (57-fold and 4.5-fold increase, respectively), susceptible M line snails did not display a FREP response. Expression of FREP 3 and 7 was not significantly elevated in any snail/trematode combination. These expression profiles support the hypothesis that some FREPs play a role in the anti-trematode responses in B. glabrata.

Fibrinogen and fibrin

Fibrinogen is a large, complex, fibrous glycoprotein with three pairs of polypeptide chains linked together by 29 disulfide bonds. It is 45 nm in length, with globular domains at each end and in the middle connected by alpha-helical coiled-coil rods. Both strongly and weakly bound calcium ions are important for maintenance of fibrinogen's structure and functions. The fibrinopeptides, which are in the central region, are cleaved by thrombin to convert soluble fibrinogen to insoluble fibrin polymer, via intermolecular interactions of the "knobs" exposed by fibrinopeptide removal with "holes" always exposed at the ends of the molecules. Fibrin monomers polymerize via these specific and tightly controlled binding interactions to make half-staggered oligomers that lengthen into protofibrils. The protofibrils aggregate laterally to make fibers, which then branch to yield a three-dimensional network-the fibrin clot-essential for hemostasis. X-ray crystallographic structures of portions of fibrinogen have provided some details on how these interactions occur. Finally, the transglutaminase, Factor XIIIa, covalently binds specific glutamine residues in one fibrin molecule to lysine residues in another via isopeptide bonds, stabilizing the clot against mechanical, chemical, and proteolytic insults. The gene regulation of fibrinogen synthesis and its assembly into multichain complexes proceed via a series of well-defined steps. Alternate splicing of two of the chains yields common variant molecular isoforms. The mechanical properties of clots, which can be quite variable, are essential to fibrin's functions in hemostasis and wound healing. The fibrinolytic system, with the zymogen plasminogen binding to fibrin together with tissue-type plasminogen activator to promote activation to the active enzyme plasmin, results in digestion of fibrin at specific lysine residues. Fibrin(ogen) also specifically binds a variety of other proteins, including fibronectin, albumin, thrombospondin, von Willebrand factor, fibulin, fibroblast growth factor-2, vascular endothelial growth factor, and interleukin-1. Studies of naturally occurring dysfibrinogenemias and variant molecules have increased our understanding of fibrinogen's functions. Fibrinogen binds to activated alphaIIbbeta3 integrin on the platelet surface, forming bridges responsible for platelet aggregation in hemostasis, and also has important adhesive and inflammatory functions through specific interactions with other cells. Fibrinogen-like domains originated early in evolution, and it is likely that their specific and tightly controlled intermolecular interactions are involved in other aspects of cellular function and developmental biology.

A (13)-beta-d-glucan recognition protein from the sponge Suberites domuncula. Mediated activation of fibrinogen-like protein and epidermal growth factor gene expression

Sponges (phylum Porifera) live in a symbiotic relationship with microorganisms, primarily bacteria. Until now, molecular proof for the capacity of sponges to recognize fungi in the surrounding aqueous milieu has not been available. Here we demonstrate, for the demosponge Suberites domuncula (Porifera, Demospongiae, Hadromerida), a cell surface receptor that recognizes (1-->3)-beta-D-glucans, e.g. curdlan or laminarin. This receptor, the (1-->3)-beta-D-glucan-binding protein, was identified and its cDNA analysed. The gene coding for the 45 kDa protein was found to be upregulated in tissue after incubation with carbohydrate. Simultaneously with the increased expression of this gene, two further genes showed an elevated steady state level of expression; one codes for a fibrinogen-like protein and the other for the epidermal growth factor precursor. Expression of the (1-->3)-beta-D-glucan-binding protein and the fibrinogen-like protein occurred in cells on the sponge surface, in the pinacoderm. By Western blotting, the product of the fibrinogen-like protein gene was identified, the recombinant protein isolated, and antibodies raised to this protein. Their application revealed that a 5 kDa factor is produced, which is apparently processed from the 77 kDa epidermal growth factor precursor. Finally, we provided evidence that a tyrosine kinase pathway is initiated in response to exposure to D-glucan; its phosphorylation activity could be blocked by aeroplysinin. In turn, the increased expression of the downstream genes was suppressed. We conclude that sponges possess a molecular mechanism for recognizing fungi via the d-glucan carbohydrates on their surfaces.

