A Family of Non–Collagen-Based Cartilages in the Skeleton of the Sea Lamprey, Petromyzon marinus

Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans

Pharyngeal arches are a key innovation that likely contributed to the evolution of the jaws and braincase of vertebrates. It has long been hypothesized that the pharyngeal (branchial) arch evolved from an unjointed cartilaginous rod in vertebrate ancestors such as that in the nonvertebrate chordate amphioxus, but whether such ancestral anatomy existed remains unknown. The pharyngeal skeleton of controversial Cambrian animals called yunnanozoans may contain the oldest fossil evidence constraining the early evolution of the arches, yet its correlation with that of vertebrates is still disputed. By examining additional specimens in previously unexplored techniques (for example, x-ray microtomography, scanning and transmission electron microscopy, and energy dispersive spectrometry element mapping), we found evidence that yunnanozoan branchial arches consist of cellular cartilage with an extracellular matrix dominated by microfibrils, a feature hitherto considered specific to vertebrates. Our phylogenetic analysis provides further support that yunnanozoans are stem vertebrates.

Identification of a unique lamprey gene with tandemly repeated sequences and pharyngeal chondrocyte-specific expression

Recent studies have revealed a common cartilage genetic regulatory network among vertebrates, cephalochordates, and arthropods. It has been proposed that this network was originally established for the dense connective tissues of ancestral invertebrates and subsequently recruited for chondrocyte differentiation in various lineages. This reasoning prompted questions about whether the evolution of cartilage from dense connective tissues occurred in the common ancestors of vertebrates. Alternatively, the evolution of cartilage may have occurred independently in agnathans and in gnathostomes, because extant agnathans (cyclostomes) are known to possess a matrix composition different from that of gnathostomes. Here, we identified the gene which is likely to encode one of the matrix proteins unique to lamprey cartilage, which we designated pharymprin. Pharymprin shows specific expression in larval pharyngeal chondrocytes. Like lamprins, which are the known matrix proteins of lamprey trabecular cartilage, pharymprin is also composed of repeated sequences. However, the repeated sequence is distinct from that of lamprins. The presence of two distinct matrix proteins in lamprey cartilage supports the hypothesis that true cartilage evolved independently in cyclostomes and gnathostomes.

Nitrogenous compounds characterized in the deterrent skin extract of migratory adult sea lamprey from the Great Lakes region

The sea lamprey (Petromzons marinus) is a devastating invasive species that represents a significant impediment to restoration of the Laurentian Great Lakes. There is substantial interest in developing environmentally benign control strategies for sea lamprey, and many other aquatic invasive species, that employ the manipulation of semiochemical information (pheromones and chemical cues) to guide the movements of invaders into control opportunities (e.g. traps, locations for safe pesticide application, etc.). A necessary precursor to the use of semiochemicals in conservation activities is the identification of the chemical constituents that compose the odors. Here, we characterize the major nitrogenous substances from the water-soluble fraction of a skin extract that contains the sea lamprey alarm cue, a powerful repellent that has proven effective in guiding the movements of migrating sea lamprey in rivers. Nitrogenous compounds are suspected components of fish alarm cues as the olfactory sensory neurons that mediate alarm responses transduce amino acids and related compounds. A laboratory assay confirmed the behavioral activity contained in the alarm cue resides in the water-soluble fraction of the skin extract. This water-soluble fraction consisted primarily of creatine (70%), heterocyclic nitrogenous compounds (4.3%) and free amino acids (18.4%), respectively. Among the free amino acids characterized in our study, essential amino acids constituted 13% of the water-soluble fraction. Free amino acids isolated from the water-soluble fraction composed of arginine, phenylalanine, threonine, and asparagine 3.9, 2.7, 2.6 and 2.4% of the water-soluble fraction, respectively. We discuss the implications of these findings for understanding the nature and use of the sea lamprey alarm cue in conservation activities.

