Rodlet cells in teleosts: a new insight into their nature and functions

The nature of rodlet cells (RCs) and their functions is subject to a number of different interpretations. This review provides a detailed analysis of the parasitic and endogenous origin of these cells. Two new functional aspects of RCs are considered in detail. The possible function of RCs as immune cells was derived from studies that reported an increase in the number of RCs in fish infected with protozoan and metazoan parasites, particularly at the site of the pathogen infection and/or attachment. Accordingly, RCs represent inflammatory cells, with a similar role to eosinophile granule cells, epithelioid cells and mesothelial cells. Rodlet cells may potentially act as biomarkers. Experimental studies that examined the response of RCs in fish exposed to chemical substances such as metals and herbicides reported an increase in the number of RCs in the tissues of the fish. Fish exposed to these substances expressed myelinic figures in the cytoplasm of the RCs and various degrees of rodlet degeneration and high vacuolization of RC cytoplasm were often noticed. Further lines of research are suggested that might elucidate the true function of these enigmatic cells.     

Ultrastructural study on the intestine of Senegal sole, Solea senegalensis

The intestinal epithelium of Senegal sole, Solea senegalensis Kaup is composed of three main cell types: epithelial, goblet and rodlet. The cytoplasm of columnar epithelial cells – enterocytes – has spherical lipid droplets. The dominant feature throughout the intestinal mucosa was goblet cells filled with numerous mucous droplets of high density. The cytoplasm of the rodlet cells contained peripheral filamentous, pycnotic nuclei, and numerous cytoplasmic inclusions (rodlets), with a very dense cylindrical core surrounded by flocculent material. Some physiological implications related to ultrastructural features of the intestine are also discussed.     

A histological and histochemical study of the oesophagus and oesogaster of the Senegal sole, Solea senegalensis.

A histological and histochemical study was performed in the buccal cavity and papillae, which were around the teeth, as well as in the oesophagus and oesogaster of the Senegal sole, Solea senegalensis adult specimens. The oesophagus and oesogaster were made up of four distinct layers: mucosa, submucosa, muscular and serous. Two morphological types of epithelial cells were distinguishable in the oesophageal mucosa: the more numerous type cells possessed an electron-dense cytoplasm, whereas the cytoplasm was electron-clear in the other cells. Mucus-secreting cells were the dominant feature of the epithelium throughout the oesophagus. These goblet cells were filled with numerous mucous droplets of low electron-density. The oesophagus was devoid of taste buds. In the oesogaster mucosa, three types of cells were distinguished: dark, rodlet and light epithelial cells. Dark epithelial cells showed different characteristics from that in the oesophagus: the nucleus was irregular with an electron-dense hyaloplasm, the cytoplasm had a scarce smooth and granular endoplasmic reticulum; a Golgi apparatus consisted of four parallel cisternae, dense granules without membrane, lysosomes and numerous mitochondria. The rodlet cells were elongated, contained rod-like structures and were surrounded by an electron-dense capsule-like structure. The bulk of the rodlet cell was composed of up to 20 extended rodlet units. Light epithelial cells of the oesogaster had the same characteristics as those observed in the oesophagus and contained numerous mitochondria with a dense matrix, abundant smooth endoplasmic reticulum and numerous vesicles. In the goblet cells of the papillae, sulfomucin was recognised, since they showed alcianophilia (alcian blue pH 1.0 and 0.5). These cells were negative to protein reaction (bromophenol blue) and contained -S-S- and SH groups. Enzymatic activities (alkaline phosphatase, acid phosphatase, ATPase (pH 7.2 and 9.4) and lipid reactions were negative in the goblet cells of the buccal cavity. Epithelial cells of oesophagus contained a weak presence of acid and neutral mucopolysaccharides. Oesophageal goblet cells contained carboxylated, sulphated (weakly and strongly ionised) mucosubstances and sialic acid. Most goblet cells did not contain proteins and presented disulphide (-S-S-) and sulphydril (-SH) groups. Proteins in general, and in particular those rich in lysine, tyrosine and arginine were present in the epithelium, lamina propria, submucosa and muscular layer of the oesophagus. Lipids in general and phospholipids were observed in the oesophageal epithelium while unsaturated, acid and neutral lipids were not observed. The lamina propria and submucosa contained a weak presence of phospholipids and unsaturated lipids. Acid phosphatase and ATPase (pH 7.2) activities were observed in the lamina propria, submucosa and muscular regions, while ATPase (pH 9.2) activity was weak in these areas. ATPase activity (pH 7.2 and 9.5) was very weak in the epithelium. Oesophageal goblet cells were negative to lipid and enzymatic reactions.     