Gene transcription of fgl2 in endothelial cells is controlled by Ets-1 and Oct-1 and requires the presence of both Sp1 and Sp3

The immune coagulant fgl2/fibroleukin has been previously shown to play a pivotal role in the pathogenesis of murine and human fulminant hepatitis and fetal loss syndrome. Constitutive expression of fgl2 transcripts at low levels are seen in cytotoxic T cells, endothelial, intestinal and trophoblast cells, while specific factors (such as virus and cytokines) are required to induce high levels of fgl2 expression in other cell types including monocytes/macrophages. To address the transcriptional mechanisms that regulate constitutive expression of fgl2, murine genomic clones were characterized and the transcription start site was defined by 5'-RACE and primer extension. A comprehensive assessment of basal fgl2 promoter activity in murine vascular endothelial cells defined a minimal 119 bp region responsible for constitutive fgl2 transcription. A complex positive regulatory domain (PRD) spanning a 39-bp sequence from -87 to -49 (relative to the transcription start site) was identified. Electrophoretic mobility shift assay studies in vascular endothelial cells revealed that the nucleoprotein complexes that form on this positive regulatory domain (PRD) contain Sp1/Sp3 family members, Oct-1, and Ets-1. Heterologous expression studies in Drosophila Schneider cells confirmed that the constitutive expression of this gene is controlled by Ets-1 and requires the presence both of the Sp1 and Sp3 transcription factors. The presence of this complex multicomponent PRD in the fgl2 proximal promoter is consistent with the observation that, in vivo, fgl2 expression is tightly regulated. Moreover, viral induced fgl2 expression also requires the presence of this PRD. These results clearly demonstrate that multiple cis DNA elements in a clustered region work cooperatively to regulate constitutive fgl2 expression and interact with inducible elements to regulate viral-induced fgl2 expression in endothelial cells.

Molecular basis of non-self recognition by the horseshoe crab tachylectins

The self/non-self discrimination by innate immunity through simple ligands universally expressed both on pathogens and hosts, such as monosaccharides and acetyl group, depends on the density or clustering patterns of the ligands. The specific recognition by the horseshoe crab tachylectins with a propeller-like fold or a propeller-like oligomeric arrangement is reinforced by the short distance between the individual binding sites that interact with pathogen-associated molecular patterns (PAMPs). There is virtually no conformational change in the main or side chains of tachylectins upon binding with the ligands. This low structural flexibility of the propeller structures must be very important for specific interaction with PAMPs. Mammalian lectins, such as mannose-binding lectin and ficolins, trigger complement activation through the lectin pathway in the form of opsonins. However, tachylectins have no effector collagenous domains and no lectin-associated serine proteases found in the mammalian lectins. Furthermore, no complement-like proteins have been found in horseshoe crabs, except for alpha(2)-macroglobulin. The mystery of the molecular mechanism of the scavenging pathway of pathogens in horseshoe crabs remains to be solved.

A large-scale analysis of mRNAs expressed by primary mesenchyme cells of the sea urchin embryo

The primary mesenchyme cells (PMCs) of the sea urchin embryo have been an important model system for the analysis of cell behavior during gastrulation. To gain an improved understanding of the molecular basis of PMC behavior, a set of 8293 expressed sequenced tags (ESTs) was derived from an enriched population of mid-gastrula stage PMCs. These ESTs represented approximately 1200 distinct proteins, or about 15% of the mRNAs expressed by the gastrula stage embryo. 655 proteins were similar (P&lt;10−7 by BLAST comparisons) to other proteins in GenBank, for which some information is available concerning expression and/or function. Another 116 were similar to ESTs identified in other organisms, but not further characterized. We conservatively estimate that sequences encoding at least 435 additional proteins were included in the pool of ESTs that did not yield matches by BLAST analysis. The collection of newly identified proteins includes many candidate regulators of primary mesenchyme morphogenesis, including PMC-specific extracellular matrix proteins, cell surface proteins, spicule matrix proteins and transcription factors. This work provides a basis for linking specific molecular changes to specific cell behaviors during gastrulation. Our analysis has also led to the cloning of several key components of signaling pathways that play crucial roles in early sea urchin development.

