Gap junctions and intercellular communication in the hepatopancreas of the crayfish (Orconectes propinquus) during molt

Summary The crustacean hepatopancreas is a major metabolic center intimately involved in molting and vitellogenesis. Cells of the hepatopancreas exhibit one of the richest endowments of gap junctions known and are thus presumed to be linked for intercellular communication. In order to monitor hepatopancreatic activity during the molt cycle of crayfish (Orconectes propinquus), the electrical coupling between cells of the hepatopancreatic tubules was measured during postmolt, intermolt and premolt. Samples of hepatopancreas from each of these stages were fixed and freeze-fractured to correlate morphologic features of gap junctions with electrophysiological data. Analysis of the data revealed that ionic coupling was greater in postmolt and premolt tubule cells than in cells of intermolt animals. Platinum replicas of hepatopancreatocyte plasmalemmata revealed that in postmolt, gap junction plaques were smaller and more numerous than those in intermolt and premolt; however, the total area of gap junction plaques per unit membrane area analyzed was approximately the same for hepatopancreatocytes from all molt stages. Although the hepatopancreatic gap junctions exhibited no quantitative differences, those from post- and premolt animals were rounded with tightly packed particles, while plaques from intermolt animals were generally pleomorphic with loosely packed particles. Results of this study suggest that cells of the crayfish hepatopancreas are more coupled in pre- and postmolt, with macular plaques of tightly packed particles, perhaps as a response to the increased metabolic demands of molt, and less well coupled, with irregular plaques of loosely packed junctional particles, during intermolt. The only recognizable morphological correlates of increased cell coupling were tight packing of junctional particles into rounded plaques, while decreased coupling corresponded to junctions with loosely packed irregular aggregates of particles.Supported by the Natural Sciences and Engineering Research Council of Canada (RRS)     

Development of cell-to-cell relationships in the thyroid gland of the chick embryo

Summary Thyroid glands of 7 to 21 day-old chick embryos were examined by electron microscopy using freeze-fracture and thin-section preparations. The primitive follicle lumen first appears between two adjacent epithelial cells in 8 day-old embryos, and is formed in the region of a focal tight junction (macula occludens). The focal tight junction develops into the zonula occludens when the primitive follicle lumen first forms.The zonula occludens is, at first, composed of 4.6 ± 2.45 strands, but with increasing embryonic age the number of strands increases to 5.9 ± 1.41 in 13 day-old, and 8.0 ± 1.75 in 19 day-old embryos.Thyroglobulin stored within the embryonic gland lumina is isolated from the mesenchymal tissue even at the first appearance of these follicle cavities.Well developed gap junctions already occur in the thyroid gland of the 7 day-old embryo, so that an intimate relationship and communication between these cells already exists at the time of their functional differentiation.This study was supported by a grant from the Japan Ministry of Education     

Intercellular junctions in the corpora cardiaca of locusts

Summary The intercellular junctions in the corpora cardiaca of the locusts Schistocerca gregaria and Locusta migratoria were investigated by transmission electron microscopy. In the glandular lobes, complexes consisting of scalariform junctions and associated mitochondria, comparable to those previously observed in ion transporting epithelia, are formed between gland cells, and more rarely between gland cells and the neurons innervating them. Their structure and abundance are apparently unaffected by the stage of development or by the various experimental conditions employed. In the neural lobe, scalariform junctions form between glial cells and show close association with the endoplasmic reticulum. Gap junctions are present among glandular, neural and glial elements, and are formed between cells of the same type and of different types. Contacts resembling punctate tight junctions are widely distributed in the gland, but would be unlikely to form a barrier to diffusion. Septate junctions are formed exclusively between glial cells.     

