Ultrastructure of the adenohypophysis in the larval anadromous sea lamprey,Petromyzon marinus L.

The ultrastructure of the adenohypophysis (AH) in the larval anadromous sea lamprey, Petromyzon marinus L., was examined. The AH is subdivided into three regions, the pro-, meso-, and meta-AH. Cells of the nasopharyngeal stalk extend directly beneath the pro- and meso-AH to form the ventral surface of the gland. Some cells in the pro- and meso-AH are arranged into small follicles. Each region of the AH is characterized by a single granulated (secretory) cell type. Granulated cells constitute 80–90% of the pro-AH and contain secretory granules that range from 800 to 2400 Å in diameter. Only 10–20% of the cells in the meso-AH are granulated and they contain much smaller secretory granules (400 to 1250 Å diameter) than those in the pro-AH. Granulated cells constitute 80–90% of the meta-AH and contain only a few secretory granules, ranging from 1000 to 2500 Å in diameter, and many vesicles containing either a loose flocculent or dense granular material. Nongranulated (stellate) cells are found in all regions. They are characterized by their long cell processes, abundant cytoplasmic filaments, and variable electron density. The appearance of organelles in these cells suggests they are nonsecretory. They may play a role in maintaining the structural integrity of the gland and the regulation of granule release in the pro-AH. Two types of nongranulated cells make up 80–90% of the meso-AH. Type I are stellate cells, type II may be undifferentiated cells. The functional significance of the secretory cells in the larval AH is discussed.     

Immunocytochemical localization of thyroglobulin in the endostyle of the anadromous sea lamprey, Petromyzon marinus L

Thyroglobulin (TG) was localized in the endostyle of the anadromous sea lamprey, Petromyzon marinus L. by means of the unlabeled antibody peroxidase-antiperoxidase immunocytochemical method. TG was found localized on the apical surface and within the cytoplasm of type 2c and 3 cells and in some type 5 cells. By identifying the cells of the endostyle immunocytochemically it may be possible to study more readily the events of endostylar transformation during metamorphosis.     

The hemoglobin of the sea lamprey,Petromyzon marinus

The blood hemoglobin of the sea lamprey presents a curious mixture of primitive and highly specialized properties. Like muscle hemoglobin, it has a molecular weight of about 17,000, and apparently contains a single heme. Its isoelectric point is like that of a typical invertebrate hemoglobin. Its amino acid composition is partly characteristic of invertebrate) partly of vertebrate hemoglobins (Pedersen; Roche and Fontaine). In the present experiments, the oxygen equilibrium curve of this pigment was measured at several pH's. As expected, it is a rectangular hyperbola, the first such function to be observed in a vertebrate blood hemoglobin. Other hemoglobins known to possess this type of oxygen dissociation curve—those of vertebrate muscle, the worm Nippostrongylus, and the bot-fly larva—appear to serve primarily the function of oxygen storage rather than transport. Lamprey hemoglobin on the contrary is an efficient oxygen-transporting agent. It achieves this status by having, unlike muscle hemoglobin, a relatively low oxygen affinity, and a very large Bohr effect. In these properties it rivals the most effective vertebrate blood hemoglobins.     

Transformation of the intestinal epithelium of the larval anadromous sea lamprey Petromyzon marinus L. during metamorphosis

The events in the transformation of the intestine of the larval lamprey into the adult intestine were followed through the seven (1–7) stages of metamorphosis in anadromous Petromyzon marinus L. Light and electron-microscope observations demonstrated that the processes of degeneration, differentiation, and proliferation are involved in the transformation. In the anterior intestine, degeneration of cells and the extrusion of others into the lumen results in the disappearance of secretory (zymogen) cells and the decline in numbers of endocrine and ciliated cells. Larval absorptive cells, with a prominent brush border, are believed to dedifferentiate into unspecialized columnar cells with few microvilli. Degeneration and removal of cells occurs by both autophagy and heterography and cells extruded into the lumen in the anterior intestine are phagocytosed by epithelial cells of the posterior intestine. The loss of epithelial cells during transformation results in the folding and degradation of parts of the basal lamina and in an extensive widening of the lateral intercellular spaces in all parts of the intestine. As metamorphosis is a nontrophic period of the lamprey life cycle, the possible morphological effects of starvation on the intestinal epithelium are discussed. The development of longitudinal folds is a consequence of the events of metamorphic transformation of the intestinal mucosa. Although an interaction between the epithelium and the underlying tissues is believed to be importent, the actual mechanism of fold development is unknown. The intestinal epithelium of adult lampreys develops from surviving cells of the larval (primary) epithelium. Unlike the situation in amphibians, there does not appear to be a group (nest) of undifferentiated larval cells which differentiate into the adult (secondary) epithelium. Instead, in lampreys, columnar cells that persist through the degradative processes seem to be the source of absorptive and ciliated cells and probably are responsible for mucous and secretory cells. Preliminary observations indicate that the intestinal epithelium of feeding adults is specialized into an anterior region which liberates a secretion, absorbs lipid, and possesses the machinery for ion transport. A posterior region absorbs lipid, secretes mucus, and likely is involved in some protein absorption.     

