28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes

Resolving the interrelationships of three major extant lineages of vertebrates (hagfishes, lampreys, and gnathostomes) is a particularly important issue in evolution, because the basal resolution critically influences our understanding of primitive vertebrate characters. A consensus has emerged over the last 20 years that lampreys are the sister group to the gnathostomes and the hagfishes represent an ancient, basal lineage. This hypothesis has essentially displaced the classical hypothesis of monophyly of the cyclostomes (lampreys plus hagfishes). To test these hypotheses, we compared nearly complete ribosomal DNA sequences from each of these major lineages, as well as those from a cephalochordate and a urochordate, which represent a paraphyletic outgroup for assessing the basal vertebrate relationships. For this comparison, 92%-99% complete 28S rDNA sequences were obtained from the lancelet Branchiostoma floridae, the hagfish Eptatretus stouti, the lamprey Petromyzon marinus, and cartilaginous fishes Hydrolagus colliei and Squalus acanthias and were then analyzed with previously reported 28S and 18S rDNA sequences from other chordates. We conducted conventional (nonparametric) bootstrap analyses, under maximum-likelihood, parsimony, and minimum-evolution (using LogDet distances) criteria, of both 28S and 18S rDNA sequences considered separately and combined. All these analyses provide moderate to very strong support for the monophyly of the cyclostomes. Furthermore, the currently accepted hypothesis of a lamprey-gnathostome clade is moderately rejected by the Kishino-Hasegawa test (P = 0.099) and resoundingly rejected by parametric bootstrap tests (P < 0.01) in favor of monophyly of living cyclostomes. Another significant finding is that the hagfish E. stouti has the longest 28S rDNA gene known in any organism (> 5,200 nt).

Lamprey Dlx genes and early vertebrate evolution

Gnathostome vertebrates have multiple members of the Dlx family of transcription factors that are expressed during the development of several tissues considered to be vertebrate synapomorphies, including the forebrain, cranial neural crest, placodes, and pharyngeal arches. The Dlx gene family thus presents an ideal system in which to examine the relationship between gene duplication and morphological innovation during vertebrate evolution. Toward this end, we have cloned Dlx genes from the lamprey Petromyzon marinus, an agnathan vertebrate that occupies a critical phylogenetic position between cephalochordates and gnathostomes. We have identified four Dlx genes in P. marinus, whose orthology with gnathostome Dlx genes provides a model for how this gene family evolved in the vertebrate lineage. Differential expression of these lamprey Dlx genes in the forebrain, cranial neural crest, pharyngeal arches, and sensory placodes of lamprey embryos provides insight into the developmental evolution of these structures as well as a model of regulatory evolution after Dlx gene duplication events.

Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group

Lampreys and hagfishes (cyclostomes) traditionally were considered to be a natural (monophyletic) group. Recently, the consensus of opinion, based largely on morphological analyses, has shifted to a view that lampreys are more closely related to jawed vertebrates (gnathostomes) than to hagfishes. Phylogenetic comparisons of 18S ribosomal RNA sequences from two hagfishes, two lampreys, a tunicate, a lancelet, and a number of gnathostomes support the monophyly of the cyclostomes. These data force a reassessment of several features of early vertebrate evolution.

The complete nucleotide sequence of the mitochondrial genome of the lungfish (Protopterus dolloi) supports its phylogenetic position as a close relative of land vertebrates

The complete DNA sequence (16,646 bp) of the mitochondrial genome of the African lungfish, Protopterus dolloi, was determined. The evolutionary position of lungfish as possibly the closest living relative among fish of land vertebrates made its mitochondrial DNA sequence particularly interesting. Its mitochondrial gene order conforms to the consensus vertebrate gene order. Several sequence motifs and secondary structures likely involved in the regulation of the initiation of replication and transcription of the mitochondrial genome are conserved in the lungfish and are more similar to those of land vertebrates than those of ray-finned fish. A novel feature discovered is that the putative origin of L-strand replication partially overlaps the adjacent tRNA(Cys). The phylogenetic analyses of genes coding for tRNAs and proteins confirm the intermediate phylogenetic position of lungfish between ray-finned fishes and tetrapods. The complete nucleotide sequence of the African lungfish mitochondrial genome was used to estimate which mitochondrial genes are most appropriate to elucidate deep branch phylogenies. Only a combined set of either protein or tRNA mitochondrial genes (but not each gene alone) is able to confidently recover the expected phylogeny among vertebrates that have diverged up to but not over approximately 400 mya.