The tenascin family of ECM glycoproteins: structure, function, and regulation during embryonic development and tissue remodeling

The determination of animal form depends on the coordination of events that lead to the morphological patterning of cells. This epigenetic view of development suggests that embryonic structures arise as a consequence of environmental influences acting on the properties of cells, rather than an unfolding of a completely genetically specified and preexisting invisible pattern. Specialized cells of developing multicellular organisms are surrounded by a complex extracellular matrix (ECM), comprised largely of different collagens, proteoglycans, and glycoproteins. This ECM is a substrate for tissue morphogenesis, lends support and flexibility to mature tissues, and acts as an epigenetic informational entity in the sense that it transduces and integrates intracellular signals via distinct cell surface receptors. Consequently, ECM-receptor interactions have a profound influence on major cellular programs including growth, differentiation, migration, and survival. In contrast to many other ECM proteins, the tenascin (TN) family of glycoproteins (TN-C, TN-R, TN-W, TN-X, and TN-Y) display highly restricted and dynamic patterns of expression in the embryo, particularly during neural development, skeletogenesis, and vasculogenesis. These molecules are reexpressed in the adult during normal processes such as wound healing, nerve regeneration, and tissue involution, and in pathological states including vascular disease, tumorigenesis, and metastasis. In concert with a multitude of associated ECM proteins and cell surface receptors that include members of the integrin family, TN proteins impart contrary cellular functions, depending on their mode of presentation (i.e., soluble or substrate-bound) and the cell types and differentiation states of the target tissues. Expression of tenascins is regulated by a variety of growth factors, cytokines, vasoactive peptides, ECM proteins, and biomechanical factors. The signals generated by these factors converge on particular combinations of cis-regulatory elements within the recently identified TN gene promoters via specific transcriptional activators or repressors. Additional complexity in regulating TN gene expression is achieved through alternative splicing, resulting in variants of TN polypeptides that exhibit different combinations of functional protein domains. In this review, we discuss some of the recent advances in TN biology that provide insights into the complex way in which the ECM is regulated and how it functions to regulate tissue morphogenesis and gene expression.

Molecular and functional analysis of the human prothrombinase gene (HFGL2) and its role in viral hepatitis

In the present studies, we report the cloning and structural characterization of the HFGL2 gene and its functional role in human fulminant hepatitis. The HFGL2 gene is approximately 7 kb in length with 2 exons. The putative promoter contains cis element consensus sequences that strongly suggest the inducibility of its expression. From the nucleotide sequence of the human gene, a 439-amino acid long protein is predicted. The overall identity between the murine fgl2 and hfgl2 coded proteins is over 70%. About 225 amino acids at the carboxyl end of these molecules are almost 90% identical, and correspond to a well-conserved fibrinogen-related domain. Both HFGL2 and FGL2 encode a type II transmembrane protein with a predicted catalytic domain toward the amino terminus of the protein. Transient transfection of Chinese hamster ovary (CHO) cells with a full-length cDNA of HFGL2 coding region resulted in high levels of prothrombinase activity. Livers from 8 patients transplanted for fulminant viral hepatitis were examined for extent of necrosis, inflammation, fibrin deposition, and HFGL2 induction. In situ hybridization showed positive staining of macrophages in areas of active hepatocellular necrosis. Fibrin stained positively in these areas and was confirmed by electron microscopy. These studies define a unique prothrombinase gene (HFGL2) and implicate its importance in the pathogenesis of fulminant viral hepatitis.

A unique primary structure, cDNA cloning and function of a galactose-specific lectin from ascidian plasma

The complete amino acid sequence of a galactose-specific lectin from the plasma of the ascidian Halocynthia roretzi has been determined by sequential Edman degradation analysis of peptide fragments derived by proteolytic fragmentation and chemical cleavage of the reductive S-pyridylethylated lectin. Peptide fragments were separated by reverse-phase HPLC. The N-terminal and C-terminal amino acid sequences were determined by Edman degradation and enzymatic digestion. The H. roretzi plasma lectin is a single-chain protein consisting of 327 amino acids and four disulfide bonds, one of which was found to be cross-linked intramolecularly. A comparison of the amino acid sequence of the H. roretzi plasma lectin with the sequences of other proteins reveals that the H. roretzi lectin has a structure consisting of a twice-repeated sequence, a fibrinogen-related sequence and a C-type lectin-homologous sequence. The above amino acid sequence was verified by cDNA cloning of this lectin. Three cDNA clones that have single ORFs encoding the lectin precursor were isolated from an H. roretzi hepatopancreas cDNA library. The deduced amino acid sequences in the three cDNA clones contain the same sequence of the mature lectin molecule and the same putative signal sequence. In addition, it was demonstrated that this lectin can enhance phagocytosis by H. roretzi hemocytes. Thus, the plasma lectin is constructed into an oligomer structure via intermolecular disulfide bonds and plays a role in the biological defense of H. roretzi as a defense molecule.

