Characterizations of sea urchin fibrillar collagen and its cDNA clone

Identification of new skeletogenic genes of the sea urchin embryo by use of conserved sequence motifs among the SM50 gene family

Spicule formation in the sea urchin is one of the conspicuous cellular processes occurring in early embryo-genesis, in which stereotyped spicules form through deposition of minerals onto the spicule matrix protein scaffold. This process requires many genes to be functional: the spicule matrix alone needs more than 50 different genes. Until now, however, only a few skeletogenic genes have been known. Recently SM37, a new putative spicule matrix protein gene, was cloned and found to be linked to SM50 (Lee et al., 1999). The structure of the new gene raised the possibility of the presence of a gene family involved in skeletogenesis which consists of SM50, SM37 and LSM34 (a homologue of SM50) (Benson et al., 1987; Livingston et al., 1991). Characteristics of the gene family include: (1) skeletongenic mesenchyme-specific expression, (2) onset of gene expression as early as the mesenchyme blastula, (3) presence of glycine, proline and glutamine-rich repeats in the middle of the proteins. Another feature of the family is the presence of conserved sequence motifs at both the amino-terminal and carboxyl-terminal regions of the proteins – SCYR(A/Y)F and PNPXXXRPRM(L/Y)QE, respectively – which we speculate play a role in protein guidance.

Production, characterization and biocompatibility of marine collagen matrices from an alternative and sustainable source: the sea urchin Paracentrotus lividus

Collagen has become a key-molecule in cell culture studies and in the tissue engineering field. Industrially, the principal sources of collagen are calf skin and bones which, however, could be associated to risks of serious disease transmission. In fact, collagen derived from alternative and riskless sources is required, and marine organisms are among the safest and recently exploited ones. Sea urchins possess a circular area of soft tissue surrounding the mouth, the peristomial membrane (PM), mainly composed by mammalian-like collagen. The PM of the edible sea urchin Paracentrotus lividus therefore represents a potential unexploited collagen source, easily obtainable as a food industry waste product. Our results demonstrate that it is possible to extract native collagen fibrils from the PM and produce suitable substrates for in vitro system. The obtained matrices appear as a homogeneous fibrillar network (mean fibril diameter 30-400 nm and mesh < 2 μm) and display remarkable mechanical properties in term of stiffness (146 ± 48 MPa) and viscosity (60.98 ± 52.07 GPa·s). In vitro tests with horse pbMSC show a good biocompatibility in terms of overall cell growth. The obtained results indicate that the sea urchin P. lividus can be a valuable low-cost collagen source for mechanically resistant biomedical devices.

Mutable collagenous tissue: overview and biotechnological perspective

The mutable collagenous tissue (MCT) of echinoderms can undergo extreme changes in passive mechanical properties within a timescale of less than 1 s to a few minutes, involving a mechanism that is under direct neural control and coordinated with the activities of muscles. MCT occurs at a variety of anatomical locations in all echinoderm classes, is involved in every investigated echinoderm autotomy mechanism, and provides a mechanism for the energy-sparing maintenance of posture. It is therefore crucially important for the biology of extant echinoderms. This chapter summarises current knowledge of the physiology and organisation of MCT, with particular attention being given to its molecular organisation and the molecular mechanism of mutability. The biotechnological potential of MCT is discussed. It is argued that MCT could be a source of, or inspiration for, (1) new pharmacological agents and strategies designed to manipulate therapeutically connective tissue mechanical properties and (2) new composite materials with biomedical applications.

