Lamprey VLRB participates in pathogen detection, VLRB/L-BLNK/L-NF-κB (B-like cells) signal transduction, and development

In jawed vertebrates, B cell receptors (BCR) are primary pathogen detectors that activate downstream signaling pathways to express adaptive immune effectors. In jawless vertebrates, the variable lymphocyte receptors (VLR) B positive lymphocytes can express and secrete specific VLRB molecules in an analogous manner to that of immunoglobulins by B cells in jawed vertebrates. Our study is the first to demonstrate the possibility of incubation of fertilized eggs and artificial breeding of Lampetra morii larvae throughout their life cycle under laboratory condition. We also found that VLRB, lamprey B-cell linker (L-BLNK), and lamprey nuclear factor-kappa B (L-NF-κB) play key roles in early larval development. Aeromonas hydrophila was found to be a lethal pathogen of L. morii larvae causing rapid infection at a concentration of 10⁷ cfu/mL qRT-PCR results revealed that gene expression levels of VLRB, L-BLNK, and L-NF-κB were up-regulated significantly. Ten-day infection trials showed that VLRB, L-BLNK, and L-NF-κB are crucial for lamprey immune response. Furthermore, the expression levels of L-BLNK and L-NF-κB were down-regulated drastically both at mRNA and protein levels after bacterial infection than in the naive group of VLRB morphants. A similar expression pattern of VLRB and L-BLNK was found in L-NF-κB morphants post bacterial infection. The results were strikingly different in the other two morphants. The VLRB and L-NF-κB expression levels were found to be down-regulated at mRNA and protein levels by less than 30% and 45%, respectively, in L-BLNK morphants compared to those in the naive group. These results indicate that L-BLNK and L-NF-κB might participate in VLRB-mediated immune response. Additionally, in VLRB morphants, the mRNA expression levels of some genes, especially the ones expressed in VLRB⁺ lymphocytes but not in VLRA⁺ lymphocytes, were found to be affected. Therefore, these findings of B-like lymphocytes in lamprey offer key evidence with regard to the evolution of adaptive immunity.

Novel developmental bases for the evolution of hypobranchial muscles in vertebrates

BACKGROUND

Vertebrates are characterized by possession of hypobranchial muscles (HBMs). Cyclostomes, or modern jawless vertebrates, possess a rudimentary and superficial HBM lateral to the pharynx, whereas the HBM in jawed vertebrates is internalized and anteroposteriorly specified. Precursor cells of the HBM, marked by expression of Lbx1, originate from somites and undergo extensive migration before becoming innervated by the hypoglossal nerve. How the complex form of HBM arose in evolution is relevant to the establishment of the vertebrate body plan, but despite having long been assumed to be similar to that of limb muscles, modification of developmental mechanisms of HBM remains enigmatic.

RESULTS

Here we characterize the expression of Lbx genes in lamprey and hagfish (cyclostomes) and catshark (gnathostome; jawed vertebrates). We show that the expression patterns of the single cyclostome Lbx homologue, Lbx-A, do not resemble the somitic expression of mammalian Lbx1. Disruption of Lbx-A revealed that LjLbx-A is required for the formation of both HBM and body wall muscles, likely due to the insufficient extension of precursor cells rather than to hindered muscle differentiation. Both homologues of Lbx in the catshark were expressed in the somitic muscle primordia, unlike in amniotes. During catshark embryogenesis, Lbx2 is expressed in the caudal HBM as well as in the abdominal rectus muscle, similar to lamprey Lbx-A, whereas Lbx1 marks the rostral HBM and pectoral fin muscle.

CONCLUSIONS

We conclude that the vertebrate HBM primarily emerged as a specialized somatic muscle to cover the pharynx, and the anterior internalized HBM of the gnathostomes is likely a novelty added rostral to the cyclostome-like HBM, for which duplication and functionalization of Lbx genes would have been a prerequisite.

Predicting larval metamorphosis of Pacific lamprey Entosphenus tridentatus through measurements of length and mass

The utility of length and mass measurements to predict the larval metamorphosis of Pacific lamprey Entosphenus tridentatus was evaluated. During 2004-2008, larval E. tridentatus were collected from Cedar Creek (Washington, USA) in either the spring or autumn, measured for total length and total mass, reared in captivity and monitored for metamorphosis. The minimum total length, total mass and condition factor of larvae that were observed to go through metamorphosis were 102 mm, 2.0 g and 1.52, respectively. Logistic models indicated that total length and condition factor in both spring and autumn were the most significant variables for predicting metamorphosis of Pacific lamprey during the subsequent summer. Mass in the autumn also appeared important to predict whether metamorphosis occurred in the subsequent summer. Collectively, all models using specific minimums of total length, total mass or condition factor of larvae as criteria for them to metamorphose were sometimes (5 of 14 cases) able to predict the percentage of larvae that would metamorphose but rarely (1 of 12 cases) able to predict which individual larvae would metamorphose. Similar to other anadromous species of lampreys, the size and condition of larval E. tridentatus have utility for predicting metamorphic fate.

Genetic variation and population structure among larval Lethenteron spp. within the Yukon River drainage, Alaska

The absence of information on genetic variation and population structure of lampreys Lethenteron spp. in the eastern part of their distribution limits our understanding of the migration ecology and spatial population genetic structure of the species. We examined genetic variation within and among three aggregations of Lethenteron spp. larvae in the Yukon River drainage, Alaska, using microsatellite genotypes. A total of 120 larval lampreys were genotyped at eight microsatellite loci. Global F_ST was 0.053 (95% CI 0.021-0.086), while pairwise F_ST values ranged from 0.048-0.057. Model-based Bayesian clustering analyses with sample locality priors (LOCPRIOR) identified three distinct, but admixed, genetic clusters that corresponded with the three aggregations. Estimates of contemporary gene flow indicate substantial reciprocal migration among sites consistent with no or low-fidelity natal homing. These results are largely in agreement with previous reports of historic and contemporary gene flow among Lethenteron spp. in other parts of their geographic distribution.

Cloning and characterization of a second lamprey pituitary glycoprotein hormone, thyrostimulin (GpA2/GpB5)

A novel heterodimeric glycoprotein hormone (GpH) comprised of alpha (GpA2) and beta (GpB5) subunits was discovered in 2002 and called thyrostimulin for its ability to activate the TSH receptor in mammals, but its central function in vertebrates has not been firmly established. We report here the cloning and expression of lamprey (l)GpB5, and its ability to heterodimerize with lGpA2 to form a functional l-thyrostimulin. The full-length cDNA of lGpB5 encodes 174 amino acids with ten conserved cysteine residues and one glycosylation site that is conserved with other vertebrate GpB5 sequences. Phylogenetic and synteny analyses support that lGpB5 belongs to the vertebrate GpB5 clade. Heterodimerization of lGpB5 and lGpA2 was shown by nickel pull-down of histidine-tagged recombinant subunits. RNA transcripts of lGpB5 were detected in the pituitary of lampreys during both parasitic and adult life stages. Intraperitoneal injection with lGnRH-III (100 μg/kg) increased pituitary lGpA2, lGpB5, and lGpHβ mRNA expression in sexually mature, adult female lampreys. A recombinant l-thyrostimulin produced by expression of a fusion gene in Pichia pastoris activated lamprey GpH receptors I and II as measured by cAMP enzymeimmunoassay. In contrast to jawed vertebrates that have pituitary LH, FSH, and TSH, our data support that lampreys only have two functional pituitary GpHs, lGpH and l-thyrostimulin, which consist of lGpA2 and unique beta subunits. It is hypothesized that lGpH and l-thyrostimulin differentially regulate reproductive and thyroid activities in some unknown way(s) in lampreys.

