Localization of somatostatin-like immunoreactivity in the pancreatic islets of the hagfish, Myxine glutinosa and the lamprey Lampetra fluviatilis

Somatostatin in the ovary of an African lungfish (Protopterus annectens): an in situ hybridisation, immunohistochemical, and autoradiographical study

In mammals, somatostatin seems to be involved in the control of ovarian steroidogenesis. There have been no studies on the presence or actions of somatostatin in the ovary of nonmammalian vertebrates. The localisation of somatostatin-14 was examined immunohistochemically using the antibody to somatostatin-14 in the ovary of the African lungfish Protopterus annectens. Immunoreactivity was present in the granulosa cells of mature ovarian follicle examined by light microscopy. Using an oligonucleotide probe complementary to mRNA for somatostatin-14 and labelled at the 3'-end with alpha-35S, in situ hybridisation demonstrated somatostatin-14 mRNA distributed in cells showing the same localisation as that of the immunoreactive cells. Binding sites for SST-14 were identified with autoradiography using [125I]somatostatin-14. Binding sites were localised on granulosa and theca cells. Somatostatin-14 may be thus synthesised in the lungfish ovary.

Development of the adult endocrine pancreas during metamorphosis in the sea lamprey, Petromyzon marinus L. I. Light microscopy and autoradiography

The results of this study were found to support the hypothesis put forth by Boenig (Z. Mikrosk-Anat. Forsch., 17:125-184, 1929) that the caudal pancreas of adult lamprey develops from the epithelium of the extrahepatic common bile duct in that the bile duct cells were found to undergo a great proliferation during the early stages of metamorphosis, with a large number of the cells incorporating 3H-thymidine. If the bile duct degenerated as suggested by Barrington (The Biology of Lampreys. Academic Press, London, pp. 135-169, 1972), this uptake would not be expected. The cranial pancreas was determined to develop in a similar manner to the larval islets, with formation of the islets taking place within the intestinal/diverticular epithelium. The newly formed islets would migrate into the surrounding connective tissue. During the later stages of metamorphosis a small number of cells was found to incorporate the tritiated thymidine within mature islets.

Distribution of somatostatin-immunoreactivity in the brain of the larval lamprey (Petromyzon marinus)

The detailed distribution of somatostatinergic neurons and fibre tracts in the brain of larval lamprey was studied in serially sectioned material using immunocytochemical techniques. Neurons were found to be arranged in four nuclei: a hypothalamic nucleus consisting of both small cerebrospinal fluid-contacting neurons and larger non-contacting neurons, a thalamomesencephalic nucleus and two isthmotrigeminal reticular nuclei. The hypothalamic nucleus is the first to differentiate. Analysis of young larvae showed that somatostatin-immunoreactivity first appeared in hypothalamic cells (12 mm larvae), while it appeared later in the other nuclei. The different somatostatin-immunoreactive fibre tracts innervate different regions of the brain. In addition, somatostatin-immunoreactive fibres originating from hypothalamic neurons were found in the anterior neurohypophysis, which suggests the presence of a hypothalamohypophysial somatostatinergic system in lampreys.

Distribution of two forms of somatostatin and peptides belonging to the pancreatic polypeptide family in tissues of larval lampreys, Petromyzon marinus L.: an immunohistochemical study

Immunohistochemistry on tissues of larval lampreys, Petromyzon marinus L., was used to determine the distribution of invariant somatostatin-14 (SST-14) and lamprey somatostatin-34 (SST-34) in the brain while antisera against porcine peptide tyrosine tyrosine (PYY), human neuropeptide Y (NPY), anglerfish peptide YG (aPY), salmon glucagon-like peptide (GLP), SST-14, and SST-34 were used in studies of the pancreas and anterior intestine. In the brain, SST-14 is the major form of somatostatin. SST-14- and SST-34-immunoreactive nerve fibers are distributed throughout the telencephalon, diencephalon, and mesencephalon. In the latter region SST-14 immunoreactivity is concentrated in nerve tracts in the nucleus interpeduncularis. Nerve cells within the olfactory bulbs are immunoreactive only to anti-SST-34. Cells immunostained with anti-SST-14 were localized within the ependymal and subependymal layers of the pars ventralis hypothalami and the subependymal layers of the pars dorsalis thalami. SST-14-immunoreactive perikarya are also distributed within the tegmentum mesencephali. Nerve fibers and cells immunoreactive to anti-SST-34 are detected in the pars ventralis hypothalami but these cells do not colocalize SST-14. Pancreatic islets, distributed within the epithelium and in the submucosal connective tissue at the esophageal-intestinal junction, are only immunoreactive to anti-insulin. The antisera revealed three distinct cell types in the intestinal epithelium: type 1 colocalizes aPY, NPY, and PYY; type 2 colocalizes SST-14 and SST-34; and type 3 demonstrates immunoreactivity only to anti-SST-34. Immunoreactivity to anti-GLP is absent.