Distinct maturations of N-propeptide domains in fibrillar procollagen molecules involved in the formation of heterotypic fibrils in adult sea urchin collagenous tissues

We have characterized the primary structure of a new sea urchin fibrillar collagen, the 5alpha chain, including nine repeats of the sea urchin fibrillar module in its N-propeptide. By Western blot and immunofluorescence analyses, we have shown that 5alpha is co-localized in adult collagenous ligaments with the 2alpha fibrillar collagen chain and fibrosurfin, two other extracellular matrix proteins possessing sea urchin fibrillar modules. At the ultrastructural level, the 5alpha N-propeptide is detected at the surface of fibrils, suggesting the retention of this domain in mature collagen molecules. Biochemical characterization of pepsinized collagen molecules extracted from the test tissue (the endoskeleton) together with a matrix-assisted laser desorption ionization time-of-flight analysis allowed us to determine that 5alpha is a quantitatively minor fibrillar collagen chain in comparison with the 1alpha and 2alpha chains. Moreover, 5alpha forms heterotrimeric molecules with two 1alpha chains. Hence, as in vertebrates, sea urchin collagen fibrils are made up of quantitatively major and minor fibrillar molecules undergoing distinct maturation of their N-propeptide regions and participating in the formation of heterotypic fibrils.

Localization and association to cytoskeleton of COLL1alpha mRNA in Paracentrotus lividus egg requires cis- and trans-acting factors

COLL1alpha mRNA is asymmetrically distributed in the Paracentrotus lividus egg. Here we examine the involvement of the cytoskeleton in the localization process of collagen mRNA. The use of drugs such as colchicine and cytochalasin B reveals a perturbation of localization collagen mRNA. Moreover, the presence of specific cis-and trans-acting factors involved in cytoskeleton binding and the localization process was investigated. By Northwestern experiment we found that the 3'UTR of COLL1alpha mRNA is also able to bind two proteins of 54 and 40 kDa in a cellular fraction containing the cytoskeleton. Finally, we found that the protein of 54 kDa is LP54, a protein that binds the 3'UTRs of P. lividus maternal bep messengers and is necessary for their localization.

Sea urchin fibrillar collagen 2alpha chain participates in heterotrimeric molecules of (1alpha)(2)2alpha stoichiometry

In sea urchin, two fibrillar collagen chains (alpha1 and alpha2) have been characterized by molecular biology while two biochemically detected chains (alpha1 and alpha2) have been reported. Here, to determine the relationship between these results, Western-blotting and Edman degradation sequencing of the amino-termini of pepsinized sea urchin fibrillar collagen chains were performed. The data demonstrate that the 2alpha chain corresponds to the alpha2 chain and is involved in the formation of heterotrimeric molecules [(1alpha)(2)2alpha].

Cell-substrate interactions during sea urchin gastrulation: migrating primary mesenchyme cells interact with and align extracellular matrix fibers that contain ECM3, a molecule with NG2-like and multiple calcium-binding domains

The migratory primary mesenchyme cells (PMCs) of the sea urchin embryo are a model experimental system for the analysis of cell-extracellular matrix (ECM) interactions. Although the behavior of PMCs during gastrulation has been analyzed in considerable detail, it has proven difficult to identify specific substrate molecules with which these cells interact. Here, using a new monoclonal antibody (2.5C4) generated by an in vitro immunization procedure, we show that migrating PMCs interact with a distinct class of ECM fiber. The 2.5C4-positive fibers are distributed in a vegetal (high) to animal (low) gradient on the basal surface of the ectoderm. Three observations indicate that PMC filopodia interact directly with the fibers: (1) During gastrulation, 2.5C4-positive fibers gradually become oriented in a prominent circumferential belt that corresponds precisely to the position of the subequatorial PMC ring. (2) This fiber pattern is blocked by microsurgical removal of PMCs but is restored if PMCs are reintroduced into the embryo. (3) Examination of immunostained embryo whole mounts by confocal microscopy reveals a striking association between PMC filopodial roots and foci of fiber bundling. Double-immunostaining experiments using 2.5C4 and antibodies against previously identified matrix constituents show that the protein ECM3 is a component of the fibers. We have determined the complete amino acid sequence of ECM3 and find that this large protein (3103 amino acids) consists of an N-terminal domain similar to the mammalian chondroitin sulfate proteoglycan core protein NG2, a central region composed of five tandem repeats of a domain contained within the regulatory Ca2+-binding loop of Na+-Ca2+ exchange proteins, and a C-terminal region with no homology to known proteins. The general structure of ECM3 is similar in several respects to that of a sponge protein, MAFp4. MAFp4 is a major component of aggregation factor, an ECM complex that mediates the calcium-dependent, species-specific sorting of sponge cells. These studies establish ECM3 as a strong candidate for a PMC substrate molecule and point to several possible mechanisms by which interactions between PMC filopodia and ECM3-containing fibers could provide guidance information to migrating PMCs.