Three-dimensional structural studies on fragments of fibrinogen and fibrin

Fibrinogen is a 340 kDa glycoprotein found in the blood plasma of all vertebrates. It is transformed into a fibrin clot by the action of thrombin. Recent X-ray structures of core fragments of both fibrinogen and fibrin have revealed many details about this polymerization event. These include structures of a 30 kDa recombinant gammaC domain, an 86 kDa fragment D from human fibrinogen and a cross-linked double-D fragment from fibrin.

Formation of the Human Fibrinogen Subclass Fib420: Disulfide Bonds and Glycosylation in Its Unique (EChain) Domains

COS cell transfection has been used to monitor the assembly and secretion of fibrinogen molecules, both those of the subclass containing the novel E chain and those of the more abundant subclass whose  chains lack E’s globular C-terminus. That region, referred to as the EC domain, is closely related to the ends of β and γ chains of fibrinogen (βC and γC). Transfection of COS cells with E, β, and γ cDNAs alone results in secretion of the symmetrical molecule (Eβγ)2, also known as Fib420. Cotransfection with cDNA for the shorter  chain yielded secretion of both (βγ)2 and (Eβγ)2 but no mixed molecules of the structure E(βγ)2. Exploiting the COS cells’ fidelity with regard to Fib420 production, identification was made of the highly conserved Asn667 as the sole site of N-linked glycosylation in the E chain. No evidence from Cys → Ser replacements was found for interchain disulfide bridges involving the four cysteines of the EC domain. However, for fibrinogen secretion, the E, β, and γ subunits do exhibit different requirements for integrity of the two intradomain disulfide bridges located at homologous positions in their respective C-termini, indicating dissimilar structural roles in the process of fibrinogen assembly.

© 1998 by The American Society of Hematology.

Formation of the Human Fibrinogen Subclass Fib420: Disulfide Bonds and Glycosylation in Its Unique (EChain) Domains

COS cell transfection has been used to monitor the assembly and secretion of fibrinogen molecules, both those of the subclass containing the novel E chain and those of the more abundant subclass whose  chains lack E’s globular C-terminus. That region, referred to as the EC domain, is closely related to the ends of β and γ chains of fibrinogen (βC and γC). Transfection of COS cells with E, β, and γ cDNAs alone results in secretion of the symmetrical molecule (Eβγ)2, also known as Fib420. Cotransfection with cDNA for the shorter  chain yielded secretion of both (βγ)2 and (Eβγ)2 but no mixed molecules of the structure E(βγ)2. Exploiting the COS cells’ fidelity with regard to Fib420 production, identification was made of the highly conserved Asn667 as the sole site of N-linked glycosylation in the E chain. No evidence from Cys → Ser replacements was found for interchain disulfide bridges involving the four cysteines of the EC domain. However, for fibrinogen secretion, the E, β, and γ subunits do exhibit different requirements for integrity of the two intradomain disulfide bridges located at homologous positions in their respective C-termini, indicating dissimilar structural roles in the process of fibrinogen assembly.

© 1998 by The American Society of Hematology.

Ficolins and the fibrinogen-like domain

Ficolins are a group of proteins containing collagen-like and fibrinogen-like (FBG) sequences and they have a similar overall structure to C1q and the collectins. There are two types of ficolin in man: L-ficolin and M-ficolin. L-ficolin is synthesized in the liver and secreted into the plasma. It binds to several apparently unrelated structures including sugar residues and enhances phagocytosis of bound bacteria. M-ficolin is synthesized mainly in monocytes and is detected on the monocyte surface. The polypeptide sequences of ficolins, the collectins and C1q diverge mainly in their C-terminal globular regions which are, respectively, FBG domains, Ca(2+)-dependent carbohydrate recognition domains (C-type CRD), and collagen-related sequences. The FBG domain consists of 220-250 residues and is found in a number of proteins besides fibrinogen and ficolins. The crystal structure of the FBG domain has been characterized and the elucidation of its binding properties should provide essential insights into its role in ficolins and other proteins.