Immunoreactivity to peptides belonging to the pancreatic polypeptide family (NPY, aPY, PP, PYY) and to glucagon-like peptide in the endocrine pancreas and anterior intestine of adult lampreys, Petromyzon marinus: an immunohistochemical study

Immunoreactivity of antisera directed against human neuropeptide Y (NPY), anglerfish polypeptide YG (aPY), bovine pancreatic polypeptide (bPP), salmon pancreatic polypeptide (sPP), porcine peptide tyrosine tyrosine (PYY), and salmon glucagon-like peptide (GLP) was investigated in the endocrine pancreas and anterior intestine of adult lampreys, Petromyzon marinus, by immunohistochemical analysis. There was no immunoreactivity to anti-sPP and anti-bPP in any tissue and anti-GLP immunostaining was only present in the anterior intestine. The immunoreactivity to antisera raised against NPY, aPY, and PYY was colocalized within the same small number of cells in the caudal and cranial pancreas of juveniles and the caudal pancreas of upstream migrant adults. These antibodies did not immunostain B- or D-cells and thus, NPY, aPY, and PYY were likely localized in a third cell type (3a) in the lamprey pancreas. Immunostaining of a few cells with only anti-aPY suggested the possibility of a fourth cell type (3b). Immunoreactivity was similar in the cranial and caudal pancreas of male upstream migrants; however, in the female cranial pancreas, a few cells demonstrated intense immunoreaction to anti-aPY, while weaker immunostaining with this antiserum was observed in B-cells. In the intestine of juvenile and upstream migrant lampreys, positive immunostaining to GLP, NPY, aPY, and PYY antibodies was colocalized within the same cell. We believe that this cell may contain PYY/glucagon family peptides. Other intestinal cells immunostained with either GLP or somatostatin-34 antiserum.

Somatostatin concentrations in the pancreatic-intestinal tissues of the sea lamprey, Petromyzon marinus L., at various periods of its life cycle

1. Somatostatin concentrations were measured in homogenates of the pancreas-intestinal tissues from each period of the life cycle of Petromyzon marinus using radioimmunoassay. 2. Levels were very low in larva (4.0 pg/mg wet weight) and in the first three stages of metamorphosis, but increased from stage 4 onwards and reached a high in upstream-migrating adults (210.0 ng/mg). 3. These data correlate well with our previous morphological and immunohistochemical observations on the morphogenesis of somatostatin-containing D-cells during the life cycle and indicate that the increased concentration of hormone accompanies the development of the endocrine pancreas in lampreys.

Distribution of two forms of somatostatin in the brain, anterior intestine, and pancreas of adult lampreys (Petromyzon marinus)

The distribution of two major immunoreactive forms of somatostatin, somatostatin-14 and somatostatin-34, within the brain, pancreas and intestine of adult lampreys, Petromyzon marinus, was identified using antisera raised against these peptides. Immunostaining of the brain is similar in juveniles and upstream migrants, and somatostatin-14 is the major somatostatin form demonstrated. A few somatostatin-34-containing cells are localized within the olfactory bulbs, thalamus and hypothalamus, but cells immunoreactive to anti-somatostatin-34 in the hypothalamus and thalamus do not co-localize somatostatin-14. Immunostaining of pinealocytes within the pineal pellucida with anti-somatostatin-14 may infer a novel function for this structure. Somatostatin-14 and somatostatin-34 are co-localized within D-cells of the cranial pancreas and caudal pancreas of juveniles and upstream migrants. Numerous somatostatin-34-immunoreactive cells are distributed within the epithelial mucosa of the anterior intestine but not all of these cells cross-react with anti-somatostatin-14. It appears that somatostatin-34 is the major somatostatin in the pancreo-gastrointestinal system of adult lampreys.