Abalone collagens: immunological properties and seasonal changes of their mRNA levels

The antisera were raised against pepsin-solubilized abalone collagen and its corresponding gelatin. The reactivity against abalone collagen was higher with the anti-collagen than anti-gelatin antiserum. The two antisera recognized all type I collagens from various vertebrates, whereas these had no reactivity against vertebrate type III and type V collagens. Furthermore, both antisera reacted with only alpha 2(I) chains from chicken, rat, and calf. The strong reactivity was observed against the two antisera in the case of invertebrate and protochordate collagens, especially for turban shell collagen. The seasonal changes of collagen mRNA levels were examined in relation to those of collagen content. Haliotis discus collagens (Hdcols) 1 alpha and 2 alpha coding for abalone collagen pro alpha-chains showed quite similar patterns. The highest mRNA levels in adductor and foot muscles for the two collagens were observed in December and January, in good agreement with the increase of collagen content. The mRNA levels decreased in July and August when collagen content decreased. These results indicate that collagen transcription levels are closely related to collagen contents.

Phosphorylation-dependent regulation of skeletogenesis in sea urchin micromere-derived cells and embryos

Sea urchin embryo micromeres when isolated and cultured in vitro differentiate to produce spicules. Although several authors have used this model, almost nothing is known about the signaling pathways responsible for initiating skeletogenesis. In order to investigate the potential involvement of phosphorylation events in spiculogenesis, the effect of inhibitors of protein kinases and phosphatases on skeleton formation was studied. Results obtained using both cultured micromeres and embryos revealed that protein tyrosine kinase and phosphatase inhibitors blocked skeleton formation, but not serine/threonine phosphatase inhibitors. The inhibitors showed a dose-dependent effect and when removed from micromere or embryo culture, spicule formation resumed. Inhibition of tyrosine phosphatases resulted in an increase in the tyrosine phosphorylation level of two major proteins and a modest decrease in the expression of the mRNA coding for type I fibrillar collagen. These findings strongly suggest that tyrosine phosphorylation and dephosphorylation is required for micromere differentiation and for normal skeletogenesis during sea urchin embryo development.

The occurrence of two types of collagen proalpha-chain in the abalone Haliotis discus muscle

Acid-soluble collagens were prepared from connective tissues in the abalone Haliotis discus foot and adductor muscles with limited proteolysis using pepsin. Collagen preparation solubilized with 1% pepsin contained two types of alpha-chains which were different in their N-terminal amino acid sequences. Accordingly, two types of full-length cDNAs coding for collagen proalpha-chains were isolated from the foot muscle of the same animal and these proteins were named Hdcols (Haliotis discus collagens) 1alpha and 2alpha. The two N-terminal amino acid sequences of the abalone pepsin-solubilized collagen preparation corresponded to either of the two sequences deduced from the cDNA clones. In addition, several tryptic peptides prepared from the pepsin-solubilized collagen and fractionated by HPLC showed N-terminal amino acid sequences identical to those deduced from the two cDNA clones. Hdcols 1alpha and 2alpha consisted of 1378 and 1439 amino acids, respectively, showing the primary structure typical to those of fibril-forming collagens. The N-terminal propeptides of the two collagen proalpha-chains contained cysteine-rich globular domains. It is of note that Hdcol 1alpha completely lacked a short Gly-X-Y triplet repeat sequence in its propeptide. An unusual structure such as this has never before been reported for any fibril-forming collagen. The main triple-helical domains for both chains consisted of 1014 amino acids, where a supposed glycine residue in the triplet at the 598th position from the N-terminus was replaced by alanine in Hdcol 1alpha and by serine in Hdcol 2alpha. Both proalpha-chains of abalone collagens contained six cysteine residues in the carboxyl-terminal propeptide, lacking two cysteine residues usually found in vertebrate collagens. Northern blot analysis demonstrated that the mRNA levels of Hdcols 1alpha and 2alpha in various tissues including muscles were similar to each other.

