Signalling Mechanisms in Platyhelminths

Abstract

Platyhelminths, or flatworms, include both free-living forms such as the freshwater planarians and parasitic forms — the flukes and tapeworms. Parasitic species infect both humans and livestock and a number represent important zoonotic infections of humans. The flatworms are the first metazoans to show centralization of the nervous system, with the formation of a “brain”. They possess a variety of potential transmitter substances and this chapter will summarise what is known about their biological activity. Evidence is accumulating for the presence of individual components of signalling pathways that are known to exist in higher organisms. This evidence will be reviewed, as will the extent to which functional signalling pathways have been unravelled in flatworms. Manipulation of signalling pathways for therapeutic intervention will also be considered. Parasitic species utilize a multiplicity of environmental and host signals for different phases of their life cycle, and they have evolved mechanisms to mimic and/or manipulate host signals and responses to favour their establishment and development; these mechanisms will be discussed.