Gut hormones in cyclostomes

The current state of knowledge about regulatory peptides in endocrine cells and nerves of the alimentary canal of lampreys and hagfishes is reviewed. Cyclostomes have a wide range of peptides similar immunochemically to those of higher vertebrates. They include, in the endocrine cells of the intestine, peptides resembling glucagon, gastrin/cholecystokinin, peptide YY (pancreatic polypeptide/neuropeptide Y), substance P, vasoactive intestinal peptide, somatostatin and, in the larval stages at least, insulin. The enteric nerves of some lamprey species contain peptides resembling bombesin (gastrin-releasing peptide) and calcitonin gene-related peptide, as well as serotonin. The occurrence of other peptides is less well documented.Little is known of the molecular structure or the biological roles of the enteric peptides in cyclostomes. Extraction, purification, sequencing and physiological experiments are greatly needed.

Morphology of the exocrine pancreas of the southern hemisphere lamprey, Geotria australis, and changes during metamorphosis

The distribution and histology of zymogen cells and the activity of digestive enzymes have been examined in the alimentary canal of larval, metamorphosing (stages 1-7), and adult Geotria australis (Geotriidae). Comparisons of the arrangement of the larval and adult zymogen cells are made with those observed in Mordacia mordax, a representative of the other Southern Hemisphere lamprey family (Mordaciidae), and with those reported elsewhere for holarctic lampreys (Petromyzontidae). In larval G. australis, epithelial zymogen cells are mainly restricted to the prominent pair of tubular diverticula which project forward from the oesophageal/intestinal junction. By contrast, zymogen cells of adults are present in the epithelium of both the anterior intestine and the intestinal caecum, a structure located at the new and more anterior oesophageal/intestinal junction which forms during metamorphosis. Amylolytic activity was greater in the larval diverticula than in the adult caecum, whereas the reverse was true for tryptic activity. This feature presumably reflects the high dietary contribution made by detritus and algae during the filter-feeding larval phase and by host muscle tissue during the predatory adult phase. The high tryptic activity in the caecum must promote the early breakdown of host tissue and thereby facilitate the digestion of lipids in the anterior intestine where lipolytic activity is high. At the commencement of metamorphosis, digestive activity and the number of zymogen cells declines markedly. By stage 4 the intestine has rotated anticlockwise almost 360 degrees; the two larval diverticula have disappeared; and the new exocrine caecum of the adult has started to develop from a forward proliferation of intestinal mucosal cells. While the exocrine pancreatic tissue of larval M. mordax is unique amongst lampreys in its location within a single, large diverticulum containing an extensive network of mucosal folds, that of the adult is found in the same position as in G. australis and holarctic lampreys.

Fine structure and immunocytochemistry of cells within the endocrine pancreas of larval and adult sea lampreys, Petromyzon marinus L

Immunocytochemistry with protein A-gold and routine electron microscopy were used to identify cell types within the endocrine pancreas of larvae, juvenile adults, and upstream-migrant adults of the sea lamprey, Petromyzon marinus. The larval pancreatic islets are composed only of insulin-immunoreactive B-cells, which are uniform in their fine structure. The cranial and caudal pancreatic tissue in both adult periods contains three cell types: B-cells, somatostatin-immunoreactive D-cells, and a third cell type of unknown content. No glucagon-immunoreactive cells are present in lampreys, but B- and D-cells exist in equal numbers in the pancreatic tissue of adults. The B-cells of adults have a fine structure similar to those in larvae. D-cells have secretory granules that are distinctly different from those both in B-cells and in the third cell type. Although B- and D-cells in lamprey pancreatic tissues have a basic morphological similarity to these cells in other vertebrates, their granules are generally of smaller dimensions. The inclusion of granules within large pleomorphic bodies in many D-cells indicates that granule turnover is common. Immunocytochemistry will be a useful tool for showing the relationship between the cells in the degenerating bile ducts and those of the developing adult pancreas.