Cloning and characterization of the full length cDNA encoding alpha2 type I collagen of bullfrog Rana catesbeiana

The present study determined nucleotide sequences of the full-length cDNA of alpha2 chain of bullfrog type I collagen. Hybridization of a bullfrog cDNA library with human alpha1 type I collagen cDNA yielded a clone named 6A-1 which was 3449 bp long and lacked a 5' region of the gene. A 5' region containing the translation initiation site was amplified by the reverse transcription polymerase chain reaction using poly(A)+RNA from tadpole tail tissues as template, and oligonucleotides encoding the translation initiation region of mammalian fibrillar collagens and the Gly-X-Y repeat region of clone 6A-1 as primers. As a result we obtained a 1518 bp long clone Y31. A 355 bp long clone Y31-9 was produced by extending clone Y31 from its ATG codon to a 127 bp upstream region. Combining these three clones, the complete nucleotide sequence of the full-length cDNA was determined which contained 4692 bp as a whole and 4065 bp in the open reading frame. The comparison of its structure with known collagen cDNAs of various vertebrates showed that the cDNA obtained codes for alpha2(I) chain of bullfrog. Its deduced amino acid sequence revealed the complete conservation of seven cysteine residues in the C-propeptide and three lysine residues in the N-telopeptide through the helical domain. Northern blot analysis revealed that the thyroid hormone regulated the expression of alpha2(I) collagen in an organ-dependent manner: intense up-regulation in the back skin and intestine, weak and transient up-regulation in the liver, and initial down-regulation, but later up-regulation in the tail. Prolactin increased its expression in both the back skin and tail. These results suggested that the expression of bullfrog alpha2(I) collagen is cooperatively regulated by these two metamorphosis-regulating hormones.

Comparative analysis of fibrillar and basement membrane collagen expression in embryos of the sea urchin, Strongylocentrotus purpuratus

The time of appearance and location of three distinct collagen gene transcripts termed 1 alpha, 2 alpha, and 3 alpha, were monitored in the developing S. purpuratus embryo by in situ hybridization. The 1 alpha and 2 alpha transcripts of fibrillar collagens were detected simultaneously in the primary (PMC) and secondary (SMC) mesenchyme cells of the late gastrula stage and subsequently expressed in the spicules and gut associated cells of the pluteus stage. The 3 alpha transcripts of the basement membrane collagen appeared earlier than 1 alpha and 2 alpha, and were first detected in the presumptive PMC at the vegetal plate of the late blastula stage. The PMC exhibited high expression of 3 alpha at the mesenchyme blastula stage, but during gastrulation the level of expression was reduced differentially among the PMC. In the late gastrula and pluteus stages, both PMC and SMC expressed 3 alpha mRNA, and thus at these stages all three collagen genes displayed an identical expression pattern by coincidence. This study thus provides the first survey of onset and localization of multiple collagen transcripts in a single sea urchin species.

