Ann Andrew

The origin of gut and pancreatic neuroendocrine (APUD) cells—the last word?

The evidence that gut and pancreatic endocrine cells are not derivatives of the neural crest is overwhelming: yet this conclusion is still not universally accepted. In this editorial attention is drawn to the body of experimental evidence which points conclusively to gut and pancreatic endocrine cells arising from endoderm, not the neural crest, the neurectoderm or neuroendocrine programmed epiblast. Copyright

An immunocytochemical survey of endocrine cells in the gastrointestinal tract of chicks at hatching.

SummaryThe distribution of gastrin-, cholecystokinin-, glucagon-, secretin-, vasoactive intestinal polypeptide-, substance P-, bombesin-, neurotensin-, motilin-, somatostatin- and avian pancreatic polypeptide-like cells, demonstrated by indirect immunocytochemistry, was studied in samples from the following regions: proventriculus, gizzard, pylorus, duodenum, upper and lower ileum, caeca and rectum. The pylorus is particularly rich in gastrin-, neurotensin- and somatostatin-like cells. No cells immunoreactive for gastric inhibitory polypeptide or insulin were detected. In a number of instances the same cells were found to stain with antisera raised to different gut peptides. This happened with antisera detecting gastrin- and neurotensin-like cells, with antisera to avian pancreatic polypeptide and glucagon and with antisera to secretin, vasoactive intestinal polypeptide, glucagon and substance P. The possibility that antigenic determinants to more than one peptide are contained in certain endocrine-like cells is considered.

An immunocytochemical study of the distribution of pancreatic endocrine cells in chicks, with special reference to the relationship between pancreatic polypeptide and somatostatin-immunoreactive cells.

SummaryAraldite sections of formalin-fixed pancreas from chicks at hatching were treated by an indirect immuno-enzyme technique to reveal cells containing APP, somatostatin, glucagon and insulin.APP cells were found scattered in the exocrine parenchyma. A few were associated with insulin-containing B islets and occasional cells occurred in and around glucagon-containing A islets. Somatostatin-immunoreactive cells were distributed peripherally in A and B islets and were dispersed in the exocrine tissue. APP cells were roughly as numerous in the exocrine parenchyma as somatostatin-immunoreactive cells.Since certain published observations point to the possible occurrence of APP and somatostatin in the same cells, consecutive sections were stained for these hormones. In no case did the two peptides occur in the same cell. Sections subjected to double-staining confirmed this result. Therefore it is likely that the described differences between APP and somatostatin-immunoreactive cells are valid.

APUD cells in the endocrine pancreas and the intestine of chick embryos

Abstract Formaldehyde-induced fluorescence has demonstrated biogenic amine-storing (APUD) cells in the duodenum of chick embryos from day 13 or 14 of incubation. These are definitive intestinal endocrine cells. If DOPA was administered to the embryos, a few cells were fluorescent only 1 day sooner. Following DOPA-treatment, fluorescence revealed cells with biogenic amine-synthesizing ability (also APUD cells) scattered in the gut groove at 16- to 18-somite stages, concentrated at the site of imminent evagination of the dorsal pancreatic bud later on, then localized within the bud in groups, and later grouped and scattered in the pancreas. In the absence of exogenous DOPA, their fluorescence was evident by day 13 or 14 only. It seems probable that the APUD cells scattered in the gut at early stages are the precursors of islet cells of one or more than one type.

Gut endocrine cells in birds: an overview, with particular reference to the chemistry of gut peptides and the distribution, ontogeny, embryonic origin and differentiation of the endocrine cells.

This review deals with gut endocrine cells in birds. It focuses on both morphological and developmental aspects of these cells, which were included members of Pearses APUD series. They comprise many cell types, which, in birds as in mammals, produce serotonin and a range of regulatory peptides. The chemical structure of most avian gut peptides has been established. These peptides and their functions are outlined here. The types and distribution of avian gut endocrine cells are detailed and compared with the situation in mammals. In birds, ultrastructural work has been limited to certain types of gut endocrine cell and not as widely applied as in mammals. However, immunocytochemistry has found widespread application in studies on birds: the hatching chick and also the adult chicken and certain other species such as the quail and duck have been studied. Gut endocrine cells showing immunoreactivity for the following peptides/serotonin have been identified: somatostatin, pancreatic polypeptide (PP), peptide YY, glucagon, secretin, vasoactive intestinal peptide, gastrin, cholecystokinin (CCK), neurotensin, motilin, gastrin-releasing peptide, substance P, enkephalin and serotonin. The colocalization of different peptides (including chromogranins) and of peptides and serotonin in the same gut endocrine cells is reviewed: notable amongst such associations are glucagon with PP and gastrin/CCK with neurotensin in the same cells. On morphological grounds cells have been identified as endocrine in avian gut from at least 9 days of incubation. Immunocytochemical studies show the majority of the various types first to appear between 12 to 14 days of incubation, with substantial numbers being recorded from 17 days onwards. Experimental studies on chicken and quail embryos have determined the embryonic origin of gut endocrine cells: evidence is unequivocal that such cells arise from the endoderm, not the neural crest, other ectoderm or the mesoderm. Studies on avian embryos have also contributed to our knowledge of mechanisms controlling the differentiation of gut endocrine cells: evidence shows that gut mesenchyme plays an important role in provoking (or inhibiting) the development of gut endocrine cells and there are indications that the endocrine cell pattern in gut is established early and that an axially-derived factor may be important in this process. The kinds of genetic mechanism possibly involved are mentioned but full elucidation of the processes concerned is awaited. A better understanding of the formation of endocrine tumours of the gut should result from the findings.