On the origin of the olfactory receptor family: receptor genes of the jawless fish (Lampetra fluviatilis)

In vertebrates, recognition of odorous compounds is based on a large repertoire of receptor subtypes encoded by a multigene family. Towards an understanding of the phylogenetic origin of the vertebrate olfactory receptor family, attempts have been made to identify related receptor genes in the river lampreys (Lampetra fluviatilis), which are descendants of the earliest craniates and living representatives of the most ancient vertebrates. Employing molecular cloning approaches led to the discovery of four genes encoding heptahelical receptors, which share only a rather low overall sequence identity but several of the characteristic structural hallmarks with vertebrate olfactory receptors. Furthermore, in situ hybridization studies demonstrated that the identified genes are expressed in chemosensory cells of the singular lamprey olfactory organ. Molecular phylogenetic analysis confirmed a close relationship of the lamprey receptors to vertebrate olfactory receptors and in addition demonstrated that olfactory genes of the agnathostomes diverged from the gnathostome receptor genes before those split into class I and class II receptors. The data indicate that the lamprey receptors represent the most ancient family of the hitherto identified vertebrate olfactory receptors.

A lamprey from the Cretaceous Jehol biota of China

Widespread nowadays in freshwater and coastal seas of the cold and temporal zones, lampreys are a jawless vertebrate group that has been in existence for more than 300 million years but left a meagre fossil record. Only two fossil lamprey species, namely Mayomyzon pieckoensis and Hardistiella montanensis, have been recognized with certainty from North American Carboniferous marine deposits. Here we report a freshwater lamprey from the Early Cretaceous epoch (about 125 million years ago) of Inner Mongolia, China. The new taxon, Mesomyzon mengae, has a long snout, a well-developed sucking oral disk, a relatively long branchial apparatus showing branchial basket, seven gill pouches, gill arches and impressions of gill filaments, about 80 myomeres and several other characters that are previously unknown or ambiguous. Our finding not only indicates Mesomyzon's closer relationship to extant lampreys but also reveals the group's invasion into a freshwater environment no later than the Early Cretaceous. The new material furthers our understanding of ancient lampreys, bridges the gap between the Carboniferous ones and their recent relatives, and adds to our knowledge of the evolutionary history of lampreys.

Molecular cloning, tissue distribution, and developmental expression of lamprey transthyretins

We isolated and cloned full-length cDNAs of transthyretin (TTR) from 2 genera of lamprey, Petromyzon marinus and Lampetra appendix. These sequences represent the first report of TTR sequences in vertebrates basal to teleost fishes. The deduced amino acid sequence of lamprey TTR cDNAs showed 36-47% identity with those from other vertebrates; secondary structure predictions and homology-based modeling were both consistent with TTRs from other vertebrates, and these cDNAs lacked the signatures found in TTR-like sequences of non-vertebrates. Of evolutionary interest is the observation that the N-termini of the lamprey TTR subunits are nine amino acids longer than those of eutherian TTRs and four to six amino acids longer than those from all other vertebrates. Sequencing of intron 1 confirmed that this longer N-terminal region is a result of the position of the intron 1/exon 2 splice site, further supporting previous studies. TTR mRNA was detected in a variety of larval lamprey tissues, with the highest levels found in the liver. TTR mRNA was also readily detected by Northern blotting, in the livers of animals at all phases of the lifecycle and was significantly elevated during metamorphosis. The upregulation of lamprey TTR gene expression during a major developmental event is consistent with observations in other vertebrates. In all other vertebrates studied to date, the transient upregulation of TTR gene expression or some other thyroid hormone distributor protein coincides with, and is thought to facilitate, the surge in serum thyroid hormone concentrations required for normal development. However, in lampreys, the upregulation of TTR gene expression occurs when serum thyroid hormone concentrations are at their lowest.