Transformation of the endostyle of the anadromous sea lamprey,Petromyzon marinus L., during metamorphosis. II. Electron microscopy

Electron microscopy was used to follow the transformation of the endostyle to a thyroid gland in the anadromous sea lamprey, Petromyzon marinus L., throughout metamorphosis (stages 1–7). Transformation of the larval (ammocoete) endostyle begins at the first signs of external change (stages 1–2), and the adult form of the gland is reached by stage 5. Only slight modifications of the gland accompany further development to the end of metamorphosis. Development of the thyroid gland involves degeneration, proliferation, and reorganization of the cells in the endostyle, and changes in their fine structure. Ultrastructural changes during early stages are most obvious in the type 1 cells that make up the shrinking glandular tracts, and involves the accumulation of cytoplasmic microfilaments and a variety of cytoplasmic inclusions. The glandular tracts and their cells gradually disappear through autolysis and, apparently, through phagocytosis by neighboring epithelial cells and macrophages. Although the fine structure of the type 2, 3, 4, and 5 cells is not altered in the early stages, by stage 3, many of these cells become either vacuolated, undergo autolysis, or are extruded. Phagocytosis of some of each of these cell types likely occurs. Thyroid follicles are first observed during stage 4. Some of their lumina seem to arise from the accumulation of material in intercellular spaces and from vacuoles among cell clusters. Other lumina may represent a portion of the original lumen of the endostyle. Many follicles appear to be comprised of cells with cytological characteristics similar to those of larval cell types 3 and 2c. Some of the other larval cell types, such as type 5, may also be involved. In young adult lampreys follicles are composed of cuboidal to columnar cells that lack the dilated cisternae of rough endoplasmic reticulum seen in follicular cells of higher vertebrates. Dense collagenous connective tissue surrounding the follicles contains relatively few blood vessels. The transformation process described may have some relevance to our understanding of the development and evolution of the vertebrate thyroid gland.     

Genomic analysis of Hox clusters in the sea lamprey Petromyzon marinus

The sea lamprey Petromyzon marinus is among the most primitive of extant vertebrates. We are interested in the organization of its Hox gene clusters, because, as a close relative of the gnathostomes, this information would help to infer Hox cluster organization at the base of the gnathostome radiation. We have partially mapped the P. marinus Hox clusters using phage, cosmid, and P1 artificial chromosome libraries. Complete homeobox sequences were obtained for the 22 Hox genes recovered in the genomic library screens and analyzed for cognate group identity. We estimate that the clusters are somewhat larger than those of mammals (roughly 140 kbp vs. 105 kbp) but much smaller than the single Hox cluster of the cephalochordate amphioxus (at more than 260 kb). We never obtained more than three genes from any single cognate group from the genomic library screens, although it is unlikely that our screen was exhaustive, and therefore conclude that P. marinus has a total of either three or four Hox clusters. We also identify four highly conserved non-coding sequence motifs shared with higher vertebrates in a genomic comparison of Hox 10 genes.     