Lamprey metamorphosis: Thyroid hormone signaling in a basal vertebrate

As one of the most basal living vertebrates, lampreys represent an excellent model system to study the evolution of thyroid hormone (TH) signaling. The lamprey hypothalamic-pituitary-thyroid and reproductive axes overlap functionally. Lampreys have 3 gonadotropin-releasing hormones and a single glycoprotein hormone from the hypothalamus and pituitary, respectively, that regulate both the reproductive and thyroid axes. TH synthesis in larval lampreys takes place in an endostyle that transforms into typical vertebrate thyroid tissue during metamorphosis; both the endostyle and follicular tissue have all the typical TH synthetic components found in other vertebrates. Furthermore, lampreys also have the vertebrate suite of peripheral regulators including TH distributor proteins (THDPs), deiodinases and TH receptors (TRs). Although at the molecular level the components of the lamprey thyroid system are ancestral to other vertebrates, their functions have been largely conserved. TH signaling as it relates to lamprey metamorphosis represents a particularly interesting phenomenon. Unlike other metamorphosing vertebrates, lamprey THs increase throughout the larval period, peak prior to metamorphosis and decline rapidly at the onset of metamorphosis; patterns of deiodinase activity are consistent with these increases and declines. Moreover, goitrogens (which suppress TH levels) initiate precocious metamorphosis, and exogenous TH treatment blocks goitrogen-induced metamorphosis and disrupts natural metamorphosis. Despite this clear physiological difference, TH action via TRs is consistent with higher vertebrates. Based on observations that TRs are upregulated in a tissue-specific fashion during morphogenesis and the finding that lamprey TRs upregulate genes via THs in a fashion similar to higher vertebrates, we propose the following hypothesis for further testing. THs have a dual role in lampreys where high TH levels promote larval feeding and growth and then at the onset of metamorphosis TH levels decrease rapidly; at this time the relatively low TH levels function via TRs in a fashion similar to that of other metamorphosing vertebrates.

Pacific lamprey (Entosphenus tridentatus) ammocoetes exposed to contaminated Portland Harbor sediments: Method development and effects on survival, growth, and behavior

Many anthropogenic disturbances have contributed to the decline of Pacific lampreys (Entosphenus tridentatus), but potential negative effects of contaminants on lampreys are unclear. Lamprey ammocoetes are the only detritivorous fish in the lower Willamette River, Oregon, USA, and have been observed in Portland Harbor sediments. Their long benthic larval stage places them at risk from the effects of contaminated sediment. The authors developed experimental methods to assess the effects of contaminated sediment on the growth and behavior of field-collected ammocoetes reared in a laboratory. Specifically, they developed methods to assess individual growth and burrowing behavior. Burrowing performance demonstrated high variability among contaminated sediments; however, ammocoetes presented with noncontaminated reference sediment initiated burrowing more rapidly and completed it faster. Ammocoete reemergence from contaminated sediments suggests avoidance of some chemical compounds. The authors conducted long-term exposure experiments on individually held ammocoetes using sediment collected from their native Siletz River, which included the following: contaminated sediments collected from 9 sites within Portland Harbor, 2 uncontaminated reference sediments collected upstream, 1 uncontaminated sediment with characteristics similar to Portland Harbor sediments, and clean sand. They determined that a 24-h depuration period was sufficient to evaluate weight changes and observed no mortality or growth effects in fish exposed to any of the contaminated sediments. However, the effect on burrowing behavior appeared to be a sensitive endpoint, with potentially significant implications for predator avoidance. Environ Toxicol Chem 2016;35:2092-2102. © 2016 SETAC.

Similarities and Differences for Swimming in Larval and Adult Lampreys

The spinal locomotor networks controlling swimming behavior in larval and adult lampreys may have some important differences. As an initial step in comparing the locomotor systems in lampreys, in larval animals the relative timing of locomotor movements and muscle burst activity were determined and compared to those previously published for adults. In addition, the kinematics for free swimming in larval and adult lampreys was compared in detail for the first time. First, for swimming in larval animals, the neuromechanical phase lag between the onsets or terminations of muscle burst activity and maximum concave curvature of the body increased with increasing distance along the body, similar to that previously shown in adults. Second, in larval lampreys, but not adults, absolute swimming speed (U; mm s(-1)) increased with animal length (L). In contrast, normalized swimming speed (U'; body lengths [bl] s(-1)) did not increase with L in larval or adult animals. In both larval and adult lampreys, U' and normalized wave speed (V') increased with increasing tail-beat frequency. Wavelength and mechanical phase lag did not vary significantly with tail-beat frequency but were significantly different in larval and adult animals. Swimming in larval animals was characterized by a smaller U/V ratio, Froude efficiency, and Strouhal number than in adults, suggesting less efficient swimming for larval animals. In addition, during swimming in larval lampreys, normalized lateral head movements were larger and normalized lateral tail movements were smaller than for adults. Finally, larval animals had proportionally smaller lateral surface areas of the caudal body and fin areas than adults. These differences are well suited for larval sea lampreys that spend most of the time buried in mud/sand, in which swimming efficiency is not critical, compared to adults that would experience significant selection pressure to evolve higher-efficiency swimming to catch up to and attach to fish for feeding as well as engage in long-distance migration during spawning. Finally, the differences in swim efficiency for larval and adult lampreys are compared to other animals employing the anguilliform mode of swimming.

Using stable isotopes and C:N ratios to examine the life-history strategies and nutritional sources of larval lampreys

Natural abundance stable-isotope analysis (δ(13)C and δ(15)N) and C:N ratios were used to study the ammocoete phase of two common non-parasitic lamprey species (least brook lamprey Lampetra aepyptera and American brook lamprey Lethenteron appendix) in two tributaries of the Ohio River (U.S.A.). The C:N ratios suggest that each species employs different lipid accumulation strategies to support its metamorphosis and recruitment into an adult animal. Ammocoete δ(13)C values generally increased with increasing C:N values. In contrast to δ(13)C, ammocoete δ(15)N values were weakly related to the total length (LT) in L. aepyptera, but positively correlated to both LT and C:N ratios in L. appendix. In L. appendix, C:N also correlated positively with LT, and presumably age. A Bayesian mixing model using δ(13)C and δ(15)N was used to estimate nutritional subsidies of different potential food resources to ammocoetes at each site. The models suggested that although nutritional subsidies to ammocoetes varied as a function of site, ammocoetes were generally reliant on large contributions (42-62% at three sites) from aquatic plants. Contributions from aquatic sediment organic matter were also important at all sites (32-63%) for ammocoetes, with terrestrially derived plant materials contributing smaller amounts (4-33%). These findings provide important insights into the feeding ecology and nutrition of two species of lampreys. They also suggest that similar and other quantitative approaches are required to (1) fully understand how the observed stable-isotopes ratios are established in ammocoetes and (2) better assess ammocoete nutritional subsidies in different natal streams.

Activation of Transducin by Bistable Pigment Parapinopsin in the Pineal Organ of Lower Vertebrates

Pineal organs of lower vertebrates contain several kinds of photosensitive molecules, opsins that are suggested to be involved in different light-regulated physiological functions. We previously reported that parapinopsin is an ultraviolet (UV)-sensitive opsin that underlies hyperpolarization of the pineal photoreceptor cells of lower vertebrates to achieve pineal wavelength discrimination. Although, parapinopsin is phylogenetically close to vertebrate visual opsins, it exhibits a property similar to invertebrate visual opsins and melanopsin: the photoproduct of parapinopsin is stable and reverts to the original dark states, demonstrating the nature of bistable pigments. Therefore, it is of evolutionary interest to identify a phototransduction cascade driven by parapinopsin and to compare it with that in vertebrate visual cells. Here, we showed that parapinopsin is coupled to vertebrate visual G protein transducin in the pufferfish, zebrafish, and lamprey pineal organs. Biochemical analyses demonstrated that parapinopsins activated transducin in vitro in a light-dependent manner, similar to vertebrate visual opsins. Interestingly, transducin activation by parapinopsin was provoked and terminated by UV- and subsequent orange-lights irradiations, respectively, due to the bistable nature of parapinopsin, which could contribute to a wavelength-dependent control of a second messenger level in the cell as a unique optogenetic tool. Immunohistochemical examination revealed that parapinopsin was colocalized with Gt2 in the teleost, which possesses rod and cone types of transducin, Gt1, and Gt2. On the other hand, in the lamprey, which does not possess the Gt2 gene, in situ hybridization suggested that parapinopsin-expressing photoreceptor cells contained Gt1 type transducin GtS, indicating that lamprey parapinopsin may use GtS in place of Gt2. Because it is widely accepted that vertebrate visual opsins having a bleaching nature have evolved from non-bleaching opsins similar to parapinopsin, these results implied that ancestral bistable opsins might acquire coupling to the transducin-mediated cascade and achieve light-dependent hyperpolarizing response of the photoreceptor cells.