Intercellular junctions in the gill epithelium of the Atlantic hagfish,Myxine glutinosa

Summary The intramembrane organization of the occluding junctions in the gill epithelium of the Atlantic hagfish, Myxine glutinosa, was studied by means of freeze-fracture electron microscopy. Mitochondria-rich cells, characterized by assemblies of rod-shaped particles in the luminal plasma membrane and by an extensive intracellular amplification of the basolateral plasma membrane, are singly distributed between the pavement cells in the gill epithelium of this marine and stenohaline cyclostome. The occluding junctions between mitochondria-rich cells and pavement cells do not differ from those between adjacent pavement cells, concerning the number of superimposed strands (median 6, range 4–9) and their geometrical organization. These observations suggest that, in contrast to marine teleosts, the paracellular pathway plays a minor role in transepithelial ion movements in the hagfish gill epithelium. The findings are in agreement with the absence of hypoosmoregulatory mechanisms in hagfish, as have been evolved in various marine vertebrates. In addition, small communicating junctions are demonstrated between pavement cells; they possibly serve for a coordinated synthesis and secretion of mucus by the pavement cells.Dedicated to Prof. H. Leonhardt on the occasion of his 70th birthday     

Structure of occluding junctions in ileal epithelial cells of suckling rats

Summary Two kinds of occluding junctions are found between ileal epithelial cells of suckling rats: apical zonulae occludentes (ZO) and fasciae occludentes (FO) which are associated with the lateral plasma membranes of many epithelial cells. In unfixed preparations, glycerol treatment induces the further proliferation of extensive fasciae occludentes. Both kinds of junction have identical structural elements when visualized in freeze fracture replicas, although the arrangement of these elements differs. Zonulae occludentes consist of networks of branching and anastomosing linear ridges or rows of 10 nm particles with 20–30 nm spaces between the rows which form narrow belt-like structures around the apical region of adjacent cells. Fasciae occludentes, on the other hand, consist of similar linear ridges or rows of particles but the junction strands are often discontinuous, open ended and only occasionally intersect with each other. Several different fracture planes through the plasma membrane in the region of the occluding junctions have been observed and these provide further evidence that two components, one from each membrane, fused at the level of the extracellular space, form the junction sealing element. Furthermore, we present evidence which indicates a staggered rather than an in-register arrangement of these two components.This study was supported in part by National Institutes of Health Program Project No. NS10299 and National Institutes of Health Sciences Advancement Award No. RR06148 (J.D.R.) and by the Cancer Research Campaign (S.K.) and Medical Research Council (A.R.L.)     

Cytochemical observations of hemolymph cells during coagulation in the crayfish, Orconectes virilis

Smears of Orconectes virilis hemolymph were prepared by fixation in 10% formalin immediately upon withdrawal, and after an interval of 1, 5, or 15 minutes. These smears were then stained by a variety of histochemical means designed to identify a material which is released from both hyaline and granular cells during the coagulation process. Based upon reactions to various carbohydrate, lipid and protein tests, this material appears to consist of a glycoor muco-protein, and its localization and activity coincide with the ?fibrin ferment”? described by Hardy (1892). Its release is probably initiated from the hyaline cells, followed shortly thereafter by a similar activity of the granulocytes. While it cannot be ascertained by the methods used in this study whether or not this material participates actively in clotting, its release is nevertheless coincidental with coagulation.     

Effects of declining calcium availability on the survival,growth and calcium content of a freshwater crayfish,Orconectes virilis

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Histological and histochemical observations of the hemolymph cells in the crayfish, Orconectes virilis

Hemolymph cells of Orconectes virilis were stained during the months of August to November by a variety of histological and histochemical techniques. Cells were classified as hyaline cells, small granulocytes, and large granulocytes. Presence of mitochondrial enzymes was indicated by tests for succinic dehydrogenase and cytochrome oxidase. Reaction to test for the hydrolytic enzyme, leucine acylnaphthylamidase was intense in the granules of the large granulocytes. The PAS reaction indicated a mucopolysaccharide at the cell membrane. Lipid was found in all three hemolymph cell types of Orconectes virilis at the time of this study.     

The distribution of orthogonal arrays and their relationship to intercellular junctions in neuroglia of the freeze-fractured hypothalamo-neurohypophysial system

