Effect of insect hormones on nematodes in axenic culture

Endocrine disruption in nematodes: effects and mechanisms

This paper reviews the current knowledge on endocrine disruption in nematodes. These organisms have received little attention in the field of ecotoxicology, in spite of their important role in aquatic ecosystems. Research on endocrine regulation and disruption in nematodes, especially the more recent studies, concentrate mainly on one species, Caenorhabditis elegans. Although an endocrine system is not known in nematodes, there is evidence that many processes are regulated via hormonal pathways. As vertebrate hormones, such as steroids, may have endocrine functions in nematodes as well, endocrine disrupting chemicals (EDCs) defined for vertebrates may also be able to influence nematodes. The studies that are reviewed here, and own data showed that potential EDCs can affect nematodes on all organizational levels, from molecules to communities. It is concluded that nematodes, notably its prominent species C. elegans, are a promising organism group for the development of biomonitoring tools, provided that more mechanistic evidence is gathered on hormonal processes within these animals.

Effects of precocene analogs on the nematode Caenorhabditis remanei (var. Bangaloreiensis). I. Structure/activity relations

Precocenes (PI and PII) and 114 of their analogs (PAs) were synthetized and tested on C. remanei embryos for their precocene-like (P-like) activities resulting in unusual development at sublethal doses. The P-like activity was quantitated by plotting the probit of the percentage of the developmentally affected survivors against the (log) dose to obtain the EC plot and the half effective concentration (EC50). All five PAs (PI, PII, 7-ethoxy-PII, 7-(prop-2-ynyloxy)-PI, and 6-methoxy-7-(prop-2-ynyloxy)-PII) which exert both antiallatal activity in insects and P-like activity in nematodes are 7-alkoxy-substituted 2,2-dimethylchromenes. Both activities can be enhanced by an additional 6-MeO-substitution or by an asymmetric 6,7-dialkoxy-substitution, on condition that R-7 is longer than R-6. There are many more similarities than dissimilarities in the structural requirements needed for antiallatal and P-like activities. All but three nonantiallatal PAs effective in nematodes are 7-prop-2-ynyloxy-subsituted; two are symmetrically 6,7-disubstituted, and one is heterosubstituted (thio-PI). All PAs with antiallatal but without P-like activity are 7-monosubstituted with a relatively long alkoxy group. Certain substitutions favor antiallatal activity and others P-like activity. The severe nematocidal effect of 6,7-methylenedioxy-2,2-dimethylchromene (inert in insects) is not accompanied by P-like activity. The present findings lend some indirect support to the supposition that JH-producing cells and/or JH-dependent function(s) might exist in the nematodes.

Effects of precocene analogs on the nematode Caenorhabditis remanei (var. Bangaloreiensis). II. Competitions with a juvenile hormone analog (Methoprene)

Fourteen 7-alkoxy-2,2-dimethychromenes were synthetized and studied in JH competition experiments: precocenes (Ps) PI and PII, and synthetic analogs (PAs) including (i) three with both antiallatal and P-like activities: 7-ethoxy-PII (7-EPII); 7-(prop-2-ynyloxy)-2,-2-dimethylchromene (PPI); and 6-methoxy-7-(prop-2-ynyloxy)-2,2-dimethylchromene (PPIII); (ii) six without antiallatal activity, exerting P-like activity in nematodes; and (iii) three without either antiallatal or P-like activity, but with a strong nematocidal effect. Within the dose range 8-1000 micrograms/ml, different concentrations of each PA were applied to nematode growth medium which did or did not contain 1000 micrograms methoprene (a juvenile hormone analog JHA)/ml. Plates inoculated with Caenorhabditis embryos were incubated and scored for developmentally affected survivors. The JHA did not compete with any PA mentioned as (iii). It competed moderately with some nonantiallatal PAs (8-Me-PPI, 8-MeO-PPI, and 3,4-diCl-PPI) with strong P-like and nematocidal activities. The JHA competed most efficiently with all Ps, antiallatal PAs, and two nonantiallatal PAs (PPII and thio-PI) which exerted severe P-like activities in nematodes. Parameters assumed to be indicators of the P-like (rather than nematocidal) activity of the PAs proved more sensitive to the JHA than those of nematocidal activity. Whether the JH-compensable P-like activity of some PAs can be regarded as a real anti-JH action needs further clarification.

The nature and action of host signals

It is clear that excystations in vitro of the coccidia so far examined involves two steps, in the first of which CO2 is important, and the second, in which an external source of chymotrypsin and surface-active agents are required. However, the details of the mechanism of excystment are not clear. We do not know how the presence of CO2 changes the permeability of the oocyst wall. We do not know whether CO2 does anything to the sporozoite or sporocyst; the circumstance that mechanically-released sporocysts readily excyst under appropriate conditions without the necessity for high concentrations of, or perhaps any, CO2 suggests it does not. Circumstantial evidence suggests that the substrate in which chymotrypsin acts is the Stieda body, but whether the enzyme has other roles we do not know. Similarly, the role of bile is ill-defined, although it does seem that the induction of activity is important--but how is this brought about? The techniques available to excyst oocysts are, for many species, very efficient. If CO2 is, as it seems to be, a fundamental stimulus, then efficiency might be enhanced if more attention was given, not so much to increasing the time of exposure and amount of CO2 in the gas phase, but rather to the pH of the medium, which is rarely stated or apparently, controlled. The pH determines the proportion of the different carbonate species in solution, which may be of greater significance than the partial pressure of CO2 in the gas phase (see also Section V A). Although high numbers of excysted sporocysts can be obtained with a particular technique, this does not necessarily mean that all the signals supplied by the host are reproduced in vitro. Jackson (1962) found it necessary to wash oocysts in water or dilute buffers between the primary phase and the secondary phase, a step which implies a deficiency in the methods he used. Commonly, oocysts are exposed to a strong solution of L-cysteine. Does this reflect a general deficiency in the technique, or a counterpart of strongly reducing conditions in ruminant and non-ruminant alike? It seems that we have only a very general outline of excystment, and that we do not understand the details. Yet the problem seems to have been put aside; the most recent relevant reference we have found is dated 1983.