[Life Forms of Lampreys (Petromyzontidae) as a Manifestation of Intraspecific Diversity of Ontogenesis]

Some lamprey genera include the forms that have significantly different life cycles (the most well-known are the "anadromous" and "resident," or the "parasitic" and "nonparasitic" forms). The analysis of data on the genetic characteristics of these forms shows that, in some cases, the nonparasitic lampreys independently derived from the parasitic ones in different aqueous systems. These data, together with the results of morphological analysis as well as data on the distribution, ecology, hybridization, and observations ofjoint spawning of parasitic and nonparasitic forms show that these forms belong to the same species (except the resident forms that were isolated long ago).

Gene expression during ovarian differentiation in parasitic and non-parasitic lampreys: implications for fecundity and life history types

Lampreys diverged from the jawed vertebrate lineage approximately 500million years ago. Lampreys undergo sex differentiation much later than most other vertebrates, and ovarian differentiation occurs several years before testicular differentiation. The genetic basis of lamprey sex differentiation is of particular interest both because of the phylogenetic importance of lampreys and because of their unusual pattern of sex differentiation. As well, differences between parasitic and non-parasitic lampreys may first become evident at ovarian differentiation. However, nothing is known about the genetic basis of ovarian differentiation in lampreys. This study examined potential differences in gene expression before, during, and after ovarian differentiation in parasitic chestnut lamprey Ichthyomyzon castaneus and non-parasitic northern brook lamprey Ichthyomyzonfossor. Eight target genes (17β-hydroxysteroid dehydrogenase, germ cell-less, estrogen receptor β, insulin-like growth factor 1 receptor, daz-associated protein 1, cytochrome c oxidase subunit III, Wilms' tumour suppressor protein 1, and dehydrocholesterol reductase 7) were examined. Northern brook lamprey displayed higher expression of cytochrome c oxidase subunit III, whereas chestnut lamprey displayed higher expression of insulin-like growth factor 1 receptor; these genes may be involved in apoptosis and oocyte growth, respectively. Presumptive male larvae had higher expression of Wilms' tumour suppressor protein 1, which may be involved in the undifferentiated gonad and/or later testicular development. Differentiated females had higher expression of 17β hydroxysteroid dehydrogenase and daz-associated protein 1, which may be involved in female development. This study is the first to identify genes that may be involved in ovarian differentiation and fecundity in lampreys.

Discovery of fossil lamprey larva from the Lower Cretaceous reveals its three-phased life cycle

Lampreys are one of the two surviving jawless vertebrate groups and one of a few vertebrate groups with the best exemplified metamorphosis during their life cycle, which consists of a long-lasting larval stage, a peculiar metamorphosis, and a relatively short adulthood with a markedly different anatomy. Although the fossil records have revealed that many general features of extant lamprey adults were already formed by the Late Devonian (ca. 360 Ma), little is known about the life cycle of the fossil lampreys because of the lack of fossilized lamprey larvae or transformers. Here we report the first to our knowledge discovery of exceptionally preserved premetamorphic and metamorphosing larvae of the fossil lamprey Mesomyzon mengae from the Lower Cretaceous of Inner Mongolia, China. These fossil ammocoetes look surprisingly modern in having an eel-like body with tiny eyes, oral hood and lower lip, anteriorly positioned branchial region, and a continuous dorsal skin fin fold and in sharing a similar feeding habit, as judged from the detritus left in the gut. In contrast, the larger metamorphosing individuals have slightly enlarged eyes relative to large otic capsules, thickened oral hood or pointed snout, and discernable radials but still anteriorly extended branchial area and lack a suctorial oral disk, which characterize the early stages of the metamorphosis of extant lampreys. Our discovery not only documents the larval conditions of fossil lampreys but also indicates the three-phased life cycle in lampreys emerged essentially in their present mode no later than the Early Cretaceous.

The lamprey: a jawless vertebrate model system for examining origin of the neural crest and other vertebrate traits

Lampreys are a group of jawless fishes that serve as an important point of comparison for studies of vertebrate evolution. Lampreys and hagfishes are agnathan fishes, the cyclostomes, which sit at a crucial phylogenetic position as the only living sister group of the jawed vertebrates. Comparisons between cyclostomes and jawed vertebrates can help identify shared derived (i.e. synapomorphic) traits that might have been inherited from ancestral early vertebrates, if unlikely to have arisen convergently by chance. One example of a uniquely vertebrate trait is the neural crest, an embryonic tissue that produces many cell types crucial to vertebrate features, such as the craniofacial skeleton, pigmentation of the skin, and much of the peripheral nervous system (Gans and Northcutt, 1983). Invertebrate chordates arguably lack unambiguous neural crest homologs, yet have cells with some similarities, making comparisons with lampreys and jawed vertebrates essential for inferring characteristics of development in early vertebrates, and how they may have evolved from nonvertebrate chordates. Here we review recent research on cyclostome neural crest development, including research on lamprey gene regulatory networks and differentiated neural crest fates.

Genetic consequences of programmed genome rearrangement

The lamprey (Petromyzon marinus) undergoes developmentally programmed genome rearrangements that mediate deletion of∼20% of germline DNA from somatic cells during early embryogenesis. This genomic differentiation of germline and soma is intriguing, because the germline plays a unique biological role wherein it must possess the ability to undergo meiotic recombination and the capacity to differentiate into every cell type. These evolutionarily indispensable functions set the germline at odds with somatic tissues, because factors that promote recombination and pluripotency can potentially disrupt genome integrity or specification of cell fate when misexpressed in somatic cell lineages (e.g., in oncogenesis). Here, we describe the development of new genomic and transcriptomic resources for lamprey and use these to identify hundreds of genes that are targeted for programmed deletion from somatic cell lineages. Transcriptome sequencing and targeted validation studies further confirm that somatically deleted genes function both in adult (meiotic) germline and in the development of primordial germ cells during embryogenesis. Inferred functional information from deleted regions indicates that developmentally programmed rearrangement serves as a (perhaps ancient) biological strategy to ensure segregation of pluripotency functions to the germline, effectively eliminating the potential for somatic misexpression.

Identification and characterization of a chitinase-coding gene from Lamprey (Lampetra japonica) with a role in gonadal development and innate immunity

Chitinases (E.3.2.1.14) are ubiquitous hydrolases capable of cleaving the beta-1,4-glycosidic bonds in chitin polymers. The physiological significance of these enzymes in the development and immunity of various animals has recently been reported [Badariotti F, Thuau R, Lelong C, Dubos MP, Favrel P. Characterization of an atypical family 18 chitinase from the oyster Crassostrea gigas: evidence for a role in early development and immunity. Dev Comp Immunol 2007;31(6):559-70]. Lampreys are regarded as the most phylogenetically primitive species that may have an adaptive immune system. However, no chitinase gene has yet been identified in lamprey. We report here the identification and characterization of a chitinase-coding gene from the lamprey Lampetra japonica. The predicted amino acid sequence of the chitinase gene consisted of a typical catalytic domain and a peritrophin-A type chitin-binding domain. Real time RT-PCR analysis showed that the chitinase gene was expressed in various tissues of adult L. japonica, particularly in the liver, where a significant difference between male and female was observed during the pre-spawning period. A significant increase in expression was also observed in vivo following stimulation by bacteria or fungi. These findings seemed to suggest that in L. japonica, chitinase probably plays an important role in gonadal development as well as in innate immunity in response to invasion by microorganisms.

Windows of the brain: Towards a developmental biology of circumventricular and other neurohemal organs

We review the anatomical and functional features of circumventricular organs in vertebrates and their homologous neurohemal organs in invertebrates. Focusing on cyclostomes (lamprey) and urochordates (ascidians), we discuss the evolutionary origin of these organs as a function of their cell type specification and morphogenesis.