Evolution of vertebrate fibrin formation and the process of its dissolution

The thrombin-catalysed conversion of fibrinogen into a fibrin gel is common to all extant vertebrates. Because fibrin formation is both temporary and risky, an effective scheme for fibrinolysis evolved concomitantly. In this regard, the fibrinogen molecule is well adapted both for network polymerization and for subsequent dismantling. The question is, has it always been so? It has long been known that the three non-identical chains that compose vertebrate fibrinogen are descended from a common ancestor, and the original molecule must have been either a homotrimer or a dimer thereof. Three-dimensional studies on core fragments of fibrinogen are revealing new insights about both fibrin formation and its destruction. These studies are also showing exactly what structural changes have accompanied changes in function for the various domains. Chief among these is the reversal of direction for the alpha chain after replacement of its C-terminal domain.

A family of fibrinogen-related proteins that precipitates parasite-derived molecules is produced by an invertebrate after infection

After infection with the digenetic trematode Echinostoma paraensei, hemolymph of the snail Biomphalaria glabrata contains lectins comprised of 65-kDa subunits that precipitate polypeptides secreted by E. paraensei intramolluscan larvae. Comparable activity is lacking in hemolymph of uninfected snails. Three different cDNAs with sequence similarities to peptides derived from the 65-kDa lectins were obtained and unexpectedly found to encode fibrinogen-related proteins (FREPs). These FREPs also contained regions with sequence similarity to Ig superfamily members. B. glabrata has at least five FREP genes, three of which are expressed at increased levels after infection. Elucidation of components of the defense system of B. glabrata is relevant because this snail is an intermediate host for Schistosoma mansoni, the most widely distributed causative agent of human schistosomiasis. These results are novel in suggesting a role for invertebrate FREPs in recognition of parasite-derived molecules and also provide a model for investigating the diversity of molecules functioning in nonself-recognition in an invertebrate.

beta2 knockout mice develop parenchymal iron overload: A putative role for class I genes of the major histocompatibility complex in iron metabolism

Hemochromatosis (HC) is an inherited disorder of iron absorption, mapping within the human major histocompatibility complex (MHC). We have identified a multigene system in the murine MHC that contains excellent candidates for the murine equivalent of the human HC locus and implicate nonclassical class I genes in the control of iron absorption. This gene system is characterized by multiple copies of two head-to-head genes encoded on opposite strands and driven by one common regulatory motif. This regulatory motif has a striking homology to the promoter region of the beta-globin gene, a gene obviously involved in iron metabolism and hence termed beta-globin analogous promoter (betaGAP). Upstream of the betaGAP sequence are nonclassical class I genes. At least one of these nonclassical class I genes, Q2, is expressed in the gastrointestinal tract, the primary site of iron absorption. Also expressed in the gastrointestinal tract and downstream of the betaGAP motif is a second set of putative genes, termed Hephaestus (HEPH). Based on these observations, we hypothesized that the genes that seem to be controlled by the betaGAP regulatory motifs would be responsible for the control of Fe absorption. As a test of this hypothesis, we predicted that mice which have altered expression of class I gene products, the beta2-microglobulin knockout mice, [beta2m(-/-)], would develop Fe overload. This prediction was confirmed, and these results indicate beta2m-associated proteins are involved in the control of intestinal Fe absorption.

Human ficolin: cDNA cloning, demonstration of peripheral blood leucocytes as the major site of synthesis and assignment of the gene to chromosome 9

Pig ficolins and a number of other proteins contain sequences that are homologous to the C-terminal halves of fibrinogen beta- and gamma-chains. To clone the cDNA for human ficolin, two degenerate oligonucleotide primers were synthesized, based on two stretches of protein sequence that were highly conserved among those proteins, and used for PCR with cDNA from a human uterus lambda gt11 library as a template. A PCR product with a predicted size of 300 bp was obtained and this was used to screen a uterus cDNA library. Of the positive clones isolated, two (U1 and U2), containing inserts of 1.7 and 1.1 kb respectively, were found to encode human ficolin. The cDNA-derived amino acid sequence of human ficolin has approx. 75% identity with, and a similar domain organization to, the two pig ficolin sequences, which are characterized by the presence of a leader peptide, a short N-terminal segment followed by a collagen-like region and then by a C-terminal fibrinogen-like domain. The 1.1 kb insert of clone U2 was used in Northern-blot analysis, and a very strong signal for a 1.4 kb mRNA species was detected in mRNA from human peripheral blood leucocytes. This showed that, despite the initial characterization of pig ficolin as a putative receptor on uterine cells for transforming growth factor beta 1, blood leucocytes are probably the major site of human ficolin synthesis. Much weaker signals of the same size were also detected in spleen, lung and thymus and may be due to the presence of tissue macrophages or trapped blood in these tissues. An mRNA species of approx. 1.3 kb in human liver also weakly hybridized to the U2 probe, indicating the presence of a sequence that was distinct from, but related to, ficolin. The gene for human ficolin has been mapped to chromosome 9.

