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Observations on the mechanism of eggshell formation in the liver fluke, Fasciola hepatica

Published online by Cambridge University Press:  01 June 1998

L. M. COLHOUN
Affiliation:
The School of Biology and Biochemistry, Medical Biology Centre, The Queen's University of Belfast, Belfast BT9 7BL, Northern Ireland
I. FAIRWEATHER
Affiliation:
The School of Biology and Biochemistry, Medical Biology Centre, The Queen's University of Belfast, Belfast BT9 7BL, Northern Ireland
G. P. BRENNAN
Affiliation:
The School of Biology and Biochemistry, Medical Biology Centre, The Queen's University of Belfast, Belfast BT9 7BL, Northern Ireland

Abstract

A mechanism for eggshell production in Schistosoma mansoni has been proposed (Wells & Cordingley, 1991), and suggests that the release of eggshell protein globules from the vitelline cells occurs under alkaline conditions within the ootype followed by their subsequent fusion to form the eggshell. Fusion and tanning of these components produces eggshell which autofluoresces. The present study was carried out to determine whether a similar process operates in Fasciola hepatica. A number of drug treatments were used to disrupt key steps in the maturation of vitelline cells. Treatment with the calcium ionophore lasalocid (1×10−5m) led to the premature release of eggshell globules from the vitelline cells but not their fusion. Incubation in monensin (1×10−6m), a sodium ionophore and ammonium chloride (NH4Cl) (5×10−2m), a weak base, resulted in the premature fusion of eggshell protein globules within the vitelline cells and premature tanning of the eggshell protein material. The copper-containing enzyme, phenol oxidase, is thought to be involved in the tanning process during the production of eggs. Diethyldithiocarbamate (DDC, 1×10−3m) is a phenol oxidase inhibitor and treatment with this compound, in combination treatments with monensin and NH4Cl, prevented fusion of the vitelline cell globules and tanning of the shell protein material. The results of the study suggest that the mechanism for eggshell formation in F. hepatica is similar to that proposed for S. mansoni and may be common to other trematodes as well.

Type
Research Article
Copyright
1998 Cambridge University Press

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