Fine Structure of Triactinomyxon Early Stages and Sporogony: Myxosporean and Actinosporean Features Compared

ABSTRACT. The first ultrastructural study of the actinosporean genus Triactinomyxon was carried out on Triactinomyxon legeri from the intestinal epithelium of Tubifex tubifex. The developmental cycle starts with bi- and uninucleate cells. We propose that these cells may be an early proliferative phase of the cycle and may unite to give rise to the four-cell stage, initiating pansporoblast formation. Valvogenic cells transform in the long stylus and anchor-like projections of the spore. In the capsulogenic cells, the primordium of the polar capsules originates as a simple, dense, club-shaped structure not observed in other actinosporeans. In all other respects, actinosporean ultrastructure follows more or less similar patterns. Comparison of actinosporean and myxosporean species gives evidence of considerable structural similarity, exemplified in both classes by the occurrence of cell junctions in their multicellular spores, identical polar capsules and their morphogenesis, cell-in-cell condition, pansporoblast formation, and presence of dense bodies (sporoplasmosomes) primarily in the sporoplasm. This unity of patterns speaks in favor of the postulated actinosporean-myxosporean transformation, which warrants further study.     

Recognition of Neurohormones of the NPY Family by Their Receptors

In this review a structural approach developed to answer the question whether hormones from the neuropeptide Y (NPY) family are recognized directly from solution or from the membrane-bound state is described. The chosen strategy is built onto a comparison of a set of peptides with well-known pharmacology and investigates whether similarities of structures of pharmacologically related peptides are higher in solution or in the membrane-bound state. Moreover, we have established the membrane-association mode of these peptides and contributed to our understanding of the structural features of these hormones both when placed in bulk solution and when bound to membranes. As a result we propose a receptor recognition pathway that includes initial association with the membrane and requires the peptides to come off the membrane to diffuse into the binding pocket of the receptor. This review also presents methodology recently developed by us to simulate the structural transition the peptides undergo when diffusing from bulk solution onto the membrane.     

Ultrastructure and Sporogony of Eimeria (syn. Epieimeria) anguillae (Apicomplexa) in the Eel (Anguilla anguilla)

ABSTRACT. Ultrastructural studies on Eimeria (syn. Epieimeria ) anguillae (Apicomplexa), parasite of the digestive tract of the eel, have shown that the development of this parasite takes place completely within the host cell. Merogony and gamogony are intracellular but in the epicytoplasmic position. Sporogony is also located within the epithelial cells, which agrees with assignment of this coccidian in the family Eimeriidae. However, depending on the intensity of infection and the physiopathological reaction of the host, the gamont may behave in two ways. 1) In massive infections, gamogony stages cause a genuine destruction of intestinal epithelium. Large numbers of gamonts form nodules and parts of the seriously destroyed epithelium peel off and are released into the lumen of the gut and quickly discharged into the outer environment. This discharged epithelium envelops cells containing immature oocysts that then sporulate outside the host. 2) In light infections, the host cells, which are necrotic due to the presence of a zygote, are pushed between the surrounding intact cells towards the base of the epithelium. Closely above its basal lamella, the oocyst then undergoes sporulation. These results show no taxonomically important biological features (e.g. special mode of implantation to the host cell or active movement of the zygote). Because the morphological characteristics of Epieimeria do not differ significantly from Eimeria , we propose to suppress the genus Epieimeria Dyková and Lom, 1981, and relegate its species into the genus Eimeria .     

Sensing,Threading, Orienting,and Cutting Polymers with Rigid-Rod Pores

This short review describes synthetic pores that are made from rigid-rod molecules and can bind oligo-and polymers such as polyacetylenes, p-oligophenyls, terpenoids, polypeptides, polysaccharides, and oligonucleotides. The spotlight is on recent breakthroughs to image the longtime elusive pore-polymer host-guest complexes as single giant pseudorotaxanes.     

“Unidentified” Mobile Protozoans from the Blood of Carp and Some Unsolved Problems of Myxosporean Life Cycles1

Heavy infections with enigmatic mobile organisms have recently been found in the blood of carp (Cyprinus carpio) in Central Europe. The organisms measure up to 15 μm, are variable in shape, and exhibit an unceasing twitching or dancing movement. Their developmental cycle starts with a primary cell enclosing a secondary cell. The former grows while the latter produces inside itself by a series of binary fissions and internal cleavages up to eight secondary cells, each of which encloses an inner (tertiary) cell of its own. In addition, up to four tiny cells with compact nuclei (“residual bodies”) also result from divisions of the secondary cells. Primary cells containing the products of the division of secondary cells finally disintegrate, releasing the secondary cells, which in their turn become new primary cells and repeat the cycle all over again. The structure and behavior of these organisms were so incompatible with existing ideas on myxosporean development that their myxosporean affinity was at first unrecognized. The final proof of their identity–appearance of myxosporean spores in sterile, experimentally infected hosts–is still to be presented. The interpretation of the myxosporean features of their life cycle (i.e., [1] the pericyte nature of the primary cell, [2] proliferation by disintegration of the pseudoplasmodial primary cell, [3] no rigidly fixed pattern in vegetative development), their ultrastructure (i.e., [1] characteristic bundles of microtubules and numerous free ribosomes in secondary cells, [2] lack of centrioles, [3] membranes enclosing the secondary cells within the primary cells), and facts on their epizootiology (i.e., [1] no success at transmission via leeches, [2] the occurrence of these organisms along with Sphaerospora renicola Dykova and Lom) suggest that they are stages of S. renicola from the kidney of carp. Similar mobile organisms were found in the blood of fry of two other fishes (Gobio gobi and Tinca tinca) which are also hosts for a Sphaerospora that infects the kidney. This suggests that these organisms represent an early phase in the developmental cycle in the genus Sphaerospora. The existence of cells enveloped one within the other (secondary and tertiary cells) in the developmental cycle, a characteristic myxosporean feature itself, is an intriguing parallel to similarly enclosed cells in sporogenesis of Paramyxea (Ascetospora).     

Fish Trypanosomes: Their Position in Kinetoplastid Phylogeny and Variability as Determined from 12S rRNA Kinetoplast Sequences

Fish trypanosomes have traditionally been classified according to the host species from which they were isolated, each isolate being regarded as a distinct species. To test the soundness of this practice, the genetic variabilities of the kinetoplast 12S rRNA-encoding genes of different fish trypanosomes isolates were compared. The DNAs were extracted from trypanosomes cloned from blood samples of 15 donors representing ten different fish species in four orders from waters of three major river systems of Central and Northern Europe. Comparison with other trypanosomatid sequences revealed that the fish trypanosomes form a monophyletic group with Trypanosoma brucei as a sister group. Pairwise comparisons of genetic distances yielded a wide range of continuous variation with no indication of any discontinuities attributable to barriers to gene flow. The genetic distances did not correlate with either the identity of the host species or geography. The host specificity of fish trypanosomes appears to be limited.