Isolation and characterization of the rodlet layer of Trichophyton mentagrophytes microconidial wall.

The rodlet layer of the microconidial wall of Trichophyton mentagrophytes was isolated and partially characterized. The purified microconidial walls were first extracted with urea (8M), mercaptoethanol (1%), and sodium dodecyl sulfate (1%) followed by enzymatic digestion with glusulase (snail intestinal enzymes) and purified (1 leads to 3)-beta-D-glucanase and chitinase. The purified rodlet layer was 15 to 30 nm thick and accounted for approximately 10% of the original wall weight. The pattern of rodlet patches, as revealed by electron microscopy of freeze-etched preparations of the isolated layer, was essentially the same as that observed on the intact microconidial wall. The rodlet layer was found to be resistant to most of the common organic solvents, cell wall lytic enzymes, mild acid treatments, and surface-active agents, but was solubilized in boiling 1 N NaOH with concomitant disorientation of the rodlet patterns. A melanin or melanin-like pigment appeared to be intimately associated with this rodlet layer and was solubilized during a hot-alkali treatment. Protein (80 to 85%) and glucomannan (7 to 10%) were the major components of the rodlet layer. The rodlet layer did not contain any appreciable amounts of lipid or phosphorus.     

ORIGIN, DEVELOPMENT, AND NATURE OF INTRANUCLEAR RODLETS AND ASSOCIATED BODIES IN CHICKEN SYMPATHETIC NEURONS

Correlative data are presented here on the developmental history, dynamics, histochemistry, and fine structure of intranuclear rodlets in chicken sympathetic neurons from in vivo material and long-term organized tissue cultures. The rodlets consist of bundles of ~70 ± 10 A proteinaceous filaments closely associated with ~0.4–0.8 µ spheroidal, granulofibrillar (gf) bodies of a related nature. These bodies are already present in the developing embryo a week or more in advance of the rodlets. In early formative stages rodlets consist of small clusters of aligned filaments contiguous with the gf-bodies. As neuronal differentiation progresses these filaments increase in number and become organized into well-ordered polyhedral arrays. Time-lapse cinemicrography reveals transient changes in rodlet contour associated with intrinsic factors, changes in form and position of the nucleolus with respect to the rodlet, and activity of the gf-bodies. With the electron microscope filaments may be seen extending between the nucleolus, gf-bodies, and rodlets; nucleoli display circumscribed regions with fine structural features and staining reactions reminiscent of those of gf-bodies, We suggest that the latter may be derivatives of the nucleolus and that the two may act together in the assemblage and functional dynamics of the rodlet. The egress of rodlet filaments into the cytoplasm raises the possibility that these might represent a source of the cell's filamentous constituents.     

Observations on rodlet cells found in the vascular system and extravascular space of angelfish (Pterophyllum scalare scalare)

In the angelfish ( Pterophyllum scalare scalare ) numerous rodlet cells were found in the large post-orbital blood vessel caudal to the eye and in the surrounding extravascular space. Within the vessel the rodlet cells formed striking regular arrays, along the inner aspect of the wall. The rodlets within the cells were positive to PAS but negative to Sudan Black B, Masson's, and the Fuelgen stain. The capsule around the cells was negative for all these stains. These rodlet cells appeared to be traversing the vessel endothelium, and to be pushing the endothelium aside without damaging it. Some discharged their contents into the vessel, but we never observed the release of intact rodlets. The nuclei of rodlet cells in actual contact with the vessel were at the end of the cell more distant from the endothelial wall. Cell-to-cell adhesion structures or communications junctions between rodlet cells and the endothelium were not evident. A putative rodlet cell precursor in the extravascular space contained large electron-dense granules, and extended pseudopodia that contacted nearby rodlet cells. Based on their morphology, tissue distribution, and their behaviour, we conclude that the rodlet cell is an endogeneous teleost cell type, and possibly represents a form of matured granulocyte.     

Tyrosine phosphatase inhibitor triggers rodlet cell discharge in sunfish scale epidermis cultures

Epidermal rodlet cells were evaluated after treatment with the tyrosine phosphatase inhibitor pervanadate. Treatment of sunfish explant cell cultures with the inhibitor triggered a contraction of the rodlet cells and expulsion of cell contents. Time‐lapse video differential interference contrast (DIC) microscopy was used to evaluate rodlet cell contraction and rodlet discharge. Three general steps in pervanadate triggered discharge were identified. First the rodlet cell undergoes a constriction of the midsection. Constriction is followed by a rapid forward movement of rodlets and sacs to the apical end of cell, culminating in discharge of rodlets and other cellular contents, including the nucleus. A ring‐shaped structure around the apical pore was identified with DIC microscopy. Fluorescent‐labeled phalloidin and antibodies to alpha‐actinin and phosphotyrosine strongly stained the apical ring. A diffuse granular staining for both antibodies was also observed throughout the fibrous capsule. The results suggest that tyrosine kinases play a role in rodlet cell contraction. Alpha‐actinin is a known substrate for tyrosine kinases and is a potential target for triggering rodlet cell contraction and rodlet ejection. Modification of alpha‐actinin tyrosines could also be a mechanism for regulating the structural integrity of the fibrous capsule.     