Ectoparasites and classification

The authors present an introductory overview of the principal groups of ectoparasites (flukes, leeches, crustaceans, insects, arachnids, lampreys and vampire bats) associated with domestic animals. Currently-accepted higher-level classifications are outlined for these parasites. Almost all significant ectoparasites of domestic animals are invertebrates, the majority being arthropods (crustaceans, insects and arachnids). Some of these ectoparasites are of particular importance as vectors of pathogens. Many ectoparasite species are host-specific, and vector species typically transmit characteristic pathogens.

Cloning and characterization of a functional type II gonadotropin-releasing hormone receptor with a lengthy carboxy-terminal tail from an ancestral vertebrate, the sea lamprey

A full-length transcript encoding a functional type II GnRH receptor was cloned from the pituitary of the sea lamprey, Petromyzon marinus. The current study is the first to identify a pituitary GnRH receptor transcript in an agnathan, which is the oldest vertebrate lineage. The cloned receptor retains the conserved structural features and amino acid motifs of other known GnRH receptors and notably includes a C-terminal intracellular tail of approximately 120 amino acids, the longest C-terminal tail of any vertebrate GnRH receptor identified to date. The lamprey GnRH receptor was shown to activate the inositol phosphate (IP) signaling system; stimulation with either lamprey GnRH-I or lamprey GnRH-III led to dose-dependent responses in transiently transfected COS7 cells. Furthermore, analyses of serially truncated lamprey GnRH receptor mutants indicate perturbations of the C-terminal tail disrupts IP accumulation, however, the tailless lamprey GnRH receptor was not only functional but was also capable of stimulating IP levels equal to wild type. Expression of the receptor transcript was demonstrated in the pituitary and testes using RT-PCR, whereas in situ hybridization showed expression and localization of the transcript in the proximal pars distalis of the pituitary. The phylogenetic placement and structural and functional features of this GnRH receptor suggest that it is representative of an ancestral GnRH receptor. In addition to having an important role in lamprey reproductive processes, the extensive C-terminal tail of this lamprey GnRH receptor may have great significance for understanding the evolutionary change of this vital structural feature within the GnRH receptor family.

Macrophage migration inhibitory factor (MIF) of jawed and jawless fishes: implications for its evolutionary origin

The macrophage migration inhibitory factor (MIF) is a cytokine produced by T lymphocytes and macrophages in response to inflammatory stimuli. We sequenced MIF cDNA clones of two jawless fishes, the sea lamprey (Petromyzon marinus) and the North Atlantic hagfish (Myxine glutinosa), as well as of the jawed (cichlid) fish Paralabidochromis chilotes. The fish MIF-encoding genes have the same exon-intron organization as the mammalian MIF genes and are present in one copy per haploid genome. Secondary and tertiary structure predictions suggest that the fish MIF proteins have a topology characteristic of the entire MIF-family of proteins. Phylogenetic analysis separates the known nematode members of the family into two groups, one having a sister group relationship with the mammalian D-dopachrome tautomerase (DDT) proteins and the other being related to vertebrate MIFs. It also reveals a high degree of convergent evolution among the members of the family. Finally, it suggests that the divergence of MIF and DDT occurred before the emergence of nematodes in metazoan evolution.

European Lampreys: New Insights on Postglacial Colonization, Gene Flow and Speciation

Ice ages are known to be the most dominant palaeoclimatic feature occurring on Earth, producing severe climatic oscillations and consequently shaping the distribution and the population structure of several species. Lampreys constitute excellent models to study the colonization of freshwater systems, as they commonly appear in pairs of closely related species of anadromous versus freshwater resident adults, thus having the ability to colonize new habitats, through the anadromous species, and establish freshwater resident derivates. We used 10 microsatellite loci to investigate the spatial structure, patterns of gene flow and migration routes of Lampetra populations in Europe. We sampled 11 populations including the migratory L. fluviatilis and four resident species, L. planeri, L. alavariensis, L. auremensis and L. lusitanica, the last three endemic to the Iberian Peninsula. In this southern glacial refugium almost all sampled populations represent a distinct genetic cluster, showing high levels of allopatric differentiation, reflecting long periods of isolation. As result of their more recent common ancestor, populations from northern Europe are less divergent among them, they are represented by fewer genetic clusters, and there is evidence of strong recent gene flow among populations. These previously glaciated areas from northern Europe may have been colonized from lampreys expanding out of the Iberian refugia. The pair L. fluviatilis/L. planeri is apparently at different stages of speciation in different locations, showing evidences of high reproductive isolation in the southern refugium, and low differentiation in the north.