The structure and micromechanics of elastic tissue

Elastin is a major component of tissues such as lung and blood vessels, and endows them with the long-range elasticity necessary for their physiological functions. Recent research has revealed the complexity of these elastin structures and drawn attention to the existence of extensive networks of fine elastin fibres in tissues such as articular cartilage and the intervertebral disc. Nonlinear microscopy, allowing the visualization of these structures in living tissues, is informing analysis of their mechanical properties. Elastic fibres are complex in composition and structure containing, in addition to elastin, an array of microfibrillar proteins, principally fibrillin. Raman microspectrometry and X-ray scattering have provided new insights into the mechanisms of elasticity of the individual component proteins at the molecular and fibrillar levels, but more remains to be done in understanding their mechanical interactions in composite matrices. Elastic tissue is one of the most stable components of the extracellular matrix, but impaired mechanical function is associated with ageing and diseases such as atherosclerosis and diabetes. Efforts to understand these associations through studying the effects of processes such as calcium and lipid binding and glycation on the mechanical properties of elastin preparations in vitro have produced a confusing picture, and further efforts are required to determine the molecular basis of such effects.

Decay of vertebrate characters in hagfish and lamprey (Cyclostomata) and the implications for the vertebrate fossil record

The timing and sequence of events underlying the origin and early evolution of vertebrates remains poorly understood. The palaeontological evidence should shed light on these issues, but difficulties in interpretation of the non-biomineralized fossil record make this problematic. Here we present an experimental analysis of decay of vertebrate characters based on the extant jawless vertebrates (Lampetra and Myxine). This provides a framework for the interpretation of the anatomy of soft-bodied fossil vertebrates and putative cyclostomes, and a context for reading the fossil record of non-biomineralized vertebrate characters. Decay results in transformation and non-random loss of characters. In both lamprey and hagfish, different types of cartilage decay at different rates, resulting in taphonomic bias towards loss of 'soft' cartilages containing vertebrate-specific Col2α1 extracellular matrix proteins; phylogenetically informative soft-tissue characters decay before more plesiomorphic characters. As such, synapomorphic decay bias, previously recognized in early chordates, is more pervasive, and needs to be taken into account when interpreting the anatomy of any non-biomineralized fossil vertebrate, such as Haikouichthys, Mayomyzon and Hardistiella.

Shared antigenicity between the polar filaments of myxosporeans and other Cnidaria

Nematocysts containing coiled polar filaments are a distinguishing feature of members of the phylum Cnidaria. As a first step to characterizing the molecular structure of polar filaments, a polyclonal antiserum was raised in rabbits against a cyanogen bromide-resistant protein extract of mature cysts containing spores of Myxobolus pendula. The antiserum reacted only with proteins associated with extruded polar filaments. Western blot and whole-mount immunohistochemical analyses indicated a conservation of polar filament epitopes between M. pendula and 2 related cnidarians, i.e., the anthozoan, Nematostella vectensis, and the hydrozoan, Hydra vulgaris. This conservation of polar filament epitopes lends further support to a shared affinity between Myxozoa and cnidarians.

Expression of Sox and fibrillar collagen genes in lamprey larval chondrogenesis with implications for the evolution of vertebrate cartilage

Lampreys possess unique types of cartilage in which elastin-like proteins are the dominant matrix component, whereas gnathostome cartilage is mainly composed of fibrillar collagen. Despite the differences in protein composition, the Sox-col2a1 genetic cascade was suggested to be conserved between lamprey pharyngeal cartilage and gnathostome cartilage. We examined whether the cascade is conserved in another type of lamprey cartilage, the trabecular cartilage. We found that SoxD and SoxE are expressed in both trabecular and pharyngeal cartilages. However, trabecular cartilage shows no clade A fibrillar collagen gene expression, including genes expressed in pharyngeal cartilage of this animal. On the basis of these observations, we propose that lampreys possess an ancestral type of cartilage that is similar to amphioxus gill cartilage, and in this respect, gnathostome cartilage can be regarded as derived for the loss of elastin-like protein as a cartilage component and recruitment of fibrillar collagen, which is included as a minor component in the ancestral cartilage, as the main component.