Characteristics of Streptomyces coelicolor A3(2) aerial spore rodlet mosaic

Cytochemical analysis of Streptomyces coelicolor (A3(2) indicated that the aerial growth rodlet mosaic is a polysaccharide. Statistical analysis of frequency distributions of individual rodlet lengths from control and ether-reoriented spore mosaics indicated that the rodlet fibrillar image is the result of individual particulates, rather than evaginations in a continuous sheet of material. A model of the mature sport envelope was developed from freeze-etch-replicated, thin-sectioned, and critical point dried S. coelicolor A3(2) mature spores. The rodlet mosaic was situated between the outer spore wall and an external granuloma matrix. Mixture spore envelope layers from the inner surface to the external surface are plasma membrane, inner spore wall, outer spore wall, rodlet mosaic, an undefined granular matrix, and the sheath. The granular matrix had an uneven thickness and much of the matrix was frequently absent from the interspore spaces of mature spore chains. Streptomyces coelicolor A3(2) mosaic rodlets were isolated by acetic acid refluxing, then ethanol precipitation. Complete acid hydrolysis of rodlets released on sugar which cochromatographed with D-glucosamine-HCl and released acetic acid at 139% of the expected level. Cell associated rodlet mosaics and isolated mosaic rodlets were hydrolyzed with chitinase. Infrared spectra of isolated rodlets were similar to crab chitin spectra.     

High‐density aggregations of rodlet cells in the gonads of Greenland halibut Reinhardtius hippoglossoides,a deep‐water marine flatfish

Large aggregations of rodlet cells in the gonads of male and female Greenland halibut Reinhardtius hippoglossoides are reported for the first time. These rodlet cells were not arranged epithelially but rather were found throughout the connective tissue between oocytes (females) or within lymphatic spaces between testicular lobules (males). The reason for large aggregations of rodlet cells in the gonads and not other tissues of this species is uncertain.     

The first appearance of Rodlet cells in carp (Cyprinus carpio L.) ontogeny and their possible roles during stress and parasite infection

The origin and function of rodlet cells (RCs) are still a matter of discussion. Whereas the exogenous hypothesis considers them parasites, the endogenous hypothesis regards them as a genuine fish cell population with a secretory and/or leukocyte function. In order to shed more light on these questions we focused on the location and appearance of RCs during carp (Cyprinus carpio) ontogeny. Typical RCs were seen at 5days post fertilisation (dpf) between kidney and intestine, at 6dpf in the intestine and at 8dpf in both anterior and posterior kidney and in the abdominal cavity among the mesothelial cells. The RC number increased with age and after 14dpf they were also present in gills. The early appearance of the RCs during carp ontogeny support the endogenous hypothesis stating that RCs are genuine constituents of fish tissue and suggest that they are 'immune cells'. The fact that the RCs of the gills secrete their content into the surrounding water, combined with the strategic location around blood vessels in kidney and within intestinal epithelium, would also support an important role in host defense. To investigate whether RC numbers in gills and kidney are related to typical fluctuations in the physiology during stress and infection we counted their number in gills and kidney after parasite infection and stress. In the gills the number of RCs increased after infection but did not change after stress while in the kidney their number increased after stress and no significant changes were observed after infection.     

The formation of the rodlet layer of streptomycetes is the result of the interplay between rodlins and chaplins

Streptomycetes form hydrophobic aerial hyphae that eventually septate into hydrophobic spores. Both aerial hyphae and spores possess a typical surface layer called the rodlet layer. We present here evidence that rodlet formation is conserved in the streptomycetes. The formation of the rodlet layer is the result of the interplay between rodlins and chaplins. A strain of Streptomyces coelicolor in which the rodlin genes rdlA and/or rdlB were deleted no longer formed the rodlet layer. Instead, these surfaces were decorated with fine fibrils. Deletion of all eight chaplin genes (strain DeltachpABCDEFGH) resulted in the absence of the rodlet layer as well as the fibrils at surfaces of aerial hyphae and spores. Apart from coating these surfaces, chaplins are involved in the escape of hyphae into the air, as was shown by the strong reduction in the number of aerial hyphae in the DeltachpABCDEFGH strain. The decrease in the number of aerial hyphae correlated with a lower expression of the rdl genes in the colony. Yet, expression per aerial hypha was similar to that in the wild-type strain, indicating that expression of the rdl genes is initiated after the hypha has sensed that it has grown into the air.     