Multiple forms of glucagon and somatostatin isolated from the intestine of the southern-hemisphere lamprey Geotria australis

Current views on Agnathan phylogeny favor the hypothesis that the genera of holarctic lampreys belong to a single family (Petromyzontidae) and form an interrelated progression in which Petromyzon is near to Ichthomyzon at the base of the phylogenetic tree and Lampetra is the most derived. A stock similar to that of contemporary Ichthomyzon is considered to have given rise to the southern hemisphere lamprey Geotria australis, the sole member of the Geotriidae. In the present study, two molecular forms of glucagon were isolated from an extract of G. australis intestine that differed in structure by six amino acid residues. One form shows two amino acid substitutions (Leu14 --> Met and Ala29 --> Ser) compared with the single molecular form of glucagon isolated from the sea lamprey Petromyzon marinus and the second form shows three substitutions (Asp15 --> Glu, Ser16 --> Ala, Ile24 --> Thr) compared with the single glucagon isolated from the river lamprey Lampetra fluviatilis. As Petromyzon and Lampetra glucagons differ by six amino acid residues, the data suggest that a duplication of the glucagon gene occurred prior to or early in lamprey evolution. Although both genes are strongly expressed in G. australis, the expression of one gene predominates in P. marinus while that of the other gene predominates in L. fluviatilis. Previous work has shown that, in the islet organ of G. australis, preprosomatostatin is processed almost exclusively to somatostatin-33. However, the present study demonstrates that somatostatin-14 is the major molecular form in G. australis intestine with somatostatin-33 present only as a minor component. This result demonstrates a tissue-dependent pathway of posttranslational processing of preprosomatostatin in the Geotria enteropancreatic system.

Genetic diversity, endemism and phylogeny of lampreys within the genus Lampetra sensu stricto (Petromyzontiformes: Petromyzontidae) in western North America

Phylogenetic structure of four Lampetra species from the Pacific drainage of North America (western brook lamprey Lampetra richardsoni, Pacific brook lamprey Lampetra pacifica, river lamprey Lampetra ayresii and Kern brook lamprey Lampetra hubbsi) and unidentified Lampetra specimens (referred to as Lampetra sp.) from 36 locations was estimated using the mitochondrial cytochrome b gene. Maximum parsimony and Bayesian inferences did not correspond with any taxonomic scheme proposed to date. Rather, although L. richardsoni (from Alaska to California) and L. ayresii (from British Columbia to California) together constituted a well-supported clade distinct from several genetically divergent Lampetra populations in Oregon and California, these two species were not reciprocally monophyletic. The genetically divergent populations included L. pacifica (from the Columbia River basin) and L. hubbsi (from the Kern River basin) and four Lampetra sp. populations in Oregon (Siuslaw River and Fourmile Creek) and California (Kelsey and Mark West Creeks). These four Lampetra sp. populations showed genetic divergence between 2.3 and 5.7% from any known species (and up to 8.0% from each other), and may represent morphologically cryptic and thus previously undescribed species. A fifth population (from Paynes Creek, California) may represent a range extension of L. hubbsi into the Upper Sacramento River.

Phylogeographical analysis reveals multiple conservation units in brook lampreys Lampetra planeri of Portuguese streams

The populations of brook lamprey Lampetra planeri of Portuguese Rivers were analysed phylogeographically using a fragment of 644 bp of the mitochondrial control region of 158 individuals from six populations. Samples representing L. planeri and migratory lampreys Lampetra fluviatilis of rivers draining to the North Sea and the Baltic Sea were also included to assess the relationships of Portuguese samples. The data support a clear differentiation of all the populations studied. Several populations, which are isolated among themselves and also from the migratory lampreys, proved to be entirely composed of private haplotypes, a finding that supports some time of independent evolutionary history for these populations. This, combined with the geographic confinement to small water bodies, justifies the recognition of at least four conservation units in the Portuguese rivers Sado, São Pedro, Nabão and Inha.