Development of the serotonergic system in the central nervous system of the sea lamprey

Lampreys belong to the most primitive extant group of vertebrates, the Agnathans, which is considered the sister group of jawed vertebrates. Accordingly, characterization of neuronal groups and their development appears useful for understanding early evolution of the nervous system in vertebrates. Here, the development of the serotonergic system in the central nervous system of the sea lamprey, Petromyzon marinus, was investigated by immunohistochemical analysis of specimens ranging from embryos to adults. The different serotonin-immunoreactive (5-HT-ir) neuronal populations that are found in adults were observed between the embryonic and metamorphic stages. The earliest serotonergic neurons were observed in the basal plate of the isthmus region of late embryos. In prolarvae, progressive appearance of new serotonergic cell groups was observed: firstly in the spinal cord, then in the pineal organ, tuberal region, zona limitans intrathalamica, rostral isthmus, and the caudal part of the rhombencephalon. In early larvae a new group of serotonergic cells was observed in the mammillary region, whereas in the pretectal region and the parapineal organ the first serotonergic cells were seen in the middle and late larval stages, respectively. The first serotonergic fibres appeared in early prolarvae, with fibres that ascend and descend from the isthmic cell group, and the number of immunoreactive fibres increased progressively until the adult stage. The results reveal strong resemblances between lampreys and other vertebrates in the spatio-temporal pattern of development of brainstem populations. This study also reveals a shared pattern of early ascending and descending serotonergic pathways in lampreys and jawed vertebrates.

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.

A lamprey from the Devonian period of South Africa

Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.

Larval lampreys possess a functional lateral line system

Morphology of larval lampreys' neuromasts was found to be very similar to that of adults. Activity in the lateral line nerve, elicited by a vibrating ball, indicated a functional lateralis system. Analysis revealed at least two populations of afferents, responding to opposite directions of water flow, with adapting responses. The response magnitude increased monotonically with stimulus amplitude. Larval lampreys' neuromasts were less sensitive than those of teleosts. At low frequencies the response showed a phase lead of 200-220 degrees with respect to the maximum of the ball displacement and a gain that was approximately linearly proportional to frequency.

Patterns of proopiomelanotropin and proopiocortin gene expression and of immunohistochemistry for gonadotropin-releasing hormones (lGnRH-I and III) during the life cycle of a nonparasitic lamprey: relationship to this adult life history type

There are two adult life history types among lamprey species, nonparasitic and parasitic, with the former commencing the final interval of sexual maturation immediately after metamorphosis. There are no extensive studies that directly compare hormone profiles during the life cycles of nonparasitic and parasitic lamprey species, yet such data may explain differences in development, reproductive maturation, and feeding status. The present study uses immunohistochemistry to show the life cycle profiles for gonadotropin-releasing hormones (GnRH-I and -III) in the brain of the nonparasitic species, the American brook lamprey, Lampetra appendix, for comparison with the extensive, published, immunohistochemical data on these hormones in the parasitic species, the sea lamprey, Petromyzon marinus. The complete cDNAs for the two lamprey prohormones, proopiocortin (POC), and proopiomelanotropin (POM), were cloned for L. appendix and both nucleotide and deduced amino acid sequences were compared with those previously published for P. marinus. The POC and POM cDNAs for both species were used in expression studies, with Northern blotting, throughout their life cycles. Although GnRH-I and -III immunohistochemistry revealed a similar distribution of immunoreactive cells and fibers in the two species during the life cycles, a qualitative evaluation of staining intensity in L. appendix, implied early activity in the brains of metamorphosis of this species, particularly in GnRH-I. GnRH-III seems to be important in larval life and early metamorphosis in both species. A novel feature of this immunohistochemical study is the monthly observations of the distribution and relative intensity of the two GnRHs during the critical period of final sexual maturation that lead to spawning and then the spent animal. L. appendix POC and POM nucleotide sequences had 92.9 and 94.6% identity, respectively, with P. marinus POC and POM and there was an earlier increase in their expression during metamorphosis and postmetamorphic life. Since there was some correlation between the timing of metamorphic development, gonad maturation, and brain irGnRH intensity with POC and POM expression in L. appendix, it was concluded that these prohormones yield posttranslational products that likely play a substantial role in development and maturation events that lead to the nonparasitic adult life history of this species.

Fluorogold labeling of descending brain neurons in larval lamprey does not cause cell death

In our previous double-labeling studies, the fluorescent anatomical tracers Fluorogold (FG) and Texas red dextran amine (TRDA) were used to demonstrate that descending brain neurons, approximately 80% of which are reticulospinal (RS) neurons, in spinal cord-transected larval lamprey regenerate their axons. However, the numbers of FG-labeled descending brain neurons decreased significantly with increasing recovery times, from 2 to 16 weeks. For some FG-labeled mammalian neurons, FG appears to degrade and/or be lost over time, while in other neurons this tracer can kill neurons. In the present study, these possibilities were examined in larval lamprey for FG-labeled descending brain neurons. As in our previous studies, FG was applied to the spinal cord at 40% body length (BL, relative distance from the head) to retrogradely labeled descending brain neurons, and after recovery times of 2, 8, or 16 weeks, HRP, a non-toxic retrograde tracer, was applied to the spinal cord at 20% BL to determine if the numbers of HRP-labeled neurons were reduced. At these three recovery times, the numbers of HRP-labeled descending brain neurons were not significantly different than the numbers of HRP-labeled neurons in control animals that were not labeled with FG. Furthermore, the size and morphology of cell bodies and dendritic trees were not noticeably different in descending brain neurons with and without FG. Thus, in larval lamprey, FG does not appear to kill these neurons, but some FG probably is degraded and/or lost from neurons with increasing recovery times.

Lamprey type II collagen and Sox9 reveal an ancient origin of the vertebrate collagenous skeleton

Type II collagen is the major cartilage matrix protein in the jawed vertebrate skeleton. Lampreys and hagfishes, by contrast, are thought to have noncollagenous cartilage. This difference in skeletal structure has led to the hypothesis that the vertebrate common ancestor had a noncollagenous skeleton, with type II collagen becoming the predominant cartilage matrix protein after the divergence of jawless fish from the jawed vertebrates approximately 500 million years ago. Here we report that lampreys have two type II collagen (Col2alpha1) genes that are expressed during development of the cartilaginous skeleton. We also demonstrate that the adult lamprey skeleton is rich in Col2alpha1 protein. Furthermore, we have isolated a lamprey orthologue of Sox9, a direct transcriptional regulator of Col2alpha1 in jawed vertebrates, and show that it is coexpressed with both Col2alpha1 genes during skeletal development. These results reveal that the genetic pathway for chondrogenesis in lampreys and gnathostomes is conserved through the activation of cartilage matrix molecules and suggest that a collagenous skeleton evolved surprisingly early in vertebrate evolution.

Genes coding for intermediate filament proteins closely related to the hagfish "thread keratins (TK)" alpha and gamma also exist in lamprey, teleosts and amphibians

The "thread keratins (TK)" alpha and gamma so far have been considered highly specialized intermediate filament (IF) proteins restricted to hagfish. From lamprey, we now have sequenced five novel IF proteins closely related to TKalpha and TKgamma, respectively. Moreover, we have detected corresponding sequences in EST and genomic databases of teleosts and amphibians. The structure of the TKalpha genes and the positions of their deduced amino acid sequences in a phylogenetic tree clearly support their classification as type II keratins. The genes encoding TKgamma show a structure typical for type III IF proteins, whereas their positions in phylogenetic trees favor a close relationship to the type I keratins. Considering that most keratin-like sequences detected in the lancelet also exhibit a gene structure typical for type III IF proteins, it seems likely that the keratin gene(s) originated from an ancient type III IF protein gene. According to EST analyses, the expression of the thread keratins in teleost fish and amphibians may be particularly restricted to larval stages, which, in conjunction with the observed absence of TKalpha and TKgamma genes in any of the available Amniota databases, indicates a thread keratin function closely related to larval development in an aquatic environment.

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.

Developmental changes of the GABA-immunoreactive fibers in the lamprey spinal cord

The changes in distribution and number of GABA immunoreactive (GABA-ir) fibers from postembryonic stages to adulthood in the lamprey spinal cord white matter were studied by using immunocytochemical techniques. From prolarvae to adult spawning animals there was an increase of the number of GABA-ir fibers. Three phases can be distinguished: (a) from prolarvae to middle size larvae (around 50 mm in body length) an increase in the number of GABA-ir fibers per section is observed. Furthermore, an adult-like pattern of GABA-ir fibers distribution is established during this phase. (b) Then, the number of GABA-ir fibers remains stable until metamorphosis, the end of the larval period. (c) Finally, in young postmetamorphic and adult animals the number of GABA-ir fibers is higher than in larvae. These observations, joined to the changes previously reported in the GABA-ir neurons, indicate that at least parts of the GABA inhibitory component of the spinal locomotor network is reorganized during the lamprey life cycle and it may indicate different inhibitory requirements in the locomotor network.