The fine structure of muscle fibres of roach, Rutilus rutilus (L.), and chub, Leuciscus cephalus (L.), Cyprinidae, Teleostei: interspecific differences and effects of habitat and season

Red and white axial muscle fibres from roach and chub were investigated by electron microscopy. Fish from three different localities were compared. Qualitative and quantitative analysis of myofibrils, mitochondria, lipid and subsarcolemmal cytoplasm with regard to muscle fibre type, species, season and habitat were made. Muscle fibre types differ significantly with the exception of the subsarcolemmal cytoplasm in roach. Within-species lipid content of red fibres differs between seasons. However, the most marked effect on red muscle fibres within species and season as regards volume density of lipid and mitochondria can be attributed to the different localities. The results are discussed in relation to mode of life and differences in habitat.     

Ontogenetic changes in diel activity,food habits and spatial distribution of juvenile and adult creek chub,Semotilus atromaculatus

Synopsis Juvenile creek chub, Semotilus atromaculatus, differed ecologically from adults. They were essentially diurnal, fed on small prey (adult diptera and aquatic adult coleoptera) and were found mainly in shallow littoral water (0.8 m depth) of a Québec oligotrophic lake. In contrast, adults were principally nocturnal, fed on larger prey (Gammaridae, diptera larvae, diptera pupae and ephemeroptera larvae) and were found in deeper water (1.2, 2.0 and 2.9 m depth). The overlap in diet between juvenile and adult fish was 10 percent. We found that predation by brook charr, Salvelinus fontinalis, upon creek chub was low, as only 5 chart stomachs of the 302 examined contained a total of 16 juvenile chub and none contained adult chub. Laboratory observations revealed that under low light intensity (0.17 lux) adult creek chub fed as efficiently as under high light intensity (22 lux). Several possible hypotheses to explain the evolution of the two different strategies exhibed by adult and juvenile creek chub are discussed.     

A description of rodlet cells from the alimentary canal of Anguilla anguilla and their relationship with parasitic helminths

Rodlet cells in intestinal epithelia of infected and uninfected European eels Anguilla anguilla from brackish and fresh water were studied by light and electron microscopy. Deropristis inflata (Trematoda) was found in eels from brackish water, whereas eels from fresh water were infected with Acanthocephalus clavula (Acanthocephala). In a comparison between uninfected and infected eels from brackish water, a higher number of rodlet cells was recorded in the intestinal epithelia of infected fish. Evidence is presented that rodlet cells secrete their contents in a holocrine manner into the lumen of the eel intestine. The occurrence of organelles within the mature rodlet cell was rare. ? 1998 The Fisheries Society of the British Isles     

Fine structure and cytochemistry of the endothelial cells and rodlet cells in the bulbus arteriosus in species of Cichlidae (Teleostei)

The ultrastructure of endothelial cells and rodlet cells in the bulbus arteriosus of specimens representing six genera of Cichlidae is described. The former are very closely packed by membrane–bound and mainly electron–dense inclusion bodies (0.3–0.7μm).
In Apistogramma ramirezi I observed numerous subendothelial rodlet cells throughout the entire length of the bulbus arteriosus. These cells penetrate the endothelium and connect to the latter by desmosomes and tight junctions. The luminal part of the cell contains numerous vesicles and tubules (width 50–100 nm), whereas the basal part is occupied by a number of membrane–bound, club–like inclusions (length ≤ 5 μm). Between these two layers there occurs a layer of small, elongated mitochondria. Peripherally, these cells consist of a filamentous wall, except in the apical area.
The endothelial and rodlet cell inclusion bodies do not react with phosphotungstic acid (pH 1) or Sudan black B stain. The endothelial cells react strongly with periodic acid–Schiff (PAS) stain, whereas the rodlet cells are only moderately coloured by this stain.
The present results are discussed and compared with those reported previously for endothelial/ endocardial cells and rodlet cells in bony fish.     