Revalidation of the Argentinian pouched lamprey Geotria macrostoma (Burmeister, 1868) with molecular and morphological evidence

BACKGROUND

The Argentinian pouched lamprey, classified as Petromyzon macrostomus Burmeister, 1868 was first described in 1867 in De La Plata River, in Buenos Aires, Argentina, and subsequently recorded in several rivers from Patagonia. Since its original description, the validity of P. macrostomus was questioned by several ichthyologists and 36 years after its original discovery it was considered a junior synonym of Geotria australis Gray, 1851. For a long time, the taxonomic status of G. australis has been uncertain, largely due to the misinterpretations of the morphological alterations that occur during sexual maturation, including the arrangement of teeth, size and position of fins and cloaca, and the development of an exceptionally large gular pouch in males. In this study, the taxonomic status of Geotria from across the "species" range was evaluated using both molecular analysis and examination of morphological characteristics.

METHODOLOGY/PRINCIPAL FINDINGS

Phylogenetic and species delimitation analyses based on mitochondrial DNA sequences of Cytochrome b (Cyt b) and Cytochrome C Oxidase Subunit 1 (COI) genes, along with morphological analysis of diagnostic characters reported in the original descriptions of the species were used to assess genetic and morphological variation within Geotria and to determine the specific status of the Argentinian lamprey. These analyses revealed that Geotria from Argentina constitutes a well differentiated lineage from Chilean and Australasian populations. The position of the cloaca and the distance between the second dorsal and caudal fins in sub-adult individuals, and at previous life stages, can be used to distinguish between the two species. In addition, the genetic distance between G. macrostoma and G. australis for the COI and Cyt b mitochondrial genes is higher than both intra- and inter-specific distances reported for other Petromyzontiformes.

CONCLUSIONS/SIGNIFICANCE

Our results indicate that the Argentinian pouched lamprey, found along a broad latitudinal gradient on the south-west Atlantic coast of South America, should be named as Geotria macrostoma (Burmeister, 1868) and not as G. australis Gray 1851, returning to its earliest valid designation in Argentina. Geotria macrostoma can now be considered as the single lamprey species inhabiting Argentinian Patagonia, with distinct local adaptations and evolutionary potential. It is essential that this distinctiveness is recognized in order to guide future conservation and management actions against imminent threats posed by human actions in the major basins of Patagonia.

Molecular cloning, expression and antioxidant activity of a peroxiredoxin 2 homologue from Lampetra japonica

Peroxiredoxin (Prx) is a cellular antioxidant protein family that plays important roles in oxidative stress and immune cytotoxicity. In this study, we cloned a homologue of the Prx2 from the buccal gland of Lampetra japonica (L. japonica). L. japonica Prx2 (Lj-Prx2) contained two highly conserved motifs and shared more than 70% identity with the homologs from other vertebrate species. Phylogenetic analysis revealed that Lj-Prx2 is closely related to other available teleost Prx2. The real-time PCR results demonstrated that the Prx2 gene was widely expressed in adult lamprey. In addition, the expression of Prx2 gene was particularly up-regulated in red blood cells (RBCs) after the experimental animals were challenged with lipopolysaccharide (LPS) in vivo. Lj-Prx2 gene was subcloned into the pET23b vector and expressed in Escherichia coli BL21 (DE3). The recombinant L. japonica Prx2 (rLj-Prx2) was purified by using His Bind affinity chromatography. Polyclonal antibody to rLj-Prx2 was generated in New Zealand Rabbit. Western blot analysis showed that the Lj-Prx2 is present in the buccal gland secretion, suggesting the secretory feature of it. The function assays revealed that rLj-Prx2 has the capability to reduce the H2O2 when dithiothreitol (DTT) is used as a reducing equivalent and to protect DNA from oxidative damage. These findings suggested that Lj-Prx2 probably plays an essential role in antioxidant defense in RBCs to keep lamprey alive.