Tenascins, a growing family of extracellular matrix proteins

The tenascins are a family of large multimeric extracellular matrix proteins consisting of repeated structural modules including heptad repeats, epidermal growth factor (EGF)-like repeats, fibronectin type III repeats, and a globular domain shared with the fibrinogens. The tenascins are believed to be involved in the morphogenesis of many organs and tissues. To date three members of the tenascin family have been described, tenascin-C, tenascin-R, and tenascin-X. Tenascin-R seems to be specific for the central and peripheral nervous system, tenascin-X is most prominent in skeletal and heart muscle, while tenascin-C is present in a large number of developing tissues including the nervous system, but is absent in skeletal and heart muscles. Tenascin-C was the original tenascin discovered, partly because of its overexpression in tumors. Inferring from cell biological studies, it has been proposed that tenascin-C is an adhesion-modulating protein.

The minor form alpha' chain from lamprey fibrinogen is rapidly crosslinked during clotting

Lampreys have two genes for the alpha chains of fibrinogen, the second of which encodes a minor form with a carboxyl-terminal domain homologous to the carboxyl-terminal domains of beta and gamma chains. Initially, we referred to the alternative chain as alpha-II; we now use the designation alpha' in order to facilitate reference to crosslinked dimers. Antisera raised to synthetic peptides based on the cDNA sequence confirmed that the alpha' chain was present in fibrinogen prepared directly from plasma. The same antibodies were used to determine the size and properties of the carboxyl-terminal domain after its release by mild tryptic digestion, a fragment of apparent molecular weight 35,000-40,000 being produced. Unlike fragment D generated in the same digestions, the alpha' fragment did not bind to Gly-Pro-Arg or Gly-Val-Arg peptide affinity columns. During clotting under conditions where factor XIII is active, the alpha' chains became crosslinked very much more rapidly than ordinary alpha chains, the principal product being an apparent dimer, but smaller amounts of higher multimers being detectable. The crosslinking was inhibited by various amines, as well as by peptides that prevent polymerization.

The distribution of tenascin-X is distinct and often reciprocal to that of tenascin-C

We have isolated a cDNA encoding mouse tenascin-X (TN-X), a new member of the family of tenascin genes. The TN-X gene lies in the major histocompatibility complex (MHC) class III region, as it is the case for its human counterpart. On Northern blots we detected a TN-X mRNA of approximately 13 kb in most tissues analyzed, whereas in various mouse cell lines mRNAs of approximately 11 and 13 kb were detected, suggesting the possibility of alternative splicing of TN-X transcripts. We raised antibodies against mouse TN-X fragments expressed in bacteria and used these antibodies to identify the TN-X protein in heart cell extracts and in the conditioned medium of a renal carcinoma cell line. The subunit molecular size of TN-X is approximately 500 kD, suggesting that the protein may contain up to 40 fibronectin type III repeats, making it the largest tenascin family member known yet. TN-X in conditioned medium, as well as the purified protein bind to heparin, but no binding to tenascin-C (TN-C), fibronectin, laminin or collagens could be detected. Thus the heparin-binding activity may be a common feature of the tenascins. The TN-X mRNA as well as the protein are predominantly expressed in heart and skeletal muscle, but the mRNA is found in most tissues at a low level. Immunostaining showed the protein to be associated with the extracellular matrix of the muscle tissues and with blood vessels in all of the tissues analyzed. Although the TN-X gene lies in the MHC class III locus, it is not expressed in the lymphoid organs analyzed, except for the staining around blood vessels. In skin and tissues of the digestive tract often a reciprocal distribution of TN-X and TN-C was observed.