An elasmobranchian somatostatin: primary structure and tissue distribution in Torpedo marmorata

Extracts of brain, stomach, pancreas, and intestine from Torpedo marmorata, an elasmobranchian cartilaginous fish, contained somatostatin-like immunoreactivity. Gel filtration studies demonstrated that material with the elution volume of somatostatin-14 was the only component detected in all tissue extracts. This result contrasts with the situation in mammals where prosomatostatin is processed to multiple molecular forms in a tissue-specific manner. Somatostatin from pancreas and gut was purified to homogeneity and amino acid sequence analysis indicated that T. marmorata somatostatin from both tissues has the same structure as somatostatin-14 isolated from the higher vertebrates. Further examination of other lower vertebrate species is required in order to test the hypothesis that the ability to regulate the production of multiple forms of a regulatory peptide from a single precursor molecule developed only relatively late in evolution.

Distribution, histochemistry and ultrastructure of somatostatin-like immunoreactive cells in the gastroenteric tract of the cartilaginous fish Scyliorhinus stellaris (L.)

Somatostatin-like immunoreactive cells of an open type have been identified in the digestive tract of the cartilaginous fish Scyliorhinus stellaris (L.) by the use of immunocytochemical techniques. In the stomach these cells are numerous both in the corpus (neck zone and tubular glands) and in the pyloric portion (crypts). In the spiral valve, somatostatin-like cells are rare, situated in the intestinal epithelium and without any particular localization. Using semithin serial sections, somatostatin-like cells are found to be Davenport-negative and weakly positive towards the Grimelius silver reaction, and using the semithin and ultrathin technique have been identified at the ultrastructural level; their secretory granules appear electron dense, round or slightly polygonal, and with a limiting membrane tightly adherent to the core. The mean diameter varies from 250-300 nm.

The morphology and histology of the endocrine pancreas of the southern hemisphere lamprey, Geotria australis gray

The location and arrangement of the pancreatic endocrine tissue in larval and adult Geotria australis (Geotriidae) differ markedly from those exhibited by the comparable stages of Northern Hemisphere lampreys (Petromyzontidae). In larval Geotria australis, the main zones of islet proliferation are located laterally between the oesophagus and the inner edge of the two large intestinal diverticula unique to this species rather than dorsal and ventral to the oesophagus. In adult Geotria australis, the islet follicles are closely packed into a single discrete capsule which could be easily removed surgically, rather than into cranial, intermediate, and caudal cords. The differences in the adult can be related to a lack of involvement of the bile duct in islet formation during metamorphosis. While B cells were found in both larval and adult islet follicles, the PI acidophilic cells and argyrophilic cells, which appeared respectively at stages 3 and 4 in metamorphosis, were present in all adult stages.

Substance P-, neurotensin- and bombesin-like immunoreactivities in the gill epithelium of Ciona intestinalis L

Substance P-, neurotensin- and bombesin-like immunoreactivities were localised in some gill epithelial cells in the pharynx of Ciona intestinalis L. No immunoreactivity was obtained with antisera to gastrin, glucagon, insulin, pancreatic polypeptide or calcitonin. Some of the epithelial cells of the gills were shown to be argyrophilic with the Grimelius technique.

Localization of somatostatin-, substance P- and calcitonin-like immunoreactivity in the neural ganglion of Ciona intestinalis L. (Ascidiaceae)

Indirect immunofluorescence studies using antisera to synthetic somatostatin, human calcitonin and substance P indicate, in the neural complex of the sea-squirt, Ciona intestinalis L., that these polypeptides are present in large perikarya situated at the periphery of the cerebral ganglion as well as in some smaller perikarya in the medulla. In the medullary and transitional zone, there are nerve fibres that cross-react positively with anti-calcitonin and anti-substance P.

Pancreatic endocrine cells of Barbus conchonius (Teleostei, Cyprinidae), and their relation to the enteroendocrine cells

The pancreatic endocrine cells of Barbus conchonius are concentrated in a large (principal) islet, located near the gall bladder, and in a number of smaller islets. Five types of endocrine cells can be distinguished in there pancreatic islets: B cells, A1 (or D cells), 2 types of A2 cells (A2r cells with round granules; and A2fl cells with flocculent granules) and a scarce 5th cell type. The hormones produced by B and A2fl cells are probably insulin and glucagon respectively. The A2r cell contains granules with the same diameter as the granules of the enteroendocrine type III cell of the gut. Both cell types may resemble the enteroglucagon-producing EG cell of mammals. The function of the A1 cells, which are frequently found without secretory granules, and of the 5th cell type, will be discussed. The pancreastic islets of B. conchonius are strongly innervated, which suggests thatpresence of a direct nervous control system. Some intermediate or mixed cells containing exocrine and endocrine A2r granules are found continguous with the principal islet. The origin of pancreatic endocrine cells is also the subject of discussion.