Growth and intermediary metabolism of larval and metamorphosing stages of the landlocked sea lamprey,Petromyzon marinus L

Synopsis Seasonal changes in blood, liver and muscle substrate (glucose, glycogen and lipid) concentrations and enzyme (pyruvate kinase (PyK), fructose diphosphatase (FDPase), NADP-isocitrate dehydrogenase (ICDH), malic enzyme (ME) and the hexose monophosphate shunt dehydrogenases (HMSD)) activities were assessed in ammocoete and metamorphosing stages of a stream stock of the landlocked sea lamprey, Petromyzon marinus L. In all developmental stages studied, muscle rather than liver tissue served as the main site of carbohydrate and fat storage. Blood glucose and muscle lipid exhibited a positive relationship while liver HMSD and muscle ME activity, a negative relationship, with ammocoete weight. These responses were attributed to a proliferation of red fibers and adipocytes in the ammocoete muscle as the time of metamorphosis approched. Muscle lipid stores of ammocoetes in their last year of larval life increased dramatically during the fall and winter preceding metamorphosis. Changes in tissue enzyme activity of ammocoetes in their last year of larval life indicated that the liver was the site of amino acid incorporation into fat while muscle was the site of lipogenesis from glucose. During the non-trophic period of metamorphosis, stored material was catabolized to provide energy for protein synthesis.     

Sea lamprey Petromyzon marinus: an exception to the rule of homing in anadromous fishes

Anadromous fishes are believed to make regular circuits of migration in the sea before homing to their natal rivers. Sea lamprey Petromyzon marinus is an anadromous fish that is an exception to this life-history pattern. It also differs from other anadromous fishes in that its adult phase is parasitic, a feeding strategy that should make homing problematic for lamprey cohorts that become widely dispersed through transport by the diverse hosts they parasitize. We sequenced a portion of the mitochondrial DNA control region from sea lampreys collected from 11 North American east coast rivers to test for genetic evidence of homing. There were no significant differences (chi2=235.1, p=0.401) in haplotype frequencies among them, with almost 99 per cent of haplotypic diversity occurring within populations. These findings, together with concordant genetic results from other geographical regions and ancillary information on pheromonal communication, suggest that sea lamprey does not home but rather exhibits regional panmixia while using a novel 'suitable river' strategy to complete its life cycle.     

Changes in the ventral dermis and development of iridophores in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis: an ultrastructural study.

The ultrastructural changes that take place in the ventral dermis along with the development of iridophores were examined in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis. There is a disruption of all components of the ventral dermis and a reformation that results in a structure very similar to that prior to metamorphosis. Although not a dermal component, a layer of iridophores develops directly beneath the dermis during late metamorphosis. The dermal endothelium is lost by mid metamorphosis (stage 4) and the highly organized collagenous lamellae making up the bulk of the dermis become disrupted by the migration of fibroblasts into the region. Many of these fibroblasts are involved in the degradation of the lamellae. By stage 5 of metamorphosis some fibroblasts become highly active collagen synthesizing cuboidal shaped cells that align to form a layer above the reformed dermal endothelium. New lamellae are formed by these cuboidal cells which then divide and migrate into the lamellae where they assume the characteristic attenuated appearance of fibroblasts in the adult dermal lamellae region. Iridophores first appear during stage 5 directly beneath the dermal endothelium. Reflecting platelets develop from double membraned vesicles associated with the Golgi apparatus. By late metamorphosis, stacks of trapezoidal shaped platelets fill the cytoplasm of the iridophores. The significance of the changes in the dermis during metamorphosis are discussed. This work is part of a continuing series of studies on the connective tissues in the anadromous sea lamprey.     

Photokinetic responses and diel activity of sea lamprey Petromyzon marinus ammocoete larvae

Twenty-four ammocoete larvae of the sea lamprey Petromyzon marinus were tested individually for 3-day periods in electronic shuttleboxes (Ichthyotrons) with natural lighting through windows, to determine their diel activity pattern in terms of hourly percentages of the 24-h total. Mean hourly activity was slightly greater during the day (4–7 % h⁻¹) than at night (3·7% h⁻¹). Peak hourly activity (7·2% h⁻¹) occurred during the dawn crepuscular period as light levels were increasing, while the minimum hourly activity (1·6 % h^-l) occurred during the dusk crepuscular period while light levels were decreasing. The observed activity pattern is atypical of other aquatic animals similarly tested, and might be explained as an extraptically mediated photoinetic response.     