Characterization of the heat shock response in the gills of sea lampreys and a brook lamprey at different intervals of their life cycles

The heat shock response (HSR) was characterized in the gills of two lamprey species that differ with respect to their adult life history. In vivo labelling with [35S]methionine revealed an enhanced synthesis of heat shock proteins (HSPs) having approximate molecular weights of 70 kDa (HSP70) and 90 kDa (HSP90) following heat treatment. Induction of the HSR occurred in larval lampreys (ammocoetes) following temperature elevations of 13-16 degrees C for the parasitic species, the sea lamprey (Petromyzon marinus) and 16-20 degrees C for the nonparasitic species, the brook lamprey (Lampetra appendix). The case in L. appendix represents the greatest increase in temperature required to induce the HSR in gill tissue among aquatic poikilotherms studied to data and induction occurs within a temperature range (25-29 degrees C) not normally experienced by these animals. Western blotting detected the presence of 70 and 90 kDa HSPs and HSP70 levels were greater in post-metamorphic L. appendix than in ammocoetes both before and after heat shock. The HSR of lampreys appears to be induced during times of emergency when large, rapid temperature increases are experienced. The high set-point temperature for induction of the response may be a consequence of both the environments they presently inhabit and their experiences during evolution.

A lamprey view on the origins of neuroendocrine regulation of the thyroid axis

This mini review summarizes the current knowledge of the hypothalamic-pituitary-thyroid (HPT) endocrine system in lampreys, jawless vertebrates. Lampreys and hagfish are the only two extant members of the class of agnathans, the oldest lineage of vertebrates. The high conservation of the hypothalamic-pituitary-gonadal (HPG) axis in lampreys makes the lamprey model highly appropriate for comparative and evolutionary analyses. However, there are still many unknown questions concerning the hypothalamic-pituitary (HP) axis in its regulation of thyroid activities in lampreys. As an example, the hypothalamic and pituitary hormone(s) that regulate the HPT axis have not been confirmed and/or characterized. Similar to gnathostomes (jawed vertebrates), lampreys produce thyroxine (T4) and triiodothyronine (T3) from thyroid follicles that are suggested to be involved in larval development, metamorphosis, and reproduction. The existing data provide evidence of a primitive, overlapping yet functional HPG and HPT endocrine system in lamprey. We hypothesize that lampreys are in an evolutionary intermediate stage of hypothalamic-pituitary development, leading to the emergence of the highly specialized HPG and HPT endocrine axes in jawed vertebrates. Study of the ancient lineage of jawless vertebrates, the agnathans, is key to understanding the origins of the neuroendocrine system in vertebrates.

A Noninvasive Tool to Assess the Distribution of Pacific Lamprey (Entosphenus tridentatus) in the Columbia River Basin

The Pacific lamprey (Entosphenus tridentatus) is an anadromous fish once abundant throughout coastal basins of western North America that has suffered dramatic declines in the last century due primarily to human activities. Here, we describe the development of an environmental DNA (eDNA) assay to detect Pacific lamprey in the Columbia River basin. The eDNA assay successfully amplified tissue derived DNA of Pacific lamprey collected from 12 locations throughout the Columbia River basin. The assay amplifies DNA from other Entosphenus species found outside of the Columbia River basin, but is species-specific within this basin. As a result, the assay presented here may be useful for detecting Entosphenus spp. in geographic range beyond the Columbia River Basin. The assay did not amplify tissue or synthetically derived DNA of 14 commonly sympatric non-target species, including lampreys of the genus Lampetra, which are morphologically similar to Pacific lamprey in the freshwater larval stage.

The structure of Mordacia mordax insulin supports the monophyly of the Petromyzontiformes and an ancient divergence of Mordaciidae and Geotriidae

The phylogenetic relationships between the two southern hemisphere lamprey families (Geotriidae and Mordaciidae) and their northern hemisphere counterparts (Petromyzontidae) are unresolved. Insulin was isolated from an extract of islet-containing intestinal tissue from ammocoetes of the Australian lamprey, Mordacia mordax. Its primary structure was established as A-chain: GIVEQCCHRK10CSIYDMENYC20N and B-chain: SALMGTGGTH10LCGSHLVEAL20YVVCGQRGFF30 YTP[SKG]. Although the residues in parentheses are only tentatively assigned, mass spectrometry supports the proposed sequence and demonstrates that Mordacia proinsulin, unlike proinsulin from Geotria australis, is fully processed to mature insulin. Insulins from M. mordax and G. australis and from the northern hemisphere lampreys Petromyzon marinus and Lampetra fluviatilis share a pentapeptide extension to N-terminus of the B-chain (Ser-Ala-Leu-Xaa-Gly) that has never been found in the insulins of any other vertebrate class. This observation provides support for the claim that the Petromyzontiformes constitute a monophyletic group. M. mordax insulin differs from that of G. australis by 18 amino acid residues but by only four residues from the common sequence of P. marinus and L. fluviatilis insulin. These data are consistent with the view that Geotriidae and Mordaciidae have been separated for a long period and suggest that G. australis insulin has undergone an accelerated rate of molecular evolution.

