Strongyloides stercoralis: Amphidial neuron pair ASJ triggers significant resumption of development by infective larvae under host-mimicking in vitro conditions

Abstract

Resumption of development by infective larvae (L3i) of parasitic nematodes upon entering a host is a critical first step in establishing a parasitic relationship with a definitive host. It is also considered equivalent to exit from the dauer stage by the free-living nematode Caenorhabditis elegans. Initiation of feeding, an early event in this process, is induced in vitro in L3i of Strongyloides stercoralis, a parasite of humans, other primates and dogs, by culturing the larvae in DMEM with 10% canine serum and 5mM glutathione at 37 degrees C with 5% CO(2). Based on the developmental neurobiology of C. elegans, resumption of development by S. stercoralis L3i should be mediated, in part at least, by neurons homologous to the ASJ pair of C. elegans. To test this hypothesis, the ASJ neurons in S. stercoralis first-stage larvae (L1) were ablated with a laser microbeam. This resulted in a statistically significant (33%) reduction in the number of L3i that resumed feeding in culture. In a second expanded investigation, the thermosensitive ALD neurons, along with the ASJ neurons, were ablated, but there was no further decrease in the initiation of feeding by these worms compared to those in which only the ASJ pair was ablated.

Fig. 1

Fluorescence micrograph of S. stercoralis L3i which have ingested FITC-containing culture medium. The pharyngi of the two worms, which are coiled about each other, fluoresce strongly, while their intestines also contain fluorescent material (non-feeding, control larvae show almost no structure under these conditions).

Fig. 2

Percentage of S. stercoralis L3i that initiated feeding after: Exposure to the anesthetic, but no further treatment (see Section 2), laser microbeam ablation of the ASK neurons, or laser microbeam ablation of the ASJ neurons. Error bars indicate the Standard Error of the Mean.

Fig. 3

Percentage of S. stercoralis L3i that initiated feeding after: exposure to the anesthetic, but no further treatment (see Section 2), laser microbeam ablation of the ASK and ALD neurons, or laser microbeam ablation of the ASJ and ALD neurons. Error bars indicate the Standard Error of the Mean.