Summary Using freeze-fracture techniques, we have investigated membrane specializations of the glia associated with the hypothalamo-neurohypophysial system of the rat. In the paraventricular (PVN) and supraoptic (SON) nuclei, astrocytes in areas of high neuronal density (i.e., magnocellular regions) display orthogonal arrays of 6–7 nm particles soley near gap junctions, while astrocytes in areas of lower neuronal density (i.e., parvocellular regions) contain additional arrays in membranes not displaying gap junctions. Arrays are especially numerous on astrocytic perivascular end-feet in both nuclei and in the laminations of the pial-glial limitans ventral to the SON. Ependymal cells near the PVN show arrays both on their lateral surfaces (displaying gap junctions) and on their apical surfaces (facing the CSF). Tight junctions are not noted on astrocytes or ependymal cells, but are noted on both the somas and myelin lamellae of oligodendroglia. Both of these latter membranes occasionally contain gap junctions as well; however, orthogonal arrays are never noted on oligodendroglia.The plasma membranes of pituicytes in the neurohypophysis display gap junctions, complex junctions, and tight junctions. Orthogonal arrays are noted near the first two of these, but not near the last. Arrays in the neural lobe appear most dense on membranes adjacent to subpial or perivascular spaces. Pituicyte membranes containing orthogonal arrays appear infrequently near the neural stalk, increasing towards the distal end of the neural lobe. The distribution of orthogonal arrays in this system, as well as in other systems in which they have been noted, suggests a polarization of membrane activity.     

Some factors regulating cohort production of the crayfish, Orconectes virilis

SUMMARY. Cohort production of the crayfish. Orconectes virilis , ranged from 148.8 to 70.2 kg in North Twin Lake (surface area 1.9 ha) and from 151.9 to 84.9 kg in West Lost Lake (surface area 1.4 ha). Both cohort production (P) and cohort mean biomass (B) showed a long-term decrease with time. The cohort P/B ratios did not show such a trend but remained steady. The P/B ratio approximated the life cycle instantaneous rate of growth (G) which could then be used for estimating cohort production from mean biomass.
Production remained consistently higher in West Lost Lake. Analysis of horizontal life table data revealed no inherent difference between survival and fecundity rates of the crayfish population in each lake. Slight differences in basin morphometry between the two lakes determined nursery habitat availability and this affected recruitment of young from each female brood stock. Small differences in carrying capacity between two similar sized nearby lakes, along with a decrease in carrying capacity over time, were sufficient to nullify attempts to manage these populations using a maximum sustainable yield model.     

The mate pursuit-predation avoidance tradeoff in the virile crayfish, Orconectes virilis

To better understand the tradeoff between mate pursuit and predation risk avoidance, the responses of male virile crayfish (Orconectes virilis) to female sex pheromone and conspecific alarm cue, alone and in combination were tested. Male crayfish were more active and exhibited less antipredator behavior in the pheromone treatment than in either the pheromone + alarm or alarm treatment. The results suggest a tradeoff in favor of risk avoidance when pheromone and risk stimuli are encountered together.     

The mate pursuit-predation avoidance tradeoff in the virile crayfish,Orconectes virilis

To better understand the tradeoff between mate pursuit and predation risk avoidance, the responses of male virile crayfish (Orconectes virilis) to female sex pheromone and conspecific alarm cue, alone and in combination were tested. Male crayfish were more active and exhibited less antipredator behavior in the pheromone treatment than in either the pheromone?+?alarm or alarm treatment. The results suggest a tradeoff in favor of risk avoidance when pheromone and risk stimuli are encountered together.     

Prokaryotic-eukaryotic cell junctions between spiral-shaped bacteria and cecal epithelium of the guinea pig

Summary Scanning electron microscopy demonstrated that the cecum of the guinea-pig is colonized by numerous spiral-shaped bacteria; these microorganisms, which adhere to mucosa at one end, were found exclusively on the brush border of the surface epithelium. The membranes of sectioned bacteria have a set of electron-dense bands girdling the tip adhered to epithelium. Freeze-fracture replicas of the bacteria revealed the prokaryote-eukaryote junction as a set of ridges on the P-face of outer membrane; the numerous particles of E-face were arranged in parallel rows; on the other hand, the apical plasma membrane and subjacent cytoplasm of epithelium occupied by the spiral-shaped bacteria did not show a structural counterpart. Observations suggest that one end of the spiral-shaped bacteria possesses specialized membrane components that permit specific attachment to the apical surface of epithelial cells.     

