Endocrine Basis for Ecdysis in a Parasitic Nematode

Abstract

MOULTING in nematodes can be separated into two distinct processes: the deposition of the new cuticle and ecdysis, or the shedding of the old. This notion that the two events are distinct is supported by the work of Rogers and his colleagues^1–3 on exsheathment in trichostrongyles. In Trichostrongylus and Haemonchus, the free-living second-stage larva deposits a new cuticle but fails to ecdyse in the absence of stimuli from the host. Thus the infective third stage larva remains ensheathed within the unshed second stage cuticle. Exsheathment, or ecdysis, is brought about by the release of an “exsheathing fluid” into the space between the new and old cuticles in response to a stimulus from the host. The exsheathing fluid is a complex system, but the component which appears to be responsible for digesting the old cuticle is the enzyme leucine aminopeptidase⁴. The suggestion that an endocrine link connects the reception of the stimulus from the host and the release of the exsheathing fluid by the parasite has been widely canvassed in the literature^1,3,5–7, but there has been no evidence to support this attractive hypothesis.