The membranous labyrinth during larval development in lamprey (Lampetra planeri, Bloch, 1784)

SEM and CLSM studies were performed on the membranous labyrinth of Lampetra planeri, a threatened species of brook lamprey, spanning from the 1st to the 4th year of ammocoetes larval stages and on the adults. In all the examined stages, the entire membranous labyrinth does not show any morphologic differences, but only a progressive increase in size. SEM and CLSM observations show that the ciliated chamber is lined with numerous unsensorial multiciliated cells. In the early stages, the ciliary bundles were approximately 15 microm long, while in the late stages they reached 30 microm. In the crista sensory area, we observed two populations of hair cells. "Type II" cells are peculiar for this species and show both long stereocilia decreasing in length and a long kinocilium (10-12 microm). Two other types of ciliary bundles have been found on the sensory hair cells of the Macula communis: the first one has both kinocilium and stereocilia about 4-5 microm long; the second shows a long kinocilium (7-10 microm in length) and short stereocilia bundles with a gradual increase in length. In the early stages of development, the three macular areas show few and sparsely distributed hair cells. In the late developmental stages, hair cells become more numerous and densely populated.

Magnetization transfer micro-MR imaging of live excised lamprey spinal cord: characterization and immunohistochemical correlation

BACKGROUND AND PURPOSE

Membrane constituents may play a key role in the magnetization transfer (MT) effect. In lamprey spinal cord, axonal diameters range from <1 microm in the dorsal region to 20-40 microm in the ventral region. There is a corresponding range of axonal, and hence cell membrane, density. These characteristics permit determination of the effect of cell membrane density on MT. The purpose of this study was to characterize regional MT effects in lamprey spinal cord.

METHODS

Excised spinal cords from eight sea lampreys were measured with a 9.4-T MR imaging system. MT saturation was applied for spin-echo sequences. The MT ratio (MTR) was calculated in each location (dorsal, lateral, and ventral columns). Spinal cords from five other lampreys were prepared with an antibody to lamprey glial keratin (LCM 29). The percentage of area staining with LCM29 was calculated for each location.

RESULTS

Mean MTR (+/- SD) for the dorsal, lateral, and ventral columns were 62.4 +/- 4.2, 59.2 +/- 2.7, and 56.9 +/- 3.0, respectively; all differences were significant (P < .05). Mean LCM29-positive areas for the dorsal, lateral, and ventral columns were 85.1%, 69.7%, and 50.9%, respectively. MTR and percentage LCM29-positive area were significantly correlated (r(2) = 0.98).

CONCLUSION

Regional differences in MT effect exist in the lamprey spinal cord. MTR is well correlated with percentage LCM29-positive area. These results support the hypothesis that membrane constituents are at least partly responsible for regional variations in MT effect.

Cell proliferation in the lamprey central nervous system

After spinal cord transection, axons regenerate both in larval and adult lampreys. It is not known to what degree cells proliferate, even in the uninjured animal. Therefore, we have determined the prevalence of mitosis in the lamprey central nervous system (CNS). Bromodeoxyuridine (BrdU) was injected and incorporated for 4 hours into 2- to 5-year-old larvae, animals undergoing metamorphosis, and young adults. Labeled cells were counted in the rhombencephalon (where most supraspinal projecting neurons are located) and spinal cord. A mitotic index (MI) was calculated as the percentage of nuclei that were labeled. There was a seasonal variation in mitotic activity, with higher MIs occurring in summer. Within the summer, there was an additional transient spike in mitosis, especially in the rhombencephalon. There was no correlation between age and MI within the range of developmental stages examined. Baseline MIs in the rhombencephalon and spinal cord were approximately 0.15% and 0.20%, respectively. In most animals, the highest mitotic rates in both the rhombencephalon and spinal cord were seen in the ependyma, but many labeled cells were found in nonependymal regions as well. During the summer spike, almost all of the additional mitosis in the rhombencephalon was in the ependyma, but this finding was not true in the spinal cord. Many BrdU-labeled cells in the spinal cord and rhombencephalon were also stained by monoclonal antibodies specific for lamprey glial keratin but were never labeled by anti-neurofilament antibodies. These results suggest that (1) neurogenesis is uncommon in the lamprey CNS; (2) during most of the year, baseline gliogenesis occurs mainly in the ependyma with substantial contribution by nonependymal areas. During the summer, a spike of mitotic activity occurs in the ependyma of the rhombencephalon and throughout the spinal cord.

Isolation, partial purification, and characterization of a novel petromyzonol sulfotransferase from Petromyzon marinus (lamprey) larval liver

We have isolated, partially purified, and characterized the 5 alpha-petromyzonol (5 alpha-PZ), (5 alpha-cholan- 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-) sulfotransferase (PZ-SULT) from larval lamprey liver. Crude liver extracts exhibited a PZ-SULT activity of 0.9120 pmol/min/mg in juvenile and 12.62 pmol/min/mg in larvae. Using crude larval liver extracts and various 5 beta-cholan substrates and allocholic acid there was negligible activity, however, with 5 alpha-PZ and 3-keto-5 alpha-PZ the SULT activity was 231.5 pmol/min/mg and 180.8 pmol/min/mg respectively. This established that the sulfotransferase of lamprey larval liver extracts prefers (5 alpha) substrates and it is selective for hydroxyl at C-24. PZ-SULT was purified through various chromatography procedures. Partially purified PZ-SULT exhibited a pH optimum of 8.0, a temperature optimum of 22 degrees C, and activity was linear for 1h. PZ-SULT exhibited a K(m) of 2.5 microM for PAPS and a K(m) of 8 microM for PZ. The affinity purified peak PZ-SULT exhibited a specific activity of 2,038 pmol/min/mg. The peak protein upon SDS-PAGE, correlated to an Mw 47 kDa. Photoaffinity labeling with PAP(35)S, specifically crosslinked the 47 kDa protein, further confirming the identity of PZ-SULT. Partial amino acid sequencing of the putative 47 kDa PZ-SULT protein yielded a peptide sequence (M)SISQAVDAAFXEI, which possessed an overall (approximately 35-40%) homology with mammalian SULT2B1a.

Development of GABA-immunoreactive cells in the spinal cord of the sea lamprey,P. marinus

The lamprey spinal cord increases in length and size during all its life cycle; thus, it is expected that new cells will be generated. This expectation suggests that the locomotor circuits must be continuously remodeled. Key elements in the cellular network controlling locomotor behavior are inhibitory cells. Here, we studied the gamma-aminobutyric acid-immunoreactive (GABA-ir) cells in the lamprey spinal cord during postembryonic development. Three major populations of GABA-ir cells were identified according to their distribution: those located in the gray matter, those contacting the cerebrospinal liquid (LC cells), and those located in the white matter. The results show (1). the number of GABA-ir cells per segment increase from prolarvae (<10 mm) to adulthood; (2). the lower number of GABA-ir cells in 100 microm of spinal cord is 66 +/- 7, found in premetamorphic larvae, and the highest is 107 +/- 6, found in postmetamorphic animals; (3). the gray matter and LC GABA-ir cells show different variations in number depending on the developmental period. Thus, in the 10-mm larvae, the gray matter GABA-ir cells are more abundant than LC cells, whereas in the young postmetamorphic specimens, the contrary occurs. Most of the GABA-ir cells located in the white matter were classified as edge cells. They increase in number from the beginning of the prolarval period, where there are not white matter-positive cells, to the middle larval period, where there are 9 +/- 4 GABA-ir edge cells per segment. This value was unaltered in later periods, where GABA-ir edge cells represent 20-30% of the total number of edge cells per segment. The increase in number of GABA-ir cells in these populations during a specific point of the lamprey life cycle may indicate different inhibitory requirements of the locomotor circuit at different developmental periods.