Localization of four polypeptide hormones in the saurian pancreas

Glucagon, insulin, somatostatin, and pancreatic polypeptide have been localized in the anolian pancreas using peroxidase-antiperoxidase immunocytochemistry. The most abundant endocrine cell type contains glucagon. Insulin-containing cells are the next most numerous. Somatostatin-immunoreactive cells tend to be localized at the periphery of the islet cords. Pancreatic polypeptide-containing cells are a minor endocrine component scattered throughout the exocrine pancreas and occasionally within the islet areas. No staining was observed after application of antigastrin serum.

Localisation of somatostatin- and gastrin-like immunoreactivity in the gastrointestinal tract of Ciona intestinalis L

Somatostatin- and gastrin-like immunoreactivity has been found by immunofluorescence in cells of the stomach and intestinal epithelia of Ciona intestinalis L. The cells containing the peptide immunoreactive to mammalian anti-gastrin can be restained with Grimelius' technique for argyrophilia.

Phylogeny of insulin. Some evolutionary aspects of insulin production with particular regard to the biosynthesis of insulin in Myxine glutinosa

Preceding phylogenetic studies on the occurrence of insulin have shown--e.g. by bioassays and immunocytochemical procedures--that insulin producing B-cells are present in all vertebrates and even in several invertebrates, both protostomian and deuterostomian. The most original B-cells are obviously endocrine cells of open type, situated in the mucosa of the alimentary tract. Moreover, the results of these studies show that insulin is not only a polypeptide hormone of considerable age but also that the insulin molecule seems to have been kept surprisingly stable during evolution. Best known of all non-mammalian insulins is that from the hagfish, Myxine glutinosa. It is probably the most original insulin of all in the vertebrate series. Both the amino-acid sequence and the three-dimensional structure of the dimer of hagfish insulin differ only little from those of pig insulin. The biosynthesis occurs via proinsulin and is also in most respects similar to mammalian insulin biosynthesis. There are, however, some differences. Although it readily crystallizes as tetragonal bipyramids, hagfish insulin does not form hexamers. In a test system, with isolated rat fat cells, its binding affinity is 23% and its potency 5% of that of pig insulin, a discrepancy indicating a "partial antagonism" on the receptors. Although the conversion of proinsulin to insulin seems to occur in the secretion granules, they contain no crystalline cores. Since a strictly tryptic-like enzyme was found to destroy hagfish insulin rapidly, the enzyme converting proinsulin to insulin must--in addition to a carboxy-peptidase-B-like activity--have a different specificity in Myxine.

Structural analysis of the molecular evolution of some gastro-entero-pancreatic hormones

By means of a statistical analysis of the occurrence of amino-acid residues in the polypeptide chains of several gastro-entero-pancreatic (GEP) hormones an investigation was undertaken to determine whether any of these hormones might be related to each other--possibly from an evolutionary point of view. Particular interest was paid to the occurrence of small charged segments, i.e. those with acidic or basic amino acid residues, since such segments can be presumed to play a role in hormonal receptor binding mechanisms. By this method hormonal relationships were suggested by the observation that these small charged amino-acid sequences, contained in the hormonal structures, match as a result of non-randomness. It was found that hagfish and human insulin were related on a molecular level not only to the newly discovered (avian, bovine, human) pancreatic polypeptide (PP) but also to some other GEP hormones (VIP, GIP, glucagon) as well as to calcitonin and to the alpha-subunit of the glycoprotein hormones. Interpretation of the statistical data suggests that all these peptide hormones are related by a common hexapeptide sequence which contributed, at an evolutionary point, to their molecular architecture. A hexapeptide segment of APP is statistically related to a sequence of equal size in the carboxy terminal region of the A-chain of both hagfish and human insulin, providing the first instance of their structural similarity. Correlations between PP, insulin, glucagon, VIP, and calcitonin provide a tentative basis for predicting the production of one or more of these peptide hormones by immature or de-differentiated cells of neoplasms and non-neoplastic pathologic lesions of the GEP endocrine system.