Sequences and domain structures of mammalian, avian, amphibian and teleost tropoelastins: Clues to the evolutionary history of elastins

Tropoelastin is the monomeric form of elastin, a polymeric extracellular matrix protein responsible for properties of extensibility and elastic recoil in connective tissues of most vertebrates. As an approach to investigate how sequence and structural characteristics of tropoelastin assist in polymeric assembly and account for the elastomeric properties of this polymer, and to better understand the evolutionary history of elastin, we have identified and characterized tropoelastins from frog (Xenopus tropicalis) and zebrafish (Danio rerio), comparing these to their mammalian and avian counterparts. Unlike other species, two tropoelastin genes were expressed in zebrafish. All tropoelastins shared a predominant and characteristic alternating domain arrangement, as well as the fundamental crosslinking sequence motifs. However, zebrafish and frog tropoelastins had several unusual characteristics, including increased exon numbers and protein molecular weights, and decreased hydropathies. For all tropoelastins there was evidence of evolutionary expansion of the proteins by extensive replication of a hydrophobic-crosslinking exon pair. This was particularly apparent for zebrafish and frog tropoelastin genes, where remnants of sequence similarity were also seen in introns flanking the replicated exon pair. While overall alignment of mammalian, avian, frog and zebrafish tropoelastin sequences was not possible because of sequence variability, the C-terminal exon was well-conserved in all species. In addition, good sequence alignment was possible for several exons just upstream of the putative region of replication, suggesting that these conserved domains may represent 'primordial' core sequences present in the ancestral sequence common to all tropoelastins and in some way essential to the structure/function of elastin.

Comparative equilibrium mechanical properties of bovine and lamprey cartilaginous tissues

In contrast to all other vertebrate cartilages, the major extracellular matrix protein of lamprey cartilages is not collagen. Instead, there exists a unique family of noncollagenous structural proteins, the significance of which is not completely understood. A custom-built uniaxial testing apparatus was used to quantify and compare equilibrium stress-relaxation behavior (equilibrium moduli, stress decay behavior, recovery times and relaxation times) of (1) lamprey pericardial cartilages with perichondria tested in tension (young adult and aged), (2) annular cartilages without perichondria tested in compression (young adult and aged) and (3) bovine auricular cartilage samples without perichondria tested in both tension and compression. Results of this study demonstrated that all cartilages were highly viscoelastic but with varying relaxation times; approximately 120 min for annular and pericardial cartilages and 30 min for bovine auricular cartilages. For mean equilibrium moduli, young adult lamprey annular cartilages (0.71 MPa) and pericardial cartilages (2.87 MPa) were found to be statistically different. The mean moduli of all bovine auricular cartilages were statistically identical to lamprey cartilages except in the case of aged adult pericardial cartilages, which were statistically larger than all other cartilages at 4.85 MPa. Taken together, the results of this study suggest that lamprey cartilages are able to exhibit mechanical properties largely similar to those of mammalian cartilages despite unique structural proteins and differences in extracellular matrix organization.

Origin and early evolution of vertebrate skeletonization

Data from living and extinct faunas of primitive vertebrates imply very different scenarios for the origin and evolution of the dermal and oral skeletal developmental system. A direct reading of the evolutionary relationships of living primitive vertebrates implies that the dermal scales, teeth, and jaws arose synchronously with a cohort of other characters that could be considered unique to jawed vertebrates: the dermoskeleton is primitively composed of numerous scales, each derived from an individual dental papilla; teeth are primitively patterned such that they are replaced in a classical conveyor-belt system. The paleontological record provides a unique but complementary perspective in that: 1) the organisms in which the skeletal system evolved are extinct and we have no recourse but to fossils if we aim to address this problem; 2) extinct organisms can be classified among, and in the same way as, living relatives; 3) a holistic approach to the incorporation of all data provides a more complete perspective on early vertebrate evolution. This combined approach is of no greater significance than in dealing with the origin of the skeleton and, combined with recent discoveries and new phylogenetic analyses, we have been able to test and reject existing hypotheses for the origin of the skeleton and erect a new model in their place.

The Mechanism of Hemolysis by Surfactants: Effect of Solution Composition

The effect of ionic strength, solute size, and osmolarity of the suspending solution on surfactant-induced erythrocyte hemolysis was studied. Two possible mechanisms of hemolysis were considered: osmotic lysis (affected by solute particle size) and solubilization (not affected by solute particle size). It was found that the ionic strength of the solution has a major effect on the hemolysis process, depending on the surfactant nature and concentration. An increase in the ionic strength lowers the rate of hemolysis induced by DTAB, and enhances SDS-induced hemolysis. Changes in ionic strength have little effect on hemolysis induced by Triton X-100. To explain these effects, it was assumed that the changes in ionic strength differently affect the adsorption of cationic and anionic surfactants to the membrane. The change in the amount of adsorbed surfactant either influences the rate of osmotic hemolysis by changing the membrane permeability or induces a transition from the osmotic mechanism to solubilization. These phenomena were observed for isotonic as well as hypertonic solutions.

