Cytochemical, immunofluorescence, and ultrastructural investigations on polypeptide hormone containing cells in the intestinal mucosa of a cyclostome, Myxine glutinosa

Development and evolution of gut structures: from molecules to function

The emergence of a specialized system for food digestion and nutrient absorption was a crucial innovation for multicellular organisms. Digestive systems with different levels of complexity evolved in different animals, with the endoderm-derived one-way gut of most bilaterians to be the prevailing and more specialized form. While the molecular events regulating the early phases of embryonic tissue specification have been deeply investigated in animals occupying different phylogenetic positions, the mechanisms underlying gut patterning and gut-associated structures differentiation are still mostly obscure. In this review, we describe the main discoveries in gut and gut-associated structures development in echinoderm larvae (mainly for sea urchin and, when available, for sea star) and compare them with existing information in vertebrates. An impressive degree of conservation emerges when comparing the transcription factor toolkits recruited for gut cells and tissue differentiation in animals as diverse as echinoderms and vertebrates, thus suggesting that their function emerged in the deuterostome ancestor.

Forgotten and novel aspects in pancreas development

Diseases related to the pancreas are of highest importance in public health. It is anticipated that a detailed understanding of the molecular events that govern the embryonic development of this organ will have an immediate impact on clinical research relating to this issue. One major aim is the reconstruction of embryonic development in vitro with appropriate precursor cells, a second strategy is aimed at understanding the transdifferentiation of non-pancreatic into pancreatic tissue, and a third avenue is defined by the stimulation of the intrinsic ability of the pancreas to regenerate. Recent progress in developmental biology with respect to these different topics is reviewed in the present article. In addition, we also address evolutionary aspects of pancreas development, emphasizing the role of the South African clawed frog, Xenopus laevis, as an additional useful model system to study the molecular control of pancreas development.

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.

Neurohormonal peptides in the gut of the Atlantic hagfish (Myxine glutinosa) detected using antisera raised against mammalian regulatory peptides

Concentrations of regulatory peptides in an extract of the intestine of the cyclostome, Myxine glutinosa (Atlantic hagfish), were measured by radioimmunoassay using 12 antisera of defined regional specificity that were raised against mammalian gastrointestinal peptides. The hagfish gut contained somatostatin-, cholecystokinin/gastrin-, C-terminal substance P-, and neurokinin A-like immunoreactivity in concentrations that were 10 to 100 times less than the corresponding concentrations in the rat intestine. The hagfish gut also contained glucagon-like immunoreactivity, measured with both C- and N-terminally directed antisera, but the immunoreactivity did not dilute in parallel with the porcine glucagon standard in radio-immunoassay. No immunoreactivity was detected using antisera to calcitonin gene-related peptide, gastrin-releasing peptide, neuromedin U, neurotensin, N-terminal substance P, and vasoactive intestinal polypeptide. The somatostatin-like immunoreactivity in the hagfish gut was resolved by HPLC into components with the retention times of somatostatin-34 and somatostatin-14, previously isolated from the hagfish islet organ (relative abundance 2:1). The retention times of hagfish glucagon and of the multiple molecular forms of the tachykinin-like peptides were appreciably different from the retention times of the corresponding mammalian peptides.

Localization of immunoreactive gastrin-like cells in the alimentary tract of the ascidian Styela plicata

The occurrence of a gastrin-like immunoreactivity in the alimentary tract of the ascidian Styela plicata has been investigated using immunocytochemical methods. Gastrin-like cells are present only in the gastric epithelium among the cell types responsible for digestion and absorption of food. The physiological role played by the ascidian gastrin-like peptides is discussed together with the evolutionary history of peptides of the gastrin/cholecystokinin family.

Substance P is a vasoactive hormone in the Atlantic hagfish Myxine glutinosa (Cyclostomata)

The in vitro effects of synthetic substance P (SP) on rings of the ventral aorta and on the systemic heart of Myxine glutinosa were investigated by the use of an organ bath. Increasing molar amounts (10(-16) to 10(-8) M) of SP were applied and the reaction of the aortic rings was recorded with isometric transducers. SP was found to contract the Myxine aorta in a dose-dependent manner starting at a threshold concentration of 10(-14) M and reaching a plateau at 10(-11) M. Therefore, the effective dose of SP seems to be in a physiological range. On the other hand, the heart was found to be insensitive to SP even in doses as high as 10(-5) M. By means of immunohistochemistry, SP-immunoreactive endocrine cells were found throughout the Myxine intestine while no SP-immunoreactive nerve fibers were detected at the Myxine aorta. Thus, under physiological conditions the observed contractile effect of SP on the ventral aorta may be raised by SP-like material released from enteroendocrine cells.

Structure and function of the intestinal epithelial cells in the perch (Perca fluviatillis L.)

An ultrastructural study of the intestinal absorptive epithelium in perch (Perca fluviatilis) has shown that the perch intestine can be divided into three segments: the proximal segment, the middle segment and the distal segment. The enterocytes of the proximal segment are found to be concerned with lipid absorption. The adsorbed fat gives rise to the presence of two forms of inclusions: lipid particles and lipid droplets. Enterocytes of the middle segment exhibit the typical ultrastructural features of pinocytosis; these consist of extensive invaginations of the luminal surface membrane and acculation of vacuoles in the apical cytoplasm. Exogenous proteins are ingested by absorptive cells from the intestinal lumen by a process similar to that described in neonatal mammals. In the distal segment the absorptive cells have few, short microvilli. Besides the absorptive epithelial cells, goblet cells, endocrine cells, pear-shaped cells, and plasma cells are occasionally found.

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

Somatostatin-like immunofluorescence has been found by immunostaining in cells of the bile duct mucosa and pancreatic islet parenchyma of the hagfish, Myxine glutinosa, and the islet lobules of the lamprey, Lampetra fluviatilis.

Glucagon levels in pancreatic extracts and plasma of the lizard (1)

Levels of glucagon in the splenic pancreas and in plasma of the lizard Anolis carolinensis were estimated by radioimmunoassay. The splenic pancreas of Anolis has a glucagon concentration nearly a 1000 times greater, on a weight basis, than that of the mammalian pancreas. Glucagon-like immunoreactivity (GLI) of anolian plasma varied over a wide range, but relative to mammals the GLI levels were inappropriately elevated for the concentration of plasma glucagon secretion, particularly as related to alpha cell function in the diabetic state.