Glomerular territories in the olfactory bulb from the larval stage of the sea lamprey Petromyzon marinus

The goal of this study was to investigate the spatial organization of olfactory glomeruli and of substances relevant to olfactory sensory neuron activity in the developing agnathan, the sea lamprey Petromyzon marinus. A 45-kD protein immunoreactive to G(olf), a cAMP-dependent olfactory G protein, was present in the ciliary fraction of sea lamprey olfactory epithelium and in olfactory sensory neurons of larval and adult sea lampreys. This result implies that G(olf) expression was present during early vertebrate evolution or evolved in parallel in gnathostome and agnathostome vertebrates. Serial sectioning of the olfactory bulb revealed a consistent pattern of olfactory glomeruli stained by GS1B(4) lectin and by anterograde labeling with fluorescent dextran. These glomerular territories included the dorsal cluster, dorsal ring, anterior plexus, lateral chain, medial glomeruli, ventral ring, and ventral cluster. The dorsal, anterior, lateral, and ventral glomeruli contained olfactory sensory axon terminals that were G(olf)-immunoreactive. However, a specific subset, the medial glomeruli, did not display this immunoreactivity. Olfactory glomeruli in the dorsal hemisphere of the olfactory bulb, the dorsal cluster, dorsal ring, anterior plexus, lateral chain, and medial glomeruli, were seen adjacent to 5HT-immunoreactive fibers. However, glomeruli in the ventral hemisphere, the ventral ring, and ventral cluster did not display this association. The presence of specific glomerular territories and discrete glomerular subsets with substances relevant to olfactory sensory neuron activity suggest a spatial organization of information flow in the lamprey olfactory pathway.

Cloning of a functional vitamin D receptor from the lamprey (Petromyzon marinus), an ancient vertebrate lacking a calcified skeleton and teeth

The nuclear vitamin D receptor (VDR) mediates the actions of its 1,25-dihydroxyvitamin D(3) ligand to control gene expression in terrestrial vertebrates. Prominent functions of VDR-regulated genes are to promote intestinal absorption of calcium and phosphate for bone mineralization and to potentiate the hair cycle in mammals. We report the cloning of VDR from Petromyzon marinus, an unexpected finding because lampreys lack mineralized tissues and hair. Lamprey VDR (lampVDR) clones were obtained via RT-PCR from larval protospleen tissue and skin and mouth of juveniles. LampVDR expressed in transfected mammalian COS-7 cells bound 1,25-dihydroxyvitamin D(3) with high affinity, and transactivated a reporter gene linked to a vitamin D-responsive element from the human CYP3A4 gene, which encodes a P450 enzyme involved in xenobiotic detoxification. In tests with other vitamin D responsive elements, such as that from the rat osteocalcin gene, lampVDR showed little or no activity. Phylogenetic comparisons with nuclear receptors from other vertebrates revealed that lampVDR is a basal member of the VDR grouping, also closely related to the pregnane X receptors and constitutive androstane receptors. We propose that, in this evolutionarily ancient vertebrate, VDR may function in part, like pregnane X receptors and constitutive androstane receptors, to induce P450 enzymes for xenobiotic detoxification.

Effect of alloxan and insulin immunoneutralization on circulating thyroid hormone levels in larval landlocked sea lampreys, petromyzon marinus

The effects of alloxan, an insulin (INS)-secreting cell toxin, and INS immunoneutralization on circulating levels of thyroid hormones (thyroxine, T(4); triiodothyronine, T(3)) were examined in larval landlocked sea lampreys, Petromyzon marinus. Animals were injected intraperitoneally with either (Experiment 1) saline (0.6%) or alloxan (20 or 200 microg/g body weight), or with (Experiment 2) normal rabbit serum or anti-lamprey INS. Alloxan (200 microg/g) decreased plasma T(3), but not T(4), in larvae by about 45-80%. Three, six, or nine hr after acute immunoneutralization of lamprey INS with anti-lamprey INS, plasma T(3) levels decreased by 13-30%, relative to controls. These data indicate that INS deficiency can regulate the thyroid system of larval lampreys. There is some suggestion that INS may mediate the metamorphic processes by modulating thyroid hormone concentrations.

Pheromones of the male sea lamprey, Petromyzon marinus L.: structural studies on a new compound, 3-keto allocholic acid, and 3-keto petromyzonol sulfate

This study reports the results of chemical and chromatographic studies which establish the presence of 3-keto allocholic acid (3kACA) in water extracts from spermiating male sea lamprey, Petromyzon marinus. This is the second compound to be isolated and identified from these extracts. The first was 3-keto petromyzonol sulfate (3kPZS), which was shown to act as strong pheromonal attractant for ovulated females. Some new characterization data on 3kPZS (utilizing an only recently available synthetic preparation of the compound) is also included. The possibility that a mixture of 3kACA and 3kPZS might be a more potent pheromonal attractant than either compound alone is discussed.

Development and application of an ELISA for a sex pheromone released by the male sea lamprey (Petromyzon marinus L.)

An enzyme-linked immunosorbent assay (ELISA) has been developed for a conjugated bile acid, 7alpha,12alpha,24-trihydroxy-5alpha-cholan-3-one 24-sulfate (commonly referred to as 3-keto petromyzonol sulfate [3kPZS]), a pheromone released by reproductively mature male sea lampreys to attract sexually mature females. A polyclonal antiserum against the pheromone was raised by injecting 3-keto petromyzonol 24-hemisuccinate (3kPZ-HS) conjugated to bovine serum albumin into rabbits. The enzyme label was prepared by conjugating 3kPZ-HS to acetylcholinesterase. The standard curve had a working range of 20 pg-10 ng/well. Intra- and inter-assay variations were less than 5 and 12%, respectively. The antiserum had 100% cross-reaction with 3-keto petromyzonol and 3-keto allocholic acid but less than 0.2% cross-reaction with petromyzonol, allocholic acid, cholic acid, and taurolithocholic acid sulfate. The assay was applied to water which had been conditioned for 4h by either larvae, parasitic juveniles, ovulating females, pre-spermiating males, or spermiating males. Immunoactive material (average 200 ng/ml, which is equivalent to 500 microg animal/h) was only found in water from the reproductively mature males and diluted parallel with the standard curve. Assay of water samples collected from male lampreys in bisected aquaria also established that 99.6% of the immunoactive material emanated from the front end of the fish. This assay has applications in both physiological and ecological aspects of sea lamprey reproduction.

KClO(4) inhibits thyroidal activity in the larval lamprey endostyle in vitro

An in vitro experimental system was devised to assess the direct effects of the goitrogen, potassium perchlorate (KClO(4)), on radioiodide uptake and organification by the larval lamprey endostyle. Organification refers to the incorporation of iodide into lamprey thyroglobulin (Tg). Histological and biochemical evidence indicated that endostyles were viable at the termination of a 4h in vitro incubation. A single iodoprotein, designated as lamprey Tg, was identified in the endostylar homogenates by polyacrylamide gel electrophoresis and Western blotting. Lamprey Tg was immunoreactive with rabbit anti-human Tg serum and had an electrophoretic mobility similar to that of reduced porcine Tg. When KClO(4) was added to the incubation medium, both iodide uptake and organification by the endostyle were significantly reduced relative to controls as determined by gamma counting, and gel-autoradiography and densitometry, respectively. Western blotting showed that KClO(4) significantly lowered the total amount of lamprey Tg in the endostyle. Based on the results of this in vitro investigation, we conclude that KClO(4) acts directly on the larval lamprey endostyle to inhibit thyroidal activity. These data support a previous supposition from in vivo experimentation that KClO(4) acts directly on the endostyle to suppress the synthesis of thyroxine and triiodothyronine, resulting in a decrease in the serum levels of these two hormones.