Palaeobiology: calcification of early vertebrate cartilage

Hagfish and lampreys are unusual for modern vertebrates in that they have no jaws and their skeletons are neither calcified nor strengthened by collagen the cartilaginous elements of their endoskeleton are composed of huge, clumped chondrocytes (cartilage cells). We have discovered that the cartilage in a 370-million-year-old jawless fish, Euphanerops longaevus, was extensively calcified, even though its cellular organization was similar to the non-mineralized type found in lampreys. The calcification of this early lamprey-type cartilage differs from that seen in modern jawed vertebrates, and may represent a parallel evolutionary move towards a mineralized endoskeleton.

The elastin-like protein matrix of lamprey branchial cartilage is cross-linked by lysyl pyridinoline

The cranial skeleton of the lamprey, a primitive vertebrate, consists of cartilaginous structures that differ from vertebrate cartilages in having a noncollagenous extracellular matrix. Novel matrix proteins found in these cartilages include lamprin in the annular cartilage and an unidentified protein in the branchial cartilages. Both show biochemical similarities to elastin. The inextractability of these proteins, even to chemical cleavage by cyanogen bromide, indicates a polymer with extensive covalent cross-linking. Here we report on the type of cross-linking. Lysyl pyridinoline was found in high concentration in the elastin-like protein of lamprey branchial cartilage at a ratio of 7:1 to hydroxylysyl pyridinoline, the form that dominates in vertebrate collagens. Both forms of pyridinoline cross-link were absent from annular cartilage and desmosine cross-links, which are characteristic of vertebrate elastin, were not detected in either form of lamprey cartilage. Pyridinoline cross-links are considered to be characteristic of collagen, so their presence in an elastin-like protein in a primitive cartilage poses evolutionary questions about the tissue, the protein, and the cross-linking mechanism.

Development of dermal denticles in skates (Chondrichthyes, Batoidea): patterning and cellular differentiation

Patterning, cellular differentiation, and developmental sequences of dermal denticles (denticles) are described for the skate Leucoraja erinacea. Development of denticles proceeds caudo-rostrally in the tail and trunk. Once three rows of denticles form in the tail and trunk, denticles begin to appear in the region of the pelvic girdle, medio-caudal to the eyes and on the pectoral fins. Although timing of cellular differentiation of denticles differs among different locations of the body, cellular development of a denticle is identical in all locations. Thickening of the epidermis as a denticle lamina marks initiation of development. A single lamina for each denticle forms, and a small group of mesenchymal cells aggregates underneath it. The lamina then invaginates caudo-rostrally to form the inner- and outer-denticle epithelia (IDE and ODE, respectively). Before nuclei of IDE cells are polarized, enameloid matrix appears between the basement membrane of the IDE and the apical surface of the pre-odontoblasts. Pre-dentin is then laid down along with collagenous materials. Von Kossa stain visualizes initial mineralization of dentin, but not enameloid. During the growth of a denticle, dense fibrous connective tissue of the dermis forms the deep dermal tissue over the dorsal musculature. Attachment fibers and tendons anchor denticles and dorsal musculature, respectively, on deep dermal tissue. Basal tissue of the denticles develops as the denticle crown grows. If the basal tissue is bone of attachment, then the cells along the basal tissue would be osteoblasts. However, these cells could not be distinguished from odontoblasts using immunolocalization of type I pro-collagen (Col I), alkaline phosphatase (APase), and neural cell adhesion molecule (N-CAM). Well-developed dentin, (not pre-dentin), the enameloid matrix (probably when it begins to mineralize), and deep dermal tissue are Verhoeff stain-positive, suggesting that these tissues contain elastin and/or elastin-like molecules. Our study demonstrates that the cellular development of denticles resembles tooth development in elasmobranchs, but that dermal denticles differ from teeth in forming from a single denticle lamina. Whether the basal tissue of denticles is bone of attachment remains undetermined. Confirmation and function of Verhoeff-positive proteins in enameloid, dentin, and deep dermal tissue remain to be determined. We discuss these issues along with an analysis of recent findings of enamel and enameloid matrices.