Density and maturation of rodlet cells in brain tissue of fathead minnows (Pimephales promelas) exposed to trematode cercariae

Evidence for the presumed linkage between the enigmatic rodlet cells of fish and exposure to helminths is anecdotal and indirect. We evaluated the proliferation and development of rodlet cells in the optic lobes of fathead minnows exposed to cercariae of Ornithodiplostomum ptychocheilus. Mean rodlet cell densities (ca. 10/mm²) in the optic lobes were similar between unexposed controls and minnows with 1- and 2-week old infections. Rodlet cell densities increased at 4 weeks p.i., reaching maxima (ca. 200/mm²) at 6 weeks p.i., followed by a decline at 9 weeks. This temporal pattern of proliferation and maturation paralleled the development of metacercariae within the optic lobes. Unencysted metacercariae develop rapidly within tissues of the optic lobes for approximately 4 weeks after penetration by cercariae, then shift to the adjacent meninges to encyst. The former stage is associated with tissue damage, the latter with massive inflammation of the meninges. Thus, peak densities and maturation of rodlet cells correspond to the period when inflammation of the meninges caused by the large metacercarial cysts is at a maximum. Our results support recent contentions that rodlet cells comprise part of the host inflammatory defence response.     

Reappraisal of nuclear DNA content of rodlet cells compared to several cell types from some freshwater teleosts, using two methods of microdensitometry

Nuclear DNA contents of rodlet cells from Catostomus commersoni, Semotilus atromaculatus and Cyprinus carpio were compared with nuclear DNA of erythrocytes and larger cells of the same species, using scanning microdensitometry and averaging microdensitometry. This study reappraises the work of Barber & Westermann (1983), which employed averaging microdensitometry only, and compared rodlet cell nuclear DNA only with erythrocyte DNA. In addition, this work considers sources of error in both methods of microdensitometry, and comments upon the use of microdensitometry of either method as a mechanism for making distinctions among the DNA contents of cells of different types. The results of the present work consistently indiate no significant differences within species between nuclear DNA content of rodlet cells and larger teleost cells, using either method of microdensitometry. Because of the lack of statistically significant difference in DNA content between nuclei of rodlet cells and those of known teleost cells, it has been concluded that the rodlet cell itself is probably of teleost origin. However, the method indicates nothing about the origin of the rodlets, which have also been shown to contain DNA, but are Feulgen-negative.     

Rodlet cell biometry: interspecific and intraspecific variability

Intraspecific and interspecific variability in rodlet cell size in various tissues of several species of freshwater and marine fish were documented. Differences were attributed mainly to fish species, although tissue type contributed significantly, providing evidence for the presence of rodlet cell morphotypes.     

Rodlet cell distribution in the gall bladder epithelium of Fundulus heteroclitus

Rodlet cells within the epithelial mucosa of the gall bladder of the estuarine killifish Fundulus heteroclitus (L.) obtained from a highly contaminated creek adjacent to a landfill, were arranged within the constraints of the epithelium. Furthermore, the rodlet cells established a close intimate association with electron dense epithelioid cells. A comparison with fish from a non impacted estuary revealed a significantly greater number of rodlet cells in the 'contaminated' group. The abundance of rodlet cells within the gall bladder of the fish exposed to contaminants further strengthens the hypothesis that these cells participate in the fish's immune system.     

Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions

We suggest that the ultimate outcome of interactions between native species and invasive species (extinction or coexistence) depends on the number of simultaneous negative interactions (competition and predation), which depends on relative body sizes of the species. Multiple simultaneous interactions may constrain the ability of native species to trade fitness components (i.e., reduced growth for reduced risk of predation) causing a spiral to extinction. We found evidence for five types of interactions between the adults and juveniles of introduced western mosquitofish (Gambusia affinis) and the juveniles of native least chub (Iotichthys phlegethontis). We added ten large (23–28 mm) and seven small (9–13 mm) young-of-the-year (YOY) least chub to replicate enclosures with zero, low, and high densities of mosquitofish in a desert spring ecosystem. Treatments with mosquitofish reduced the average survival of least chub by one-third. No small YOY least chub survived in enclosures with high mosquitofish densities. We also performed two laboratory experiments to determine mortality to predation, aggressiveness, and habitat selection of least chub in the presence of mosquitofish. Mean mortality of least chub due to predation by large mosquitofish was 69.7% over a 3-h trial. Least chub were less aggressive, selected protected habitats (Potamogeton spp.), and were more stationary in the presence of mosquitofish where the dominance hierarchy was large mosquitofish>>large least chubsmall mosquitofish>>small least chub. Least chub juveniles appear to be figuratively caught in a vice. Rapid growth to a size refuge could reduce the risk of predation, but the simultaneous effects of competition decreased least chub growth and prolonged the period when juveniles were vulnerable to mosquitofish predation.