Increase in descending brain-spinal cord projections with age in larval lamprey: implications for spinal cord injury

The purpose of this study was to determine whether new descending brain-spinal cord projections are added with age in larval lamprey and might contribute substantially to restoration of these projections following spinal cord injury. Retrograde horseradish peroxidase (HRP) labeling of descending brain neurons was performed in "young" and "old" larval lamprey that differed in age by at least one year. In old larval lamprey, significantly more descending brain neurons projected to specific rostral levels of the spinal cord than in young animals. Furthermore, in young and old lamprey, the main morphological change in Müller and Mauthner cells was an increase in soma size. The major conclusion from the present study is that in larval lamprey, some new brain-spinal cord projections are added with age that could be due to axonal elongation by preexisting brain neurons and/or descending projections from new neurons (i.e., neurogenesis or maturation of incompletely differentiated neurons). Following spinal cord transections, the numbers of descending projections were not significantly different than those in normal, unlesioned animals. Thus, some new descending projections are added with age, but at a relatively slow rate, and the rate does not appear to be affected significantly by spinal cord transections. Together, the present results and those from our recent double-labeling study suggest that following spinal cord transection in larval lamprey, axonal regeneration by descending brain neurons, rather than the relatively slow addition of new brain-spinal cord projections with age, probably accounts for the majority of restored projections and recovery of locomotor function

Development of tyrosine hydroxylase-immunoreactive systems in the brain of the larval lamprey Lampetra fluviatilis

The development of the catecholaminergic system of the brain of the lamprey (Lampetra fluviatilis) was studied with immunocytochemistry in a series of larvae of different sizes by using two different antibodies directed against tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. In group 1 larvae (length: 29-54 mm, ages: 8 months to 1.5 years), the only TH-immunoreactive somata observed were located in the caudal wall of the recessus praeopticus (RP) and in the nucleus tuberculi posterioris (NTP). In group 2 larvae (length: 55-80 mm, ages: 1.5-2.5 years), the somata of immunolabeled cells of the NTP give rise to fibers, most of which are ascending and terminate in the corpus striatum. Additional immunoreactive cells are observed in the nucleus praeopticus (NP), which has differentiated, and in the spinal cord. In group 3 larvae (length: 81-110 mm, ages: 2.5-4 years), the spatial distribution of TH-immunoreactive elements (somata, fibers, and terminals) bears many resemblances to that seen in the adult. Immunolabeled cells may be observed in the olfactory bulb, in the nucleus commissurae postopticae (NCP), and in the nucleus dorsalis hypothalami (NDH). Nevertheless, some groups of TH-immunoreactive cells found in the adult are not observed in group 3 larvae; these may appear during the metamorphic phase. By comparative analysis, we show that, in spite of several differences, the spatiotemporal sequence of appearance of TH-immunoreactive cell bodies and fibers in the lamprey presents many similarities to that described in gnathostomes.

Ontogeny of gamma-aminobutyric acid-immunoreactive neuronal populations in the forebrain and midbrain of the sea lamprey

Although brain organization in lampreys is of great interest for understanding evolution in vertebrates, knowledge of early development is very scarce. Here, the development of the forebrain and midbrain gamma-aminobutyric acid (GABA)-ergic systems was studied in embryos, prolarvae, and small larvae of the sea lamprey using an anti-GABA antibody. Ancillary immunochemical markers, such as proliferating cell nuclear antigen (PCNA), calretinin, and serotonin, as well as general staining methods and semithin sections were used to characterize the territories containing GABA-immunoreactive (GABAir) neurons. Differentiation of GABAir neurons in the diencephalon begins in late embryos, whereas differentiation in the telencephalon and midbrain was delayed to posthatching stages. In lamprey prolarvae, the GABAir populations appear either as compact GABAir cell groups or as neurons interspersed among GABA-negative cells. In the telencephalon of prolarvae, a band of cerebrospinal fluid-contacting (CSF-c) GABAir neurons (septum) was separated from the major GABAir telencephalic band, the striatum (ganglionic eminence) primordium. The striatal primordium appears to give rise to most GABAir neurons observed in the olfactory bulb and striatum of early larval stages. GABAir populations in the dorsal telencephalon appear later, in 15-30-mm-long larvae. In the diencephalon, GABAir neurons appear in embryos, and the larval pattern of GABAir populations is recognizable in prolarvae. A small GABAir cluster consisting mainly of CSF-c neurons was observed in the caudal preoptic area, and a wide band of scattered CSF-c GABAir neurons extended from the preoptic region to the caudal infundibular recess. A mammillary GABAir population was also distinguished. Two compact GABAir clusters, one consisting of CSF-c neurons, were observed in the rostral (ventral) thalamus. In the caudal (dorsal) thalamus, a long band extended throughout the ventral tier. The nucleus of the medial longitudinal fascicle contained an early-appearing GABAir population. The paracommissural pretectum of prolarvae and larvae contained a large group of non-CSF-c GABAir neurons, although it was less compact than those of the thalamus, and a further group was found in the dorsal pretectum. In the midbrain of larvae, several groups of GABAir neurons were observed in the dorsal and ventral tegmentum and in the torus semicircularis. The development of GABAergic populations in the lamprey forebrain was similar to that observed in teleosts and in mouse, suggesting that GABA is a very useful marker for understanding evolution of forebrain regions. The possible relation between early GABAergic cell groups and the regions of the prosomeric map of the lamprey forebrain (Pombal and Puelles [ 1999] J. Comp. Neurol. 414:391-422) is discussed in view of these results and information obtained with ancillary markers.

Proliferating cell nuclear antigen (PCNA) immunoreactivity and development of the pineal complex and habenula of the sea lamprey

The development of the pineal complex and the habenula of the sea lamprey was studied with proliferating cell nuclear antigen (PCNA) immunocytochemistry. The pineal organ and the habenula primordia appeared in late embryos, and neuron differentiation began in prolarvae, as indicated by the presence of PCNA-negative cells. The parapineal primordium could not be distinguished until early prolarval stages, and cell differentiation was delayed to the larval period. Although the number of cycling (PCNA-immunoreactive) cells gradually decreased during the larval period in the three organs studied, their patterns of differentiation were different. We conclude that the unusual developmental pattern observed is related with the complex life cycle of lampreys.

Early development of the retina and pineal complex in the sea lamprey: comparative immunocytochemical study

Lampreys have a complex life cycle, with largely differentiated larval and adult periods. Despite the considerable interest of lampreys for understanding vertebrate evolution, knowledge of the early development of their eye and pineal complex is very scarce. Here, the early immunocytochemical organization of the pineal complex and retina of the sea lamprey was studied by use of antibodies against proliferating cell nuclear antigen (PCNA), opsin, serotonin, and gamma-aminobutyric acid (GABA). Cell differentiation in the retina, pineal organ, and habenula begins in prolarvae, as shown by the appearance of PCNA-negative cells, whereas differentiation of the parapineal vesicle was delayed until the larval period. In medium-sized to large larvae, PCNA-immunoreactive (-ir) cells were numerous in regions of the lateral retina near the differentiated part of the larval retina (central retina). A late-proliferating region was observed in the right habenula. Opsin immunoreactivity appears in the pineal vesicle of early prolarvae and 3 or 4 days later in the retina. In the parapineal organ, opsin immunoreactivity was observed only in large larvae. In the pineal organ, serotonin immunoreactivity was first observed in late prolarvae in photoreceptive (photoneuroendocrine) cells, whereas only a few of these cells appeared in the parapineal organ of large larvae. No serotonin immunoreactivity was observed in the larval retina. GABA immunoreactivity appeared earlier in the retina than in the pineal complex. No GABA-ir perikaryon was observed in the retina of larval lampreys, although a few GABA-ir centrifugal fibers innervate the inner retina in late prolarvae. First GABA-ir ganglion cells occur in the pineal organ of 15-17 mm larvae, and their number increases during the larval period. The only GABA-ir structures observed in the parapineal ganglion of larvae were afferent fibers, which appeared rather late in development. The time sequence of development in these photoreceptive structures is rather different from that observed in teleosts and other vertebrates. This suggests that the unusual development of the three photoreceptive organs in lampreys reflects specialization for their different functions during the larval and adult periods.

Otx1 null mutant mice show partial segregation of sensory epithelia comparable to lamprey ears

We investigated the development of inner ear innervation in Otx1 null mutants, which lack a horizontal canal, between embryonic day 12 (E12) and postnatal day 7 (P7) with DiI and immunostaining for acetylated tubulin. Comparable to control animals, horizontal crista-like fibers were found to cross over the utricle in Otx1 null mice. In mutants these fibers extend toward an area near the endolymphatic duct, not to a horizontal crista. Most Otx1 null mutants had a small patch of sensory hair cells at this position. Measurement of the area of the utricular macula suggested it to be enlarged in Otx1 null mutants. We suggest that parts of the horizontal canal crista remain incorporated in the utricular sensory epithelium in Otx1 null mutants. Other parts of the horizontal crista appear to be variably segregated to form the isolated patch of hair cells identifiable by the unique fiber trajectory as representing the horizontal canal crista. Comparison with lamprey ear innervation reveals similarities in the pattern of innervation with the dorsal macula, a sensory patch of unknown function. SEM data confirm that all foramina are less constricted in Otx1 null mutants. We propose that Otx1 is not directly involved in sensory hair cell formation of the horizontal canal but affects the segregation of the horizontal canal crista from the utricle. It also affects constriction of the two main foramina in the ear, but not their initial formation. Otx1 is thus causally related to horizontal canal morphogenesis as well as morphogenesis of these foramina.

