Schistocephalus plerocercoid

Brophy, P.M., Papadopoulos, A., Touraki, M., Coles, B., Korting, W. and Barrett, J. (1989) Purification of cytosolic glutathione transferases from Schistocephalus solidus (plerocercoid) interaction with anthelmintics and products of lipid peroxidation. Molecular and Biochemical Parasitology 35, 1 87-1 95. 

Hymenolepis diminuta (adult) Schistocephalus solidus (plerocercoid) Ligula intestinalis (plerocercoid)... 

Enzyme Apparent equilibrium constant granulosus0 (protoscoleces, ovine strain) Echinococcus multiloculari (protoscoleces) Moniezia expanseJ (adults) Hymenolepis microstomac (adults) Schistocephalus solidus 1 (plerocercoids) Ligula intestinalif (plerocercoids)... 

This enzyme catalyses the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate (FBP) and is the key regulatory enzyme of glycolysis. The properties of phosphofructokinase (PFK) have been investigated in some detail in adult Moniezia expansa (60) and in plerocercoids of S. solidus (65), where its activity is modulated by a number of compounds, including ATP, AMP, fructose-6-phos-phate, Mg2 +, Mn2 +, K + and NH. In general, the PFKs from both species exhibit properties similar to those of the enzymes from mammalian sources and they probably regulate glycolysis in the same manner as their mammalian counterparts. The inhibitory effects of ATP on the PFK from Schistocephalus solidus and the relief of this inhibition by AMP are shown in Fig. 5.2. 

Fig. 5.2. Plot of the activity of phosphofructokinase from plerocercoids of S. solidus against the concentration of ATP in the presence and absence of 2 mM AMP. The concentration of fructose 6-phosphate was 1 mM. (Reprinted with permission from International Journal for Parasitology, 12, Beis, I. Theophilidis, G. Phosphofructokinase in the plerocercoids of Schistocephalus solidus (Cestoda Pseudophyllidea), 1982 Pergamon Journals Ltd.)...

Schistocephalus solidus has its plerocercoid stage in an ectotherm (the fish Gasterosteus aculeatus) and its adult stage in an endoderm (a fish-eating bird) and it serves as an excellent model for the study of temperature adaptation in parasites. Walker Barrett (922,923) have studied the effect of temperature on (a) the activities of the mitochondrial enzyme adenosine triphosphatase (ATPase) and (b) the physical state of mitochondrial membranes in adult and larval S. solidus. 

Fig. 8.15. Monthly variation in the ovarian content of the three-spined stickleback, Gasterosteus aculeatus, parasitised with the progenetic plerocercoids of Schistocephalus solidus. (After Meakins, 1974.)...

Establishment is greatly facilitated in these two species by the fact that the plerocercoids are progene tic (p. 211) and rapidly reach maturity after only 48 h (Schistocephalus) or 72 h (Ligula) in their bird hosts - a process which has been successfully completed in vitro (Chapter 10). 

With the exception of a few species with progenetic plerocercoids (e.g. Schistocephalus) it is only within the definitive host that cestode tissue develops in a strobilar direction, and it is self-evident that strobilar differentiation must be induced by factors present in the intestinal environment. Clearly, any number of known parameters of the intestine (Fig. 3.1, p. 37)... 

The Pseudophyllidea contain many well-known species which infect birds and mammals and whose plerocercoids occur in cold-blooded vertebrates, especially fish. Several have progenetic (p. 214) plerocercoids, e.g. Schistocephalus and Ligula, and furthermore these larvae contain sufficient food reserves (such as glycogen) to satisfy the energy and synthetic needs of maturation without additional external nutrients being provided. Such larvae provided useful experimental models for early work in this field, as maturation could be achieved in vitro once sterility and the appropriate environmental conditions were provided (786, 787, 788). Although these... 

Fig. 10.1. Progenetic plerocercoid of the pseudophyllidean Schistocephalus solidus, (a) Enlarged view of plerocercoid showing genital anlagen. (ft) Whole plerocercoid removed from fish.

Unlike Schistocephalus and Ligula, the majority of pseudophyllidean plerocercoids are morphologically undifferentiated, and must undergo considerable growth and differentiation before sexual maturity can be achieved. 

Barrett, J. Lloyd, G. M. (1981). A novel phosphagen phosphotransferase in the plerocercoids of Schistocephalus solidus (Cestoda Pseudophyllidea). Parasitology, 82 11-16. 

Meakins, R. H. (1974). A quantitative approach to the effects of the plerocercoid of Schistocephalus solidus Muller 1776 on the ovarian maturation of the three-spined stickleback Gasterosteus aculeatus. Zeitschrift fur Parasitenkunde, 44 73-9. 

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