Development of the endoplasmic reticulum in the rodlet cell of two teleost species

Abstract

The rodlet cell found in different tissues and the blood of teleosts is distinguished by a thick capsule and bipartite rodlets, each consisting of club-like sac and a dense protein core. The development of its rough endoplasmic reticulum (RER) was ultrastructurally investigated in gill and intestinal epithelium of trout (Salmo trutta L., Oncorhynchus kisutch). The RER showed signs of hypertrophy beginning already in immature cells. The typical vesicular appearance noted in the mature cell as well as the apical labyrinth, an accumulation of dislodged mitochondria and vesicles, derives from RER dilatations shedding their ribosomes and pervading the cytoplasm. These dilatations extend also into extracapsular protrusions formerly supposed to be nutritive. A possible role of RER in the formation of the rodlets is indicated by the close association of RER-derived vesicles with rodlet sacs. Conspicuous undulations of the membranes of the sacs as well as the occurrence of tubules (ø ϭ 30 nm) in the dilated RER, rodlet sacs, and along the core support the proposed hypothesis of hypertrophy. Both features signal the storage of (membrane) protein during altered conditions ranging from slowed metabolism to viral infections. The differentiation of apical microvillar projections replaced later by cytoplasmic blebbing and disruption is compatible with surplus production resulting in discharge by pressure. Together with the occasional presence of junctional complexes, these observations argue for an aberrant cell differentiation due to an unknown cause, representing an alternative to the current interpretation of the rodlet cell as a migrating secretory or leucocytic cell with a defensive function.

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

“…Moreover, it is likely that if members of the Apicomplexa phylum were to penetrate into a host intestinal cell, they would do so from the side of the apical lumen [49] whereas it is clear that the migration of the RCs is from the basement membrane towards the lumen, previously demonstrated by Mayberry et al [5]. Finally, a possible role of the RER in the formation of the rodlets [7] also supports the endogenous theory.…”

“…According to the endogenous hypothesis, RCs are normal constituents of the fish tissue with a potential secretory and/or granulocyte function or an aberrant cell differentiation due an unknown cause [7]. Histochemical studies [8], reveal the presence of granules, as well as mitochondria with plate-like cristae that resemble those in other epithelial cells.…”

Rodlet cells in the thymus of the zebrafish Danio rerio (Hamilton, 1822)

“…Schmachtenberg's [30] results support the alternative hypothesis of high intracellular pressure resulting from the distended ER. In this case, the thickened cell border would act as an antagonist to this pressure until the cell is ready to discharge the rodlets [28].…”

“…We identified them at the surface of the thymus where they were attached in the squamous epithelial layer by desmosomes and tight junctions similar to endothelia or sites with cubic or columnar epithelia, e.g. bulbus arteriosus and epidermis [4,6,11,28,29]. The lower part of the RC was often in contact with lymphocytic cells flattened against its cell border or partially surrounded by extensions of reticular cells but never totally engulfed and taken up into vacuoles as described by Pulsford et al [13].…”

Effects of exposure to overcrowding on rodlet cells of the teleost fish Dicentrarchus labrax (L.)

“…In general, rodlet cells were observed only in teleost fish associated with the epithelium of skin, intestine, kidney and gills but they can also be found in many other tissues, such as the mesentery and under the mesothelium of visceral organs like the liver and pancreas (Manera and Dezfuli 2004;Reite 2005). They were observed in both freshwater and marine teleosts (Morrison and Odense 1978;Dezfuli et al 1998;Bielek 2005;Abbate et al 2006;Dezfuli et al 2007a, b;Mazon et al 2007) and appear with a thick distinctive cell cortex, an usually basal nucleus and conspicuous inclusions called rodlets (Manera and Dezfuli 2004). An increased number of these cells in different teleost tissues seems to be related to different stress conditions such as: exposure to heavy metals (cadmium, copper chloride, lead acetate and mercury) (Manera and Dezfuli 2004;Giari et al 2007Giari et al , 2008, herbicides (Manera and Dezfuli 2004;Dezfuli et al 2006) and parasite infections (Dezfuli et al 2007b, c;Mazon et al 2007).…”