Comparative biochemical analysis of sea urchin peristome and rat tail tendon collagen

We report here a biochemical comparison between type 1 rat tail tendon collagen and collagen isolated from sea urchin peristome tissue. The sea urchin collagen consisted of two species of apparent mol masses, 140 and 116 kDa. Amino acid compositional analysis of the 140 and 116 kDa species revealed the presence of hydroxyproline and hydroxylysine as well as a glycine content of 28.1 mol.%. In solubility experiments the rat tail tendon collagen was found to precipitate at sodium chloride concentrations between 1 and 2 M while peristome collagen remained soluble at salt concentrations as high as 4 M. Incubation of the peristome and rat tail tendon collagen preparations with a sea urchin collagenase/gelatinase resulted in cleavage of the former but not the latter collagen. Upon heat denaturation at 60 degrees C, however, the rat tail tendon collagen served as a substrate for the gelatinase. Cyanogen bromide cleavage of rat tail and peristome collagens generated largely unique peptide maps. Collectively, these results suggest that structural differences exist between echinoderm and vertebrate type 1 collagens.

Cloning of an annelid fibrillar-collagen gene and phylogenetic analysis of vertebrate and invertebrate collagens

Arenicola marina possesses cuticular and interstitial collagens, which are mostly synthesised by its epidermis. A cDNA library was constructed from the body wall. This annelid cDNA library was screened with a sea-urchin-collagen cDNA probe, and several overlapping clones were isolated. Nucleotide sequencing of these clones revealed an open reading frame of 2052 nucleotides. The translation product exhibits a triple helical domain of 138 Gly-Xaa-Yaa repeats followed by a 269-residue-long C-terminal non-collagenous domain (C-propeptide). The triple helical domain exhibits an imperfection that has been previously described in a peptide produced by cyanogen bromide digestion (CNBr peptide) of A. marina interstitial collagen. This imperfection occurs at the same place in the interstitial collagen of the vestimentiferan Riftia pachyptila. This identifies the clone as coding for the C-terminal part of a fibrillar collagen chain. It was called FAm1alpha, for fibrillar collagen 1alpha chain of A. marina. The non-collagenous domain possesses a structure similar to carboxy-terminal propeptides of fibrillar pro-alpha chains. Only six conserved cysteine residues are observed in A. marina compared with seven or eight in all other known C-propeptides. This provides information on the importance of disulfide bonds in C-propeptide interactions and in the collagen-assembly process. Phylogenetic studies indicate that the fibrillar collagen 1alpha chain of A. marina is homologous to the R. pachyptila interstitial collagen and that the FAm1alpha gene evolved independently from the other alpha-chain genes. Complementary analyses indicate that the vertebrate fibrillar collagen family is composed of two monophyletic subgroups with a specific position of the collagen type-V chains.

Collagen fibrillogenesis during sea urchin development--retention of SURF motifs from the N-propeptide of the 2alpha chain in mature fibrils

The sea urchin 2alpha fibrillar collagen chain has a unique amino-propeptide structure with several repetitions of a still unknown 140-145-amino-acid, four-Cys module called SURF (for sea urchin fibrillar module). To follow the expression of the amino-propeptide of the 2alpha chain and assign a function to this domain, we have overproduced in Escherichia coli several recombinant proteins corresponding either to the amino-propeptide or to the amino-telopeptide. Monoclonal and/or polyclonal antibodies against these recombinant proteins allowed us to observe a similar tissue distribution during the first stages of development. A signal is first observed at the prism stage as intracellular spots in mesenchymal cells. In plutei, immunofluorescence staining is observed around the skeleton spicules and as a thin meshwork surrounding the mesenchymal cells. At the ultrastructural level, and using antibodies against the amino-propeptide, gold particles are observed at the surface of 25 nm thin periodic fibrils. By rotary shadowing, these fibrils show a brush-bottle aspect, exhibiting at their surface numerous periodically distributed thin rods ended by a small globule. These data indicate that the amino-propeptide is maintained during fibrillogenesis. As previously suggested, the retention of the amino-propeptide could play an important role in regulation of the fibril growth. We propose that the important region of this amino-propeptide in the widely encountered 25-nm-diameter fibrils is the short triple-helical segment. The globular part of the amino-propeptide will not only restrict the fibril growth but also interact with other neighbouring components and playing, as suspected from our immunofluorescence studies, a function during the spiculogenesis of the sea urchin embryo.