Morphometric discrimination of early life stageLampetra tridentata andL. richardsoni (Petromyzonidae) from the Columbia River Basin

The effectiveness of morphometric and meristic characteristics for taxonomic discrimination of Lampetra tridentata and L. richardsoni (Petromyzonidae) during embryological, prolarval, and early larval stages (i.e., age class 1) were examined. Mean chorion diameter increased with time from fertilization to hatch and was significantly greater for L. tridentata than for L. richardsoni at 1, 8, and 15 days postfertilization. Lampetra tridentata larvae had significantly more trunk myomeres than L. richardsoni; however, trunk myomere numbers were highly variable within species and deviated from previously published data. Multivariate examinations of prolarval and larval L. tridentata (7.2-11.0 mm; standard length) and L. richardsoni (6.6-10.8 mm) were conducted based on standard length and truss element lengths established from eight homologous landmarks. Principal components analysis indicated allometric relationships among the morphometric characteristics examined. Changes in body shape were indicated by groupings of morphometric characteristics associated with body regions (e.g., oral hood, branchial region, trunk region, and tail region). Discriminant function analysis using morphometric characteristics was successful in classifying a large proportion (> 94.7%) of the lampreys sampled.

Cloning of arctic lamprey Lethenteron camtschaticum cd9 with roles in the immune response

In this study, the cd9 gene, a member of the tetraspanin superfamily and involved in various cellular processes, was cloned from Lethenteron camtschaticum. Both real-time PCR and immunohistochemical assays showed broad distribution of cd9 in various L. camtschaticum tissues. In addition, expression levels of Cd9 mRNA were up-regulated in the liver and heart after stimulation by lipopolysaccharide. Flow cytometric analyses demonstrated that cd9 was detected on the leukocytes and that the expression level was higher on granulocytes than on lymphocytes, which implied that cd9 was mainly involved in innate immunity.

Molecular cytogenetic characterization of chromosome site-specific repetitive sequences in the Arctic lamprey (Lethenteron camtschaticum, Petromyzontidae)

All extant lamprey karyotypes are characterized by almost all dot-shaped microchromosomes. To understand the molecular basis of chromosome structure in lampreys, we performed chromosome C-banding and silver staining and chromosome mapping of the 18S–28S and 5S ribosomal RNA (rRNA) genes and telomeric TTAGGG repeats in the Arctic lamprey (Lethenteron camtschaticum). In addition, we cloned chromosome site-specific repetitive DNA sequences and characterized them by nucleotide sequencing, chromosome in situ hybridization, and filter hybridization. Three types of repetitive sequences were detected; a 200-bp AT-rich repetitive sequence, LCA-EcoRIa that co-localized with the 18S–28S rRNA gene clusters of 3 chromosomal pairs; a 364-bp AT-rich LCA-EcoRIb sequence that showed homology to the EcoRI sequence family from the sea lamprey (Petromyzon marinus), which contains short repeats as centromeric motifs; and a GC-rich 702-bp LCA-ApaI sequence that was distributed on nearly all chromosomes and showed significant homology with the integrase-coding region of a Ty3/Gypsy family long terminal repeat (LTR) retrotransposon. All three repetitive sequences are highly conserved within the Petromyzontidae or within Petromyzontidae and Mordaciidae. Molecular cytogenetic characterization of these site-specific repeats showed that they may be correlated with programed genome rearrangement (LCA-EcoRIa), centromere structure and function (LCA-EcoRIb), and site-specific amplification of LTR retroelements through homogenization between non-homologous chromosomes (LCA-ApaI).