Tenascin-X: a novel extracellular matrix protein encoded by the human XB gene overlapping P450c21B

A human gene termed XB overlaps the P450c21B gene encoding steroid 21-hydroxylase and encodes a protein that closely resembles extracellular matrix proteins. Sequencing of phage and cosmid clones and of cDNA fragments shows that the XB gene spans 65 kb of DNA, consisting of 39 exons that encode a 12-kb mRNA. The predicted protein of over 400 kD consists of five distinct domains: a signal peptide, a hydrophobic domain containing three heptad repeats, a series of 18.5 EGF-like repeats, 29 fibronectin type III repeats, and a carboxy-terminal fibrinogen-like domain. Because the structure of the protein encoded by the XB gene closely resembles tenascin, we term this protein tenascin-X (TN-X), and propose a simplified nomenclature system for the family of tenascins. RNase protection experiments show that the TN-X transcript is expressed ubiquitously in human fetal tissues, with the greatest expression in the fetal testis and in fetal skeletal, cardiac, and smooth muscle. Two adrenal-specific transcripts, P450c21B (steroid 21-hydroxylase) and Y (an untranslated transcript) overlap the XB gene on the complementary strand of DNA, yielding a unique array of overlapping transcripts: a "polygene." In situ hybridization histochemistry experiments show that the TN-X transcript and the P450c21 and Y transcripts encoded on the complementary DNA strand are all expressed in the same cells of the human adrenal cortex. Genetic data suggest that TN-X may be essential for life.

Carboxy-terminal-extended variant of the human fibrinogen alpha subunit: a novel exon conferring marked homology to beta and gamma subunits

Similarities between the N-terminal regions of the three subunits of the clotting protein fibrinogen--(alpha beta gamma)2--suggest that they evolved from a common progenitor. However, to date no human alpha chain has been found with the strong C-terminal homology shared by the beta and gamma chains. Here we examine the natural product of a novel fibrinogen alpha chain transcript bearing a separate open reading frame that supplies the missing C-terminal homology to the other chains. Additional splicing leads to the use of this extra sequence as a sixth exon elongating the alpha chain by 35%. Since the extended alpha chain (alpha E) is assembled into fibrinogen molecules and its synthesis is enhanced by interleukin-6, it suggests participation in both the acute phase response and normal physiology.

A detailed consideration of a principal domain of vertebrate fibrinogen and its relatives

Vertebrate fibrinogen is a complex multidomained protein, the structure of which has been inferred mainly from electron microscopy and amino acid sequence studies. Among its most prominent features are two terminal globules, moieties that are mostly composed of the carboxyl-terminal two-thirds of the beta and gamma chains. Sequences homologous to the latter segments are found in several other animal proteins, always as the carboxyl-terminal contributions. An alignment of 15 amino acid sequences from various fibrinogens and related proteins has been used to make judgments about secondary structure. The nature of amino acids at each position in the alignment was used to distinguish alpha helices and beta structure on the one hand from loops and turns on the other, and the resulting assignments compared with predictions of secondary structure by other methods. Additionally, constraints imposed by the locations of cystines, carbohydrate attachment residues, and proteinase-sensitive points provided further insights into the general organization of the postulated secondary structures. Other ancillary data, including the effects of bound calcium and the locations of labeled or variant residues, were also considered. An intriguing similarity to a portion of the recently reported structure of a calcium-dependent lectin is noted.

Maintenance of patency after vascular trauma by topical irrigation with a peptide homologous to the carboxy-terminus of the fibrinogen gamma chain

Synthetic peptides with amino acid sequences homologous to the carboxy-terminal sequence of the gamma chain of human fibrinogen were evaluated for their capacity to inhibit thrombus development. A 21-residue peptide effectively inhibited surface-mediated fibrin clot propagation in vitro. Since this effect was localized to the surface, we proceeded with in vivo evaluation, using site-specific topical application only. In a rat model of arterial trauma and microvascular repair, topical application of the 21-residue peptide significantly reduced the rate of thrombosis to 17%, as compared with a control rate of 83%; in comparison, a 12-residue homologue reduced the thrombosis rate only modestly to 61%, which was not significant compared with the control rate. These results indicate the feasibility of antithrombotic therapy with topically applied agents, an approach that may obviate the use of systemic anticoagulation in extremity-replantation surgery.