Ontogeny of the antennal glands in the crayfish Astacus leptodactylus (Crustacea, Decapoda): anatomical and cell differentiation

The ontogeny of the antennal glands was studied during the embryonic and post-embryonic development of Astacus leptodactylus. The future glands arising from undifferentiated columnar cells were detectable at the metanauplius stage EI 150 m (EI: eye index; approximately 440 m at hatching). The tubule and labyrinth differentiated in embryos at EI 190 m, and the bladder and coelomosac at EI 250 m. At EI 350 m, the tubule lengthened and divided into proximal and distal sub-regions. In later stages, the gland retained the same morpho-anatomy but the differentiation and size of each part increased. The cells of the coelomosac displayed the cytological features of podocytes in late embryonic development at EI 440 m. Only small apical microvilli and a few mitochondria were observable in the labyrinth cells at EI 250 m; by EI 440 m, these cells presented well-shaped apical microvilli, formed bodies, basal infoldings and mitochondria. In the cells of the tubules and bladder, mitochondria and basal infoldings occurred at EI 440 m and EI 250 m, respectively. The differentiation of the tubules and bladder cells suggested that they were involved in active transport at EI 440 m. Following hatching, the differentiation of the cells and the size of the glands increased. The ontogeny of the antennal glands thus starts in early embryos, the specific cellular functional features being differentiated in the various parts of the glands by EI 440 m. The antennal glands are probably functional just before hatching, i.e., before the juveniles are confronted with the low osmolality of freshwater.Thanks are due to the University of Tarbiat Modarres and Ministry of Science, Research and Technology, Islamic Republic of Iran, for financial aid and support. Special thanks are also extended to the Société Française dExportation des Ressources Educatives (SFERE) for a scholarship to S.K.     

Exploration of potential microbial control agents for the invasive crayfish,Orconectes virilis

The introduced crayfish, Orconectes virilis (Cambarinae; Hagen 1870), has become a serious invasive species in Arizona (USA), altering stream ecosystems and contributing to the decline of native species. But because it is native to the eastern US, and related crayfish including endangered species inhabit nearby states, introduction of a biological control agent presents a unique challenge. This represents a feasibility study, in which we explored bacteria, nematodes, and a virus as potential biological control agents for O. virilis while avoiding harm to native species. White Spot Syndrome Virus (WSSV) from shrimp was found to be highly pathogenic and readily passed by cannibalistic behavior but not by water transmission. Potential activity of WSSV against representative non-target arthropods that may be found in the same ecosystems was also explored.     

The tradeoff between reproductive and food resources in the crayfish Orconectes virilis

The conflict between mating and foraging is one of the many tradeoffs associated with reproduction. The relative attraction to sex pheromone and food stimuli by male virile crayfish (Orconectes virilis) were tested using two experiments. In the first experiment, the responses by males to pheromone and food stimuli alone were assessed. In the second experiment, males were exposed to both pheromone and food stimuli in a choice maze. To determine the effects of feeding motivation, the males in the choice experiment were fed either one day or seven days prior to observation. Male crayfish exhibited similar responses to the pheromone and food stimuli individually. Males exhibited a preference for the pheromone stimulus over the food stimulus in the choice trials, and that preference that was not influenced by starvation.     

The uptake and storage of iron and lead in cells of the crayfish (Orconectes propinquus) hepatopancreas and antennal gland

The heavy metals iron and lead are taken up and metabolized in a similar manner by the crayfish hepatopancreas, but only lead appears to enter cells of the antennal gland (green gland). Iron, on the other hand, which apparently is not taken up by the antennal gland cells following systemic injections of low doses (0.05 mg), exerts striking alterations in cell ultrastructure after pericardial injections of massive doses (0.5 mg). Electron microscopic examination and atomic absorption spectrophotometric analyses of the hepatopancreas and antennal glands of iron-injected crayfish revealed that iron was selectively stored in metal-containing vacuoles of R- and F-cells in the hepatopancreatic cells, where it accumulated in concentrations that were toxic to these cells. High doses of iron caused alterations in the ultrastructural morphology of the cells of the antennal glands, although no accumulation of iron was apparent. Lead was similarly stored in metal-containing vacuoles of the cells of the hepatopancreas of lead-injected crayfish, but also accumulated in high concentrations (prior to being excreted) in vacuoles, cytoplasmic bodies and vesicles in the cells of the antennal gland. In contrast, lead in high concentrations was relatively non-toxic to any of these cells, suggesting that crayfish were more efficient in detoxifying and eliminating lead than iron.