The embryonic origin of endocrine cells of the gastrointestinal tract

Abstract Combinations of quail endoderm with chick mesoderm and vice versa were cultured in in vitro and then as chorioallantoic grafts. The areas of the germ layers used were delimited in head fold to 8-somite embryos so as to exclude neural crest cells. Various categories of gut endocrine-like cells were distinguished from each other in the grafts by immunocytochemistry and electron microscopy. In the categories consisting of adequate numbers of cells, when quail endoderm was combined with chick mesoderm, the gut endocrine cells contained the exceptionally large nucleoli characteristic of quail cells. When quail mesoderm and chick endoderm were combined, the endocrine cells contained chick nuclei. It is concluded that at least the majority of gut endocrine cell types at present known are derived from the endoderm and not from the neural crest, other ectoderm, or mesoderm.

Failure of insulin cells to develop in cultured embryonic chick pancreas: A model system for the detection of factors supporting insulin cell differentiation

SummaryLittle being known about factors necessary for insulin cell differentiation, we tested the chance observation that these cells were virtually absent from collagen gel cultures of embryonic avian pancreas in which the other pancreatic endocrine cells were numerous. Five-day dorsal buds stripped of their enveloping mesenchyme were embedded in gel and overlaid by a defined medium containing serum, then cultured for 7 days. Immunocytochemical evaluation showed a very low proportion of insulin cells. Substitution of the gel by a polyamino acid coating slightly increased the proportion. In an attempt to test for ability of insulin cell formation to recover, we transferred explants first cultured in collagen gel to polyamino-acid-coated dishes for a further 7 days. No improvement resulted. In controls grown for 14 days on a polyamino acid coating, insulin cells disappeared completely. We conclude that collagen gel does not support survival and differentiation of chick embryonic insulin cells and that the medium used is lacking in some essential factor(s). Determination of their identity should prove possible by exploitation of this model.

Distribution of serotonin-immunoreactive gut endocrine cells in chicks at hatching

Serotonin-immunoreactive, i.e. enterochromaffin (EC) cells were found to be widely distributed in the intestine of the newly hatched chick but sparse in the stomach, and being particularly abundant in the duodenum, upper ileum and rectum. Although in birds, as in mammals, EC cells are most abundant in the intestine, in the stomach they are far sparser than in mammals. Comparison of adjacent sections immunostained for serotonin and a peptide provided no evidence that EC cells in the hatching chick contain motilin or substance P, and that at least the great majority of bombesin-immunoreactive cells contain no serotonin: it is apparent that the mammalian pattern of distribution of peptides in EC cells does not occur in the chick, at least at hatching. Cross reaction of an antiserum to substance P with serotonin was discovered, suggesting the need for a review of existing evidence for co-localisation of this peptide with serotonin.

Effects of tri-iodothyronine (T3), insulin, insulin-like growth factor I (IGF-I) and transforming growth factor beta1 (TGFβ1) on the proportion of insulin cells in cultured embryonic chick pancreas

Abstract With a view to ultimately identifying factors involved in the development of pancreatic insulin cells, we have cultured dorsal pancreatic buds from 5-day chick embryos on a basement membrane matrix (Matrigel) in a serum-free medium supplemented with selected factors. The endodermal components of the buds were freed of almost all the mesenchyme so as to eradicate as much as possible of this source of some such factors. In 7-day cultures, insulin and glucagon cells were demonstrated immunocytochemically; numbers of insulin cells were expressed as a percentage of insulin plus glucagon cell counts. Our standard medium contained insulin. Addition of tri-iodothyronine to this medium did not increase the proportion of insulin cells, but in combination with raised concentrations of glucose and essential amino acids it improved somewhat the marked increase previously recorded for these nutrient conditions. Omission of insulin from the standard medium greatly reduced the proportion of these cells; substitution of insulin by insulin-like growth factor I increased the proportion considerably more than did insulin. To test for an overall effect of growth factors, explants were cultured in standard medium on Matrigel containing reduced amounts of growth factors: the proportion of insulin cells proved to be increased over that reached on normal Matrigel. The suspicion that transforming growth factor β1, a component of Matrigel, might act to reduce the proportion of insulin cells was tested and found to be correct. It is suggested that the different factors studied here may affect either or both of proliferation and determination in the differentiation pathway of insulin vis-à-vis glucagon cells.

Apud Cells and Paraneurons: Embryonic Origin

Publisher Summary This chapter reviews the main aspects of the concept of amine precursor uptake and decarboxylation (APUD) that was aimed at grouping diverse cell types whose main common feature was the ability to synthesize the so-called biogenic or monoamines. In the period of the development of the APUD concept, it was noticed that the ability to take up amine precursors such as dopa and 5-HTP and decarboxylate them with the formation of monoamines such as catecholamines and serotonin was common to a number of cell types. Criteria for the membership of the APUD series have changed in the present. This concept was extended to the paraneuron concept to emphasize the close relationship between conventional neurons and neuron-like cells, paraneurons, some of which are APUD cells located in the amphibian cutaneous glands, the placenta, the thymus, and the APUD neurons of the hypothalamus and sympathetic ganglia. Cells such as the monoamine-storing cells in the avian aortic wall are regarded as paraneurons. The study of such similarities between APUD and paraneurons cells has helped in the recognition of the fact that neurons and polypeptide-secreting endocrine cells are not completely disparate entities.