The tegument of the human parasite Schistosoma mansoni is critical for
parasite survival within the mammalian host. The role of protein kina
se C (PKC), a major effector molecule in the phosphoinositide pathway,
in maintaining the structural organization of this syncytial layer wa
s examined in adult worms. Phorbol 12-myristate, 13-acetate (PMA) and
phorbol 12,13-dibutyrate (PDB), phorbol eaters that activate PKC, indu
ced formation of surface vesicles as determined by light and scanning
electron microscopy. Similar results were seen with sn-2-dioctanoyl-gl
ycerol, a synthetic analogue of diacylglycerol. No effect was seen in
parasites incubated with 4-alpha-phorbol ester or alpha isomers of PMA
or PDB, compounds that do not activate PKC. Vesicle formation was rev
ersible in parasites treated with sn-2-dioctanoyl-glycerol but not wit
h phorbol esters. The tegument of male worms was more sensitive to the
effect of phorbol esters than females. Transmission electron microsco
py revealed vacuolization of the tegument. These data suggest that sig
nal transduction pathways may have a critical role in the maintenance
of the structural integrity of the tegument of parasitic helminths.