Theory on the evolutionary history of lamprey metamorphosis: role of reproductive and thyroid axes

Metamorphosis is a developmental strategy used by only a small number of extant fishes and little is known about its phylogenetic development during the evolution history of this large group of vertebrates. The present report provides a putative evolutionary history of metamorphosis in the lamprey, an extant agnathan with direct descendancy from some of the oldest known vertebrates. The study reviews recent data on the role of the thyroid gland and its hormones in metamorphosis, summarizes some recent views on the evolution of the endostyle/follicular thyroid in lampreys, and provides new data on the content of two gonadotropin-releasing hormones (GnRH-I and -III) in brain during goitrogen-stimulated, precocious metamorphosis. These new data support an earlier viewpoint of a relationship between thyroid and reproductive axes during metamorphosis. It is proposed that the earliest lampreys were paedomorphic larvae and they lived in a marine environment; as such, they resembled in many ways the larvae from which the ancient protochordates, Larvacea, are derived. The iodide-concentrating efficiency of the endostyle was a critical factor in the evolution of metamorphosis and this gland was replaced by a follicular thyroid, for postmetamorphic animals needed to store iodine following their invasion of freshwater. Larval growth and postmetamorphic reproduction in freshwater became fixtures in the lamprey life cycle; a non-parasitic adult life-history type appeared later. The presence among extant lampreys of two different adult life-history types, and examples of the lability of the timing of sexual maturation in some species, imply that there has been a complex interplay between the thyroid and reproductive axes during the evolution of metamorphosis in lampreys. This proposal is consistent with what we know of interplay of these axes in extant adult lampreys and with the long-held viewpoint that thyroid function and sexual maturation are an association with an ancient history.

The distribution of melanin-concentrating hormone in the lamprey brain

In addition to its novel, colour-regulating hormonal role in teleosts, the melanin-concentrating hormone (MCH) serves as a neuromodulatory peptide in all vertebrate brains. In gnathostome vertebrates, it is produced in several neuronal cell groups in the hypothalamus. The present work examines the organisation of the MCH system in the brain of lampreys, which separated from gnathostome vertebrates at an early stage in evolution. In all three lamprey genera examined-Petromyzon, Lampetra, and Geotria spp.-MCH perikarya were found in one major anatomical site, the periventricular dorsal hypothalamic nucleus of the posterior hypothalamus. Axons from these cell bodies projected medially into the ventricular cavity, and laterally to the neuropile of the lateral hypothalamus. From here, they extended anteriorly and posteriorly to the fore- and hindbrain. Other fibres extended dorsomedially to the habenular nucleus. In Lampetra, but not in Petromyzon, MCH fibres were seen in the pituitary neurohypophysis, most prominantly above the proximal pars distalis. The hypothalamic region in which the MCH perikarya are found forms part of the paraventricular organ (PVO), which is rich in monoamines and other neuropeptides. The association of MCH neurones with the PVO, which occurs also in many other nonmammalian vertebrates, may reflect the primary location of the MCH system. These MCH neurones were present in ammocoetes, postmetamorphic juveniles, and adults. They were more heavily granulated in adults than in young lampreys but showed no marked change in secretory appearance associated with metamorphosis or experimental osmotic challenge to indicate a role in feeding or osmoregulation. In sexually maturing Lampetra fluviatilis, however, a second group of small MCH neurones became detectable in the telencephalon, suggesting a potential role in reproduction and/or behaviour.

Axonal regeneration of descending brain neurons in larval lamprey demonstrated by retrograde double labeling

In larval lamprey, the large, identified descending brain neurons (Müller and Mauthner cells) are capable of axonal regeneration. However, smaller, unidentified descending brain neurons, such as many of the reticulospinal (RS) neurons, probably initiate locomotion, and it is not known whether the majority of these neurons regenerate their axons after spinal cord transection. In the present study, this issue was addressed by using double labeling of descending brain neurons. In double-label control animals, in which Fluoro-Gold (FG) was applied to the spinal cord at 40% body length (BL; measured from anterior to posterior from tip of head) and Texas red dextran amine (TRDA) was applied later to the spinal cord at 20% BL, an average of 98% of descending brain neurons were double labeled. In double-label experimental animals, FG was applied to the spinal cord at 40% BL; two weeks later the spinal cord was transected at 10% BL; and, eight weeks or 16 weeks after spinal cord transection, TRDA was applied to the spinal cord at 20% BL. At eight weeks and 16 weeks after spinal cord transection, an average of 49% and 68%, respectively, of descending brain neurons, including many unidentified RS neurons, were double labeled. These results in larval lamprey are the first to demonstrate that the majority of descending brain neurons, including small, unidentified RS neurons, regenerate their axons after spinal cord transection. Therefore, in spinal cord-transected lamprey, axonal regeneration of descending brain neurons probably contributes significantly to the recovery of locomotor function.

Effects of insulin on lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus

This study was designed to examine the role of insulin (INS) in regulating changes in lipid metabolism of larval and metamorphosing landlocked lamprey, Petromyzon marinus. Larvae and stage 6 metamorphosing individuals were injected intraperitoneally once per day for 2 days with either saline (0.6%), bovine INS (100 ng/g body weight), or alloxan (0.2 mg/g body weight). Insulin administration resulted in depressed plasma fatty acid (FA) levels, whereas alloxan injection elevated plasma FA levels at both life cycle intervals. In larvae, INS-induced hypolipidemia was attended by increased lipid concentration in kidney and muscle, reduced rates of lipolysis in kidney, liver, and muscle (as indicated by decreased triacylglycerol lipase activity), and, to a lesser extent, by higher rates of lipogenesis in kidney and muscle (as evidenced by higher acetyl-CoA carboxylase and/or diacylglycerol acyltransferase activities). In general, the effects of alloxan were opposite of those of INS. The alloxan-induced increase in plasma FA was supported by an enhanced rate of lipolysis in the kidney, a relatively lower rate of fatty acid synthesis in kidney, liver, and muscle, and a relatively lower renal rate of TG synthesis. In stage 6 metamorphosing lamprey, the INS-induced decline in plasma FA was attended by reduced renal and hepatic rates of lipolysis and by enhanced lipogenesis, as indicated by increased renal and hepatic rates of de novo fatty acid synthesis and hepatic and muscular rates of TG synthesis. In contrast, the increase in plasma FA induced by alloxan in stage 6 animals was supported by reduced TG synthesis in liver. Immunocytochemistry revealed that alloxan was not cytotoxic to pancreatic beta cells, suggesting that the effects of alloxan were extrapancreatic in the time frame of our study. Because insulin-induced lipogenesis and antilipolysis is similar to the pattern of lipid metabolism (phase I) displayed by lamprey during their spontaneous metamorphosis, INS may play a role, possibly in concert with other factors, in coordinating metamorphosis-associated changes in lipid metabolism.

Temperature can alter the function outcome of spinal cord regeneration in larval lampreys

Now that spinal cord regeneration has been demonstrated in mammals [Bregman B. S. et al. (1995) Nature 378, 498-501; Cheng H. et al. (1996) Science 273, 510-513], we must examine the consequences and look for means of avoiding negative outcomes. The larval lamprey, which readily regenerates cut spinal axons, offers a model for this important next step. In the present study, one group of larval lampreys with spinal lesions was kept at room temperature during recovery. Another group was returned to their usual cold room temperature. A majority of animals kept at room temperature recovered full locomotor behavioral function, while a majority of those that recovered at a colder temperature exhibited dysfunctional locomotor behavior. The dysfunction most often consisted of segments rostral and caudal to the lesion site lacking the usual coordination and apparently interfering with each. In both groups, there was a close association between the presence of dysfunction and the quality of the intersegmental coordination as assessed in the isolated spinal cord preparation. These results suggest that a relatively minor difference in conditions under which an animal recovers may drastically alter the likelihood of a favorable functional outcome.