Ultrastructure of the pronephric kidney in upstream migrant sea lamprey, Petromyzon marinus L

The pronephric kidneys were examined in upstream migrant sea lampreys, Petromyzon marinus L., by transmission and scanning electron microscopy. Each pronephros consists of an enlarged renal corpuscle (glomus) and ciliated nephrostomes, but there are no renal tubules. The renal corpuscle contains an extensive mesangium, which consists of a highly fibrous extracellular matrix, numerous mesangial cells, granulocytes, and macrophages. The extracellular matrix contains microfibrils with a morphology similar to amyloid P microfibrils, fibrils with a periodicity similar to fibrin, and abundant collagen. Often these fibrillar components are aggregated in the region of the basement membrane, giving it a thickened appearance. Some podocytes of the visceral epithelium appear swollen, and their cytoplasm contains numerous vacuolar inclusions, and many have only primary major processes with only a few or no foot processes. The morphological features of the pronephric kidney of the lamprey at this time in the life cycle reflect the regression of this organ, but some features also resemble those seen in renal pathologies of higher vertebrates.     

Ultrastructure of chloride cells in young adults of the anadromous sea lamprey, Petromyzon marinus L., in fresh water and during adaptation to sea water.

The chloride cells in the interlamellar areas of the gills of young adult, anadromous sea lampreys, Petromyzon marinus L., captured in fresh water undergo structural modification during the adaptation of these animals to sea water. In fresh water the chloride cells are partially overlapped by mucus-secreting superficial cells and contain an extensive reticulum of cytoplasmic tubules, which are confluent with both lateral and basal plasma membranes, numerous mitochondria, a Golgi complex of moderate size, and numerous apical vesicles. Adaptation to sea water results in a retraction of the superficial cells, exposing the entire apical surface of the chloride cells, and a proliferation of both cytoplasmic tubules and mitochondria. Extensive enlargement of the Golgi complex in the chloride cells of these animals suggests the involvement of this organelle in the proliferation of cytoplasmic tubules. The extracellular tracer, ruthenium red, enters the tubules from the lateral or basal intercellular spaces in both freshwater- and seawater-adapted animals but never enters either tubules or vesicles from the apical surfaces, indicating that these are not confluent. The presence of dividing basal cells and newly-forming chloride cells, combined with evidence of degeneration of chloride cells, suggests that there is a turnover of this cell type. Both superficial and basal cells are phagocytic and involved in heterophagy of degenerating chloride cells. This phenomenon occurs in both fresh water and sea water indicating that the chloride cells may be functional in both environments.     

The haematophagous feeding stage of anadromous populations of sea lamprey Petromyzon marinus: low host selectivity and wide range of habitats

Limited information is available regarding habitat use and host species of the haematophagous feeding stage of the anadromous sea lamprey Petromyzon marinus Linnaeus, 1758, due to the difficulties in capturing feeding lampreys and wounded hosts. The aim of this study is to provide new records of P. marinus feeding on host species and to review the available information in this regard to better know the ecology and distribution of sea lamprey during this stage. Thus, new records of P. marinus individuals or wounds on 23 species of fishes and cetaceans are provided. Nineteen of these species were described for the first time as hosts of P. marinus. As a result, an updated list of 54 host species is provided. They belong to diverse taxonomic groups and exhibit different morphological, physiological and ecological patterns. The attacks were located from fresh and brackish waters to open sea. The results suggest that the marine distribution of P. marinus is mainly related to coastal areas with part of the population widely dispersed in offshore areas. This remarkable capacity of inhabiting a broad range of aquatic ecosystems and exploiting different host species could have favoured the dispersal ability and evolutionary success of sea lamprey.     

Ultrastructure of the pronephric kidney of embryos and prolarvae of the sea lamprey, Petromyzon marinus

Embryos of lampreys Petromyzon marinus were obtained through a technique of artificial fertilization. Samples of developmental intervals to the prolarval stage were prepared for transmission electron microscopy and the pronephros was examined. The pronephros was visible in the cardiac region of the coelom prior to the time of hatching of embryos and consisted of a renal corpuscle, nephrostomes, and proximal tubules connected to a pronephric duct. The renal corpuscle was comprised of poorly-defined vascular channels and a visceral epithelium of yolk-filled cells, the podocytes, with short major processes and pedicels resting on a basal lamina. The first proximal tubules possessed a delicate brush border of short microvilli but subsequent cellular differentiation yielded cells with all the components required for the process of endocytosis, a process which was demonstrated by uptake of the tracer, horseradish peroxidase. The distal tubules appeared later in development and were noted for abundant mitochondria and an extensive smooth tubular network. The timing of differentiation of various components of the nephron corresponds to that seen during morphogenesis of other vertebrate kidneys.