OBSERVATIONS ON THE MECHANISM OF EGGSHELL FORMATION IN THE LIVER FLUKE, FASCIOLA-HEPATICA

A mechanism for eggshell production in Schistosoma mansoni has been pr oposed (Wells & Cordingley, 1991), and suggests that the release of eg gshell protein globules from the vitelline cells occurs under alkaline conditions within the ootype followed by their subsequent fusion to f orm the eggshell. Fusion and tanning of these components produces eggs hell which autofluoresces. The present study was carried out to determ ine 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 x 10(-5) M) led to the premature release of eggshell globules from the v itelline cells but not their fusion. Incubation in monensin (1 x 10(-6 ) M), a sodium ionophore and ammonium chloride (NH4Cl) (5 x 10(-2) M), a weak base, resulted in the premature fusion of eggshell protein glo bules within the vitelline cells and premature tanning of the eggshell protein material. The copper-containing enzyme, phenol oxidase, is th ought to be involved in the tanning process during the production of e ggs. Diethyldithiocarbamate (DDC, 1 x 10(-3) M) is a phenol oxidase in hibitor and treatment with this compound, in combination treatments wi th monensin and NH4Cl, prevented fusion of the vitelline cell globules and tanning of the shell protein material. The results of the study s uggest that the mechanism for eggshell formation in F. hepatica is sim ilar to that proposed for S. mansoni and may be common to other tremat odes as well.